[Core Libraries] Eliminate the fork in the core libraries.

Move the nnbd core libraries from sdk_nnbd to sdk, and updates
references in build files and elsewhere accordingly.

Change-Id: I09760fe1e006657aacdfe80f3b22fdf6f7e30a9f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151121
Commit-Queue: Leaf Petersen <leafp@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

BUILD.gn

@@ -80,24 +80,12 @@ group("runtime_precompiled") {
   ]
 }
 
-if (dont_use_nnbd) {
-  group("create_sdk") {
-    public_deps = [ "sdk:create_sdk" ]
-  }
-} else {
-  group("create_sdk") {
-    public_deps = [ "sdk_nnbd:create_sdk" ]
-  }
+group("create_sdk") {
+  public_deps = [ "sdk:create_sdk" ]
 }
 
-if (dont_use_nnbd) {
-  group("create_platform_sdk") {
-    public_deps = [ "sdk:create_platform_sdk" ]
-  }
-} else {
-  group("create_platform_sdk") {
-    public_deps = [ "sdk_nnbd:create_platform_sdk" ]
-  }
+group("create_platform_sdk") {
+  public_deps = [ "sdk:create_platform_sdk" ]
 }
 
 group("dart2js") {

PRESUBMIT.py

@@ -19,49 +19,6 @@ def is_cpp_file(path):
     return path.endswith('.cc') or path.endswith('.h')
 
 
-def _CheckNnbdSdkSync(input_api, output_api):
-    files = [git_file.LocalPath() for git_file in input_api.AffectedTextFiles()]
-    unsynchronized_files = []
-    for file in files:
-        if file.startswith('sdk/'):
-            nnbd_file = 'sdk_nnbd/' + file[4:]
-            if not nnbd_file in files:
-                unsynchronized_files.append(nnbd_file)
-    if unsynchronized_files:
-        return [
-            output_api.PresubmitPromptWarning(
-                'Changes were made to sdk/ that were not made to sdk_nnbd/\n'
-                'Please update these files as well:\n'
-                '\n'
-                '%s' % ('\n'.join(unsynchronized_files)))
-        ]
-    return []
-
-
-def _CheckSdkDdcRuntimeSync(input_api, output_api):
-    files = [git_file.LocalPath() for git_file in input_api.AffectedTextFiles()]
-    unsynchronized_files = []
-    runtime_lib = 'lib/_internal/js_dev_runtime/private/ddc_runtime/'
-    for nnbd_file in files:
-        if nnbd_file.startswith('sdk_nnbd/' + runtime_lib):
-            file = 'sdk/' + nnbd_file[9:]
-            if not file in files:
-                unsynchronized_files.append(file)
-    if unsynchronized_files:
-        return [
-            output_api.PresubmitPromptWarning(
-                'Changes were made to '
-                'sdk_nnbd/lib/_internal/js_dev_runtime/private/ddc_runtime/ '
-                'that were not made to '
-                'sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/ '
-                'Please copy those changes (without Null Safety syntax) to '
-                'these files as well:\n'
-                '\n'
-                '%s' % ('\n'.join(unsynchronized_files)))
-        ]
-    return []
-
-
 def _CheckNnbdTestSync(input_api, output_api):
     """Make sure that any forked SDK tests are kept in sync. If a CL touches
     a test, the test's counterpart (if it exists at all) should be in the CL
@@ -369,8 +326,6 @@ def _CheckTestMatrixValid(input_api, output_api):
 
 def _CommonChecks(input_api, output_api):
     results = []
-    results.extend(_CheckNnbdSdkSync(input_api, output_api))
-    results.extend(_CheckSdkDdcRuntimeSync(input_api, output_api))
     results.extend(_CheckNnbdTestSync(input_api, output_api))
     results.extend(_CheckValidHostsInDEPS(input_api, output_api))
     results.extend(_CheckDartFormat(input_api, output_api))

WATCHLISTS

@@ -28,7 +28,6 @@
       'filepath': (
         '^pkg/compiler|'
         '^sdk/lib/_internal/js_runtime|'
-        '^sdk_nnbd/lib/_internal/js_runtime|'
         '^tests/compiler/dart2js'
       )
     },
@@ -36,7 +35,6 @@
       'filepath': (
         '^pkg/dev_compiler|'
         '^sdk/lib/_internal/js_dev_runtime|'
-        '^sdk_nnbd/lib/_internal/js_dev_runtime|'
         '^tests/compiler/dartdevc_native'
       )
     },

pkg/compiler/test/helpers/memory_compiler.dart

@@ -29,7 +29,7 @@ export 'diagnostic_helper.dart';
 bool isDart2jsNnbd =
     !Platform.environment['DART_CONFIGURATION'].endsWith('Legacy');
 
-String sdkPath = isDart2jsNnbd ? 'sdk_nnbd/lib' : 'sdk/lib';
+String sdkPath = 'sdk/lib';
 
 String sdkLibrariesSpecificationPath = '$sdkPath/libraries.json';
 

pkg/compiler/tool/modular_test_suite.dart

@@ -132,10 +132,7 @@ class SourceToDillStep implements IOModularStep {
         return;
       }
       sources = ['dart:core'];
-      extraArgs = [
-        '--libraries-file',
-        '$rootScheme:///sdk_nnbd/lib/libraries.json'
-      ];
+      extraArgs = ['--libraries-file', '$rootScheme:///sdk/lib/libraries.json'];
       assert(transitiveDependencies.isEmpty);
     } else {
       sources = module.sources.map(sourceToImportUri).toList();
@@ -342,7 +339,7 @@ class RunD8 implements IOModularStep {
     if (_options.verbose) print("\nstep: d8 on $module");
     List<String> d8Args = [
       sdkRoot
-          .resolve('sdk_nnbd/lib/_internal/js_runtime/lib/preambles/d8.js')
+          .resolve('sdk/lib/_internal/js_runtime/lib/preambles/d8.js')
           .toFilePath(),
       root.resolveUri(toUri(module, jsId)).toFilePath(),
     ];

pkg/dev_compiler/lib/src/compiler/shared_command.dart

@@ -339,9 +339,7 @@ Map placeSourceMap(Map sourceMap, String sourceMapPath, String multiRootScheme,
         // TODO(sigmund): extract all source-map normalization outside ddc. This
         // custom logic is BUILD specific and could be shared with other tools
         // like dart2js.
-        var shortPath = uri.path
-            .replaceAll('/sdk/', '/dart-sdk/')
-            .replaceAll('/sdk_nnbd/', '/dart-sdk/');
+        var shortPath = uri.path.replaceAll('/sdk/', '/dart-sdk/');
         var multiRootPath = "${multiRootOutputPath ?? ''}$shortPath";
         multiRootPath = p.url.relative(multiRootPath, from: sourceMapDir);
         return multiRootPath;

pkg/dev_compiler/test/modular_suite.dart

@@ -77,7 +77,7 @@ class SourceToSummaryDillStep implements IOModularStep {
       sources = ['dart:core'];
       extraArgs = [
         '--libraries-file',
-        '$rootScheme:///sdk_nnbd/lib/libraries.json',
+        '$rootScheme:///sdk/lib/libraries.json',
         '--enable-experiment',
         'non-nullable',
       ];
@@ -157,7 +157,7 @@ class DDCStep implements IOModularStep {
       extraArgs = [
         '--compile-sdk',
         '--libraries-file',
-        '$rootScheme:///sdk_nnbd/lib/libraries.json',
+        '$rootScheme:///sdk/lib/libraries.json',
         '--enable-experiment',
         'non-nullable',
       ];

pkg/dev_compiler/test/modular_suite_nnbd.dart

@@ -77,7 +77,7 @@ class SourceToSummaryDillStep implements IOModularStep {
       sources = ['dart:core'];
       extraArgs = [
         '--libraries-file',
-        '$rootScheme:///sdk_nnbd/lib/libraries.json',
+        '$rootScheme:///sdk/lib/libraries.json',
       ];
       assert(transitiveDependencies.isEmpty);
     } else {
@@ -159,7 +159,7 @@ class DDCStep implements IOModularStep {
       extraArgs = [
         '--compile-sdk',
         '--libraries-file',
-        '$rootScheme:///sdk_nnbd/lib/libraries.json',
+        '$rootScheme:///sdk/lib/libraries.json',
       ];
       assert(transitiveDependencies.isEmpty);
     } else {

pkg/dev_compiler/tool/check_nnbd_sdk.dart

@@ -37,7 +37,7 @@ void main(List<String> argv) {
 
   var librariesJson = args['libraries'] != null
       ? resolveInputUri(args['libraries'] as String)
-      : Platform.script.resolve('../../../sdk_nnbd/lib/libraries.json');
+      : Platform.script.resolve('../../../sdk/lib/libraries.json');
   var target = args['target'] as String;
   patch.main([
     '--libraries',
@@ -115,8 +115,7 @@ main() {}
   var result = Process.runSync(dart.toFilePath(), [
     // The NNBD dart binaries / snapshots require this flag to be enabled at
     // VM level.
-    if (analyzerSnapshot.contains('NNBD'))
-      '--enable-experiment=non-nullable',
+    if (analyzerSnapshot.contains('NNBD')) '--enable-experiment=non-nullable',
     analyzerSnapshot,
     '--dart-sdk=${sdkDir}',
     '--format',
@@ -198,7 +197,7 @@ main() {}
 final _parser = ArgParser()
   ..addOption('libraries',
       help: 'Path to the nnbd libraries.json (defaults to the one under '
-          'sdk_nnbd/lib/libraries.json.')
+          'sdk/lib/libraries.json.')
   ..addOption('out',
       help: 'Path to an output folder (defaults to a new tmp folder).')
   ..addOption('target',

pkg/front_end/lib/src/api_prototype/experimental_flags.dart

@@ -9,7 +9,7 @@ part 'experimental_flags_generated.dart';
 /// The set of experiments enabled for SDK and packages.
 ///
 /// This are derived from an `allowed_experiments.json` file whose default is
-/// located in `sdk_nnbd/lib/_internal/allowed_experiments.json`.
+/// located in `sdk/lib/_internal/allowed_experiments.json`.
 class AllowedExperimentalFlags {
   /// The set of experiments that are enabled for all SDK libraries other than
   /// for those which are specified in [sdkLibraryExperiments].

pkg/front_end/testcases/general/sdk_diagnostic.dart.outline.expect

@@ -12,7 +12,7 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //

pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general/sdk_diagnostic.dart:12:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/general/sdk_diagnostic.dart.strong.transformed.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general/sdk_diagnostic.dart:12:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart.outline.expect

@@ -12,7 +12,7 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// org-dartlang-sdk:///sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //

pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart.strong.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// org-dartlang-sdk:///sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart:14:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// org-dartlang-sdk:///sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart.strong.transformed.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// org-dartlang-sdk:///sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart:14:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// org-dartlang-sdk:///sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart.weak.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart:14:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart.weak.transformed.expect

@@ -12,14 +12,14 @@ library;
 //
 // class C extends Iterable<Object> {
 //       ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
+// sdk/lib/core/iterable.dart:158:19: Context: 'Iterable.iterator' is defined here.
 //   Iterator<E> get iterator;
 //                   ^^^^^^^^
 //
 // pkg/front_end/testcases/general_nnbd_opt_out/sdk_diagnostic.dart:14:8: Error: Too few positional arguments: 1 required, 0 given.
 //   print(incorrectArgument: "fisk");
 //        ^
-// org-dartlang-sdk:///sdk_nnbd/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
+// sdk/lib/core/print.dart:8:6: Context: Found this candidate, but the arguments don't match.
 // void print(Object? object) {
 //      ^^^^^
 //

pkg/front_end/testcases/incremental_initialize_from_dill/no_outline_change_22.yaml.world.1.expect

@@ -10,13 +10,13 @@ library from "org-dartlang-test:///main.dart" as main {
     abstract member-signature get length() → dart.core::int*;
     abstract member-signature operator [](dart.core::int* index) → dart.core::int*;
     abstract member-signature operator []=(dart.core::int* index, generic-covariant-impl dart.core::int* value) → void;
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ iterator() → dart.core::Iterator<dart.core::int*>
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ iterator() → dart.core::Iterator<dart.core::int*>
       return new dart._internal::ListIterator::•<dart.core::int*>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ elementAt(dart.core::int index) → dart.core::int*
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ elementAt(dart.core::int index) → dart.core::int*
       return this.{dart.core::List::[]}(index);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ followedBy(generic-covariant-impl dart.core::Iterable<dart.core::int*> other) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ followedBy(generic-covariant-impl dart.core::Iterable<dart.core::int*> other) → dart.core::Iterable<dart.core::int*>
       return dart._internal::FollowedByIterable::firstEfficient<dart.core::int*>(this, other);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ forEach((dart.core::int*) → void action) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ forEach((dart.core::int*) → void action) → void {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         action.call(this.{dart.core::List::[]}(i));
@@ -26,11 +26,11 @@ library from "org-dartlang-test:///main.dart" as main {
       }
     }
     @#C3
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ isEmpty() → dart.core::bool
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ isEmpty() → dart.core::bool
       return this.{dart.core::List::length}.{dart.core::num::==}(0);
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ isNotEmpty() → dart.core::bool
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ isNotEmpty() → dart.core::bool
       return !this.{dart.collection::ListMixin::isEmpty};
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ contains(dart.core::Object? element) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ contains(dart.core::Object? element) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(this.{dart.core::List::[]}(i).{dart.core::Object::==}(element))
@@ -41,7 +41,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ every((dart.core::int*) → dart.core::bool test) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ every((dart.core::int*) → dart.core::bool test) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(!test.call(this.{dart.core::List::[]}(i)))
@@ -52,7 +52,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return true;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ any((dart.core::int*) → dart.core::bool test) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ any((dart.core::int*) → dart.core::bool test) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(test.call(this.{dart.core::List::[]}(i)))
@@ -63,7 +63,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ firstWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ firstWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         dart.core::int* element = this.{dart.core::List::[]}(i);
@@ -77,7 +77,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = length.{dart.core::num::-}(1); i.{dart.core::num::>=}(0); i = i.{dart.core::num::-}(1)) {
         dart.core::int* element = this.{dart.core::List::[]}(i);
@@ -91,7 +91,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ singleWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ singleWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       late dart.core::int* match;
       dart.core::bool matchFound = false;
@@ -114,7 +114,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ join([dart.core::String separator = #C4]) → dart.core::String {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ join([dart.core::String separator = #C4]) → dart.core::String {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         return "";
       dart.core::StringBuffer buffer = let final dart.core::StringBuffer #t1 = new dart.core::StringBuffer::•() in block {
@@ -122,15 +122,15 @@ library from "org-dartlang-test:///main.dart" as main {
       } =>#t1;
       return buffer.{dart.core::StringBuffer::toString}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ where((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ where((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::WhereIterable::•<dart.core::int*>(this, test);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ whereType<T extends dart.core::Object? = dynamic>() → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::whereType::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ whereType<T extends dart.core::Object? = dynamic>() → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::whereType::T%>
       return new dart._internal::WhereTypeIterable::•<main::_WithListMixin&Object&ListMixin::whereType::T%>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ map<T extends dart.core::Object? = dynamic>((dart.core::int*) → main::_WithListMixin&Object&ListMixin::map::T% f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::map::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ map<T extends dart.core::Object? = dynamic>((dart.core::int*) → main::_WithListMixin&Object&ListMixin::map::T% f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::map::T%>
       return new dart._internal::MappedListIterable::•<dart.core::int*, main::_WithListMixin&Object&ListMixin::map::T%>(this, f);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ expand<T extends dart.core::Object? = dynamic>((dart.core::int*) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%> f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ expand<T extends dart.core::Object? = dynamic>((dart.core::int*) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%> f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%>
       return new dart._internal::ExpandIterable::•<dart.core::int*, main::_WithListMixin&Object&ListMixin::expand::T%>(this, f);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ reduce(generic-covariant-impl (dart.core::int*, dart.core::int*) → dart.core::int* combine) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ reduce(generic-covariant-impl (dart.core::int*, dart.core::int*) → dart.core::int* combine) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       if(length.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
@@ -143,7 +143,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return value;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ fold<T extends dart.core::Object? = dynamic>(main::_WithListMixin&Object&ListMixin::fold::T% initialValue, (main::_WithListMixin&Object&ListMixin::fold::T%, dart.core::int*) → main::_WithListMixin&Object&ListMixin::fold::T% combine) → main::_WithListMixin&Object&ListMixin::fold::T% {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ fold<T extends dart.core::Object? = dynamic>(main::_WithListMixin&Object&ListMixin::fold::T% initialValue, (main::_WithListMixin&Object&ListMixin::fold::T%, dart.core::int*) → main::_WithListMixin&Object&ListMixin::fold::T% combine) → main::_WithListMixin&Object&ListMixin::fold::T% {
       main::_WithListMixin&Object&ListMixin::fold::T% value = initialValue;
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
@@ -154,17 +154,17 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return value;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ skip(dart.core::int count) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ skip(dart.core::int count) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, count, null);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ skipWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ skipWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
       return new dart._internal::SkipWhileIterable::•<dart.core::int*>(this, test);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ take(dart.core::int count) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ take(dart.core::int count) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, 0, count);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ takeWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ takeWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
       return new dart._internal::TakeWhileIterable::•<dart.core::int*>(this, test);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toList({dart.core::bool growable = #C5}) → dart.core::List<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toList({dart.core::bool growable = #C5}) → dart.core::List<dart.core::int*> {
       if(this.{dart.collection::ListMixin::isEmpty})
         return dart.core::List::empty<dart.core::int*>(growable: growable);
       dart.core::int* first = this.{dart.core::List::[]}(0);
@@ -174,14 +174,14 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toSet() → dart.core::Set<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toSet() → dart.core::Set<dart.core::int*> {
       dart.core::Set<dart.core::int*> result = dart.collection::LinkedHashSet::•<dart.core::int*>();
       for (dart.core::int i = 0; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
         result.{dart.core::Set::add}(this.{dart.core::List::[]}(i));
       }
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ addAll(generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ addAll(generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       dart.core::int i = this.{dart.core::List::length};
       {
         dart.core::Iterator<dart.core::int*> :sync-for-iterator = iterable.{dart.core::Iterable::iterator};
@@ -195,7 +195,7 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ remove(dart.core::Object? element) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ remove(dart.core::Object? element) → dart.core::bool {
       for (dart.core::int i = 0; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
         if(this.{dart.core::List::[]}(i).{dart.core::Object::==}(element)) {
           this.{dart.collection::ListMixin::_closeGap}(i, i.{dart.core::num::+}(1));
@@ -204,7 +204,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _closeGap(dart.core::int start, dart.core::int end) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _closeGap(dart.core::int start, dart.core::int end) → void {
       dart.core::int length = this.{dart.core::List::length};
       assert(0.{dart.core::num::<=}(start));
       assert(start.{dart.core::num::<}(end));
@@ -215,13 +215,13 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       this.{dart.core::List::length} = length.{dart.core::num::-}(size);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeWhere((dart.core::int*) → dart.core::bool test) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeWhere((dart.core::int*) → dart.core::bool test) → void {
       this.{dart.collection::ListMixin::_filter}(test, false);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ retainWhere((dart.core::int*) → dart.core::bool test) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ retainWhere((dart.core::int*) → dart.core::bool test) → void {
       this.{dart.collection::ListMixin::_filter}(test, true);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _filter((dart.core::int*) → dart.core::bool test, dart.core::bool retainMatching) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _filter((dart.core::int*) → dart.core::bool test, dart.core::bool retainMatching) → void {
       dart.core::List<dart.core::int*> retained = <dart.core::int*>[];
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
@@ -238,12 +238,12 @@ library from "org-dartlang-test:///main.dart" as main {
         this.{dart.core::List::length} = retained.{dart.core::List::length};
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ cast<R extends dart.core::Object? = dynamic>() → dart.core::List<main::_WithListMixin&Object&ListMixin::cast::R%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ cast<R extends dart.core::Object? = dynamic>() → dart.core::List<main::_WithListMixin&Object&ListMixin::cast::R%>
       return dart.core::List::castFrom<dart.core::int*, main::_WithListMixin&Object&ListMixin::cast::R%>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ sort([(dart.core::int*, dart.core::int*) →? dart.core::int compare = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ sort([(dart.core::int*, dart.core::int*) →? dart.core::int compare = #C2]) → void {
       dart._internal::Sort::sort<dart.core::int*>(this, let final (dart.core::int*, dart.core::int*) →? dart.core::int #t2 = compare in #t2.{dart.core::Object::==}(null) ?{(dart.core::int*, dart.core::int*) → dart.core::int} #C6 : #t2{(dart.core::int*, dart.core::int*) → dart.core::int});
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ shuffle([dart.math::Random? random = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ shuffle([dart.math::Random? random = #C2]) → void {
       random.{dart.core::Object::==}(null) ?{dart.math::Random} random = dart.math::Random::•() : null;
       if(random{dart.math::Random}.{dart.core::Object::==}(null))
         throw "!";
@@ -256,10 +256,10 @@ library from "org-dartlang-test:///main.dart" as main {
         this.{dart.core::List::[]=}(pos, tmp);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ asMap() → dart.core::Map<dart.core::int, dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ asMap() → dart.core::Map<dart.core::int, dart.core::int*> {
       return new dart._internal::ListMapView::•<dart.core::int*>(this);
     }
-    operator /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ +(generic-covariant-impl dart.core::List<dart.core::int*> other) → dart.core::List<dart.core::int*>
+    operator /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ +(generic-covariant-impl dart.core::List<dart.core::int*> other) → dart.core::List<dart.core::int*>
       return block {
         final dart.core::List<dart.core::int*> #t3 = <dart.core::int*>[];
         {
@@ -277,7 +277,7 @@ library from "org-dartlang-test:///main.dart" as main {
           }
         }
       } =>#t3;
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ sublist(dart.core::int start, [dart.core::int? end = #C2]) → dart.core::List<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ sublist(dart.core::int start, [dart.core::int? end = #C2]) → dart.core::List<dart.core::int*> {
       dart.core::int listLength = this.{dart.core::List::length};
       end.{dart.core::num::==}(null) ?{dart.core::int} end = listLength : null;
       if(end{dart.core::int}.{dart.core::num::==}(null))
@@ -285,24 +285,24 @@ library from "org-dartlang-test:///main.dart" as main {
       dart.core::RangeError::checkValidRange(start, end{dart.core::int}, listLength);
       return dart.core::List::from<dart.core::int*>(this.{dart.collection::ListMixin::getRange}(start, end{dart.core::int}));
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ getRange(dart.core::int start, dart.core::int end) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ getRange(dart.core::int start, dart.core::int end) → dart.core::Iterable<dart.core::int*> {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, start, end);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeRange(dart.core::int start, dart.core::int end) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeRange(dart.core::int start, dart.core::int end) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       if(end.{dart.core::num::>}(start)) {
         this.{dart.collection::ListMixin::_closeGap}(start, end);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ fillRange(dart.core::int start, dart.core::int end, [generic-covariant-impl dart.core::int? fill = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ fillRange(dart.core::int start, dart.core::int end, [generic-covariant-impl dart.core::int? fill = #C2]) → void {
       dart.core::int* value = let dart.core::int? #t6 = fill in #t6.==(null) ?{dart.core::int*} #t6 : #t6{dart.core::int*};
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       for (dart.core::int i = start; i.{dart.core::num::<}(end); i = i.{dart.core::num::+}(1)) {
         this.{dart.core::List::[]=}(i, value);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ setRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable, [dart.core::int skipCount = #C7]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ setRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable, [dart.core::int skipCount = #C7]) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       dart.core::int length = end.{dart.core::num::-}(start);
       if(length.{dart.core::num::==}(0))
@@ -332,7 +332,7 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ replaceRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> newContents) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ replaceRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> newContents) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       if(start.{dart.core::num::==}(this.{dart.core::List::length})) {
         this.{dart.collection::ListMixin::addAll}(newContents);
@@ -382,7 +382,7 @@ library from "org-dartlang-test:///main.dart" as main {
           this.{dart.collection::ListMixin::setRange}(start, insertEnd, newContents);
         }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ indexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int start = #C7]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ indexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int start = #C7]) → dart.core::int {
       if(start.{dart.core::num::<}(0))
         start = 0;
       for (dart.core::int i = start; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
@@ -391,7 +391,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ indexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int start = #C7]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ indexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int start = #C7]) → dart.core::int {
       if(start.{dart.core::num::<}(0))
         start = 0;
       for (dart.core::int i = start; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
@@ -400,7 +400,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastIndexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int? start = #C2]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastIndexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int? start = #C2]) → dart.core::int {
       if(start.{dart.core::num::==}(null) || start{dart.core::int}.{dart.core::num::>=}(this.{dart.core::List::length}))
         start = this.{dart.core::List::length}.{dart.core::num::-}(1);
       if(start{dart.core::int}.{dart.core::num::==}(null))
@@ -411,7 +411,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastIndexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int? start = #C2]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastIndexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int? start = #C2]) → dart.core::int {
       if(start.{dart.core::num::==}(null) || start{dart.core::int}.{dart.core::num::>=}(this.{dart.core::List::length}))
         start = this.{dart.core::List::length}.{dart.core::num::-}(1);
       if(start{dart.core::int}.{dart.core::num::==}(null))
@@ -422,7 +422,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ insert(dart.core::int index, generic-covariant-impl dart.core::int* element) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ insert(dart.core::int index, generic-covariant-impl dart.core::int* element) → void {
       dart.core::ArgumentError::checkNotNull<dart.core::int>(index, "index");
       dart.core::RangeError::checkValueInInterval(index, 0, this.{dart.core::List::length}, "index");
       if(index.{dart.core::num::==}(this.{dart.core::List::length})) {
@@ -433,12 +433,12 @@ library from "org-dartlang-test:///main.dart" as main {
       this.{dart.collection::ListMixin::setRange}(index.{dart.core::num::+}(1), this.{dart.core::List::length}, this, index);
       this.{dart.core::List::[]=}(index, element);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeAt(dart.core::int index) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeAt(dart.core::int index) → dart.core::int* {
       dart.core::int* result = this.{dart.core::List::[]}(index);
       this.{dart.collection::ListMixin::_closeGap}(index, index.{dart.core::num::+}(1));
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ insertAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ insertAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       dart.core::RangeError::checkValueInInterval(index, 0, this.{dart.core::List::length}, "index");
       if(index.{dart.core::num::==}(this.{dart.core::List::length})) {
         this.{dart.collection::ListMixin::addAll}(iterable);
@@ -465,7 +465,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       this.{dart.collection::ListMixin::setAll}(index, iterable);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ setAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ setAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       if(iterable is{ForNonNullableByDefault} dart.core::List<dynamic>) {
         this.{dart.collection::ListMixin::setRange}(index, index.{dart.core::num::+}(iterable.{dart.core::Iterable::length}), iterable);
       }
@@ -481,9 +481,9 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ reversed() → dart.core::Iterable<dart.core::int*>
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ reversed() → dart.core::Iterable<dart.core::int*>
       return new dart._internal::ReversedListIterable::•<dart.core::int*>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toString() → dart.core::String
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toString() → dart.core::String
       return dart.collection::IterableBase::iterableToFullString(this, "[", "]");
     abstract member-signature get _identityHashCode() → dart.core::int*;
     abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → dart.core::bool*;
@@ -495,40 +495,40 @@ library from "org-dartlang-test:///main.dart" as main {
     abstract member-signature method noSuchMethod(dart.core::Invocation* invocation) → dynamic;
     abstract member-signature get runtimeType() → dart.core::Type*;
     abstract member-signature set length(dart.core::int* newLength) → void;
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ first() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ first() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       return this.{dart.core::List::[]}(0);
     }
-    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ first(generic-covariant-impl dart.core::int* value) → void {
+    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ first(generic-covariant-impl dart.core::int* value) → void {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       this.{dart.core::List::[]=}(0, value);
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ last() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ last() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       return this.{dart.core::List::[]}(this.{dart.core::List::length}.{dart.core::num::-}(1));
     }
-    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ last(generic-covariant-impl dart.core::int* value) → void {
+    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ last(generic-covariant-impl dart.core::int* value) → void {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       this.{dart.core::List::[]=}(this.{dart.core::List::length}.{dart.core::num::-}(1), value);
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ single() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ single() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       if(this.{dart.core::List::length}.{dart.core::num::>}(1))
         throw dart._internal::IterableElementError::tooMany();
       return this.{dart.core::List::[]}(0);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ add(generic-covariant-impl dart.core::int* element) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ add(generic-covariant-impl dart.core::int* element) → void {
       this.{dart.core::List::[]=}(let final dart.core::int #t9 = this.{dart.core::List::length} in let final dart.core::int #t10 = this.{dart.core::List::length} = #t9.{dart.core::num::+}(1) in #t9, element);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ clear() → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ clear() → void {
       this.{dart.core::List::length} = 0;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeLast() → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeLast() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0)) {
         throw dart._internal::IterableElementError::noElement();
       }
@@ -536,7 +536,7 @@ library from "org-dartlang-test:///main.dart" as main {
       this.{dart.core::List::length} = this.{dart.core::List::length}.{dart.core::num::-}(1);
       return result;
     }
-    static method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _compareAny(dynamic a, dynamic b) → dart.core::int {
+    static method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _compareAny(dynamic a, dynamic b) → dart.core::int {
       return dart.core::Comparable::compare(a as{ForNonNullableByDefault} dart.core::Comparable<dynamic>, b as{ForNonNullableByDefault} dart.core::Comparable<dynamic>);
     }
   }

pkg/front_end/testcases/incremental_initialize_from_dill/no_outline_change_22.yaml.world.2.expect

@@ -10,13 +10,13 @@ library from "org-dartlang-test:///main.dart" as main {
     abstract member-signature get length() → dart.core::int*;
     abstract member-signature operator [](dart.core::int* index) → dart.core::int*;
     abstract member-signature operator []=(dart.core::int* index, generic-covariant-impl dart.core::int* value) → void;
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ iterator() → dart.core::Iterator<dart.core::int*>
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ iterator() → dart.core::Iterator<dart.core::int*>
       return new dart._internal::ListIterator::•<dart.core::int*>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ elementAt(dart.core::int index) → dart.core::int*
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ elementAt(dart.core::int index) → dart.core::int*
       return this.{dart.core::List::[]}(index);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ followedBy(generic-covariant-impl dart.core::Iterable<dart.core::int*> other) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ followedBy(generic-covariant-impl dart.core::Iterable<dart.core::int*> other) → dart.core::Iterable<dart.core::int*>
       return dart._internal::FollowedByIterable::firstEfficient<dart.core::int*>(this, other);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ forEach((dart.core::int*) → void action) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ forEach((dart.core::int*) → void action) → void {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         action.call(this.{dart.core::List::[]}(i));
@@ -26,11 +26,11 @@ library from "org-dartlang-test:///main.dart" as main {
       }
     }
     @#C3
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ isEmpty() → dart.core::bool
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ isEmpty() → dart.core::bool
       return this.{dart.core::List::length}.{dart.core::num::==}(0);
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ isNotEmpty() → dart.core::bool
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ isNotEmpty() → dart.core::bool
       return !this.{dart.collection::ListMixin::isEmpty};
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ contains(dart.core::Object? element) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ contains(dart.core::Object? element) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(this.{dart.core::List::[]}(i).{dart.core::Object::==}(element))
@@ -41,7 +41,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ every((dart.core::int*) → dart.core::bool test) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ every((dart.core::int*) → dart.core::bool test) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(!test.call(this.{dart.core::List::[]}(i)))
@@ -52,7 +52,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return true;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ any((dart.core::int*) → dart.core::bool test) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ any((dart.core::int*) → dart.core::bool test) → dart.core::bool {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         if(test.call(this.{dart.core::List::[]}(i)))
@@ -63,7 +63,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ firstWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ firstWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
         dart.core::int* element = this.{dart.core::List::[]}(i);
@@ -77,7 +77,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = length.{dart.core::num::-}(1); i.{dart.core::num::>=}(0); i = i.{dart.core::num::-}(1)) {
         dart.core::int* element = this.{dart.core::List::[]}(i);
@@ -91,7 +91,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ singleWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ singleWhere((dart.core::int*) → dart.core::bool test, {generic-covariant-impl () →? dart.core::int* orElse = #C2}) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       late dart.core::int* match;
       dart.core::bool matchFound = false;
@@ -114,7 +114,7 @@ library from "org-dartlang-test:///main.dart" as main {
         return orElse{() → dart.core::int*}.call();
       throw dart._internal::IterableElementError::noElement();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ join([dart.core::String separator = #C4]) → dart.core::String {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ join([dart.core::String separator = #C4]) → dart.core::String {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         return "";
       dart.core::StringBuffer buffer = let final dart.core::StringBuffer #t1 = new dart.core::StringBuffer::•() in block {
@@ -122,15 +122,15 @@ library from "org-dartlang-test:///main.dart" as main {
       } =>#t1;
       return buffer.{dart.core::StringBuffer::toString}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ where((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ where((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::WhereIterable::•<dart.core::int*>(this, test);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ whereType<T extends dart.core::Object? = dynamic>() → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::whereType::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ whereType<T extends dart.core::Object? = dynamic>() → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::whereType::T%>
       return new dart._internal::WhereTypeIterable::•<main::_WithListMixin&Object&ListMixin::whereType::T%>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ map<T extends dart.core::Object? = dynamic>((dart.core::int*) → main::_WithListMixin&Object&ListMixin::map::T% f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::map::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ map<T extends dart.core::Object? = dynamic>((dart.core::int*) → main::_WithListMixin&Object&ListMixin::map::T% f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::map::T%>
       return new dart._internal::MappedListIterable::•<dart.core::int*, main::_WithListMixin&Object&ListMixin::map::T%>(this, f);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ expand<T extends dart.core::Object? = dynamic>((dart.core::int*) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%> f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ expand<T extends dart.core::Object? = dynamic>((dart.core::int*) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%> f) → dart.core::Iterable<main::_WithListMixin&Object&ListMixin::expand::T%>
       return new dart._internal::ExpandIterable::•<dart.core::int*, main::_WithListMixin&Object&ListMixin::expand::T%>(this, f);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ reduce(generic-covariant-impl (dart.core::int*, dart.core::int*) → dart.core::int* combine) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ reduce(generic-covariant-impl (dart.core::int*, dart.core::int*) → dart.core::int* combine) → dart.core::int* {
       dart.core::int length = this.{dart.core::List::length};
       if(length.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
@@ -143,7 +143,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return value;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ fold<T extends dart.core::Object? = dynamic>(main::_WithListMixin&Object&ListMixin::fold::T% initialValue, (main::_WithListMixin&Object&ListMixin::fold::T%, dart.core::int*) → main::_WithListMixin&Object&ListMixin::fold::T% combine) → main::_WithListMixin&Object&ListMixin::fold::T% {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ fold<T extends dart.core::Object? = dynamic>(main::_WithListMixin&Object&ListMixin::fold::T% initialValue, (main::_WithListMixin&Object&ListMixin::fold::T%, dart.core::int*) → main::_WithListMixin&Object&ListMixin::fold::T% combine) → main::_WithListMixin&Object&ListMixin::fold::T% {
       main::_WithListMixin&Object&ListMixin::fold::T% value = initialValue;
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
@@ -154,17 +154,17 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return value;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ skip(dart.core::int count) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ skip(dart.core::int count) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, count, null);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ skipWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ skipWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
       return new dart._internal::SkipWhileIterable::•<dart.core::int*>(this, test);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ take(dart.core::int count) → dart.core::Iterable<dart.core::int*>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ take(dart.core::int count) → dart.core::Iterable<dart.core::int*>
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, 0, count);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ takeWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ takeWhile((dart.core::int*) → dart.core::bool test) → dart.core::Iterable<dart.core::int*> {
       return new dart._internal::TakeWhileIterable::•<dart.core::int*>(this, test);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toList({dart.core::bool growable = #C5}) → dart.core::List<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toList({dart.core::bool growable = #C5}) → dart.core::List<dart.core::int*> {
       if(this.{dart.collection::ListMixin::isEmpty})
         return dart.core::List::empty<dart.core::int*>(growable: growable);
       dart.core::int* first = this.{dart.core::List::[]}(0);
@@ -174,14 +174,14 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toSet() → dart.core::Set<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toSet() → dart.core::Set<dart.core::int*> {
       dart.core::Set<dart.core::int*> result = dart.collection::LinkedHashSet::•<dart.core::int*>();
       for (dart.core::int i = 0; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
         result.{dart.core::Set::add}(this.{dart.core::List::[]}(i));
       }
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ addAll(generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ addAll(generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       dart.core::int i = this.{dart.core::List::length};
       {
         dart.core::Iterator<dart.core::int*> :sync-for-iterator = iterable.{dart.core::Iterable::iterator};
@@ -195,7 +195,7 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ remove(dart.core::Object? element) → dart.core::bool {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ remove(dart.core::Object? element) → dart.core::bool {
       for (dart.core::int i = 0; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
         if(this.{dart.core::List::[]}(i).{dart.core::Object::==}(element)) {
           this.{dart.collection::ListMixin::_closeGap}(i, i.{dart.core::num::+}(1));
@@ -204,7 +204,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return false;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _closeGap(dart.core::int start, dart.core::int end) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _closeGap(dart.core::int start, dart.core::int end) → void {
       dart.core::int length = this.{dart.core::List::length};
       assert(0.{dart.core::num::<=}(start));
       assert(start.{dart.core::num::<}(end));
@@ -215,13 +215,13 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       this.{dart.core::List::length} = length.{dart.core::num::-}(size);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeWhere((dart.core::int*) → dart.core::bool test) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeWhere((dart.core::int*) → dart.core::bool test) → void {
       this.{dart.collection::ListMixin::_filter}(test, false);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ retainWhere((dart.core::int*) → dart.core::bool test) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ retainWhere((dart.core::int*) → dart.core::bool test) → void {
       this.{dart.collection::ListMixin::_filter}(test, true);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _filter((dart.core::int*) → dart.core::bool test, dart.core::bool retainMatching) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _filter((dart.core::int*) → dart.core::bool test, dart.core::bool retainMatching) → void {
       dart.core::List<dart.core::int*> retained = <dart.core::int*>[];
       dart.core::int length = this.{dart.core::List::length};
       for (dart.core::int i = 0; i.{dart.core::num::<}(length); i = i.{dart.core::num::+}(1)) {
@@ -238,12 +238,12 @@ library from "org-dartlang-test:///main.dart" as main {
         this.{dart.core::List::length} = retained.{dart.core::List::length};
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ cast<R extends dart.core::Object? = dynamic>() → dart.core::List<main::_WithListMixin&Object&ListMixin::cast::R%>
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ cast<R extends dart.core::Object? = dynamic>() → dart.core::List<main::_WithListMixin&Object&ListMixin::cast::R%>
       return dart.core::List::castFrom<dart.core::int*, main::_WithListMixin&Object&ListMixin::cast::R%>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ sort([(dart.core::int*, dart.core::int*) →? dart.core::int compare = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ sort([(dart.core::int*, dart.core::int*) →? dart.core::int compare = #C2]) → void {
       dart._internal::Sort::sort<dart.core::int*>(this, let final (dart.core::int*, dart.core::int*) →? dart.core::int #t2 = compare in #t2.{dart.core::Object::==}(null) ?{(dart.core::int*, dart.core::int*) → dart.core::int} #C6 : #t2{(dart.core::int*, dart.core::int*) → dart.core::int});
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ shuffle([dart.math::Random? random = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ shuffle([dart.math::Random? random = #C2]) → void {
       random.{dart.core::Object::==}(null) ?{dart.math::Random} random = dart.math::Random::•() : null;
       if(random{dart.math::Random}.{dart.core::Object::==}(null))
         throw "!";
@@ -256,10 +256,10 @@ library from "org-dartlang-test:///main.dart" as main {
         this.{dart.core::List::[]=}(pos, tmp);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ asMap() → dart.core::Map<dart.core::int, dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ asMap() → dart.core::Map<dart.core::int, dart.core::int*> {
       return new dart._internal::ListMapView::•<dart.core::int*>(this);
     }
-    operator /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ +(generic-covariant-impl dart.core::List<dart.core::int*> other) → dart.core::List<dart.core::int*>
+    operator /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ +(generic-covariant-impl dart.core::List<dart.core::int*> other) → dart.core::List<dart.core::int*>
       return block {
         final dart.core::List<dart.core::int*> #t3 = <dart.core::int*>[];
         {
@@ -277,7 +277,7 @@ library from "org-dartlang-test:///main.dart" as main {
           }
         }
       } =>#t3;
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ sublist(dart.core::int start, [dart.core::int? end = #C2]) → dart.core::List<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ sublist(dart.core::int start, [dart.core::int? end = #C2]) → dart.core::List<dart.core::int*> {
       dart.core::int listLength = this.{dart.core::List::length};
       end.{dart.core::num::==}(null) ?{dart.core::int} end = listLength : null;
       if(end{dart.core::int}.{dart.core::num::==}(null))
@@ -285,24 +285,24 @@ library from "org-dartlang-test:///main.dart" as main {
       dart.core::RangeError::checkValidRange(start, end{dart.core::int}, listLength);
       return dart.core::List::from<dart.core::int*>(this.{dart.collection::ListMixin::getRange}(start, end{dart.core::int}));
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ getRange(dart.core::int start, dart.core::int end) → dart.core::Iterable<dart.core::int*> {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ getRange(dart.core::int start, dart.core::int end) → dart.core::Iterable<dart.core::int*> {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       return new dart._internal::SubListIterable::•<dart.core::int*>(this, start, end);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeRange(dart.core::int start, dart.core::int end) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeRange(dart.core::int start, dart.core::int end) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       if(end.{dart.core::num::>}(start)) {
         this.{dart.collection::ListMixin::_closeGap}(start, end);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ fillRange(dart.core::int start, dart.core::int end, [generic-covariant-impl dart.core::int? fill = #C2]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ fillRange(dart.core::int start, dart.core::int end, [generic-covariant-impl dart.core::int? fill = #C2]) → void {
       dart.core::int* value = let dart.core::int? #t6 = fill in #t6.==(null) ?{dart.core::int*} #t6 : #t6{dart.core::int*};
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       for (dart.core::int i = start; i.{dart.core::num::<}(end); i = i.{dart.core::num::+}(1)) {
         this.{dart.core::List::[]=}(i, value);
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ setRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable, [dart.core::int skipCount = #C7]) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ setRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable, [dart.core::int skipCount = #C7]) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       dart.core::int length = end.{dart.core::num::-}(start);
       if(length.{dart.core::num::==}(0))
@@ -332,7 +332,7 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ replaceRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> newContents) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ replaceRange(dart.core::int start, dart.core::int end, generic-covariant-impl dart.core::Iterable<dart.core::int*> newContents) → void {
       dart.core::RangeError::checkValidRange(start, end, this.{dart.core::List::length});
       if(start.{dart.core::num::==}(this.{dart.core::List::length})) {
         this.{dart.collection::ListMixin::addAll}(newContents);
@@ -382,7 +382,7 @@ library from "org-dartlang-test:///main.dart" as main {
           this.{dart.collection::ListMixin::setRange}(start, insertEnd, newContents);
         }
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ indexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int start = #C7]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ indexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int start = #C7]) → dart.core::int {
       if(start.{dart.core::num::<}(0))
         start = 0;
       for (dart.core::int i = start; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
@@ -391,7 +391,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ indexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int start = #C7]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ indexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int start = #C7]) → dart.core::int {
       if(start.{dart.core::num::<}(0))
         start = 0;
       for (dart.core::int i = start; i.{dart.core::num::<}(this.{dart.core::List::length}); i = i.{dart.core::num::+}(1)) {
@@ -400,7 +400,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastIndexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int? start = #C2]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastIndexOf(generic-covariant-impl dart.core::Object? element, [dart.core::int? start = #C2]) → dart.core::int {
       if(start.{dart.core::num::==}(null) || start{dart.core::int}.{dart.core::num::>=}(this.{dart.core::List::length}))
         start = this.{dart.core::List::length}.{dart.core::num::-}(1);
       if(start{dart.core::int}.{dart.core::num::==}(null))
@@ -411,7 +411,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ lastIndexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int? start = #C2]) → dart.core::int {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ lastIndexWhere((dart.core::int*) → dart.core::bool test, [dart.core::int? start = #C2]) → dart.core::int {
       if(start.{dart.core::num::==}(null) || start{dart.core::int}.{dart.core::num::>=}(this.{dart.core::List::length}))
         start = this.{dart.core::List::length}.{dart.core::num::-}(1);
       if(start{dart.core::int}.{dart.core::num::==}(null))
@@ -422,7 +422,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       return 1.{dart.core::int::unary-}();
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ insert(dart.core::int index, generic-covariant-impl dart.core::int* element) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ insert(dart.core::int index, generic-covariant-impl dart.core::int* element) → void {
       dart.core::ArgumentError::checkNotNull<dart.core::int>(index, "index");
       dart.core::RangeError::checkValueInInterval(index, 0, this.{dart.core::List::length}, "index");
       if(index.{dart.core::num::==}(this.{dart.core::List::length})) {
@@ -433,12 +433,12 @@ library from "org-dartlang-test:///main.dart" as main {
       this.{dart.collection::ListMixin::setRange}(index.{dart.core::num::+}(1), this.{dart.core::List::length}, this, index);
       this.{dart.core::List::[]=}(index, element);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeAt(dart.core::int index) → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeAt(dart.core::int index) → dart.core::int* {
       dart.core::int* result = this.{dart.core::List::[]}(index);
       this.{dart.collection::ListMixin::_closeGap}(index, index.{dart.core::num::+}(1));
       return result;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ insertAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ insertAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       dart.core::RangeError::checkValueInInterval(index, 0, this.{dart.core::List::length}, "index");
       if(index.{dart.core::num::==}(this.{dart.core::List::length})) {
         this.{dart.collection::ListMixin::addAll}(iterable);
@@ -465,7 +465,7 @@ library from "org-dartlang-test:///main.dart" as main {
       }
       this.{dart.collection::ListMixin::setAll}(index, iterable);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ setAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ setAll(dart.core::int index, generic-covariant-impl dart.core::Iterable<dart.core::int*> iterable) → void {
       if(iterable is{ForNonNullableByDefault} dart.core::List<dynamic>) {
         this.{dart.collection::ListMixin::setRange}(index, index.{dart.core::num::+}(iterable.{dart.core::Iterable::length}), iterable);
       }
@@ -481,9 +481,9 @@ library from "org-dartlang-test:///main.dart" as main {
         }
       }
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ reversed() → dart.core::Iterable<dart.core::int*>
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ reversed() → dart.core::Iterable<dart.core::int*>
       return new dart._internal::ReversedListIterable::•<dart.core::int*>(this);
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ toString() → dart.core::String
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ toString() → dart.core::String
       return dart.collection::IterableBase::iterableToFullString(this, "[", "]");
     abstract member-signature get _identityHashCode() → dart.core::int*;
     abstract member-signature method _instanceOf(dynamic instantiatorTypeArguments, dynamic functionTypeArguments, dynamic type) → dart.core::bool*;
@@ -495,40 +495,40 @@ library from "org-dartlang-test:///main.dart" as main {
     abstract member-signature method noSuchMethod(dart.core::Invocation* invocation) → dynamic;
     abstract member-signature get runtimeType() → dart.core::Type*;
     abstract member-signature set length(dart.core::int* newLength) → void;
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ first() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ first() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       return this.{dart.core::List::[]}(0);
     }
-    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ first(generic-covariant-impl dart.core::int* value) → void {
+    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ first(generic-covariant-impl dart.core::int* value) → void {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       this.{dart.core::List::[]=}(0, value);
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ last() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ last() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       return this.{dart.core::List::[]}(this.{dart.core::List::length}.{dart.core::num::-}(1));
     }
-    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ last(generic-covariant-impl dart.core::int* value) → void {
+    set /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ last(generic-covariant-impl dart.core::int* value) → void {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       this.{dart.core::List::[]=}(this.{dart.core::List::length}.{dart.core::num::-}(1), value);
     }
-    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ single() → dart.core::int* {
+    get /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ single() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0))
         throw dart._internal::IterableElementError::noElement();
       if(this.{dart.core::List::length}.{dart.core::num::>}(1))
         throw dart._internal::IterableElementError::tooMany();
       return this.{dart.core::List::[]}(0);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ add(generic-covariant-impl dart.core::int* element) → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ add(generic-covariant-impl dart.core::int* element) → void {
       this.{dart.core::List::[]=}(let final dart.core::int #t9 = this.{dart.core::List::length} in let final dart.core::int #t10 = this.{dart.core::List::length} = #t9.{dart.core::num::+}(1) in #t9, element);
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ clear() → void {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ clear() → void {
       this.{dart.core::List::length} = 0;
     }
-    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ removeLast() → dart.core::int* {
+    method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ removeLast() → dart.core::int* {
       if(this.{dart.core::List::length}.{dart.core::num::==}(0)) {
         throw dart._internal::IterableElementError::noElement();
       }
@@ -536,7 +536,7 @@ library from "org-dartlang-test:///main.dart" as main {
       this.{dart.core::List::length} = this.{dart.core::List::length}.{dart.core::num::-}(1);
       return result;
     }
-    static method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk_nnbd/lib/collection/list.dart */ _compareAny(dynamic a, dynamic b) → dart.core::int {
+    static method /*isNonNullableByDefault, from org-dartlang-sdk:///sdk/lib/collection/list.dart */ _compareAny(dynamic a, dynamic b) → dart.core::int {
       return dart.core::Comparable::compare(a as{ForNonNullableByDefault} dart.core::Comparable<dynamic>, b as{ForNonNullableByDefault} dart.core::Comparable<dynamic>);
     }
   }

pkg/front_end/tool/_fasta/generate_experimental_flags.dart

@@ -37,7 +37,7 @@ Uri computeYamlFile() {
 
 Uri computeAllowListFile() {
   return Platform.script
-      .resolve("../../../../sdk_nnbd/lib/_internal/allowed_experiments.json");
+      .resolve("../../../../sdk/lib/_internal/allowed_experiments.json");
 }
 
 String generateKernelFile() {

pkg/modular_test/lib/src/loader.dart

@@ -204,8 +204,6 @@ Future<void> _addModulePerPackage(
 Future<Module> _createSdkModule(Uri root) async {
   List<Uri> sources = [
     Uri.parse('sdk/lib/libraries.json'),
-    // TODO(#38701) Cleanup after merging the forked SDK into mainline.
-    Uri.parse('sdk_nnbd/lib/libraries.json'),
   ];
 
   // Include all dart2js, ddc, vm library sources and patch files.
@@ -213,8 +211,6 @@ Future<Module> _createSdkModule(Uri root) async {
   // it doesn't list files that are transitively imported.
   var sdkLibrariesAndPatchesRoots = [
     'sdk/lib/',
-    // TODO(#38701) Cleanup after merging the forked SDK into mainline.
-    'sdk_nnbd/lib/',
     'runtime/lib/',
     'runtime/bin/',
   ];

pkg/nnbd_migration/tool/src/package.dart

@@ -217,15 +217,4 @@ class Sdk {
   Sdk(String sdkPath) {
     this.sdkPath = path.canonicalize(sdkPath);
   }
-
-  /// Returns true if the SDK was built with --nnbd.
-  ///
-  /// May throw if [sdkPath] is invalid, or there is an error parsing
-  /// the libraries.json file.
-  bool get isNnbdSdk {
-    // TODO(jcollins-g): contact eng-prod for a more foolproof detection method
-    String libraries = path.join(sdkPath, 'lib', 'libraries.json');
-    var decodedJson = JsonDecoder().convert(File(libraries).readAsStringSync());
-    return ((decodedJson['comment:1'] as String).contains('sdk_nnbd'));
-  }
 }

pkg/nnbd_migration/tool/trial_migration.dart

@@ -27,7 +27,6 @@ main(List<String> args) async {
   Sdk sdk = Sdk(parsedArgs['sdk'] as String);
 
   warnOnNoAssertions();
-  warnOnNoSdkNnbd(sdk);
 
   Playground playground =
       Playground(defaultPlaygroundPath, parsedArgs['clean'] as bool);
@@ -218,17 +217,6 @@ void warnOnNoAssertions() {
   printWarning("You didn't --enable-asserts!");
 }
 
-void warnOnNoSdkNnbd(Sdk sdk) {
-  try {
-    if (sdk.isNnbdSdk) return;
-  } catch (e) {
-    printWarning('Unable to determine whether this SDK supports NNBD');
-    return;
-  }
-  printWarning(
-      'SDK at ${sdk.sdkPath} not compiled with --nnbd, use --sdk option');
-}
-
 class ExceptionCategory {
   final String topOfStack;
   final List<MapEntry<String, int>> exceptionCountPerPackage;

pkg/test_runner/lib/src/compiler_configuration.dart

@@ -367,9 +367,7 @@ class Dart2xCompilerConfiguration extends CompilerConfiguration {
       : super._subclass(configuration);
 
   String computeCompilerPath() {
-    var prefix =
-        // TODO(38701): Cleanup after merging the forked SDK into mainline.
-        _configuration.nnbdMode == NnbdMode.legacy ? 'sdk/bin' : 'sdk_nnbd/bin';
+    var prefix = 'sdk/bin';
     var suffix = shellScriptExtension;
 
     if (_isHostChecked) {
@@ -461,9 +459,7 @@ class Dart2jsCompilerConfiguration extends Dart2xCompilerConfiguration {
       CommandArtifact artifact) {
     var sdk = _useSdk
         ? Uri.directory(_configuration.buildDirectory).resolve('dart-sdk/')
-        : Uri.directory(Repository.dir.toNativePath()).resolve(
-            // TODO(38701): Cleanup after merging the forked SDK into mainline.
-            _configuration.nnbdMode == NnbdMode.legacy ? 'sdk/' : 'sdk_nnbd/');
+        : Uri.directory(Repository.dir.toNativePath()).resolve('sdk/');
     var preambleDir = sdk.resolve('lib/_internal/js_runtime/lib/preambles/');
     return runtimeConfiguration.dart2jsPreambles(preambleDir)
       ..add(artifact.filename);
@@ -494,10 +490,7 @@ class DevCompilerConfiguration extends CompilerConfiguration {
   bool get useKernel => _configuration.compiler == Compiler.dartdevk;
 
   String computeCompilerPath() {
-    var dir = _useSdk
-        ? "${_configuration.buildDirectory}/dart-sdk"
-        // TODO(38701): Cleanup after merging the forked SDK into mainline.
-        : _configuration.nnbdMode == NnbdMode.legacy ? "sdk" : "sdk_nnbd";
+    var dir = _useSdk ? "${_configuration.buildDirectory}/dart-sdk" : "sdk";
     return "$dir/bin/dartdevc$shellScriptExtension";
   }
 
@@ -508,8 +501,7 @@ class DevCompilerConfiguration extends CompilerConfiguration {
       ..._configuration.sharedOptions,
       ..._experimentsArgument(_configuration, testFile),
       ...testFile.ddcOptions,
-      if (_configuration.nnbdMode == NnbdMode.strong)
-        '--sound-null-safety',
+      if (_configuration.nnbdMode == NnbdMode.strong) '--sound-null-safety',
       // The file being compiled is the last argument.
       args.last
     ];
@@ -712,14 +704,11 @@ class PrecompilerCompilerConfiguration extends CompilerConfiguration
         "--snapshot-kind=app-aot-assembly",
         "--assembly=$tempDir/out.S"
       ],
-      if (_isAndroid && _isArm)
-        '--no-sim-use-hardfp',
-      if (_configuration.isMinified)
-        '--obfuscate',
+      if (_isAndroid && _isArm) '--no-sim-use-hardfp',
+      if (_configuration.isMinified) '--obfuscate',
       // The SIMARM precompiler assumes support for integer division, but the
       // Qemu arm cpus do not support integer division.
-      if (_configuration.useQemu)
-        '--no-use-integer-division',
+      if (_configuration.useQemu) '--no-use-integer-division',
       ..._replaceDartFiles(arguments, tempKernelFile(tempDir)),
     ];
 
@@ -936,9 +925,7 @@ class AnalyzerCompilerConfiguration extends CompilerConfiguration {
   int get timeoutMultiplier => 4;
 
   String computeCompilerPath() {
-    var prefix =
-        // TODO(38701): Cleanup after merging the forked SDK into mainline.
-        _configuration.nnbdMode == NnbdMode.legacy ? 'sdk/bin' : 'sdk_nnbd/bin';
+    var prefix = 'sdk/bin';
     if (_isHostChecked) {
       if (_useSdk) {
         throw "--host-checked and --use-sdk cannot be used together";

pkg/test_runner/lib/src/configuration.dart

@@ -69,8 +69,7 @@ class TestConfiguration {
       this.reproducingArguments,
       this.fastTestsOnly,
       this.printPassingStdout})
-      : _packages = packages,
-        isPreNNBD = configuration.name.split('-').contains('prennbd');
+      : _packages = packages;
 
   final Map<String, RegExp> selectors;
   final Progress progress;
@@ -99,7 +98,6 @@ class TestConfiguration {
   final bool writeResults;
   final bool writeLogs;
   final bool printPassingStdout;
-  final bool isPreNNBD;
 
   Architecture get architecture => configuration.architecture;
   Compiler get compiler => configuration.compiler;
@@ -470,13 +468,6 @@ class TestConfiguration {
     var normal = '$result$arch';
     var cross = '${result}X$arch';
 
-    // TODO(sigmund): remove once all prennbd coverage is dropped. Currently
-    // only dart2js supports opting-out of using the nnbd sdk.
-    if (isPreNNBD) {
-      normal += 'Legacy';
-      cross += 'Legacy';
-    }
-
     var outDir = system.outputDirectory;
     var normalDir = Directory(Path('$outDir$normal').toNativePath());
     var crossDir = Directory(Path('$outDir$cross').toNativePath());

runtime/bin/BUILD.gn

@@ -528,14 +528,9 @@ gen_snapshot_action("generate_snapshot_bin") {
     isolate_snapshot_data,
     isolate_snapshot_instructions,
   ]
-  args = []
-  if (!dont_use_nnbd) {
-    args += [
-      "--enable-experiment=non-nullable",
-      "--null-safety",
-    ]
-  }
-  args += [
+  args = [
+    "--enable-experiment=non-nullable",
+    "--null-safety",
     "--deterministic",
     "--snapshot_kind=" + dart_core_snapshot_kind,
     "--vm_snapshot_data=" + rebase_path(vm_snapshot_data, root_build_dir),

runtime/vm/BUILD.gn

@@ -155,12 +155,7 @@ template("gen_vm_platform") {
     }
     single_root_scheme = "org-dartlang-sdk"
     single_root_base = rebase_path("../../")
-    if (!dont_use_nnbd) {
-      libraries_specification_uri =
-          "org-dartlang-sdk:///sdk_nnbd/lib/libraries.json"
-    } else {
-      libraries_specification_uri = "org-dartlang-sdk:///sdk/lib/libraries.json"
-    }
+    libraries_specification_uri = "org-dartlang-sdk:///sdk/lib/libraries.json"
     outputs = [
       "$root_out_dir/vm_platform" + output_postfix + ".dill",
       "$root_out_dir/vm_outline" + output_postfix + ".dill",
@@ -172,11 +167,9 @@ template("gen_vm_platform") {
       "-Ddart.vm.product=$is_product_flag",
       "-Ddart.developer.causal_async_stacks=$allow_causal_async_stacks",
       "-Ddart.isVM=true",
+      "--enable-experiment=non-nullable",
+      "--nnbd-agnostic",
     ]
-    if (!dont_use_nnbd) {
-      args += [ "--enable-experiment=non-nullable" ]
-      args += [ "--nnbd-agnostic" ]
-    }
     if (defined(invoker.exclude_source) && invoker.exclude_source) {
       args += [ "--exclude-source" ]
     }

sdk/BUILD.gn

@@ -618,11 +618,15 @@ copy("copy_dart2js_dill_files") {
   visibility = [ ":create_full_sdk" ]
   deps = [
     ":copy_libraries",
+    "../utils/compiler:compile_dart2js_nnbd_strong_platform",
     "../utils/compiler:compile_dart2js_platform",
+    "../utils/compiler:compile_dart2js_server_nnbd_strong_platform",
     "../utils/compiler:compile_dart2js_server_platform",
   ]
   sources = [
+    "$root_out_dir/dart2js_nnbd_strong_platform.dill",
     "$root_out_dir/dart2js_platform.dill",
+    "$root_out_dir/dart2js_server_nnbd_strong_platform.dill",
     "$root_out_dir/dart2js_server_platform.dill",
   ]
   outputs = [ "$root_out_dir/dart-sdk/lib/_internal/{{source_file_part}}" ]
@@ -636,9 +640,22 @@ copy("copy_dev_compiler_outline") {
     "../utils/dartdevc:dartdevc_platform",
   ]
   sources = [ "$root_out_dir/ddc_outline.dill" ]
+
+  # TODO(nshahan) Fix the name here to be consistent and merge with below.
   outputs = [ "$root_out_dir/dart-sdk/lib/_internal/ddc_sdk.dill" ]
 }
 
+# Copies DDC's SDK outline .dill with sound null safety to lib/_internal
+copy("copy_dev_compiler_outline_sound") {
+  visibility = [ "../utils/dartdevc:dartdevc_test" ]
+  deps = [
+    ":copy_libraries",
+    "../utils/dartdevc:dartdevc_platform_sound",
+  ]
+  sources = [ "$root_out_dir/ddc_outline_sound.dill" ]
+  outputs = [ "$root_out_dir/dart-sdk/lib/_internal/{{source_file_part}}" ]
+}
+
 # This rule copies DDK's JS SDK and require.js to lib/dev_compiler/kernel/amd.
 copy("copy_dev_compiler_js_amd_kernel") {
   visibility = [ ":copy_dev_compiler_js" ]

sdk/bin/dart2js

@@ -52,4 +52,4 @@ DART_ROOT="$(cd "${SDK_DIR}/.." ; pwd -P)"
 
 DART2JS="package:compiler/src/dart2js.dart"
 
-exec "$DART" "--packages=$DART_ROOT/.packages" "${EXTRA_VM_OPTIONS[@]}" "$DART2JS" "${EXTRA_OPTIONS[@]}" "$@"
+exec "$DART" "--packages=$DART_ROOT/.packages" --enable-experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$DART2JS" "${EXTRA_OPTIONS[@]}" "$@"

sdk/bin/dart2js_sdk

@@ -55,4 +55,4 @@ if [[ $DART_VM_OPTIONS ]]; then
   EXTRA_VM_OPTIONS+=("${OPTIONS[@]}")
 fi
 
-exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "${EXTRA_OPTIONS[@]}" "$@"
+exec "$DART" --enable-experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "${EXTRA_OPTIONS[@]}" "$@"

sdk/bin/dartanalyzer

@@ -28,6 +28,7 @@ DART="$BIN_DIR/dart"
 
 unset EXTRA_VM_OPTIONS
 declare -a EXTRA_VM_OPTIONS
+EXTRA_VM_OPTIONS+=("--enable_experiment=non-nullable")
 
 case $0 in
   *_developer)

sdk/bin/dartanalyzer_sdk

@@ -28,4 +28,4 @@ SNAPSHOT="$BIN_DIR/snapshots/dartanalyzer.dart.snapshot"
 
 # We are running the snapshot in the built SDK.
 DART="$BIN_DIR/dart"
-exec "$DART" "$SNAPSHOT" "$SDK_ARG" "$@"
+exec "$DART" --enable_experiment=non-nullable "$SNAPSHOT" "$SDK_ARG" "$@"

sdk/bin/dartdevc

@@ -45,4 +45,4 @@ DART_ROOT="$(cd "${SDK_DIR}/.." ; pwd -P)"
 
 DEV_COMPILER="$DART_ROOT/pkg/dev_compiler/bin/dartdevc.dart"
 
-exec "$DART" "--packages=$DART_ROOT/.packages" "${EXTRA_VM_OPTIONS[@]}" "$DEV_COMPILER" "$SDK_ARG" "$@"
+exec "$DART" "--packages=$DART_ROOT/.packages" --enable_experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$DEV_COMPILER" "$SDK_ARG" "$@"

sdk/bin/dartdevc_sdk

@@ -35,4 +35,4 @@ if [[ $DART_VM_OPTIONS ]]; then
   EXTRA_VM_OPTIONS+=("${OPTIONS[@]}")
 fi
 
-exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "$@"
+exec "$DART" --enable_experiment=non-nullable "${EXTRA_VM_OPTIONS[@]}" "$SNAPSHOT" "$@"

sdk/lib/_http/crypto.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 class _CryptoUtils {
@@ -68,7 +66,7 @@ class _CryptoUtils {
     }
     final String lookup = urlSafe ? _encodeTableUrlSafe : _encodeTable;
     // Size of 24 bit chunks.
-    final int remainderLength = len.remainder(3);
+    final int remainderLength = len.remainder(3) as int;
     final int chunkLength = len - remainderLength;
     // Size of base output.
     int outputLen = ((len ~/ 3) * 4) + ((remainderLength > 0) ? 4 : 0);
@@ -76,7 +74,7 @@ class _CryptoUtils {
     if (addLineSeparator) {
       outputLen += ((outputLen - 1) ~/ LINE_LENGTH) << 1;
     }
-    List<int> out = new List<int>(outputLen);
+    List<int> out = new List<int>.filled(outputLen, 0);
 
     // Encode 24 bit chunks.
     int j = 0, i = 0, c = 0;
@@ -120,7 +118,7 @@ class _CryptoUtils {
       [bool ignoreInvalidCharacters = true]) {
     int len = input.length;
     if (len == 0) {
-      return new List<int>(0);
+      return new List<int>.empty();
     }
 
     // Count '\r', '\n' and illegal characters, For illegal characters,
@@ -149,7 +147,7 @@ class _CryptoUtils {
       if (currentCodeUnit == PAD) padLength++;
     }
     int outputLen = (((len - extrasLen) * 6) >> 3) - padLength;
-    List<int> out = new List<int>(outputLen);
+    List<int> out = new List<int>.filled(outputLen, 0);
 
     for (int i = 0, o = 0; o < outputLen;) {
       // Accumulate 4 valid 6 bit Base 64 characters into an int.
@@ -182,7 +180,6 @@ const _BYTES_PER_WORD = 4;
 abstract class _HashBase {
   // Hasher state.
   final int _chunkSizeInWords;
-  final int _digestSizeInWords;
   final bool _bigEndianWords;
   int _lengthInBytes = 0;
   List<int> _pendingData;
@@ -190,12 +187,10 @@ abstract class _HashBase {
   List<int> _h;
   bool _digestCalled = false;
 
-  _HashBase(
-      this._chunkSizeInWords, this._digestSizeInWords, this._bigEndianWords)
-      : _pendingData = [] {
-    _currentChunk = new List(_chunkSizeInWords);
-    _h = new List(_digestSizeInWords);
-  }
+  _HashBase(this._chunkSizeInWords, int digestSizeInWords, this._bigEndianWords)
+      : _pendingData = [],
+        _currentChunk = new List.filled(_chunkSizeInWords, 0),
+        _h = new List.filled(digestSizeInWords, 0);
 
   // Update the hasher with more data.
   add(List<int> data) {
@@ -271,7 +266,7 @@ abstract class _HashBase {
 
   // Convert a 32-bit word to four bytes.
   List<int> _wordToBytes(int word) {
-    List<int> bytes = new List(_BYTES_PER_WORD);
+    List<int> bytes = new List.filled(_BYTES_PER_WORD, 0);
     bytes[0] = (word >> (_bigEndianWords ? 24 : 0)) & _MASK_8;
     bytes[1] = (word >> (_bigEndianWords ? 16 : 8)) & _MASK_8;
     bytes[2] = (word >> (_bigEndianWords ? 8 : 16)) & _MASK_8;
@@ -397,9 +392,11 @@ class _MD5 extends _HashBase {
 
 // The SHA1 hasher is used to compute an SHA1 message digest.
 class _SHA1 extends _HashBase {
+  List<int> _w;
+
   // Construct a SHA1 hasher object.
   _SHA1()
-      : _w = new List(80),
+      : _w = List<int>.filled(80, 0),
         super(16, 5, true) {
     _h[0] = 0x67452301;
     _h[1] = 0xEFCDAB89;
@@ -455,6 +452,4 @@ class _SHA1 extends _HashBase {
     _h[3] = _add32(d, _h[3]);
     _h[4] = _add32(e, _h[4]);
   }
-
-  List<int> _w;
 }

sdk/lib/_http/embedder_config.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 /// Embedder-specific `dart:_http` configuration.

sdk/lib/_http/http.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._http;
 
 import 'dart:async';
@@ -18,7 +16,8 @@ import 'dart:collection'
         UnmodifiableMapView;
 import 'dart:convert';
 import 'dart:developer' hide log;
-import 'dart:_internal' show Since, HttpStatus;
+import 'dart:_internal'
+    show Since, valueOfNonNullableParamWithDefault, HttpStatus;
 import 'dart:math';
 import 'dart:io';
 import 'dart:typed_data';
@@ -144,7 +143,7 @@ abstract class HttpServer implements Stream<HttpRequest> {
    *
    * The default value is `null`.
    */
-  String serverHeader;
+  String? serverHeader;
 
   /**
    * Default set of headers added to all response objects.
@@ -171,7 +170,7 @@ abstract class HttpServer implements Stream<HttpRequest> {
    * The default value is `false` (compression disabled).
    * To enable, set `autoCompress` to `true`.
    */
-  bool autoCompress;
+  bool autoCompress = false;
 
   /**
    * Gets or sets the timeout used for idle keep-alive connections. If no
@@ -185,7 +184,7 @@ abstract class HttpServer implements Stream<HttpRequest> {
    *
    * To disable, set [idleTimeout] to `null`.
    */
-  Duration idleTimeout;
+  Duration? idleTimeout = const Duration(seconds: 120);
 
   /**
    * Starts listening for HTTP requests on the specified [address] and
@@ -209,13 +208,13 @@ abstract class HttpServer implements Stream<HttpRequest> {
    * [InternetAddress.loopbackIPv6], only IP version 6 (IPv6) connections
    * will be accepted.
    *
-   * If [port] has the value [:0:] an ephemeral port will be chosen by
+   * If [port] has the value 0 an ephemeral port will be chosen by
    * the system. The actual port used can be retrieved using the
    * [port] getter.
    *
    * The optional argument [backlog] can be used to specify the listen
    * backlog for the underlying OS listen setup. If [backlog] has the
-   * value of [:0:] (the default) a reasonable value will be chosen by
+   * value of 0 (the default) a reasonable value will be chosen by
    * the system.
    *
    * The optional argument [shared] specifies whether additional HttpServer
@@ -226,7 +225,7 @@ abstract class HttpServer implements Stream<HttpRequest> {
    * distributed over multiple isolates this way.
    */
   static Future<HttpServer> bind(address, int port,
-          {int backlog: 0, bool v6Only: false, bool shared: false}) =>
+          {int backlog = 0, bool v6Only = false, bool shared = false}) =>
       _HttpServer.bind(address, port, backlog, v6Only, shared);
 
   /**
@@ -246,13 +245,13 @@ abstract class HttpServer implements Stream<HttpRequest> {
    * restrict this to version 6 (IPv6) only, use [v6Only] to set
    * version 6 only.
    *
-   * If [port] has the value [:0:] an ephemeral port will be chosen by
+   * If [port] has the value 0 an ephemeral port will be chosen by
    * the system. The actual port used can be retrieved using the
    * [port] getter.
    *
    * The optional argument [backlog] can be used to specify the listen
    * backlog for the underlying OS listen setup. If [backlog] has the
-   * value of [:0:] (the default) a reasonable value will be chosen by
+   * value of 0 (the default) a reasonable value will be chosen by
    * the system.
    *
    * If [requestClientCertificate] is true, the server will
@@ -271,10 +270,10 @@ abstract class HttpServer implements Stream<HttpRequest> {
 
   static Future<HttpServer> bindSecure(
           address, int port, SecurityContext context,
-          {int backlog: 0,
-          bool v6Only: false,
-          bool requestClientCertificate: false,
-          bool shared: false}) =>
+          {int backlog = 0,
+          bool v6Only = false,
+          bool requestClientCertificate = false,
+          bool shared = false}) =>
       _HttpServer.bindSecure(address, port, context, backlog, v6Only,
           requestClientCertificate, shared);
 
@@ -295,30 +294,33 @@ abstract class HttpServer implements Stream<HttpRequest> {
    *
    * If [force] is `true`, active connections will be closed immediately.
    */
-  Future close({bool force: false});
+  Future close({bool force = false});
 
   /**
-   * Returns the port that the server is listening on. This can be
-   * used to get the actual port used when a value of 0 for [:port:] is
+   * The port that the server is listening on.
+   *
+   * This is the actual port used when a port of zero is
    * specified in the [bind] or [bindSecure] call.
    */
   int get port;
 
   /**
-   * Returns the address that the server is listening on. This can be
-   * used to get the actual address used, when the address is fetched by
-   * a lookup from a hostname.
+   * The address that the server is listening on.
+   *
+   * This is the actual address used when the original address
+   * was specified as a hostname.
    */
   InternetAddress get address;
 
   /**
    * Sets the timeout, in seconds, for sessions of this [HttpServer].
+   *
    * The default timeout is 20 minutes.
    */
   set sessionTimeout(int timeout);
 
   /**
-   * Returns an [HttpConnectionsInfo] object summarizing the number of
+   * A [HttpConnectionsInfo] object summarizing the number of
    * current connections handled by the server.
    */
   HttpConnectionsInfo connectionsInfo();
@@ -345,8 +347,9 @@ class HttpConnectionsInfo {
   int idle = 0;
 
   /**
-   * Number of connections which are preparing to close. Note: These
-   * connections are also part of the [:active:] count as they might
+   * Number of connections which are preparing to close.
+   *
+   * Note: These connections are also part of the [active] count as they might
    * still be sending data to the client before finally closing.
    */
   int closing = 0;
@@ -357,9 +360,9 @@ class HttpConnectionsInfo {
  *
  * In some situations, headers are immutable:
  *
- * * HttpRequest and HttpClientResponse always have immutable headers.
+ * * [HttpRequest] and [HttpClientResponse] always have immutable headers.
  *
- * * HttpResponse and HttpClientRequest have immutable headers
+ * * [HttpResponse] and [HttpClientRequest] have immutable headers
  *   from the moment the body is written to.
  *
  * In these situations, the mutating methods throw exceptions.
@@ -376,7 +379,7 @@ class HttpConnectionsInfo {
  *
  *     print(request.headers.value(HttpHeaders.userAgentHeader));
  *
- * An HttpHeaders object holds a list of values for each name
+ * An `HttpHeaders` object holds a list of values for each name
  * as the standard allows. In most cases a name holds only a single value,
  * The most common mode of operation is to use `set()` for setting a value,
  * and `value()` for retrieving a value.
@@ -534,6 +537,7 @@ abstract class HttpHeaders {
   @Deprecated("Use setCookieHeader instead")
   static const SET_COOKIE = setCookieHeader;
 
+  // TODO(39783): Document this.
   static const generalHeaders = const [
     cacheControlHeader,
     connectionHeader,
@@ -606,71 +610,71 @@ abstract class HttpHeaders {
   static const REQUEST_HEADERS = requestHeaders;
 
   /**
-   * Gets and sets the date. The value of this property will
-   * reflect the 'date' header.
+   * The date specified by the [dateHeader] header, if any.
    */
-  DateTime date;
+  DateTime? date;
 
   /**
-   * Gets and sets the expiry date. The value of this property will
-   * reflect the 'expires' header.
+   * The date and time specified by the [expiresHeader] header, if any.
    */
-  DateTime expires;
+  DateTime? expires;
 
   /**
-   * Gets and sets the "if-modified-since" date. The value of this property will
-   * reflect the "if-modified-since" header.
+   * The date and time specified by the [ifModifiedSinceHeader] header, if any.
    */
-  DateTime ifModifiedSince;
+  DateTime? ifModifiedSince;
 
   /**
-   * Gets and sets the host part of the 'host' header for the
-   * connection.
+   * The value of the [hostHeader] header, if any.
    */
-  String host;
+  String? host;
 
   /**
-   * Gets and sets the port part of the 'host' header for the
-   * connection.
+   * The value of the port part of the [hostHeader] header, if any.
    */
-  int port;
+  int? port;
 
   /**
-   * Gets and sets the content type. Note that the content type in the
-   * header will only be updated if this field is set
-   * directly. Mutating the returned current value will have no
-   * effect.
+   * The [ContentType] of the [contentTypeHeader] header, if any.
    */
-  ContentType contentType;
+  ContentType? contentType;
 
   /**
-   * Gets and sets the content length header value.
+   * The value of the [contentLengthHeader] header, if any.
+   *
+   * The value is negative if there is no content length set.
    */
-  int contentLength;
+  int contentLength = -1;
 
   /**
-   * Gets and sets the persistent connection header value.
+   * Whether the connection is persistent (keep-alive).
    */
-  bool persistentConnection;
+  late bool persistentConnection;
 
   /**
-   * Gets and sets the chunked transfer encoding header value.
+   * Whether the connection uses chunked transfer encoding.
+   *
+   * Reflects and modifies the value of the [transferEncodingHeader] header.
    */
-  bool chunkedTransferEncoding;
+  late bool chunkedTransferEncoding;
 
   /**
-   * Returns the list of values for the header named [name]. If there
-   * is no header with the provided name, [:null:] will be returned.
+   * The values for the header named [name].
+   *
+   * Returns null if there is no header with the provided name,
+   * otherwise returns a new list containing the current values.
+   * Not that modifying the list does not change the header.
    */
-  List<String> operator [](String name);
+  List<String>? operator [](String name);
 
   /**
-   * Convenience method for the value for a single valued header. If
-   * there is no header with the provided name, [:null:] will be
-   * returned. If the header has more than one value an exception is
-   * thrown.
+   * Convenience method for the value for a single valued header.
+   *
+   * The value must not have more than one value.
+   *
+   * Returns `null` if there is no header with the provided name.
    */
-  String value(String name);
+  String? value(String name);
 
   /**
    * Adds a header value.
@@ -705,17 +709,24 @@ abstract class HttpHeaders {
       {@Since("2.8") bool preserveHeaderCase = false});
 
   /**
-   * Removes a specific value for a header name. Some headers have
-   * system supplied values and for these the system supplied values
-   * will still be added to the collection of values for the header.
+   * Removes a specific value for a header name.
+   *
+   * Some headers have system supplied values which cannot be removed.
+   * For all other headers and values, the [value] is converted to a string
+   * in the same way as for [add], then that string value is removed from the
+   * current values of [name].
+   * If there are no remaining values for [name], the header is no longer
+   * considered present.
    */
   void remove(String name, Object value);
 
   /**
-   * Removes all values for the specified header name. Some headers
-   * have system supplied values and for these the system supplied
-   * values will still be added to the collection of values for the
-   * header.
+   * Removes all values for the specified header name.
+   *
+   * Some headers have system supplied values which cannot be removed.
+   * All other values for [name] are removed.
+   * If there are no remaining values for [name], the header is no longer
+   * considered present.
    */
   void removeAll(String name);
 
@@ -731,25 +742,30 @@ abstract class HttpHeaders {
   void forEach(void action(String name, List<String> values));
 
   /**
-   * Disables folding for the header named [name] when sending the HTTP
-   * header. By default, multiple header values are folded into a
-   * single header line by separating the values with commas. The
-   * 'set-cookie' header has folding disabled by default.
+   * Disables folding for the header named [name] when sending the HTTP header.
+   *
+   * By default, multiple header values are folded into a
+   * single header line by separating the values with commas.
+   *
+   * The 'set-cookie' header has folding disabled by default.
    */
   void noFolding(String name);
 
   /**
-   * Remove all headers. Some headers have system supplied values and
-   * for these the system supplied values will still be added to the
-   * collection of values for the header.
+   * Removes all headers.
+   *
+   * Some headers have system supplied values which cannot be removed.
+   * All other header values are removed, and header names with not
+   * remaining values are no longer considered present.
    */
   void clear();
 }
 
 /**
  * Representation of a header value in the form:
- *
- *   [:value; parameter1=value1; parameter2=value2:]
+ * ```dart
+ * value; parameter1=value1; parameter2=value2
+ * ```
  *
  * [HeaderValue] can be used to conveniently build and parse header
  * values on this form.
@@ -759,7 +775,7 @@ abstract class HttpHeaders {
  * token characters and backslash sequences can be used to represent the double
  * quote and backslash characters themselves.
  *
- * To build an [:accepts:] header with the value
+ * To build an "accepts" header with the value
  *
  *     text/plain; q=0.3, text/html
  *
@@ -770,7 +786,7 @@ abstract class HttpHeaders {
  *     request.headers.add(HttpHeaders.acceptHeader, v);
  *     request.headers.add(HttpHeaders.acceptHeader, "text/html");
  *
- * To parse the header values use the [:parse:] static method.
+ * To parse the header values use the [parse] static method.
  *
  *     HttpRequest request = ...;
  *     List<String> values = request.headers[HttpHeaders.acceptHeader];
@@ -786,7 +802,7 @@ abstract class HeaderValue {
    * Creates a new header value object setting the value and parameters.
    */
   factory HeaderValue(
-      [String value = "", Map<String, String> parameters = const {}]) {
+      [String value = "", Map<String, String?> parameters = const {}]) {
     return new _HeaderValue(value, parameters);
   }
 
@@ -795,9 +811,9 @@ abstract class HeaderValue {
    * string with both value and optional parameters.
    */
   static HeaderValue parse(String value,
-      {String parameterSeparator: ";",
-      String valueSeparator: null,
-      bool preserveBackslash: false}) {
+      {String parameterSeparator = ";",
+      String? valueSeparator,
+      bool preserveBackslash = false}) {
     return _HeaderValue.parse(value,
         parameterSeparator: parameterSeparator,
         valueSeparator: valueSeparator,
@@ -805,52 +821,57 @@ abstract class HeaderValue {
   }
 
   /**
-   * Gets the header value.
+   * The value of the header.
    */
   String get value;
 
   /**
-   * Gets the map of parameters.
+   * A map of parameters.
    *
-   * This map cannot be modified. Invoking any operation which would
-   * modify the map will throw [UnsupportedError].
+   * This map cannot be modified.
    */
-  Map<String, String> get parameters;
+  Map<String, String?> get parameters;
 
   /**
    * Returns the formatted string representation in the form:
-   *
-   *     value; parameter1=value1; parameter2=value2
+   * ```
+   * value; parameter1=value1; parameter2=value2
+   * ```
    */
   String toString();
 }
 
 abstract class HttpSession implements Map {
   /**
-   * Gets the id for the current session.
+   * The id of the current session.
    */
   String get id;
 
   /**
-   * Destroys the session. This will terminate the session and any further
+   * Destroys the session.
+   *
+   * This terminates the session and any further
    * connections with this id will be given a new id and session.
    */
   void destroy();
 
   /**
    * Sets a callback that will be called when the session is timed out.
+   *
+   * Calling this again will overwrite the previous value.
    */
   void set onTimeout(void callback());
 
   /**
-   * Is true if the session has not been sent to the client yet.
+   * Whether the session has not yet been sent to the client.
    */
   bool get isNew;
 }
 
 /**
- * Representation of a content type. An instance of [ContentType] is
- * immutable.
+ * A MIME/IANA media type used as the value of the [contentTypeHeader] header.
+ *
+ * A [ContentType] is immutable.
  */
 abstract class ContentType implements HeaderValue {
   /**
@@ -899,7 +920,7 @@ abstract class ContentType implements HeaderValue {
    * or in `parameters`, will have its value converted to lower-case.
    */
   factory ContentType(String primaryType, String subType,
-      {String charset, Map<String, String> parameters = const {}}) {
+      {String? charset, Map<String, String?> parameters = const {}}) {
     return new _ContentType(primaryType, subType, charset, parameters);
   }
 
@@ -911,32 +932,47 @@ abstract class ContentType implements HeaderValue {
    *
    *     text/html; charset=utf-8
    *
-   * will create a content type object with primary type [:text:], sub
-   * type [:html:] and parameter [:charset:] with value [:utf-8:].
+   * will create a content type object with primary type "text",
+   * subtype "html" and parameter "charset" with value "utf-8".
+   * There may be more parameters supplied, but they are not recognized
+   * by this class.
    */
   static ContentType parse(String value) {
     return _ContentType.parse(value);
   }
 
   /**
-   * Gets the mime-type, without any parameters.
+   * Gets the MIME type and subtype, without any parameters.
+   *
+   * For the full content type `text/html;charset=utf-8`,
+   * the [mimeType] value is the string `text/html`.
    */
   String get mimeType;
 
   /**
    * Gets the primary type.
+   *
+   * For the full content type `text/html;charset=utf-8`,
+   * the [primaryType] value is the string `text`.
    */
   String get primaryType;
 
   /**
-   * Gets the sub type.
+   * Gets the subtype.
+   *
+   * For the full content type `text/html;charset=utf-8`,
+   * the [subType] value is the string `html`.
+   * May be the empty string.
    */
   String get subType;
 
   /**
-   * Gets the character set.
+   * Gets the character set, if any.
+   *
+   * For the full content type `text/html;charset=utf-8`,
+   * the [charset] value is the string `utf-8`.
    */
-  String get charset;
+  String? get charset;
 }
 
 /**
@@ -956,7 +992,7 @@ abstract class Cookie {
    * `(`, `)`, `<`, `>`, `@`, `,`, `;`, `:`, `\`, `"`, `/`, `[`, `]`, `?`, `=`,
    * `{`, and `}`.
    */
-  String name;
+  late String name;
 
   /**
    * The value of the cookie.
@@ -969,39 +1005,39 @@ abstract class Cookie {
    * Cookie values may be wrapped in a single pair of double quotes
    * (U+0022, `"`).
    */
-  String value;
+  late String value;
 
   /**
    * The time at which the cookie expires.
    */
-  DateTime expires;
+  DateTime? expires;
 
   /**
    * The number of seconds until the cookie expires. A zero or negative value
    * means the cookie has expired.
    */
-  int maxAge;
+  int? maxAge;
 
   /**
-   * The domain the cookie applies to.
+   * The domain that the cookie applies to.
    */
-  String domain;
+  String? domain;
 
   /**
-   * The path within the [domain] the cookie applies to.
+   * The path within the [domain] that the cookie applies to.
    */
-  String path;
+  String? path;
 
   /**
    * Whether to only send this cookie on secure connections.
    */
-  bool secure;
+  bool secure = false;
 
   /**
    * Whether the cookie is only sent in the HTTP request and is not made
    * available to client side scripts.
    */
-  bool httpOnly;
+  bool httpOnly = false;
 
   /**
    * Creates a new cookie setting the name and value.
@@ -1123,7 +1159,7 @@ abstract class HttpRequest implements Stream<Uint8List> {
   HttpHeaders get headers;
 
   /**
-   * The cookies in the request, from the Cookie headers.
+   * The cookies in the request, from the "Cookie" headers.
    */
   List<Cookie> get cookies;
 
@@ -1139,14 +1175,13 @@ abstract class HttpRequest implements Stream<Uint8List> {
    * or if the server does not request a client certificate, or if the client
    * does not provide one.
    */
-  X509Certificate get certificate;
+  X509Certificate? get certificate;
 
   /**
    * The session for the given request.
    *
-   * If the session is
-   * being initialized by this call, [:isNew:] is true for the returned
-   * session.
+   * If the session is being initialized by this call,
+   * [HttpSession.isNew] is true for the returned session.
    * See [HttpServer.sessionTimeout] on how to change default timeout.
    */
   HttpSession get session;
@@ -1160,9 +1195,9 @@ abstract class HttpRequest implements Stream<Uint8List> {
   /**
    * Information about the client connection.
    *
-   * Returns [:null:] if the socket is not available.
+   * Returns `null` if the socket is not available.
    */
-  HttpConnectionInfo get connectionInfo;
+  HttpConnectionInfo? get connectionInfo;
 
   /**
    * The [HttpResponse] object, used for sending back the response to the
@@ -1231,10 +1266,12 @@ abstract class HttpResponse implements IOSink {
    * the response is not known in advance set the content length to
    * -1, which is also the default if not set.
    */
-  int contentLength;
+  int contentLength = -1;
 
   /**
-   * Gets and sets the status code. Any integer value is accepted. For
+   * The status code of the response.
+   *
+   * Any integer value is accepted. For
    * the official HTTP status codes use the fields from
    * [HttpStatus]. If no status code is explicitly set the default
    * value [HttpStatus.ok] is used.
@@ -1243,24 +1280,25 @@ abstract class HttpResponse implements IOSink {
    * to. Setting the status code after writing to the response body or
    * closing the response will throw a `StateError`.
    */
-  int statusCode;
+  int statusCode = HttpStatus.ok;
 
   /**
-   * Gets and sets the reason phrase. If no reason phrase is explicitly
-   * set a default reason phrase is provided.
+   * The reason phrase for the response.
+   *
+   * If no reason phrase is explicitly set, a default reason phrase is provided.
    *
    * The reason phrase must be set before the body is written
    * to. Setting the reason phrase after writing to the response body
-   * or closing the response will throw a `StateError`.
+   * or closing the response will throw a [StateError].
    */
-  String reasonPhrase;
+  late String reasonPhrase;
 
   /**
    * Gets and sets the persistent connection state. The initial value
    * of this property is the persistent connection state from the
    * request.
    */
-  bool persistentConnection;
+  late bool persistentConnection;
 
   /**
    * Set and get the [deadline] for the response. The deadline is timed from the
@@ -1272,7 +1310,7 @@ abstract class HttpResponse implements IOSink {
    *
    * The [deadline] is `null` by default.
    */
-  Duration deadline;
+  Duration? deadline;
 
   /**
    * Gets or sets if the [HttpResponse] should buffer output.
@@ -1282,7 +1320,7 @@ abstract class HttpResponse implements IOSink {
    * __Note__: Disabling buffering of the output can result in very poor
    * performance, when writing many small chunks.
    */
-  bool bufferOutput;
+  bool bufferOutput = true;
 
   /**
    * Returns the response headers.
@@ -1310,7 +1348,7 @@ abstract class HttpResponse implements IOSink {
    * This method will also call `close`, and the returned future is
    * the future returned by `close`.
    */
-  Future redirect(Uri location, {int status: HttpStatus.movedTemporarily});
+  Future redirect(Uri location, {int status = HttpStatus.movedTemporarily});
 
   /**
    * Detaches the underlying socket from the HTTP server. When the
@@ -1324,13 +1362,13 @@ abstract class HttpResponse implements IOSink {
    * to the socket before it's detached. If `false`, the socket is detached
    * immediately, without any data written to the socket. Default is `true`.
    */
-  Future<Socket> detachSocket({bool writeHeaders: true});
+  Future<Socket> detachSocket({bool writeHeaders = true});
 
   /**
-   * Gets information about the client connection. Returns [:null:] if the
+   * Gets information about the client connection. Returns `null` if the
    * socket is not available.
    */
-  HttpConnectionInfo get connectionInfo;
+  HttpConnectionInfo? get connectionInfo;
 }
 
 /**
@@ -1416,7 +1454,7 @@ abstract class HttpResponse implements IOSink {
  * By default the HttpClient uses the proxy configuration available
  * from the environment, see [findProxyFromEnvironment]. To turn off
  * the use of proxies set the [findProxy] property to
- * [:null:].
+ * `null`.
  *
  *     HttpClient client = new HttpClient();
  *     client.findProxy = null;
@@ -1435,7 +1473,8 @@ abstract class HttpClient {
   ///
   /// Default is `false`.
   static set enableTimelineLogging(bool value) {
-    _enableTimelineLogging = value ?? false;
+    _enableTimelineLogging =
+        valueOfNonNullableParamWithDefault<bool>(value, false);
   }
 
   /// Current state of HTTP request logging from all [HttpClient]s to the
@@ -1450,7 +1489,7 @@ abstract class HttpClient {
   /// connections.
   ///
   /// The default value is 15 seconds.
-  Duration idleTimeout;
+  Duration idleTimeout = const Duration(seconds: 15);
 
   /// Gets and sets the connection timeout.
   ///
@@ -1460,7 +1499,7 @@ abstract class HttpClient {
   ///
   /// When this is `null`, the OS default timeout is used. The default is
   /// `null`.
-  Duration connectionTimeout;
+  Duration? connectionTimeout;
 
   /**
    * Gets and sets the maximum number of live connections, to a single host.
@@ -1472,7 +1511,7 @@ abstract class HttpClient {
    *
    * Default is `null`.
    */
-  int maxConnectionsPerHost;
+  int? maxConnectionsPerHost;
 
   /**
    * Gets and sets whether the body of a response will be automatically
@@ -1500,7 +1539,7 @@ abstract class HttpClient {
    *
    * Default is `true`.
    */
-  bool autoUncompress;
+  bool autoUncompress = true;
 
   /// Gets and sets the default value of the `User-Agent` header for all requests
   /// generated by this [HttpClient].
@@ -1509,10 +1548,10 @@ abstract class HttpClient {
   ///
   /// If the userAgent is set to `null`, no default `User-Agent` header will be
   /// added to each request.
-  String userAgent;
+  String? userAgent;
 
-  factory HttpClient({SecurityContext context}) {
-    HttpOverrides overrides = HttpOverrides.current;
+  factory HttpClient({SecurityContext? context}) {
+    HttpOverrides? overrides = HttpOverrides.current;
     if (overrides == null) {
       return new _HttpClient(context);
     }
@@ -1679,12 +1718,12 @@ abstract class HttpClient {
    *
    * The function returns a [Future] which should complete when the
    * authentication has been resolved. If credentials cannot be
-   * provided the [Future] should complete with [:false:]. If
+   * provided the [Future] should complete with `false`. If
    * credentials are available the function should add these using
    * [addCredentials] before completing the [Future] with the value
-   * [:true:].
+   * `true`.
    *
-   * If the [Future] completes with [:true:] the request will be retried
+   * If the [Future] completes with `true` the request will be retried
    * using the updated credentials, however, the retried request will not
    * carry the original request payload. Otherwise response processing will
    * continue normally.
@@ -1695,7 +1734,7 @@ abstract class HttpClient {
    * of a failed request, or issues due to missing request payload on retried
    * request.
    */
-  set authenticate(Future<bool> f(Uri url, String scheme, String realm));
+  void set authenticate(Future<bool> f(Uri url, String scheme, String realm)?);
 
   /**
    * Add credentials to be used for authorizing HTTP requests.
@@ -1716,7 +1755,7 @@ abstract class HttpClient {
    *
    *     "PROXY host:port"
    *
-   * for using the proxy server [:host:] on port [:port:].
+   * for using the proxy server `host` on port `port`.
    *
    * A configuration can contain several configuration elements
    * separated by semicolons, e.g.
@@ -1727,7 +1766,7 @@ abstract class HttpClient {
    * be used to implement proxy server resolving based on environment
    * variables.
    */
-  set findProxy(String f(Uri url));
+  void set findProxy(String f(Uri url)?);
 
   /**
    * Function for resolving the proxy server to be used for a HTTP
@@ -1781,8 +1820,8 @@ abstract class HttpClient {
    * to set credentials for proxies which require authentication.
    */
   static String findProxyFromEnvironment(Uri url,
-      {Map<String, String> environment}) {
-    HttpOverrides overrides = HttpOverrides.current;
+      {Map<String, String>? environment}) {
+    HttpOverrides? overrides = HttpOverrides.current;
     if (overrides == null) {
       return _HttpClient._findProxyFromEnvironment(url, environment);
     }
@@ -1797,17 +1836,17 @@ abstract class HttpClient {
    *
    * The function returns a [Future] which should complete when the
    * authentication has been resolved. If credentials cannot be
-   * provided the [Future] should complete with [:false:]. If
+   * provided the [Future] should complete with `false`. If
    * credentials are available the function should add these using
    * [addProxyCredentials] before completing the [Future] with the value
-   * [:true:].
+   * `true`.
    *
-   * If the [Future] completes with [:true:] the request will be retried
+   * If the [Future] completes with `true` the request will be retried
    * using the updated credentials. Otherwise response processing will
    * continue normally.
    */
-  set authenticateProxy(
-      Future<bool> f(String host, int port, String scheme, String realm));
+  void set authenticateProxy(
+      Future<bool> f(String host, int port, String scheme, String realm)?);
 
   /**
    * Add credentials to be used for authorizing HTTP proxies.
@@ -1824,8 +1863,8 @@ abstract class HttpClient {
    * server returns a server certificate that cannot be authenticated, the
    * callback is called asynchronously with the [X509Certificate] object and
    * the server's hostname and port.  If the value of [badCertificateCallback]
-   * is [:null:], the bad certificate is rejected, as if the callback
-   * returned [:false:]
+   * is `null`, the bad certificate is rejected, as if the callback
+   * returned `false`
    *
    * If the callback returns true, the secure connection is accepted and the
    * [:Future<HttpClientRequest>:] that was returned from the call making the
@@ -1837,8 +1876,8 @@ abstract class HttpClient {
    * the request is made, even if the value of badCertificateCallback
    * has changed since then.
    */
-  set badCertificateCallback(
-      bool callback(X509Certificate cert, String host, int port));
+  void set badCertificateCallback(
+      bool callback(X509Certificate cert, String host, int port)?);
 
   /// Shuts down the HTTP client.
   ///
@@ -1848,7 +1887,7 @@ abstract class HttpClient {
   /// closed connections will receive an error event to indicate that the client
   /// was shut down. In both cases trying to establish a new connection after
   /// calling [close] will throw an exception.
-  void close({bool force: false});
+  void close({bool force = false});
 }
 
 /**
@@ -1883,23 +1922,25 @@ abstract class HttpClient {
  */
 abstract class HttpClientRequest implements IOSink {
   /**
-   * Gets and sets the requested persistent connection state.
+   * The requested persistent connection state.
    *
-   * The default value is [:true:].
+   * The default value is `true`.
    */
-  bool persistentConnection;
+  bool persistentConnection = true;
 
   /**
-   * Set this property to [:true:] if this request should
-   * automatically follow redirects. The default is [:true:].
+   * Whether to follow redirects automatically.
+   *
+   * Set this property to `false` if this request should not
+   * automatically follow redirects. The default is `true`.
    *
    * Automatic redirect will only happen for "GET" and "HEAD" requests
-   * and only for the status codes [:HttpStatus.movedPermanently:]
-   * (301), [:HttpStatus.found:] (302),
-   * [:HttpStatus.movedTemporarily:] (302, alias for
-   * [:HttpStatus.found:]), [:HttpStatus.seeOther:] (303) and
-   * [:HttpStatus.temporaryRedirect:] (307). For
-   * [:HttpStatus.seeOther:] (303) automatic redirect will also happen
+   * and only for the status codes [HttpStatus.movedPermanently]
+   * (301), [HttpStatus.found] (302),
+   * [HttpStatus.movedTemporarily] (302, alias for
+   * [HttpStatus.found]), [HttpStatus.seeOther] (303) and
+   * [HttpStatus.temporaryRedirect] (307). For
+   * [HttpStatus.seeOther] (303) automatic redirect will also happen
    * for "POST" requests with the method changed to "GET" when
    * following the redirect.
    *
@@ -1907,7 +1948,7 @@ abstract class HttpClientRequest implements IOSink {
    * request(s). However, any body send with the request will not be
    * part of the redirection request(s).
    */
-  bool followRedirects;
+  bool followRedirects = true;
 
   /**
    * Set this property to the maximum number of redirects to follow
@@ -1916,7 +1957,7 @@ abstract class HttpClientRequest implements IOSink {
    *
    * The default value is 5.
    */
-  int maxRedirects;
+  int maxRedirects = 5;
 
   /**
    * The method of the request.
@@ -1932,7 +1973,7 @@ abstract class HttpClientRequest implements IOSink {
   ///
   /// If the size of the request is not known in advance set content length to
   /// -1, which is also the default.
-  int contentLength;
+  int contentLength = -1;
 
   /**
    * Gets or sets if the [HttpClientRequest] should buffer output.
@@ -1942,7 +1983,7 @@ abstract class HttpClientRequest implements IOSink {
    * __Note__: Disabling buffering of the output can result in very poor
    * performance, when writing many small chunks.
    */
-  bool bufferOutput;
+  bool bufferOutput = true;
 
   /**
    * Returns the client request headers.
@@ -1972,8 +2013,8 @@ abstract class HttpClientRequest implements IOSink {
 
   /// Gets information about the client connection.
   ///
-  /// Returns [:null:] if the socket is not available.
-  HttpConnectionInfo get connectionInfo;
+  /// Returns `null` if the socket is not available.
+  HttpConnectionInfo? get connectionInfo;
 }
 
 /**
@@ -2063,14 +2104,14 @@ abstract class HttpClientResponse implements Stream<List<int>> {
    * request. However, any body sent with the request will not be
    * part of the redirection request.
    *
-   * If [followLoops] is set to [:true:], redirect will follow the redirect,
-   * even if the URL was already visited. The default value is [:false:].
+   * If [followLoops] is set to `true`, redirect will follow the redirect,
+   * even if the URL was already visited. The default value is `false`.
    *
    * The method will ignore [HttpClientRequest.maxRedirects]
    * and will always perform the redirect.
    */
   Future<HttpClientResponse> redirect(
-      [String method, Uri url, bool followLoops]);
+      [String? method, Uri? url, bool? followLoops]);
 
   /**
    * Returns the client response headers.
@@ -2098,13 +2139,13 @@ abstract class HttpClientResponse implements Stream<List<int>> {
    * Returns the certificate of the HTTPS server providing the response.
    * Returns null if the connection is not a secure TLS or SSL connection.
    */
-  X509Certificate get certificate;
+  X509Certificate? get certificate;
 
   /**
-   * Gets information about the client connection. Returns [:null:] if the socket
+   * Gets information about the client connection. Returns `null` if the socket
    * is not available.
    */
-  HttpConnectionInfo get connectionInfo;
+  HttpConnectionInfo? get connectionInfo;
 }
 
 /// Enum that specifies the compression state of the byte stream of an
@@ -2215,12 +2256,13 @@ abstract class DetachedSocket {
 
 class HttpException implements IOException {
   final String message;
-  final Uri uri;
+  final Uri? uri;
 
   const HttpException(this.message, {this.uri});
 
   String toString() {
     var b = new StringBuffer()..write('HttpException: ')..write(message);
+    var uri = this.uri;
     if (uri != null) {
       b.write(', uri = $uri');
     }

sdk/lib/_http/http_date.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 /**
@@ -123,7 +121,6 @@ class HttpDate {
 
     int index = 0;
     String tmp;
-    int format;
 
     void expect(String s) {
       if (date.length - index < s.length) {
@@ -147,21 +144,18 @@ class HttpDate {
         index = pos + 1;
         weekday = wkdays.indexOf(tmp);
         if (weekday != -1) {
-          format = formatAsctime;
-          return weekday;
+          return formatAsctime;
         }
       } else {
         tmp = date.substring(index, pos);
         index = pos + 1;
         weekday = wkdays.indexOf(tmp);
         if (weekday != -1) {
-          format = formatRfc1123;
-          return weekday;
+          return formatRfc1123;
         }
         weekday = weekdays.indexOf(tmp);
         if (weekday != -1) {
-          format = formatRfc850;
-          return weekday;
+          return formatRfc850;
         }
       }
       throw new HttpException("Invalid HTTP date $date");
@@ -200,10 +194,10 @@ class HttpDate {
       }
     }
 
-    int weekday = expectWeekday();
-    int day;
-    int month;
+    int format = expectWeekday();
     int year;
+    int month;
+    int day;
     int hours;
     int minutes;
     int seconds;
@@ -248,7 +242,7 @@ class HttpDate {
 
     int position = 0;
 
-    void error() {
+    Never error() {
       throw new HttpException("Invalid cookie date $date");
     }
 
@@ -302,10 +296,10 @@ class HttpDate {
       while (!isEnd() && isDelimiter(date[position])) position++;
     }
 
-    String timeStr;
-    String dayOfMonthStr;
-    String monthStr;
-    String yearStr;
+    String? timeStr;
+    String? dayOfMonthStr;
+    String? monthStr;
+    String? yearStr;
 
     for (var token in tokens) {
       if (token.length < 1) continue;

sdk/lib/_http/http_headers.dart

@@ -2,30 +2,28 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 class _HttpHeaders implements HttpHeaders {
   final Map<String, List<String>> _headers;
   // The original header names keyed by the lowercase header names.
-  Map<String, String> _originalHeaderNames;
+  Map<String, String>? _originalHeaderNames;
   final String protocolVersion;
 
   bool _mutable = true; // Are the headers currently mutable?
-  List<String> _noFoldingHeaders;
+  List<String>? _noFoldingHeaders;
 
   int _contentLength = -1;
   bool _persistentConnection = true;
   bool _chunkedTransferEncoding = false;
-  String _host;
-  int _port;
+  String? _host;
+  int? _port;
 
   final int _defaultPortForScheme;
 
   _HttpHeaders(this.protocolVersion,
-      {int defaultPortForScheme: HttpClient.defaultHttpPort,
-      _HttpHeaders initialHeaders})
+      {int defaultPortForScheme = HttpClient.defaultHttpPort,
+      _HttpHeaders? initialHeaders})
       : _headers = new HashMap<String, List<String>>(),
         _defaultPortForScheme = defaultPortForScheme {
     if (initialHeaders != null) {
@@ -42,12 +40,13 @@ class _HttpHeaders implements HttpHeaders {
     }
   }
 
-  List<String> operator [](String name) => _headers[_validateField(name)];
+  List<String>? operator [](String name) => _headers[_validateField(name)];
 
-  String value(String name) {
+  String? value(String name) {
     name = _validateField(name);
-    List<String> values = _headers[name];
+    List<String>? values = _headers[name];
     if (values == null) return null;
+    assert(values.isNotEmpty);
     if (values.length > 1) {
       throw new HttpException("More than one value for header $name");
     }
@@ -86,8 +85,6 @@ class _HttpHeaders implements HttpHeaders {
     }
     if (preserveHeaderCase && name != lowercaseName) {
       (_originalHeaderNames ??= {})[lowercaseName] = name;
-    } else {
-      _originalHeaderNames?.remove(lowercaseName);
     }
     _addAll(lowercaseName, value);
   }
@@ -96,12 +93,9 @@ class _HttpHeaders implements HttpHeaders {
     _checkMutable();
     name = _validateField(name);
     value = _validateValue(value);
-    List<String> values = _headers[name];
+    List<String>? values = _headers[name];
     if (values != null) {
-      int index = values.indexOf(value);
-      if (index != -1) {
-        values.removeRange(index, index + 1);
-      }
+      values.remove(_valueToString(value));
       if (values.length == 0) {
         _headers.remove(name);
         _originalHeaderNames?.remove(name);
@@ -128,8 +122,7 @@ class _HttpHeaders implements HttpHeaders {
 
   void noFolding(String name) {
     name = _validateField(name);
-    if (_noFoldingHeaders == null) _noFoldingHeaders = new List<String>();
-    _noFoldingHeaders.add(name);
+    (_noFoldingHeaders ??= <String>[]).add(name);
   }
 
   bool get persistentConnection => _persistentConnection;
@@ -142,7 +135,7 @@ class _HttpHeaders implements HttpHeaders {
       if (protocolVersion == "1.1") {
         remove(HttpHeaders.connectionHeader, "close");
       } else {
-        if (_contentLength == -1) {
+        if (_contentLength < 0) {
           throw new HttpException(
               "Trying to set 'Connection: Keep-Alive' on HTTP 1.0 headers with "
               "no ContentLength");
@@ -176,7 +169,7 @@ class _HttpHeaders implements HttpHeaders {
       if (chunkedTransferEncoding) chunkedTransferEncoding = false;
       _set(HttpHeaders.contentLengthHeader, contentLength.toString());
     } else {
-      removeAll(HttpHeaders.contentLengthHeader);
+      _headers.remove(HttpHeaders.contentLengthHeader);
       if (protocolVersion == "1.1") {
         chunkedTransferEncoding = true;
       }
@@ -193,8 +186,8 @@ class _HttpHeaders implements HttpHeaders {
     }
     if (chunkedTransferEncoding == _chunkedTransferEncoding) return;
     if (chunkedTransferEncoding) {
-      List<String> values = _headers[HttpHeaders.transferEncodingHeader];
-      if ((values == null || !values.contains("chunked"))) {
+      List<String>? values = _headers[HttpHeaders.transferEncodingHeader];
+      if (values == null || !values.contains("chunked")) {
         // Headers does not specify chunked encoding - add it if set.
         _addValue(HttpHeaders.transferEncodingHeader, "chunked");
       }
@@ -206,25 +199,26 @@ class _HttpHeaders implements HttpHeaders {
     _chunkedTransferEncoding = chunkedTransferEncoding;
   }
 
-  String get host => _host;
+  String? get host => _host;
 
-  void set host(String host) {
+  void set host(String? host) {
     _checkMutable();
     _host = host;
     _updateHostHeader();
   }
 
-  int get port => _port;
+  int? get port => _port;
 
-  void set port(int port) {
+  void set port(int? port) {
     _checkMutable();
     _port = port;
     _updateHostHeader();
   }
 
-  DateTime get ifModifiedSince {
-    List<String> values = _headers[HttpHeaders.ifModifiedSinceHeader];
+  DateTime? get ifModifiedSince {
+    List<String>? values = _headers[HttpHeaders.ifModifiedSinceHeader];
     if (values != null) {
+      assert(values.isNotEmpty);
       try {
         return HttpDate.parse(values[0]);
       } on Exception {
@@ -234,16 +228,21 @@ class _HttpHeaders implements HttpHeaders {
     return null;
   }
 
-  void set ifModifiedSince(DateTime ifModifiedSince) {
+  void set ifModifiedSince(DateTime? ifModifiedSince) {
     _checkMutable();
-    // Format "ifModifiedSince" header with date in Greenwich Mean Time (GMT).
-    String formatted = HttpDate.format(ifModifiedSince.toUtc());
-    _set(HttpHeaders.ifModifiedSinceHeader, formatted);
+    if (ifModifiedSince == null) {
+      _headers.remove(HttpHeaders.ifModifiedSinceHeader);
+    } else {
+      // Format "ifModifiedSince" header with date in Greenwich Mean Time (GMT).
+      String formatted = HttpDate.format(ifModifiedSince.toUtc());
+      _set(HttpHeaders.ifModifiedSinceHeader, formatted);
+    }
   }
 
-  DateTime get date {
-    List<String> values = _headers[HttpHeaders.dateHeader];
+  DateTime? get date {
+    List<String>? values = _headers[HttpHeaders.dateHeader];
     if (values != null) {
+      assert(values.isNotEmpty);
       try {
         return HttpDate.parse(values[0]);
       } on Exception {
@@ -253,16 +252,21 @@ class _HttpHeaders implements HttpHeaders {
     return null;
   }
 
-  void set date(DateTime date) {
+  void set date(DateTime? date) {
     _checkMutable();
-    // Format "DateTime" header with date in Greenwich Mean Time (GMT).
-    String formatted = HttpDate.format(date.toUtc());
-    _set("date", formatted);
+    if (date == null) {
+      _headers.remove(HttpHeaders.dateHeader);
+    } else {
+      // Format "DateTime" header with date in Greenwich Mean Time (GMT).
+      String formatted = HttpDate.format(date.toUtc());
+      _set(HttpHeaders.dateHeader, formatted);
+    }
   }
 
-  DateTime get expires {
-    List<String> values = _headers[HttpHeaders.expiresHeader];
+  DateTime? get expires {
+    List<String>? values = _headers[HttpHeaders.expiresHeader];
     if (values != null) {
+      assert(values.isNotEmpty);
       try {
         return HttpDate.parse(values[0]);
       } on Exception {
@@ -272,14 +276,18 @@ class _HttpHeaders implements HttpHeaders {
     return null;
   }
 
-  void set expires(DateTime expires) {
+  void set expires(DateTime? expires) {
     _checkMutable();
-    // Format "Expires" header with date in Greenwich Mean Time (GMT).
-    String formatted = HttpDate.format(expires.toUtc());
-    _set(HttpHeaders.expiresHeader, formatted);
+    if (expires == null) {
+      _headers.remove(HttpHeaders.expiresHeader);
+    } else {
+      // Format "Expires" header with date in Greenwich Mean Time (GMT).
+      String formatted = HttpDate.format(expires.toUtc());
+      _set(HttpHeaders.expiresHeader, formatted);
+    }
   }
 
-  ContentType get contentType {
+  ContentType? get contentType {
     var values = _headers[HttpHeaders.contentTypeHeader];
     if (values != null) {
       return ContentType.parse(values[0]);
@@ -288,9 +296,13 @@ class _HttpHeaders implements HttpHeaders {
     }
   }
 
-  void set contentType(ContentType contentType) {
+  void set contentType(ContentType? contentType) {
     _checkMutable();
-    _set(HttpHeaders.contentTypeHeader, contentType.toString());
+    if (contentType == null) {
+      _headers.remove(HttpHeaders.contentTypeHeader);
+    } else {
+      _set(HttpHeaders.contentTypeHeader, contentType.toString());
+    }
   }
 
   void clear() {
@@ -447,42 +459,41 @@ class _HttpHeaders implements HttpHeaders {
   }
 
   void _addValue(String name, Object value) {
-    List<String> values = _headers[name];
-    if (values == null) {
-      values = new List<String>();
-      _headers[name] = values;
-    }
+    List<String> values = (_headers[name] ??= <String>[]);
+    values.add(_valueToString(value));
+  }
+
+  String _valueToString(Object value) {
     if (value is DateTime) {
-      values.add(HttpDate.format(value));
+      return HttpDate.format(value);
     } else if (value is String) {
-      values.add(value);
+      return value; // TODO(39784): no _validateValue?
     } else {
-      values.add(_validateValue(value.toString()));
+      return _validateValue(value.toString()) as String;
     }
   }
 
   void _set(String name, String value) {
     assert(name == _validateField(name));
-    List<String> values = new List<String>();
-    _headers[name] = values;
-    values.add(value);
+    _headers[name] = <String>[value];
   }
 
-  _checkMutable() {
+  void _checkMutable() {
     if (!_mutable) throw new HttpException("HTTP headers are not mutable");
   }
 
-  _updateHostHeader() {
-    bool defaultPort = _port == null || _port == _defaultPortForScheme;
-    _set("host", defaultPort ? host : "$host:$_port");
+  void _updateHostHeader() {
+    var host = _host;
+    if (host != null) {
+      bool defaultPort = _port == null || _port == _defaultPortForScheme;
+      _set("host", defaultPort ? host : "$host:$_port");
+    }
   }
 
-  _foldHeader(String name) {
-    if (name == HttpHeaders.setCookieHeader ||
-        (_noFoldingHeaders != null && _noFoldingHeaders.indexOf(name) != -1)) {
-      return false;
-    }
-    return true;
+  bool _foldHeader(String name) {
+    if (name == HttpHeaders.setCookieHeader) return false;
+    var noFoldingHeaders = _noFoldingHeaders;
+    return noFoldingHeaders == null || !noFoldingHeaders.contains(name);
   }
 
   void _finalize() {
@@ -540,7 +551,7 @@ class _HttpHeaders implements HttpHeaders {
 
   List<Cookie> _parseCookies() {
     // Parse a Cookie header value according to the rules in RFC 6265.
-    var cookies = new List<Cookie>();
+    var cookies = <Cookie>[];
     void parseCookieString(String s) {
       int index = 0;
 
@@ -603,7 +614,7 @@ class _HttpHeaders implements HttpHeaders {
       }
     }
 
-    List<String> values = _headers[HttpHeaders.cookieHeader];
+    List<String>? values = _headers[HttpHeaders.cookieHeader];
     if (values != null) {
       values.forEach((headerValue) => parseCookieString(headerValue));
     }
@@ -632,26 +643,28 @@ class _HttpHeaders implements HttpHeaders {
   }
 
   String _originalHeaderName(String name) {
-    return (_originalHeaderNames == null ? null : _originalHeaderNames[name]) ??
-        name;
+    // TODO: Update syntax to_originalHeaderNames?[name].
+    return _originalHeaderNames?.[name] ?? name;
   }
 }
 
 class _HeaderValue implements HeaderValue {
   String _value;
-  Map<String, String> _parameters;
-  Map<String, String> _unmodifiableParameters;
+  Map<String, String?>? _parameters;
+  Map<String, String?>? _unmodifiableParameters;
 
-  _HeaderValue([this._value = "", Map<String, String> parameters = const {}]) {
-    if (parameters != null && parameters.isNotEmpty) {
-      _parameters = new HashMap<String, String>.from(parameters);
+  _HeaderValue([this._value = "", Map<String, String?> parameters = const {}]) {
+    // TODO(40614): Remove once non-nullability is sound.
+    Map<String, String?>? nullableParameters = parameters;
+    if (nullableParameters != null && nullableParameters.isNotEmpty) {
+      _parameters = new HashMap<String, String?>.from(nullableParameters);
     }
   }
 
   static _HeaderValue parse(String value,
-      {parameterSeparator: ";",
-      valueSeparator: null,
-      preserveBackslash: false}) {
+      {String parameterSeparator = ";",
+      String? valueSeparator,
+      bool preserveBackslash = false}) {
     // Parse the string.
     var result = new _HeaderValue();
     result._parse(value, parameterSeparator, valueSeparator, preserveBackslash);
@@ -660,9 +673,10 @@ class _HeaderValue implements HeaderValue {
 
   String get value => _value;
 
-  Map<String, String> _ensureParameters() => _parameters ??= <String, String>{};
+  Map<String, String?> _ensureParameters() =>
+      _parameters ??= <String, String?>{};
 
-  Map<String, String> get parameters =>
+  Map<String, String?> get parameters =>
       _unmodifiableParameters ??= UnmodifiableMapView(_ensureParameters());
 
   static bool _isToken(String token) {
@@ -684,8 +698,9 @@ class _HeaderValue implements HeaderValue {
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb.write(_value);
+    var parameters = this._parameters;
     if (parameters != null && parameters.length > 0) {
-      _parameters.forEach((String name, String value) {
+      parameters.forEach((String name, String? value) {
         sb..write("; ")..write(name);
         if (value != null) {
           sb.write("=");
@@ -712,7 +727,7 @@ class _HeaderValue implements HeaderValue {
     return sb.toString();
   }
 
-  void _parse(String s, String parameterSeparator, String valueSeparator,
+  void _parse(String s, String parameterSeparator, String? valueSeparator,
       bool preserveBackslash) {
     int index = 0;
 
@@ -728,10 +743,11 @@ class _HeaderValue implements HeaderValue {
     String parseValue() {
       int start = index;
       while (!done()) {
-        if (s[index] == " " ||
-            s[index] == "\t" ||
-            s[index] == valueSeparator ||
-            s[index] == parameterSeparator) break;
+        var char = s[index];
+        if (char == " " ||
+            char == "\t" ||
+            char == valueSeparator ||
+            char == parameterSeparator) break;
         index++;
       }
       return s.substring(start, index);
@@ -753,17 +769,17 @@ class _HeaderValue implements HeaderValue {
     }
 
     void parseParameters() {
-      var parameters = new HashMap<String, String>();
-      _parameters = new UnmodifiableMapView(parameters);
+      var parameters = _ensureParameters();
 
       String parseParameterName() {
         int start = index;
         while (!done()) {
-          if (s[index] == " " ||
-              s[index] == "\t" ||
-              s[index] == "=" ||
-              s[index] == parameterSeparator ||
-              s[index] == valueSeparator) break;
+          var char = s[index];
+          if (char == " " ||
+              char == "\t" ||
+              char == "=" ||
+              char == parameterSeparator ||
+              char == valueSeparator) break;
           index++;
         }
         return s.substring(start, index).toLowerCase();
@@ -775,19 +791,21 @@ class _HeaderValue implements HeaderValue {
           StringBuffer sb = new StringBuffer();
           index++;
           while (!done()) {
-            if (s[index] == "\\") {
+            var char = s[index];
+            if (char == "\\") {
               if (index + 1 == s.length) {
                 throw new HttpException("Failed to parse header value");
               }
               if (preserveBackslash && s[index + 1] != "\"") {
-                sb.write(s[index]);
+                sb.write(char);
               }
               index++;
-            } else if (s[index] == "\"") {
+            } else if (char == "\"") {
               index++;
               return sb.toString();
             }
-            sb.write(s[index]);
+            char = s[index];
+            sb.write(char);
             index++;
           }
           throw new HttpException("Failed to parse header value");
@@ -835,27 +853,30 @@ class _ContentType extends _HeaderValue implements ContentType {
   String _primaryType = "";
   String _subType = "";
 
-  _ContentType(String primaryType, String subType, String charset,
-      Map<String, String> parameters)
+  _ContentType(String primaryType, String subType, String? charset,
+      Map<String, String?> parameters)
       : _primaryType = primaryType,
         _subType = subType,
         super("") {
-    if (_primaryType == null) _primaryType = "";
-    if (_subType == null) _subType = "";
+    // TODO(40614): Remove once non-nullability is sound.
+    String emptyIfNull(String? string) => string ?? "";
+    _primaryType = emptyIfNull(_primaryType);
+    _subType = emptyIfNull(_subType);
     _value = "$_primaryType/$_subType";
-    if (parameters != null) {
-      _ensureParameters();
-      parameters.forEach((String key, String value) {
+    // TODO(40614): Remove once non-nullability is sound.
+    Map<String, String?>? nullableParameters = parameters;
+    if (nullableParameters != null) {
+      var parameterMap = _ensureParameters();
+      nullableParameters.forEach((String key, String? value) {
         String lowerCaseKey = key.toLowerCase();
         if (lowerCaseKey == "charset") {
           value = value?.toLowerCase();
         }
-        this._parameters[lowerCaseKey] = value;
+        parameterMap[lowerCaseKey] = value;
       });
     }
     if (charset != null) {
-      _ensureParameters();
-      this._parameters["charset"] = charset.toLowerCase();
+      _ensureParameters()["charset"] = charset.toLowerCase();
     }
   }
 
@@ -867,7 +888,6 @@ class _ContentType extends _HeaderValue implements ContentType {
     int index = result._value.indexOf("/");
     if (index == -1 || index == (result._value.length - 1)) {
       result._primaryType = result._value.trim().toLowerCase();
-      result._subType = "";
     } else {
       result._primaryType =
           result._value.substring(0, index).trim().toLowerCase();
@@ -882,16 +902,16 @@ class _ContentType extends _HeaderValue implements ContentType {
 
   String get subType => _subType;
 
-  String get charset => parameters["charset"];
+  String? get charset => parameters["charset"];
 }
 
 class _Cookie implements Cookie {
   String _name;
   String _value;
-  DateTime expires;
-  int maxAge;
-  String domain;
-  String path;
+  DateTime? expires;
+  int? maxAge;
+  String? domain;
+  String? path;
   bool httpOnly = false;
   bool secure = false;
 
@@ -913,7 +933,9 @@ class _Cookie implements Cookie {
     _value = newValue;
   }
 
-  _Cookie.fromSetCookieValue(String value) {
+  _Cookie.fromSetCookieValue(String value)
+      : _name = "",
+        _value = "" {
     // Parse the 'set-cookie' header value.
     _parseSetCookieValue(value);
   }
@@ -999,6 +1021,7 @@ class _Cookie implements Cookie {
   String toString() {
     StringBuffer sb = new StringBuffer();
     sb..write(_name)..write("=")..write(_value);
+    var expires = this.expires;
     if (expires != null) {
       sb..write("; Expires=")..write(HttpDate.format(expires));
     }
@@ -1038,7 +1061,7 @@ class _Cookie implements Cookie {
     ];
     if (newName == null) throw new ArgumentError.notNull("name");
     for (int i = 0; i < newName.length; i++) {
-      int codeUnit = newName.codeUnits[i];
+      int codeUnit = newName.codeUnitAt(i);
       if (codeUnit <= 32 ||
           codeUnit >= 127 ||
           separators.indexOf(newName[i]) >= 0) {

sdk/lib/_http/http_parser.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 // Global constants.
@@ -112,19 +110,19 @@ class _MessageType {
  */
 class _HttpDetachedStreamSubscription implements StreamSubscription<Uint8List> {
   StreamSubscription<Uint8List> _subscription;
-  Uint8List _injectData;
+  Uint8List? _injectData;
+  Function? _userOnData;
   bool _isCanceled = false;
-  int _pauseCount = 1;
-  Function _userOnData;
   bool _scheduled = false;
+  int _pauseCount = 1;
 
   _HttpDetachedStreamSubscription(
       this._subscription, this._injectData, this._userOnData);
 
   bool get isPaused => _subscription.isPaused;
 
-  Future<T> asFuture<T>([T futureValue]) =>
-      _subscription.asFuture<T>(futureValue);
+  Future<T> asFuture<T>([T? futureValue]) =>
+      _subscription.asFuture<T>(futureValue as T);
 
   Future cancel() {
     _isCanceled = true;
@@ -132,20 +130,20 @@ class _HttpDetachedStreamSubscription implements StreamSubscription<Uint8List> {
     return _subscription.cancel();
   }
 
-  void onData(void handleData(Uint8List data)) {
+  void onData(void handleData(Uint8List data)?) {
     _userOnData = handleData;
     _subscription.onData(handleData);
   }
 
-  void onDone(void handleDone()) {
+  void onDone(void handleDone()?) {
     _subscription.onDone(handleDone);
   }
 
-  void onError(Function handleError) {
+  void onError(Function? handleError) {
     _subscription.onError(handleError);
   }
 
-  void pause([Future resumeSignal]) {
+  void pause([Future? resumeSignal]) {
     if (_injectData == null) {
       _subscription.pause(resumeSignal);
     } else {
@@ -177,21 +175,20 @@ class _HttpDetachedStreamSubscription implements StreamSubscription<Uint8List> {
       // To ensure that 'subscription.isPaused' is false, we resume the
       // subscription here. This is fine as potential events are delayed.
       _subscription.resume();
-      if (_userOnData != null) {
-        _userOnData(data);
-      }
+      _userOnData?.call(data);
     });
   }
 }
 
 class _HttpDetachedIncoming extends Stream<Uint8List> {
-  final StreamSubscription<Uint8List> subscription;
-  final Uint8List bufferedData;
+  final StreamSubscription<Uint8List>? subscription;
+  final Uint8List? bufferedData;
 
   _HttpDetachedIncoming(this.subscription, this.bufferedData);
 
-  StreamSubscription<Uint8List> listen(void onData(Uint8List event),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription<Uint8List> listen(void onData(Uint8List event)?,
+      {Function? onError, void onDone()?, bool? cancelOnError}) {
+    var subscription = this.subscription;
     if (subscription != null) {
       subscription
         ..onData(onData)
@@ -205,7 +202,7 @@ class _HttpDetachedIncoming extends Stream<Uint8List> {
         ..resume();
     } else {
       // TODO(26379): add test for this branch.
-      return new Stream<Uint8List>.fromIterable([bufferedData]).listen(onData,
+      return new Stream<Uint8List>.fromIterable([bufferedData!]).listen(onData,
           onError: onError, onDone: onDone, cancelOnError: cancelOnError);
     }
   }
@@ -236,13 +233,13 @@ class _HttpParser extends Stream<_HttpIncoming> {
   bool _parserCalled = false;
 
   // The data that is currently being parsed.
-  Uint8List _buffer;
-  int _index;
+  Uint8List? _buffer;
+  int _index = -1;
 
   final bool _requestParser;
-  int _state;
-  int _httpVersionIndex;
-  int _messageType;
+  int _state = _State.START;
+  int? _httpVersionIndex;
+  int _messageType = _MessageType.UNDETERMINED;
   int _statusCode = 0;
   int _statusCodeLength = 0;
   final List<int> _method = [];
@@ -252,11 +249,11 @@ class _HttpParser extends Stream<_HttpIncoming> {
   // The limit for method, uriOrReasonPhrase, header field and value
   int _headerSizeLimit = 8 * 1024;
 
-  int _httpVersion;
+  int _httpVersion = _HttpVersion.UNDETERMINED;
   int _transferLength = -1;
-  bool _persistentConnection;
-  bool _connectionUpgrade;
-  bool _chunked;
+  bool _persistentConnection = false;
+  bool _connectionUpgrade = false;
+  bool _chunked = false;
 
   bool _noMessageBody = false;
   int _remainingContent = -1;
@@ -264,18 +261,18 @@ class _HttpParser extends Stream<_HttpIncoming> {
   bool _transferEncoding = false;
   bool connectMethod = false;
 
-  _HttpHeaders _headers;
+  _HttpHeaders? _headers;
 
   // The limit for parsing chunk size
   int _chunkSizeLimit = 0x7FFFFFFF;
 
   // The current incoming connection.
-  _HttpIncoming _incoming;
-  StreamSubscription<Uint8List> _socketSubscription;
+  _HttpIncoming? _incoming;
+  StreamSubscription<Uint8List>? _socketSubscription;
   bool _paused = true;
   bool _bodyPaused = false;
-  StreamController<_HttpIncoming> _controller;
-  StreamController<Uint8List> _bodyController;
+  final StreamController<_HttpIncoming> _controller;
+  StreamController<Uint8List>? _bodyController;
 
   factory _HttpParser.requestParser() {
     return new _HttpParser._(true);
@@ -285,30 +282,28 @@ class _HttpParser extends Stream<_HttpIncoming> {
     return new _HttpParser._(false);
   }
 
-  _HttpParser._(this._requestParser) {
-    _controller = new StreamController<_HttpIncoming>(
-        sync: true,
-        onListen: () {
-          _paused = false;
-        },
-        onPause: () {
-          _paused = true;
-          _pauseStateChanged();
-        },
-        onResume: () {
-          _paused = false;
-          _pauseStateChanged();
-        },
-        onCancel: () {
-          if (_socketSubscription != null) {
-            _socketSubscription.cancel();
-          }
-        });
+  _HttpParser._(this._requestParser)
+      : _controller = new StreamController<_HttpIncoming>(sync: true) {
+    _controller
+      ..onListen = () {
+        _paused = false;
+      }
+      ..onPause = () {
+        _paused = true;
+        _pauseStateChanged();
+      }
+      ..onResume = () {
+        _paused = false;
+        _pauseStateChanged();
+      }
+      ..onCancel = () {
+        _socketSubscription?.cancel();
+      };
     _reset();
   }
 
-  StreamSubscription<_HttpIncoming> listen(void onData(_HttpIncoming event),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription<_HttpIncoming> listen(void onData(_HttpIncoming event)?,
+      {Function? onError, void onDone()?, bool? cancelOnError}) {
     return _controller.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
@@ -341,6 +336,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
   // parsing and return. This will be in case of either an upgrade
   // request or a request or response with an empty body.
   bool _headersEnd() {
+    var headers = _headers!;
     // If method is CONNECT, response parser should ignore any Content-Length or
     // Transfer-Encoding header fields in a successful response.
     // [RFC 7231](https://tools.ietf.org/html/rfc7231#section-4.3.6)
@@ -349,14 +345,14 @@ class _HttpParser extends Stream<_HttpIncoming> {
         _statusCode < 300 &&
         connectMethod) {
       _transferLength = -1;
-      _headers.chunkedTransferEncoding = false;
+      headers.chunkedTransferEncoding = false;
       _chunked = false;
-      _headers.removeAll(HttpHeaders.contentLengthHeader);
-      _headers.removeAll(HttpHeaders.transferEncodingHeader);
+      headers.removeAll(HttpHeaders.contentLengthHeader);
+      headers.removeAll(HttpHeaders.transferEncodingHeader);
     }
-    _headers._mutable = false;
+    headers._mutable = false;
 
-    _transferLength = _headers.contentLength;
+    _transferLength = headers.contentLength;
     // Ignore the Content-Length header if Transfer-Encoding
     // is chunked (RFC 2616 section 4.4)
     if (_chunked) _transferLength = -1;
@@ -373,30 +369,28 @@ class _HttpParser extends Stream<_HttpIncoming> {
       _state = _State.UPGRADED;
       _transferLength = 0;
     }
-    _createIncoming(_transferLength);
+    var incoming = _createIncoming(_transferLength);
     if (_requestParser) {
-      _incoming.method = new String.fromCharCodes(_method);
-      _incoming.uri = Uri.parse(new String.fromCharCodes(_uriOrReasonPhrase));
+      incoming.method = new String.fromCharCodes(_method);
+      incoming.uri = Uri.parse(new String.fromCharCodes(_uriOrReasonPhrase));
     } else {
-      _incoming.statusCode = _statusCode;
-      _incoming.reasonPhrase = new String.fromCharCodes(_uriOrReasonPhrase);
+      incoming.statusCode = _statusCode;
+      incoming.reasonPhrase = new String.fromCharCodes(_uriOrReasonPhrase);
     }
     _method.clear();
     _uriOrReasonPhrase.clear();
     if (_connectionUpgrade) {
-      _incoming.upgraded = true;
+      incoming.upgraded = true;
       _parserCalled = false;
-      var tmp = _incoming;
       _closeIncoming();
-      _controller.add(tmp);
+      _controller.add(incoming);
       return true;
     }
     if (_transferLength == 0 ||
         (_messageType == _MessageType.RESPONSE && _noMessageBody)) {
       _reset();
-      var tmp = _incoming;
       _closeIncoming();
-      _controller.add(tmp);
+      _controller.add(incoming);
       return false;
     } else if (_chunked) {
       _state = _State.CHUNK_SIZE;
@@ -410,7 +404,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
       _state = _State.BODY;
     }
     _parserCalled = false;
-    _controller.add(_incoming);
+    _controller.add(incoming);
     return true;
   }
 
@@ -433,7 +427,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
       throw HttpException("Data on failed connection");
     }
     while (_buffer != null &&
-        _index < _buffer.length &&
+        _index < _buffer!.length &&
         _state != _State.FAILURE &&
         _state != _State.UPGRADED) {
       // Depending on _incoming, we either break on _bodyPaused or _paused.
@@ -442,7 +436,9 @@ class _HttpParser extends Stream<_HttpIncoming> {
         _parserCalled = false;
         return;
       }
-      int byte = _buffer[_index++];
+      int index = _index;
+      int byte = _buffer![index];
+      _index = index + 1;
       switch (_state) {
         case _State.START:
           if (byte == _Const.HTTP[0]) {
@@ -463,22 +459,23 @@ class _HttpParser extends Stream<_HttpIncoming> {
           break;
 
         case _State.METHOD_OR_RESPONSE_HTTP_VERSION:
-          if (_httpVersionIndex < _Const.HTTP.length &&
-              byte == _Const.HTTP[_httpVersionIndex]) {
+          var httpVersionIndex = _httpVersionIndex!;
+          if (httpVersionIndex < _Const.HTTP.length &&
+              byte == _Const.HTTP[httpVersionIndex]) {
             // Continue parsing HTTP version.
-            _httpVersionIndex++;
-          } else if (_httpVersionIndex == _Const.HTTP.length &&
+            _httpVersionIndex = httpVersionIndex + 1;
+          } else if (httpVersionIndex == _Const.HTTP.length &&
               byte == _CharCode.SLASH) {
             // HTTP/ parsed. As method is a token this cannot be a
             // method anymore.
-            _httpVersionIndex++;
+            _httpVersionIndex = httpVersionIndex + 1;
             if (_requestParser) {
               throw HttpException("Invalid request line");
             }
             _state = _State.RESPONSE_HTTP_VERSION;
           } else {
             // Did not parse HTTP version. Expect method instead.
-            for (int i = 0; i < _httpVersionIndex; i++) {
+            for (int i = 0; i < httpVersionIndex; i++) {
               _addWithValidation(_method, _Const.HTTP[i]);
             }
             if (byte == _CharCode.SP) {
@@ -495,23 +492,24 @@ class _HttpParser extends Stream<_HttpIncoming> {
           break;
 
         case _State.RESPONSE_HTTP_VERSION:
-          if (_httpVersionIndex < _Const.HTTP1DOT.length) {
+          var httpVersionIndex = _httpVersionIndex!;
+          if (httpVersionIndex < _Const.HTTP1DOT.length) {
             // Continue parsing HTTP version.
-            _expect(byte, _Const.HTTP1DOT[_httpVersionIndex]);
-            _httpVersionIndex++;
-          } else if (_httpVersionIndex == _Const.HTTP1DOT.length &&
+            _expect(byte, _Const.HTTP1DOT[httpVersionIndex]);
+            _httpVersionIndex = httpVersionIndex + 1;
+          } else if (httpVersionIndex == _Const.HTTP1DOT.length &&
               byte == _CharCode.ONE) {
             // HTTP/1.1 parsed.
             _httpVersion = _HttpVersion.HTTP11;
             _persistentConnection = true;
-            _httpVersionIndex++;
-          } else if (_httpVersionIndex == _Const.HTTP1DOT.length &&
+            _httpVersionIndex = httpVersionIndex + 1;
+          } else if (httpVersionIndex == _Const.HTTP1DOT.length &&
               byte == _CharCode.ZERO) {
             // HTTP/1.0 parsed.
             _httpVersion = _HttpVersion.HTTP10;
             _persistentConnection = false;
-            _httpVersionIndex++;
-          } else if (_httpVersionIndex == _Const.HTTP1DOT.length + 1) {
+            _httpVersionIndex = httpVersionIndex + 1;
+          } else if (httpVersionIndex == _Const.HTTP1DOT.length + 1) {
             _expect(byte, _CharCode.SP);
             // HTTP version parsed.
             _state = _State.RESPONSE_LINE_STATUS_CODE;
@@ -550,20 +548,21 @@ class _HttpParser extends Stream<_HttpIncoming> {
           break;
 
         case _State.REQUEST_LINE_HTTP_VERSION:
-          if (_httpVersionIndex < _Const.HTTP1DOT.length) {
-            _expect(byte, _Const.HTTP11[_httpVersionIndex]);
-            _httpVersionIndex++;
+          var httpVersionIndex = _httpVersionIndex!;
+          if (httpVersionIndex < _Const.HTTP1DOT.length) {
+            _expect(byte, _Const.HTTP11[httpVersionIndex]);
+            _httpVersionIndex = httpVersionIndex + 1;
           } else if (_httpVersionIndex == _Const.HTTP1DOT.length) {
             if (byte == _CharCode.ONE) {
               // HTTP/1.1 parsed.
               _httpVersion = _HttpVersion.HTTP11;
               _persistentConnection = true;
-              _httpVersionIndex++;
+              _httpVersionIndex = httpVersionIndex + 1;
             } else if (byte == _CharCode.ZERO) {
               // HTTP/1.0 parsed.
               _httpVersion = _HttpVersion.HTTP10;
               _persistentConnection = false;
-              _httpVersionIndex++;
+              _httpVersionIndex = httpVersionIndex + 1;
             } else {
               throw HttpException("Invalid response, invalid HTTP version");
             }
@@ -627,12 +626,12 @@ class _HttpParser extends Stream<_HttpIncoming> {
           break;
 
         case _State.HEADER_START:
-          _headers = new _HttpHeaders(version);
+          _headers = new _HttpHeaders(version!);
           if (byte == _CharCode.CR) {
             _state = _State.HEADER_ENDING;
           } else if (byte == _CharCode.LF) {
             _state = _State.HEADER_ENDING;
-            _index--; // Make the new state see the LF again.
+            _index = _index - 1; // Make the new state see the LF again.
           } else {
             // Start of new header field.
             _addWithValidation(_headerField, _toLowerCaseByte(byte));
@@ -700,6 +699,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
                 _statusCode = HttpStatus.badRequest;
               }
             }
+            var headers = _headers!;
             if (headerField == HttpHeaders.connectionHeader) {
               List<String> tokens = _tokenizeFieldValue(headerValue);
               final bool isResponse = _messageType == _MessageType.RESPONSE;
@@ -713,10 +713,10 @@ class _HttpParser extends Stream<_HttpIncoming> {
                     (isUpgrade && isResponse && isUpgradeCode)) {
                   _connectionUpgrade = true;
                 }
-                _headers._add(headerField, tokens[i]);
+                headers._add(headerField, tokens[i]);
               }
             } else {
-              _headers._add(headerField, headerValue);
+              headers._add(headerField, headerValue);
             }
             _headerField.clear();
             _headerValue.clear();
@@ -725,7 +725,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
               _state = _State.HEADER_ENDING;
             } else if (byte == _CharCode.LF) {
               _state = _State.HEADER_ENDING;
-              _index--; // Make the new state see the LF again.
+              _index = _index - 1; // Make the new state see the LF again.
             } else {
               // Start of new header field.
               _state = _State.HEADER_FIELD;
@@ -794,8 +794,9 @@ class _HttpParser extends Stream<_HttpIncoming> {
 
         case _State.BODY:
           // The body is not handled one byte at a time but in blocks.
-          _index--;
-          int dataAvailable = _buffer.length - _index;
+          _index = _index - 1;
+          var buffer = _buffer!;
+          int dataAvailable = buffer.length - _index;
           if (_remainingContent >= 0 && dataAvailable > _remainingContent) {
             dataAvailable = _remainingContent;
           }
@@ -803,12 +804,12 @@ class _HttpParser extends Stream<_HttpIncoming> {
           // cases like this, and the user will not experience different data
           // typed (which could lead to polymorphic user code).
           Uint8List data = new Uint8List.view(
-              _buffer.buffer, _buffer.offsetInBytes + _index, dataAvailable);
-          _bodyController.add(data);
+              buffer.buffer, buffer.offsetInBytes + _index, dataAvailable);
+          _bodyController!.add(data);
           if (_remainingContent != -1) {
             _remainingContent -= data.length;
           }
-          _index += data.length;
+          _index = _index + data.length;
           if (_remainingContent == 0) {
             if (!_chunked) {
               _reset();
@@ -832,18 +833,19 @@ class _HttpParser extends Stream<_HttpIncoming> {
     }
 
     _parserCalled = false;
-    if (_buffer != null && _index == _buffer.length) {
+    var buffer = _buffer;
+    if (buffer != null && _index == buffer.length) {
       // If all data is parsed release the buffer and resume receiving
       // data.
       _releaseBuffer();
       if (_state != _State.UPGRADED && _state != _State.FAILURE) {
-        _socketSubscription.resume();
+        _socketSubscription!.resume();
       }
     }
   }
 
   void _onData(Uint8List buffer) {
-    _socketSubscription.pause();
+    _socketSubscription!.pause();
     assert(_buffer == null);
     _buffer = buffer;
     _index = 0;
@@ -903,7 +905,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
     _controller.close();
   }
 
-  String get version {
+  String? get version {
     switch (_httpVersion) {
       case _HttpVersion.HTTP10:
         return "1.0";
@@ -918,7 +920,9 @@ class _HttpParser extends Stream<_HttpIncoming> {
   bool get upgrade => _connectionUpgrade && _state == _State.UPGRADED;
   bool get persistentConnection => _persistentConnection;
 
-  void set isHead(bool value) => _noMessageBody = value ?? false;
+  void set isHead(bool value) {
+    _noMessageBody = valueOfNonNullableParamWithDefault<bool>(value, false);
+  }
 
   _HttpDetachedIncoming detachIncoming() {
     // Simulate detached by marking as upgraded.
@@ -926,10 +930,12 @@ class _HttpParser extends Stream<_HttpIncoming> {
     return new _HttpDetachedIncoming(_socketSubscription, readUnparsedData());
   }
 
-  Uint8List readUnparsedData() {
-    if (_buffer == null) return null;
-    if (_index == _buffer.length) return null;
-    var result = _buffer.sublist(_index);
+  Uint8List? readUnparsedData() {
+    var buffer = _buffer;
+    if (buffer == null) return null;
+    var index = _index;
+    if (index == buffer.length) return null;
+    var result = buffer.sublist(index);
     _releaseBuffer();
     return result;
   }
@@ -963,7 +969,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
 
   void _releaseBuffer() {
     _buffer = null;
-    _index = null;
+    _index = -1;
   }
 
   static bool _isTokenChar(int byte) {
@@ -977,7 +983,7 @@ class _HttpParser extends Stream<_HttpIncoming> {
   }
 
   static List<String> _tokenizeFieldValue(String headerValue) {
-    List<String> tokens = new List<String>();
+    List<String> tokens = <String>[];
     int start = 0;
     int index = 0;
     while (index < headerValue.length) {
@@ -1072,53 +1078,53 @@ class _HttpParser extends Stream<_HttpIncoming> {
     throw HttpException("$method exceeds the $_headerSizeLimit size limit");
   }
 
-  void _createIncoming(int transferLength) {
+  _HttpIncoming _createIncoming(int transferLength) {
     assert(_incoming == null);
     assert(_bodyController == null);
     assert(!_bodyPaused);
-    var incoming;
-    _bodyController = new StreamController<Uint8List>(
-        sync: true,
-        onListen: () {
-          if (incoming != _incoming) return;
-          assert(_bodyPaused);
-          _bodyPaused = false;
-          _pauseStateChanged();
-        },
-        onPause: () {
-          if (incoming != _incoming) return;
-          assert(!_bodyPaused);
-          _bodyPaused = true;
-          _pauseStateChanged();
-        },
-        onResume: () {
-          if (incoming != _incoming) return;
-          assert(_bodyPaused);
-          _bodyPaused = false;
-          _pauseStateChanged();
-        },
-        onCancel: () {
-          if (incoming != _incoming) return;
-          if (_socketSubscription != null) {
-            _socketSubscription.cancel();
-          }
-          _closeIncoming(true);
-          _controller.close();
-        });
-    incoming = _incoming =
-        new _HttpIncoming(_headers, transferLength, _bodyController.stream);
+    var controller =
+        _bodyController = new StreamController<Uint8List>(sync: true);
+    var incoming = _incoming =
+        new _HttpIncoming(_headers!, transferLength, controller.stream);
+    controller
+      ..onListen = () {
+        if (incoming != _incoming) return;
+        assert(_bodyPaused);
+        _bodyPaused = false;
+        _pauseStateChanged();
+      }
+      ..onPause = () {
+        if (incoming != _incoming) return;
+        assert(!_bodyPaused);
+        _bodyPaused = true;
+        _pauseStateChanged();
+      }
+      ..onResume = () {
+        if (incoming != _incoming) return;
+        assert(_bodyPaused);
+        _bodyPaused = false;
+        _pauseStateChanged();
+      }
+      ..onCancel = () {
+        if (incoming != _incoming) return;
+        _socketSubscription?.cancel();
+        _closeIncoming(true);
+        _controller.close();
+      };
     _bodyPaused = true;
     _pauseStateChanged();
+    return incoming;
   }
 
   void _closeIncoming([bool closing = false]) {
     // Ignore multiple close (can happen in re-entrance).
-    if (_incoming == null) return;
     var tmp = _incoming;
+    if (tmp == null) return;
     tmp.close(closing);
     _incoming = null;
-    if (_bodyController != null) {
-      _bodyController.close();
+    var controller = _bodyController;
+    if (controller != null) {
+      controller.close();
       _bodyController = null;
     }
     _bodyPaused = false;
@@ -1138,19 +1144,17 @@ class _HttpParser extends Stream<_HttpIncoming> {
   }
 
   void _reportHttpError(error, [stackTrace]) {
-    if (_socketSubscription != null) _socketSubscription.cancel();
+    _socketSubscription?.cancel();
     _state = _State.FAILURE;
     _controller.addError(error, stackTrace);
     _controller.close();
   }
 
   void _reportBodyError(error, [stackTrace]) {
-    if (_socketSubscription != null) _socketSubscription.cancel();
+    _socketSubscription?.cancel();
     _state = _State.FAILURE;
-    _bodyController.addError(error, stackTrace);
+    _bodyController?.addError(error, stackTrace);
     // In case of drain(), error event will close the stream.
-    if (_bodyController != null) {
-      _bodyController.close();
-    }
+    _bodyController?.close();
   }
 }

sdk/lib/_http/http_session.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 const String _DART_SESSION_ID = "DARTSESSID";
@@ -15,11 +13,11 @@ class _HttpSession implements HttpSession {
   bool _destroyed = false;
   bool _isNew = true;
   DateTime _lastSeen;
-  Function _timeoutCallback;
+  Function? _timeoutCallback;
   _HttpSessionManager _sessionManager;
   // Pointers in timeout queue.
-  _HttpSession _prev;
-  _HttpSession _next;
+  _HttpSession? _prev;
+  _HttpSession? _next;
   final String id;
 
   final Map _data = new HashMap();
@@ -27,6 +25,7 @@ class _HttpSession implements HttpSession {
   _HttpSession(this._sessionManager, this.id) : _lastSeen = new DateTime.now();
 
   void destroy() {
+    assert(!_destroyed);
     _destroyed = true;
     _sessionManager._removeFromTimeoutQueue(this);
     _sessionManager._sessions.remove(id);
@@ -43,7 +42,7 @@ class _HttpSession implements HttpSession {
 
   bool get isNew => _isNew;
 
-  void set onTimeout(void callback()) {
+  void set onTimeout(void callback()?) {
     _timeoutCallback = callback;
   }
 
@@ -80,7 +79,7 @@ class _HttpSession implements HttpSession {
   }
 
   Map<K, V> cast<K, V>() => _data.cast<K, V>();
-  update(key, update(value), {ifAbsent()}) =>
+  update(key, update(value), {ifAbsent()?}) =>
       _data.update(key, update, ifAbsent: ifAbsent);
 
   void updateAll(update(key, value)) {
@@ -104,9 +103,9 @@ class _HttpSession implements HttpSession {
 class _HttpSessionManager {
   Map<String, _HttpSession> _sessions;
   int _sessionTimeout = 20 * 60; // 20 mins.
-  _HttpSession _head;
-  _HttpSession _tail;
-  Timer _timer;
+  _HttpSession? _head;
+  _HttpSession? _tail;
+  Timer? _timer;
 
   _HttpSessionManager() : _sessions = {};
 
@@ -116,7 +115,7 @@ class _HttpSessionManager {
     return _CryptoUtils.bytesToHex(data);
   }
 
-  _HttpSession getSession(String id) => _sessions[id];
+  _HttpSession? getSession(String id) => _sessions[id];
 
   _HttpSession createSession() {
     var id = createSessionId();
@@ -152,55 +151,52 @@ class _HttpSessionManager {
       _startTimer();
     } else {
       assert(_timer != null);
-      assert(_tail != null);
+      var tail = _tail!;
       // Add to end.
-      _tail._next = session;
-      session._prev = _tail;
+      tail._next = session;
+      session._prev = tail;
       _tail = session;
     }
   }
 
   void _removeFromTimeoutQueue(_HttpSession session) {
-    if (session._next != null) {
-      session._next._prev = session._prev;
-    }
-    if (session._prev != null) {
-      session._prev._next = session._next;
+    var next = session._next;
+    var prev = session._prev;
+    session._next = session._prev = null;
+    next?._prev = prev;
+    prev?._next = next;
+    if (_tail == session) {
+      _tail = prev;
     }
     if (_head == session) {
+      _head = next;
       // We removed the head element, start new timer.
-      _head = session._next;
       _stopTimer();
       _startTimer();
     }
-    if (_tail == session) {
-      _tail = session._prev;
-    }
-    session._next = session._prev = null;
   }
 
   void _timerTimeout() {
     _stopTimer(); // Clear timer.
-    assert(_head != null);
-    var session = _head;
+    var session = _head!;
     session.destroy(); // Will remove the session from timeout queue and map.
-    if (session._timeoutCallback != null) {
-      session._timeoutCallback();
-    }
+    session._timeoutCallback?.call();
   }
 
   void _startTimer() {
     assert(_timer == null);
-    if (_head != null) {
-      int seconds = new DateTime.now().difference(_head.lastSeen).inSeconds;
+    var head = _head;
+    if (head != null) {
+      int seconds = new DateTime.now().difference(head.lastSeen).inSeconds;
       _timer = new Timer(
           new Duration(seconds: _sessionTimeout - seconds), _timerTimeout);
     }
   }
 
   void _stopTimer() {
-    if (_timer != null) {
-      _timer.cancel();
+    var timer = _timer;
+    if (timer != null) {
+      timer.cancel();
       _timer = null;
     }
   }

sdk/lib/_http/overrides.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 final _httpOverridesToken = new Object();
@@ -32,9 +30,9 @@ const _asyncRunZoned = runZoned;
 /// }
 /// ```
 abstract class HttpOverrides {
-  static HttpOverrides _global;
+  static HttpOverrides? _global;
 
-  static HttpOverrides get current {
+  static HttpOverrides? get current {
     return Zone.current[_httpOverridesToken] ?? _global;
   }
 
@@ -43,14 +41,14 @@ abstract class HttpOverrides {
   /// These are the [HttpOverrides] that will be used in the root Zone, and in
   /// Zone's that do not set [HttpOverrides] and whose ancestors up to the root
   /// Zone do not set [HttpOverrides].
-  static set global(HttpOverrides overrides) {
+  static set global(HttpOverrides? overrides) {
     _global = overrides;
   }
 
   /// Runs [body] in a fresh [Zone] using the provided overrides.
   static R runZoned<R>(R body(),
-      {HttpClient Function(SecurityContext) createHttpClient,
-      String Function(Uri uri, Map<String, String> environment)
+      {HttpClient Function(SecurityContext?)? createHttpClient,
+      String Function(Uri uri, Map<String, String>? environment)?
           findProxyFromEnvironment}) {
     HttpOverrides overrides =
         new _HttpOverridesScope(createHttpClient, findProxyFromEnvironment);
@@ -71,7 +69,7 @@ abstract class HttpOverrides {
   ///
   /// When this override is installed, this function overrides the behavior of
   /// `new HttpClient`.
-  HttpClient createHttpClient(SecurityContext context) {
+  HttpClient createHttpClient(SecurityContext? context) {
     return new _HttpClient(context);
   }
 
@@ -79,34 +77,37 @@ abstract class HttpOverrides {
   ///
   /// When this override is installed, this function overrides the behavior of
   /// `HttpClient.findProxyFromEnvironment`.
-  String findProxyFromEnvironment(Uri url, Map<String, String> environment) {
+  String findProxyFromEnvironment(Uri url, Map<String, String>? environment) {
     return _HttpClient._findProxyFromEnvironment(url, environment);
   }
 }
 
 class _HttpOverridesScope extends HttpOverrides {
-  final HttpOverrides _previous = HttpOverrides.current;
-
-  final HttpClient Function(SecurityContext) _createHttpClient;
-  final String Function(Uri uri, Map<String, String> environment)
+  final HttpOverrides? _previous = HttpOverrides.current;
+  final HttpClient Function(SecurityContext?)? _createHttpClient;
+  final String Function(Uri uri, Map<String, String>? environment)?
       _findProxyFromEnvironment;
 
   _HttpOverridesScope(this._createHttpClient, this._findProxyFromEnvironment);
 
   @override
-  HttpClient createHttpClient(SecurityContext context) {
-    if (_createHttpClient != null) return _createHttpClient(context);
-    if (_previous != null) return _previous.createHttpClient(context);
+  HttpClient createHttpClient(SecurityContext? context) {
+    var createHttpClient = _createHttpClient;
+    if (createHttpClient != null) return createHttpClient(context);
+    var previous = _previous;
+    if (previous != null) return previous.createHttpClient(context);
     return super.createHttpClient(context);
   }
 
   @override
-  String findProxyFromEnvironment(Uri url, Map<String, String> environment) {
-    if (_findProxyFromEnvironment != null) {
-      return _findProxyFromEnvironment(url, environment);
+  String findProxyFromEnvironment(Uri url, Map<String, String>? environment) {
+    var findProxyFromEnvironment = _findProxyFromEnvironment;
+    if (findProxyFromEnvironment != null) {
+      return findProxyFromEnvironment(url, environment);
     }
-    if (_previous != null) {
-      return _previous.findProxyFromEnvironment(url, environment);
+    var previous = _previous;
+    if (previous != null) {
+      return previous.findProxyFromEnvironment(url, environment);
     }
     return super.findProxyFromEnvironment(url, environment);
   }

sdk/lib/_http/websocket.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 /**
@@ -99,7 +97,7 @@ class CompressionOptions {
   /// If set to `null`, the client has no preference, and the compression can
   /// use up to its default maximum window size of 15 bits depending on the
   /// server's preference.
-  final int clientMaxWindowBits;
+  final int? clientMaxWindowBits;
 
   /// The maximal window size bit count requested by the server.
   ///
@@ -109,7 +107,7 @@ class CompressionOptions {
   /// If set to `null`, the server has no preference, and the compression can
   /// use up to its default maximum window size of 15 bits depending on the
   /// client's preference.
-  final int serverMaxWindowBits;
+  final int? serverMaxWindowBits;
 
   /// Whether WebSocket compression is enabled.
   ///
@@ -132,21 +130,18 @@ class CompressionOptions {
   /// value from headers. Defaults to [WebSocket.DEFAULT_WINDOW_BITS]. Returns a
   /// [_CompressionMaxWindowBits] object which contains the response headers and
   /// negotiated max window bits.
-  _CompressionMaxWindowBits _createServerResponseHeader(HeaderValue requested) {
-    var info = new _CompressionMaxWindowBits();
+  _CompressionMaxWindowBits _createServerResponseHeader(
+      HeaderValue? requested) {
+    var info = new _CompressionMaxWindowBits("", 0);
 
-    int mwb;
-    String part;
-    if (requested?.parameters != null) {
-      part = requested.parameters[_serverMaxWindowBits];
-    }
+    String? part = requested?.parameters[_serverMaxWindowBits];
     if (part != null) {
       if (part.length >= 2 && part.startsWith('0')) {
         throw new ArgumentError("Illegal 0 padding on value.");
       } else {
-        mwb = serverMaxWindowBits == null
-            ? int.tryParse(part) ?? _WebSocketImpl.DEFAULT_WINDOW_BITS
-            : serverMaxWindowBits;
+        int mwb = serverMaxWindowBits ??
+            int.tryParse(part) ??
+            _WebSocketImpl.DEFAULT_WINDOW_BITS;
         info.headerValue = "; server_max_window_bits=${mwb}";
         info.maxWindowBits = mwb;
       }
@@ -158,7 +153,7 @@ class CompressionOptions {
   }
 
   /// Returns default values for client compression request headers.
-  String _createClientRequestHeader(HeaderValue requested, int size) {
+  String _createClientRequestHeader(HeaderValue? requested, int size) {
     var info = "";
 
     // If responding to a valid request, specify size
@@ -189,7 +184,7 @@ class CompressionOptions {
   /// `server_max_window_bits` value.  This method returns a
   /// [_CompressionMaxWindowBits] object with the response headers and
   /// negotiated `maxWindowBits` value.
-  _CompressionMaxWindowBits _createHeader([HeaderValue requested]) {
+  _CompressionMaxWindowBits _createHeader([HeaderValue? requested]) {
     var info = new _CompressionMaxWindowBits("", 0);
     if (!enabled) {
       return info;
@@ -266,8 +261,8 @@ abstract class WebSocketTransformer
    * then the [WebSocket] will be created with the default [CompressionOptions].
    */
   factory WebSocketTransformer(
-      {/*String|Future<String>*/ protocolSelector(List<String> protocols),
-      CompressionOptions compression: CompressionOptions.compressionDefault}) {
+      {/*String|Future<String>*/ protocolSelector(List<String> protocols)?,
+      CompressionOptions compression = CompressionOptions.compressionDefault}) {
     return new _WebSocketTransformerImpl(protocolSelector, compression);
   }
 
@@ -289,8 +284,8 @@ abstract class WebSocketTransformer
    * then the [WebSocket] will be created with the default [CompressionOptions].
    */
   static Future<WebSocket> upgrade(HttpRequest request,
-      {protocolSelector(List<String> protocols),
-      CompressionOptions compression: CompressionOptions.compressionDefault}) {
+      {protocolSelector(List<String> protocols)?,
+      CompressionOptions compression = CompressionOptions.compressionDefault}) {
     return _WebSocketTransformerImpl._upgrade(
         request, protocolSelector, compression);
   }
@@ -347,7 +342,7 @@ abstract class WebSocket
    *
    * The default value is `null`.
    */
-  Duration pingInterval;
+  Duration? pingInterval;
 
   /**
    * Create a new WebSocket connection. The URL supplied in [url]
@@ -377,9 +372,9 @@ abstract class WebSocket
    * authentication when setting up the connection.
    */
   static Future<WebSocket> connect(String url,
-          {Iterable<String> protocols,
-          Map<String, dynamic> headers,
-          CompressionOptions compression:
+          {Iterable<String>? protocols,
+          Map<String, dynamic>? headers,
+          CompressionOptions compression =
               CompressionOptions.compressionDefault}) =>
       _WebSocketImpl.connect(url, protocols, headers, compression: compression);
 
@@ -407,9 +402,9 @@ abstract class WebSocket
    * then the [WebSocket] will be created with the default [CompressionOptions].
    */
   factory WebSocket.fromUpgradedSocket(Socket socket,
-      {String protocol,
-      bool serverSide,
-      CompressionOptions compression: CompressionOptions.compressionDefault}) {
+      {String? protocol,
+      bool? serverSide,
+      CompressionOptions compression = CompressionOptions.compressionDefault}) {
     if (serverSide == null) {
       throw new ArgumentError("The serverSide argument must be passed "
           "explicitly to WebSocket.fromUpgradedSocket.");
@@ -436,19 +431,19 @@ abstract class WebSocket
    * selected by the server. If no subprotocol is negotiated the
    * value will remain [:null:].
    */
-  String get protocol;
+  String? get protocol;
 
   /**
    * The close code set when the WebSocket connection is closed. If
    * there is no close code available this property will be [:null:]
    */
-  int get closeCode;
+  int? get closeCode;
 
   /**
    * The close reason set when the WebSocket connection is closed. If
    * there is no close reason available this property will be [:null:]
    */
-  String get closeReason;
+  String? get closeReason;
 
   /**
    * Closes the WebSocket connection. Set the optional [code] and [reason]
@@ -456,7 +451,7 @@ abstract class WebSocket
    * omitted, the peer will see [WebSocketStatus.noStatusReceived] code
    * with no reason.
    */
-  Future close([int code, String reason]);
+  Future close([int? code, String? reason]);
 
   /**
    * Sends data on the WebSocket connection. The data in [data] must
@@ -482,12 +477,12 @@ abstract class WebSocket
   /**
    * Gets the user agent used for WebSocket connections.
    */
-  static String get userAgent => _WebSocketImpl.userAgent;
+  static String? get userAgent => _WebSocketImpl.userAgent;
 
   /**
    * Sets the user agent to use for WebSocket connections.
    */
-  static set userAgent(String userAgent) {
+  static set userAgent(String? userAgent) {
     _WebSocketImpl.userAgent = userAgent;
   }
 }

sdk/lib/_http/websocket_impl.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._http;
 
 const String _webSocketGUID = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
@@ -51,7 +49,7 @@ class _EncodedString {
 class _CompressionMaxWindowBits {
   String headerValue;
   int maxWindowBits;
-  _CompressionMaxWindowBits([this.headerValue, this.maxWindowBits]);
+  _CompressionMaxWindowBits(this.headerValue, this.maxWindowBits);
   String toString() => headerValue;
 }
 
@@ -91,16 +89,16 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
   int _remainingPayloadBytes = -1;
   int _unmaskingIndex = 0;
   int _currentMessageType = _WebSocketMessageType.NONE;
-  int closeCode = WebSocketStatus.noStatusReceived;
+  int closeCode = WebSocketStatus.NO_STATUS_RECEIVED;
   String closeReason = "";
 
-  EventSink<dynamic /*List<int>|_WebSocketPing|_WebSocketPong*/ > _eventSink;
+  EventSink<dynamic /*List<int>|_WebSocketPing|_WebSocketPong*/ >? _eventSink;
 
   final bool _serverSide;
-  final List _maskingBytes = new List(4);
+  final Uint8List _maskingBytes = Uint8List(4);
   final BytesBuilder _payload = new BytesBuilder(copy: false);
 
-  _WebSocketPerMessageDeflate _deflate;
+  _WebSocketPerMessageDeflate? _deflate;
   _WebSocketProtocolTransformer([this._serverSide = false, this._deflate]);
 
   Stream<dynamic /*List<int>|_WebSocketPing|_WebSocketPong*/ > bind(
@@ -114,13 +112,14 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
     });
   }
 
-  void addError(Object error, [StackTrace stackTrace]) {
+  void addError(Object error, [StackTrace? stackTrace]) {
+    // TODO(40614): Remove once non-nullability is sound.
     ArgumentError.checkNotNull(error, "error");
-    _eventSink.addError(error, stackTrace);
+    _eventSink!.addError(error, stackTrace);
   }
 
   void close() {
-    _eventSink.close();
+    _eventSink!.close();
   }
 
   /**
@@ -308,13 +307,13 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
         switch (_opcode) {
           case _WebSocketOpcode.CLOSE:
             _state = CLOSED;
-            _eventSink.close();
+            _eventSink!.close();
             break;
           case _WebSocketOpcode.PING:
-            _eventSink.add(new _WebSocketPing());
+            _eventSink!.add(new _WebSocketPing());
             break;
           case _WebSocketOpcode.PONG:
-            _eventSink.add(new _WebSocketPong());
+            _eventSink!.add(new _WebSocketPong());
             break;
         }
         _prepareForNextFrame();
@@ -329,16 +328,17 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
   void _messageFrameEnd() {
     if (_fin) {
       var bytes = _payload.takeBytes();
-      if (_deflate != null && _compressed) {
-        bytes = _deflate.processIncomingMessage(bytes);
+      var deflate = _deflate;
+      if (deflate != null && _compressed) {
+        bytes = deflate.processIncomingMessage(bytes);
       }
 
       switch (_currentMessageType) {
         case _WebSocketMessageType.TEXT:
-          _eventSink.add(utf8.decode(bytes));
+          _eventSink!.add(utf8.decode(bytes));
           break;
         case _WebSocketMessageType.BINARY:
-          _eventSink.add(bytes);
+          _eventSink!.add(bytes);
           break;
       }
       _currentMessageType = _WebSocketMessageType.NONE;
@@ -364,15 +364,15 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
           }
         }
         _state = CLOSED;
-        _eventSink.close();
+        _eventSink!.close();
         break;
 
       case _WebSocketOpcode.PING:
-        _eventSink.add(new _WebSocketPing(_payload.takeBytes()));
+        _eventSink!.add(new _WebSocketPing(_payload.takeBytes()));
         break;
 
       case _WebSocketOpcode.PONG:
-        _eventSink.add(new _WebSocketPong(_payload.takeBytes()));
+        _eventSink!.add(new _WebSocketPong(_payload.takeBytes()));
         break;
     }
     _prepareForNextFrame();
@@ -397,12 +397,12 @@ class _WebSocketProtocolTransformer extends StreamTransformerBase<List<int>,
 }
 
 class _WebSocketPing {
-  final List<int> payload;
+  final List<int>? payload;
   _WebSocketPing([this.payload = null]);
 }
 
 class _WebSocketPong {
-  final List<int> payload;
+  final List<int>? payload;
   _WebSocketPong([this.payload = null]);
 }
 
@@ -413,7 +413,7 @@ class _WebSocketTransformerImpl
     implements WebSocketTransformer {
   final StreamController<WebSocket> _controller =
       new StreamController<WebSocket>(sync: true);
-  final _ProtocolSelector _protocolSelector;
+  final _ProtocolSelector? _protocolSelector;
   final CompressionOptions _compression;
 
   _WebSocketTransformerImpl(this._protocolSelector, this._compression);
@@ -431,7 +431,7 @@ class _WebSocketTransformerImpl
   }
 
   static List<String> _tokenizeFieldValue(String headerValue) {
-    List<String> tokens = new List<String>();
+    List<String> tokens = <String>[];
     int start = 0;
     int index = 0;
     while (index < headerValue.length) {
@@ -448,7 +448,7 @@ class _WebSocketTransformerImpl
   }
 
   static Future<WebSocket> _upgrade(HttpRequest request,
-      _ProtocolSelector _protocolSelector, CompressionOptions compression) {
+      _ProtocolSelector? protocolSelector, CompressionOptions compression) {
     var response = request.response;
     if (!_isUpgradeRequest(request)) {
       // Send error response.
@@ -459,13 +459,13 @@ class _WebSocketTransformerImpl
           new WebSocketException("Invalid WebSocket upgrade request"));
     }
 
-    Future<WebSocket> upgrade(String protocol) {
+    Future<WebSocket> upgrade(String? protocol) {
       // Send the upgrade response.
       response
         ..statusCode = HttpStatus.switchingProtocols
         ..headers.add(HttpHeaders.connectionHeader, "Upgrade")
         ..headers.add(HttpHeaders.upgradeHeader, "websocket");
-      String key = request.headers.value("Sec-WebSocket-Key");
+      String key = request.headers.value("Sec-WebSocket-Key")!;
       _SHA1 sha1 = new _SHA1();
       sha1.add("$key$_webSocketGUID".codeUnits);
       String accept = _CryptoUtils.bytesToBase64(sha1.close());
@@ -483,14 +483,14 @@ class _WebSocketTransformerImpl
     }
 
     var protocols = request.headers['Sec-WebSocket-Protocol'];
-    if (protocols != null && _protocolSelector != null) {
+    if (protocols != null && protocolSelector != null) {
       // The suggested protocols can be spread over multiple lines, each
       // consisting of multiple protocols. To unify all of them, first join
       // the lists with ', ' and then tokenize.
-      protocols = _tokenizeFieldValue(protocols.join(', '));
-      return new Future<String>(() => _protocolSelector(protocols))
+      var tokenizedProtocols = _tokenizeFieldValue(protocols.join(', '));
+      return new Future<String>(() => protocolSelector(tokenizedProtocols))
           .then<String>((protocol) {
-        if (protocols.indexOf(protocol) < 0) {
+        if (tokenizedProtocols.indexOf(protocol) < 0) {
           throw new WebSocketException(
               "Selected protocol is not in the list of available protocols");
         }
@@ -506,7 +506,7 @@ class _WebSocketTransformerImpl
     }
   }
 
-  static _WebSocketPerMessageDeflate _negotiateCompression(HttpRequest request,
+  static _WebSocketPerMessageDeflate? _negotiateCompression(HttpRequest request,
       HttpResponse response, CompressionOptions compression) {
     var extensionHeader = request.headers.value("Sec-WebSocket-Extensions");
 
@@ -540,23 +540,27 @@ class _WebSocketTransformerImpl
     if (request.method != "GET") {
       return false;
     }
-    if (request.headers[HttpHeaders.connectionHeader] == null) {
+    var connectionHeader = request.headers[HttpHeaders.connectionHeader];
+    if (connectionHeader == null) {
       return false;
     }
     bool isUpgrade = false;
-    request.headers[HttpHeaders.connectionHeader].forEach((String value) {
-      if (value.toLowerCase() == "upgrade") isUpgrade = true;
-    });
+    for (var value in connectionHeader) {
+      if (value.toLowerCase() == "upgrade") {
+        isUpgrade = true;
+        break;
+      }
+    }
     if (!isUpgrade) return false;
-    String upgrade = request.headers.value(HttpHeaders.upgradeHeader);
+    String? upgrade = request.headers.value(HttpHeaders.upgradeHeader);
     if (upgrade == null || upgrade.toLowerCase() != "websocket") {
       return false;
     }
-    String version = request.headers.value("Sec-WebSocket-Version");
+    String? version = request.headers.value("Sec-WebSocket-Version");
     if (version == null || version != "13") {
       return false;
     }
-    String key = request.headers.value("Sec-WebSocket-Key");
+    String? key = request.headers.value("Sec-WebSocket-Key");
     if (key == null) {
       return false;
     }
@@ -571,34 +575,26 @@ class _WebSocketPerMessageDeflate {
   int serverMaxWindowBits;
   bool serverSide;
 
-  RawZLibFilter decoder;
-  RawZLibFilter encoder;
+  RawZLibFilter? decoder;
+  RawZLibFilter? encoder;
 
   _WebSocketPerMessageDeflate(
-      {this.clientMaxWindowBits: _WebSocketImpl.DEFAULT_WINDOW_BITS,
-      this.serverMaxWindowBits: _WebSocketImpl.DEFAULT_WINDOW_BITS,
-      this.serverNoContextTakeover: false,
-      this.clientNoContextTakeover: false,
-      this.serverSide: false});
+      {this.clientMaxWindowBits = _WebSocketImpl.DEFAULT_WINDOW_BITS,
+      this.serverMaxWindowBits = _WebSocketImpl.DEFAULT_WINDOW_BITS,
+      this.serverNoContextTakeover = false,
+      this.clientNoContextTakeover = false,
+      this.serverSide = false});
 
-  void _ensureDecoder() {
-    if (decoder == null) {
-      decoder = new RawZLibFilter.inflateFilter(
-          windowBits: serverSide ? clientMaxWindowBits : serverMaxWindowBits,
-          raw: true);
-    }
-  }
+  RawZLibFilter _ensureDecoder() => decoder ??= new RawZLibFilter.inflateFilter(
+      windowBits: serverSide ? clientMaxWindowBits : serverMaxWindowBits,
+      raw: true);
 
-  void _ensureEncoder() {
-    if (encoder == null) {
-      encoder = new RawZLibFilter.deflateFilter(
-          windowBits: serverSide ? serverMaxWindowBits : clientMaxWindowBits,
-          raw: true);
-    }
-  }
+  RawZLibFilter _ensureEncoder() => encoder ??= new RawZLibFilter.deflateFilter(
+      windowBits: serverSide ? serverMaxWindowBits : clientMaxWindowBits,
+      raw: true);
 
   Uint8List processIncomingMessage(List<int> msg) {
-    _ensureDecoder();
+    var decoder = _ensureDecoder();
 
     var data = <int>[];
     data.addAll(msg);
@@ -608,20 +604,22 @@ class _WebSocketPerMessageDeflate {
     final result = new BytesBuilder();
     List<int> out;
 
-    while ((out = decoder.processed()) != null) {
+    while (true) {
+      final out = decoder.processed();
+      if (out == null) break;
       result.add(out);
     }
 
     if ((serverSide && clientNoContextTakeover) ||
         (!serverSide && serverNoContextTakeover)) {
-      decoder = null;
+      this.decoder = null;
     }
 
     return result.takeBytes();
   }
 
   List<int> processOutgoingMessage(List<int> msg) {
-    _ensureEncoder();
+    var encoder = _ensureEncoder();
     var result = <int>[];
     Uint8List buffer;
 
@@ -639,14 +637,15 @@ class _WebSocketPerMessageDeflate {
 
     encoder.process(buffer, 0, buffer.length);
 
-    List<int> out;
-    while ((out = encoder.processed()) != null) {
+    while (true) {
+      final out = encoder.processed();
+      if (out == null) break;
       result.addAll(out);
     }
 
     if ((!serverSide && clientNoContextTakeover) ||
         (serverSide && serverNoContextTakeover)) {
-      encoder = null;
+      this.encoder = null;
     }
 
     if (result.length > 4) {
@@ -670,13 +669,12 @@ class _WebSocketPerMessageDeflate {
 class _WebSocketOutgoingTransformer
     extends StreamTransformerBase<dynamic, List<int>> implements EventSink {
   final _WebSocketImpl webSocket;
-  EventSink<List<int>> _eventSink;
+  EventSink<List<int>>? _eventSink;
 
-  _WebSocketPerMessageDeflate _deflateHelper;
+  _WebSocketPerMessageDeflate? _deflateHelper;
 
-  _WebSocketOutgoingTransformer(this.webSocket) {
-    _deflateHelper = webSocket._deflate;
-  }
+  _WebSocketOutgoingTransformer(this.webSocket)
+      : _deflateHelper = webSocket._deflate;
 
   Stream<List<int>> bind(Stream stream) {
     return new Stream<List<int>>.eventTransformed(stream,
@@ -698,53 +696,55 @@ class _WebSocketOutgoingTransformer
       addFrame(_WebSocketOpcode.PING, message.payload);
       return;
     }
-    List<int> data;
+    List<int>? data;
     int opcode;
     if (message != null) {
+      List<int> messageData;
       if (message is String) {
         opcode = _WebSocketOpcode.TEXT;
-        data = utf8.encode(message);
+        messageData = utf8.encode(message);
       } else if (message is List<int>) {
         opcode = _WebSocketOpcode.BINARY;
-        data = message;
+        messageData = message;
       } else if (message is _EncodedString) {
         opcode = _WebSocketOpcode.TEXT;
-        data = message.bytes;
+        messageData = message.bytes;
       } else {
         throw new ArgumentError(message);
       }
-
-      if (_deflateHelper != null) {
-        data = _deflateHelper.processOutgoingMessage(data);
+      var deflateHelper = _deflateHelper;
+      if (deflateHelper != null) {
+        messageData = deflateHelper.processOutgoingMessage(messageData);
       }
+      data = messageData;
     } else {
       opcode = _WebSocketOpcode.TEXT;
     }
     addFrame(opcode, data);
   }
 
-  void addError(Object error, [StackTrace stackTrace]) {
+  void addError(Object error, [StackTrace? stackTrace]) {
+    // TODO(40614): Remove once non-nullability is sound.
     ArgumentError.checkNotNull(error, "error");
-    _eventSink.addError(error, stackTrace);
+    _eventSink!.addError(error, stackTrace);
   }
 
   void close() {
-    int code = webSocket._outCloseCode;
-    String reason = webSocket._outCloseReason;
-    List<int> data;
+    int? code = webSocket._outCloseCode;
+    String? reason = webSocket._outCloseReason;
+    List<int>? data;
     if (code != null) {
-      data = new List<int>();
-      data.add((code >> 8) & 0xFF);
-      data.add(code & 0xFF);
-      if (reason != null) {
-        data.addAll(utf8.encode(reason));
-      }
+      data = [
+        (code >> 8) & 0xFF,
+        code & 0xFF,
+        if (reason != null) ...utf8.encode(reason)
+      ];
     }
     addFrame(_WebSocketOpcode.CLOSE, data);
-    _eventSink.close();
+    _eventSink!.close();
   }
 
-  void addFrame(int opcode, List<int> data) {
+  void addFrame(int opcode, List<int>? data) {
     createFrame(
             opcode,
             data,
@@ -753,12 +753,12 @@ class _WebSocketOutgoingTransformer
                 (opcode == _WebSocketOpcode.TEXT ||
                     opcode == _WebSocketOpcode.BINARY))
         .forEach((e) {
-      _eventSink.add(e);
+      _eventSink!.add(e);
     });
   }
 
   static Iterable<List<int>> createFrame(
-      int opcode, List<int> data, bool serverSide, bool compressed) {
+      int opcode, List<int>? data, bool serverSide, bool compressed) {
     bool mask = !serverSide; // Masking not implemented for server.
     int dataLength = data == null ? 0 : data.length;
     // Determine the header size.
@@ -849,58 +849,59 @@ class _WebSocketOutgoingTransformer
 class _WebSocketConsumer implements StreamConsumer {
   final _WebSocketImpl webSocket;
   final Socket socket;
-  StreamController _controller;
-  StreamSubscription _subscription;
+  StreamController? _controller;
+  StreamSubscription? _subscription;
   bool _issuedPause = false;
   bool _closed = false;
   Completer _closeCompleter = new Completer<WebSocket>();
-  Completer _completer;
+  Completer? _completer;
 
   _WebSocketConsumer(this.webSocket, this.socket);
 
   void _onListen() {
-    if (_subscription != null) {
-      _subscription.cancel();
-    }
+    _subscription?.cancel();
   }
 
   void _onPause() {
-    if (_subscription != null) {
-      _subscription.pause();
+    var subscription = _subscription;
+    if (subscription != null) {
+      subscription.pause();
     } else {
       _issuedPause = true;
     }
   }
 
   void _onResume() {
-    if (_subscription != null) {
-      _subscription.resume();
+    var subscription = _subscription;
+    if (subscription != null) {
+      subscription.resume();
     } else {
       _issuedPause = false;
     }
   }
 
   void _cancel() {
-    if (_subscription != null) {
-      var subscription = _subscription;
+    var subscription = _subscription;
+    if (subscription != null) {
       _subscription = null;
       subscription.cancel();
     }
   }
 
-  _ensureController() {
-    if (_controller != null) return;
-    _controller = new StreamController(
+  StreamController _ensureController() {
+    var controller = _controller;
+    if (controller != null) return controller;
+    controller = _controller = new StreamController(
         sync: true,
         onPause: _onPause,
         onResume: _onResume,
         onCancel: _onListen);
-    var stream = _controller.stream
+    var stream = controller.stream
         .transform(new _WebSocketOutgoingTransformer(webSocket));
     socket.addStream(stream).then((_) {
       _done();
       _closeCompleter.complete(webSocket);
-    }, onError: (error, StackTrace stackTrace) {
+    }, onError: (Object error, StackTrace stackTrace) {
       _closed = true;
       _cancel();
       if (error is ArgumentError) {
@@ -912,53 +913,52 @@ class _WebSocketConsumer implements StreamConsumer {
         _closeCompleter.complete(webSocket);
       }
     });
+    return controller;
   }
 
-  bool _done([error, StackTrace stackTrace]) {
-    if (_completer == null) return false;
+  bool _done([Object? error, StackTrace? stackTrace]) {
+    var completer = _completer;
+    if (completer == null) return false;
     if (error != null) {
-      _completer.completeError(error, stackTrace);
+      completer.completeError(error, stackTrace);
     } else {
-      _completer.complete(webSocket);
+      completer.complete(webSocket);
     }
     _completer = null;
     return true;
   }
 
-  Future addStream(var stream) {
+  Future addStream(Stream stream) {
     if (_closed) {
       stream.listen(null).cancel();
       return new Future.value(webSocket);
     }
     _ensureController();
-    _completer = new Completer();
-    _subscription = stream.listen((data) {
-      _controller.add(data);
+    var completer = _completer = new Completer();
+    var subscription = _subscription = stream.listen((data) {
+      _controller!.add(data);
     }, onDone: _done, onError: _done, cancelOnError: true);
     if (_issuedPause) {
-      _subscription.pause();
+      subscription.pause();
       _issuedPause = false;
     }
-    return _completer.future;
+    return completer.future;
   }
 
   Future close() {
-    _ensureController();
-    Future closeSocket() {
-      return socket.close().catchError((_) {}).then((_) => webSocket);
-    }
+    _ensureController().close();
 
-    _controller.close();
-    return _closeCompleter.future.then((_) => closeSocket());
+    return _closeCompleter.future
+        .then((_) => socket.close().catchError((_) {}).then((_) => webSocket));
   }
 
   void add(data) {
     if (_closed) return;
-    _ensureController();
+    var controller = _ensureController();
     // Stop sending message if _controller has been closed.
     // https://github.com/dart-lang/sdk/issues/37441
-    if (_controller.isClosed) return;
-    _controller.add(data);
+    if (controller.isClosed) return;
+    controller.add(data);
   }
 
   void closeSocket() {
@@ -974,32 +974,33 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
   static const int DEFAULT_WINDOW_BITS = 15;
   static const String PER_MESSAGE_DEFLATE = "permessage-deflate";
 
-  final String protocol;
+  final String? protocol;
 
-  StreamController _controller;
-  StreamSubscription _subscription;
-  StreamSink _sink;
+  final StreamController _controller;
+  StreamSubscription? _subscription;
+  late StreamSink _sink;
 
-  final _socket;
+  final Socket _socket;
   final bool _serverSide;
   int _readyState = WebSocket.connecting;
   bool _writeClosed = false;
-  int _closeCode;
-  String _closeReason;
-  Duration _pingInterval;
-  Timer _pingTimer;
-  _WebSocketConsumer _consumer;
+  int? _closeCode;
+  String? _closeReason;
+  Duration? _pingInterval;
+  Timer? _pingTimer;
+  late _WebSocketConsumer _consumer;
 
-  int _outCloseCode;
-  String _outCloseReason;
-  Timer _closeTimer;
-  _WebSocketPerMessageDeflate _deflate;
+  int? _outCloseCode;
+  String? _outCloseReason;
+  Timer? _closeTimer;
+  _WebSocketPerMessageDeflate? _deflate;
 
   static final HttpClient _httpClient = new HttpClient();
 
   static Future<WebSocket> connect(
-      String url, Iterable<String> protocols, Map<String, dynamic> headers,
-      {CompressionOptions compression: CompressionOptions.compressionDefault}) {
+      String url, Iterable<String>? protocols, Map<String, dynamic>? headers,
+      {CompressionOptions compression =
+          CompressionOptions.compressionDefault}) {
     Uri uri = Uri.parse(url);
     if (uri.scheme != "ws" && uri.scheme != "wss") {
       throw new WebSocketException("Unsupported URL scheme '${uri.scheme}'");
@@ -1049,7 +1050,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
 
       return request.close();
     }).then((response) {
-      void error(String message) {
+      Never error(String message) {
         // Flush data.
         response.detachSocket().then((socket) {
           socket.destroy();
@@ -1057,15 +1058,15 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
         throw new WebSocketException(message);
       }
 
+      var connectionHeader = response.headers[HttpHeaders.connectionHeader];
       if (response.statusCode != HttpStatus.switchingProtocols ||
-          response.headers[HttpHeaders.connectionHeader] == null ||
-          !response.headers[HttpHeaders.connectionHeader]
-              .any((value) => value.toLowerCase() == "upgrade") ||
-          response.headers.value(HttpHeaders.upgradeHeader).toLowerCase() !=
+          connectionHeader == null ||
+          !connectionHeader.any((value) => value.toLowerCase() == "upgrade") ||
+          response.headers.value(HttpHeaders.upgradeHeader)!.toLowerCase() !=
               "websocket") {
         error("Connection to '$uri' was not upgraded to websocket");
       }
-      String accept = response.headers.value("Sec-WebSocket-Accept");
+      String? accept = response.headers.value("Sec-WebSocket-Accept");
       if (accept == null) {
         error("Response did not contain a 'Sec-WebSocket-Accept' header");
       }
@@ -1083,7 +1084,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       }
       var protocol = response.headers.value('Sec-WebSocket-Protocol');
 
-      _WebSocketPerMessageDeflate deflate =
+      _WebSocketPerMessageDeflate? deflate =
           negotiateClientCompression(response, compression);
 
       return response.detachSocket().then<WebSocket>((socket) =>
@@ -1092,13 +1093,10 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
     });
   }
 
-  static _WebSocketPerMessageDeflate negotiateClientCompression(
+  static _WebSocketPerMessageDeflate? negotiateClientCompression(
       HttpClientResponse response, CompressionOptions compression) {
-    String extensionHeader = response.headers.value('Sec-WebSocket-Extensions');
-
-    if (extensionHeader == null) {
-      extensionHeader = "";
-    }
+    String extensionHeader =
+        response.headers.value('Sec-WebSocket-Extensions') ?? "";
 
     var hv = HeaderValue.parse(extensionHeader, valueSeparator: ',');
 
@@ -1129,14 +1127,15 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
 
   _WebSocketImpl._fromSocket(
       this._socket, this.protocol, CompressionOptions compression,
-      [this._serverSide = false, _WebSocketPerMessageDeflate deflate]) {
+      [this._serverSide = false, _WebSocketPerMessageDeflate? deflate])
+      : _controller = new StreamController(sync: true) {
     _consumer = new _WebSocketConsumer(this, _socket);
     _sink = new _StreamSinkImpl(_consumer);
     _readyState = WebSocket.open;
     _deflate = deflate;
 
-    var transformer = new _WebSocketProtocolTransformer(_serverSide, _deflate);
-    _subscription = transformer.bind(_socket).listen((data) {
+    var transformer = new _WebSocketProtocolTransformer(_serverSide, deflate);
+    var subscription = _subscription = transformer.bind(_socket).listen((data) {
       if (data is _WebSocketPing) {
         if (!_writeClosed) _consumer.add(new _WebSocketPong(data.payload));
       } else if (data is _WebSocketPong) {
@@ -1145,8 +1144,8 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       } else {
         _controller.add(data);
       }
-    }, onError: (error, stackTrace) {
-      if (_closeTimer != null) _closeTimer.cancel();
+    }, onError: (Object error, StackTrace stackTrace) {
+      _closeTimer?.cancel();
       if (error is FormatException) {
         _close(WebSocketStatus.invalidFramePayloadData);
       } else {
@@ -1157,7 +1156,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       _closeReason = _outCloseReason;
       _controller.close();
     }, onDone: () {
-      if (_closeTimer != null) _closeTimer.cancel();
+      _closeTimer?.cancel();
       if (_readyState == WebSocket.open) {
         _readyState = WebSocket.closing;
         if (!_isReservedStatusCode(transformer.closeCode)) {
@@ -1172,39 +1171,38 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       _closeReason = transformer.closeReason;
       _controller.close();
     }, cancelOnError: true);
-    _subscription.pause();
-    _controller = new StreamController(
-        sync: true,
-        onListen: _subscription.resume,
-        onCancel: () {
-          _subscription.cancel();
-          _subscription = null;
-        },
-        onPause: _subscription.pause,
-        onResume: _subscription.resume);
+    subscription.pause();
+    _controller
+      ..onListen = subscription.resume
+      ..onCancel = () {
+        _subscription!.cancel();
+        _subscription = null;
+      }
+      ..onPause = subscription.pause
+      ..onResume = subscription.resume;
 
     _webSockets[_serviceId] = this;
   }
 
-  StreamSubscription listen(void onData(message),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription listen(void onData(message)?,
+      {Function? onError, void onDone()?, bool? cancelOnError}) {
     return _controller.stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
 
-  Duration get pingInterval => _pingInterval;
+  Duration? get pingInterval => _pingInterval;
 
-  void set pingInterval(Duration interval) {
+  void set pingInterval(Duration? interval) {
     if (_writeClosed) return;
-    if (_pingTimer != null) _pingTimer.cancel();
+    _pingTimer?.cancel();
     _pingInterval = interval;
 
-    if (_pingInterval == null) return;
+    if (interval == null) return;
 
-    _pingTimer = new Timer(_pingInterval, () {
+    _pingTimer = new Timer(interval, () {
       if (_writeClosed) return;
       _consumer.add(new _WebSocketPing());
-      _pingTimer = new Timer(_pingInterval, () {
+      _pingTimer = new Timer(interval, () {
         _closeTimer?.cancel();
         // No pong received.
         _close(WebSocketStatus.goingAway);
@@ -1217,27 +1215,28 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
 
   int get readyState => _readyState;
 
-  String get extensions => null;
-  int get closeCode => _closeCode;
-  String get closeReason => _closeReason;
+  String get extensions => "";
+  int? get closeCode => _closeCode;
+  String? get closeReason => _closeReason;
 
   void add(data) {
     _sink.add(data);
   }
 
   void addUtf8Text(List<int> bytes) {
+    // TODO(40614): Remove once non-nullability is sound.
     ArgumentError.checkNotNull(bytes, "bytes");
     _sink.add(new _EncodedString(bytes));
   }
 
-  void addError(error, [StackTrace stackTrace]) {
+  void addError(Object error, [StackTrace? stackTrace]) {
     _sink.addError(error, stackTrace);
   }
 
   Future addStream(Stream stream) => _sink.addStream(stream);
   Future get done => _sink.done;
 
-  Future close([int code, String reason]) {
+  Future close([int? code, String? reason]) {
     if (_isReservedStatusCode(code)) {
       throw new WebSocketException("Reserved status code $code");
     }
@@ -1260,7 +1259,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
           // Reuse code and reason from the local close.
           _closeCode = _outCloseCode;
           _closeReason = _outCloseReason;
-          if (_subscription != null) _subscription.cancel();
+          _subscription?.cancel();
           _controller.close();
           _webSockets.remove(_serviceId);
         });
@@ -1269,13 +1268,13 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
     return _sink.close();
   }
 
-  static String get userAgent => _httpClient.userAgent;
+  static String? get userAgent => _httpClient.userAgent;
 
-  static set userAgent(String userAgent) {
+  static set userAgent(String? userAgent) {
     _httpClient.userAgent = userAgent;
   }
 
-  void _close([int code, String reason]) {
+  void _close([int? code, String? reason]) {
     if (_writeClosed) return;
     if (_outCloseCode == null) {
       _outCloseCode = code;
@@ -1301,7 +1300,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       return r;
     }
     try {
-      r['socket'] = _socket._toJSON(true);
+      r['socket'] = (_socket as dynamic)._toJSON(true);
     } catch (_) {
       r['socket'] = {
         'id': _servicePath,
@@ -1313,7 +1312,7 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
     return r;
   }
 
-  static bool _isReservedStatusCode(int code) {
+  static bool _isReservedStatusCode(int? code) {
     return code != null &&
         (code < WebSocketStatus.normalClosure ||
             code == WebSocketStatus.reserved1004 ||

sdk/lib/_internal/js_dev_runtime/libraries.dart

@@ -1,313 +0,0 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// @dart = 2.6
-
-library libraries;
-
-/**
- * A bit flag used by [LibraryInfo] indicating that a library is used by dart2js
- */
-const int DART2JS_PLATFORM = 1;
-
-/**
- * A bit flag used by [LibraryInfo] indicating that a library is used by the VM
- */
-const int VM_PLATFORM = 2;
-
-/// The contexts that a library can be used from.
-enum Category {
-  /// Indicates that a library can be used in a browser context.
-  client,
-
-  /// Indicates that a library can be used in a command line context.
-  server,
-
-  /// Indicates that a library can be used from embedded devices.
-  embedded
-}
-
-Category parseCategory(String name) {
-  switch (name) {
-    case "Client":
-      return Category.client;
-    case "Server":
-      return Category.server;
-    case "Embedded":
-      return Category.embedded;
-  }
-  return null;
-}
-
-/// Mapping of "dart:" library name (e.g. "core") to information about that
-/// library.
-const Map<String, LibraryInfo> libraries = const {
-  "async": const LibraryInfo("async/async.dart",
-      categories: "Client,Server",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/async_patch.dart"),
-  "collection": const LibraryInfo("collection/collection.dart",
-      categories: "Client,Server,Embedded",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/collection_patch.dart"),
-  "convert": const LibraryInfo("convert/convert.dart",
-      categories: "Client,Server",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/convert_patch.dart"),
-  "core": const LibraryInfo("core/core.dart",
-      categories: "Client,Server,Embedded",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/core_patch.dart"),
-  "developer": const LibraryInfo("developer/developer.dart",
-      categories: "Client,Server,Embedded",
-      maturity: Maturity.UNSTABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/developer_patch.dart"),
-  "html": const LibraryInfo("html/dart2js/html_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "html_common": const LibraryInfo("html/html_common/html_common.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      dart2jsPath: "html/html_common/html_common_dart2js.dart",
-      documented: false,
-      implementation: true),
-  "indexed_db": const LibraryInfo("indexed_db/dart2js/indexed_db_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "_http":
-      const LibraryInfo("_http/http.dart", categories: "", documented: false),
-  "io": const LibraryInfo("io/io.dart",
-      categories: "Server",
-      dart2jsPatchPath: "_internal/js_runtime/lib/io_patch.dart"),
-  "isolate": const LibraryInfo("isolate/isolate.dart",
-      categories: "Client,Server",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/isolate_patch.dart"),
-  "js": const LibraryInfo("js/js.dart",
-      categories: "Client",
-      maturity: Maturity.STABLE,
-      platforms: DART2JS_PLATFORM,
-      dart2jsPatchPath: "_internal/js_runtime/lib/js_patch.dart"),
-  "js_util": const LibraryInfo("js_util/js_util.dart",
-      categories: "Client",
-      maturity: Maturity.STABLE,
-      platforms: DART2JS_PLATFORM),
-  "math": const LibraryInfo("math/math.dart",
-      categories: "Client,Server,Embedded",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/math_patch.dart"),
-  "mirrors": const LibraryInfo("mirrors/mirrors.dart",
-      categories: "Client,Server",
-      maturity: Maturity.UNSTABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/mirrors_patch.dart"),
-  "nativewrappers": const LibraryInfo("html/dartium/nativewrappers.dart",
-      categories: "Client",
-      implementation: true,
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "typed_data": const LibraryInfo("typed_data/typed_data.dart",
-      categories: "Client,Server,Embedded",
-      maturity: Maturity.STABLE,
-      dart2jsPatchPath: "_internal/js_runtime/lib/typed_data_patch.dart"),
-  "_native_typed_data": const LibraryInfo(
-      "_internal/js_runtime/lib/native_typed_data.dart",
-      categories: "",
-      implementation: true,
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "cli": const LibraryInfo("cli/cli.dart",
-      categories: "Server",
-      dart2jsPatchPath: "_internal/js_runtime/lib/cli_patch.dart"),
-  "svg": const LibraryInfo("svg/dart2js/svg_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "web_audio": const LibraryInfo("web_audio/dart2js/web_audio_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "web_gl": const LibraryInfo("web_gl/dart2js/web_gl_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "web_sql": const LibraryInfo("web_sql/dart2js/web_sql_dart2js.dart",
-      categories: "Client",
-      maturity: Maturity.WEB_STABLE,
-      platforms: DART2JS_PLATFORM),
-  "_internal": const LibraryInfo("internal/internal.dart",
-      categories: "",
-      documented: false,
-      dart2jsPatchPath: "_internal/js_runtime/lib/internal_patch.dart"),
-  "_js_helper": const LibraryInfo("_internal/js_runtime/lib/js_helper.dart",
-      categories: "", documented: false, platforms: DART2JS_PLATFORM),
-  "_interceptors": const LibraryInfo(
-      "_internal/js_runtime/lib/interceptors.dart",
-      categories: "",
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "_foreign_helper": const LibraryInfo(
-      "_internal/js_runtime/lib/foreign_helper.dart",
-      categories: "",
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "_isolate_helper": const LibraryInfo(
-      "_internal/js_runtime/lib/isolate_helper.dart",
-      categories: "",
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "_js_mirrors": const LibraryInfo("_internal/js_runtime/lib/js_mirrors.dart",
-      categories: "", documented: false, platforms: DART2JS_PLATFORM),
-  "_js_primitives": const LibraryInfo(
-      "_internal/js_runtime/lib/js_primitives.dart",
-      categories: "",
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-  "_metadata": const LibraryInfo("html/html_common/metadata.dart",
-      categories: "", documented: false, platforms: DART2JS_PLATFORM),
-  "_debugger": const LibraryInfo("_internal/js_runtime/lib/debugger.dart",
-      category: "", documented: false, platforms: DART2JS_PLATFORM),
-  "_runtime": const LibraryInfo(
-      "_internal/js_runtime/lib/ddc_runtime/runtime.dart",
-      category: "",
-      documented: false,
-      platforms: DART2JS_PLATFORM),
-};
-
-/**
- * Information about a "dart:" library.
- */
-class LibraryInfo {
-  /**
-   * Path to the library's *.dart file relative to this file.
-   */
-  final String path;
-
-  /**
-   * The categories in which the library can be used encoded as a
-   * comma-separated String.
-   */
-  final String _categories;
-
-  /**
-   * Path to the dart2js library's *.dart file relative to this file
-   * or null if dart2js uses the common library path defined above.
-   * Access using the [#getDart2JsPath()] method.
-   */
-  final String dart2jsPath;
-
-  /**
-   * Path to the dart2js library's patch file relative to this file
-   * or null if no dart2js patch file associated with this library.
-   * Access using the [#getDart2JsPatchPath()] method.
-   */
-  final String dart2jsPatchPath;
-
-  /**
-   * True if this library is documented and should be shown to the user.
-   */
-  final bool documented;
-
-  /**
-   * Bit flags indicating which platforms consume this library.
-   * See [DART2JS_LIBRARY] and [VM_LIBRARY].
-   */
-  final int platforms;
-
-  /**
-   * True if the library contains implementation details for another library.
-   * The implication is that these libraries are less commonly used
-   * and that tools like Dart Editor should not show these libraries
-   * in a list of all libraries unless the user specifically asks the tool to
-   * do so.
-   */
-  final bool implementation;
-
-  /**
-   * States the current maturity of this library.
-   */
-  final Maturity maturity;
-
-  const LibraryInfo(this.path,
-      {String categories: "",
-      this.dart2jsPath,
-      this.dart2jsPatchPath,
-      this.implementation: false,
-      this.documented: true,
-      this.maturity: Maturity.UNSPECIFIED,
-      this.platforms: DART2JS_PLATFORM | VM_PLATFORM})
-      : _categories = categories;
-
-  bool get isDart2jsLibrary => (platforms & DART2JS_PLATFORM) != 0;
-  bool get isVmLibrary => (platforms & VM_PLATFORM) != 0;
-
-  /**
-   * The categories in which the library can be used.
-   *
-   * If no categories are specified, the library is internal and can not be
-   * loaded by user code.
-   */
-  List<Category> get categories {
-    // `"".split(,)` returns [""] not [], so we handle that case separately.
-    if (_categories == "") return const <Category>[];
-    return _categories.split(",").map(parseCategory).toList();
-  }
-
-  bool get isInternal => categories.isEmpty;
-
-  /// The original "categories" String that was passed to the constructor.
-  ///
-  /// Can be used to construct a slightly modified copy of this LibraryInfo.
-  String get categoriesString {
-    return _categories;
-  }
-}
-
-/**
- * Abstraction to capture the maturity of a library.
- */
-class Maturity {
-  final int level;
-  final String name;
-  final String description;
-
-  const Maturity(this.level, this.name, this.description);
-
-  String toString() => "$name: $level\n$description\n";
-
-  static const Maturity DEPRECATED = const Maturity(0, "Deprecated",
-      "This library will be remove before next major release.");
-
-  static const Maturity EXPERIMENTAL = const Maturity(
-      1,
-      "Experimental",
-      "This library is experimental and will likely change or be removed\n"
-          "in future versions.");
-
-  static const Maturity UNSTABLE = const Maturity(
-      2,
-      "Unstable",
-      "This library is in still changing and have not yet endured\n"
-          "sufficient real-world testing.\n"
-          "Backwards-compatibility is NOT guaranteed.");
-
-  static const Maturity WEB_STABLE = const Maturity(
-      3,
-      "Web Stable",
-      "This library is tracking the DOM evolution as defined by WC3.\n"
-          "Backwards-compatibility is NOT guaranteed.");
-
-  static const Maturity STABLE = const Maturity(
-      4,
-      "Stable",
-      "The library is stable. API backwards-compatibility is guaranteed.\n"
-          "However implementation details might change.");
-
-  static const Maturity LOCKED = const Maturity(5, "Locked",
-      "This library will not change except when serious bugs are encountered.");
-
-  static const Maturity UNSPECIFIED = const Maturity(-1, "Unspecified",
-      "The maturity for this library has not been specified.");
-}

sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for the dart:async library.
 
 import 'dart:_js_helper' show notNull, patch, ReifyFunctionTypes;
@@ -26,11 +24,11 @@ import 'dart:_runtime' as dart;
 @ReifyFunctionTypes(false)
 _async<T>(Function() initGenerator) {
   var iter;
-  Object Function(Object) onValue;
-  Object Function(Object, StackTrace) onError;
+  late Object? Function(Object?) onValue;
+  late Object Function(Object, StackTrace?) onError;
 
-  onAwait(Object value) {
-    _Future f;
+  onAwait(Object? value) {
+    _Future<Object?> f;
     if (value is _Future) {
       f = value;
     } else if (value is Future) {
@@ -161,7 +159,7 @@ class _AsyncRun {
   }
 
   @ReifyFunctionTypes(false)
-  static Object _scheduleImmediateWithPromise(void Function() callback) {
+  static void _scheduleImmediateWithPromise(void Function() callback) {
     dart.addAsyncCallback();
     JS('', '#.Promise.resolve(null).then(#)', dart.global_, () {
       dart.removeAsyncCallback();
@@ -182,7 +180,7 @@ class DeferredLibrary {
 @patch
 class Timer {
   @patch
-  static Timer _createTimer(Duration duration, void callback()) {
+  static Timer _createTimer(Duration duration, void Function() callback) {
     int milliseconds = duration.inMilliseconds;
     if (milliseconds < 0) milliseconds = 0;
     return TimerImpl(milliseconds, callback);
@@ -228,7 +226,7 @@ void _rethrow(Object error, StackTrace stackTrace) {
 ///     }
 ///
 class _AsyncStarImpl<T> {
-  StreamController<T> controller;
+  late StreamController<T> controller;
   Object Function(_AsyncStarImpl<T>) initGenerator;
   @notNull
   bool isSuspendedAtYieldStar = false;
@@ -243,11 +241,11 @@ class _AsyncStarImpl<T> {
   @notNull
   bool isSuspendedAtAwait = false;
 
-  Completer cancellationCompleter;
-  Object jsIterator;
+  Completer? cancellationCompleter;
+  late Object jsIterator;
 
-  Null Function(Object, StackTrace) _handleErrorCallback;
-  void Function([Object]) _runBodyCallback;
+  Null Function(Object, StackTrace)? _handleErrorCallback;
+  void Function([Object?])? _runBodyCallback;
 
   _AsyncStarImpl(this.initGenerator) {
     controller = StreamController(
@@ -293,10 +291,10 @@ class _AsyncStarImpl<T> {
       };
       var zone = Zone.current;
       if (!identical(zone, Zone.root)) {
-        _handleErrorCallback = zone.bindBinaryCallback(_handleErrorCallback);
+        _handleErrorCallback = zone.bindBinaryCallback(_handleErrorCallback!);
       }
     }
-    return _handleErrorCallback;
+    return _handleErrorCallback!;
   }
 
   void scheduleGenerator() {
@@ -315,11 +313,11 @@ class _AsyncStarImpl<T> {
     if (_runBodyCallback == null) {
       _runBodyCallback = JS('!', '#.bind(this)', runBody);
       if (!identical(zone, Zone.root)) {
-        var registered = zone.registerUnaryCallback(_runBodyCallback);
+        var registered = zone.registerUnaryCallback(_runBodyCallback!);
         _runBodyCallback = ([arg]) => zone.runUnaryGuarded(registered, arg);
       }
     }
-    zone.scheduleMicrotask(_runBodyCallback);
+    zone.scheduleMicrotask(_runBodyCallback!);
   }
 
   void runBody(awaitValue) {
@@ -332,16 +330,16 @@ class _AsyncStarImpl<T> {
       iterResult = JS('', '#.next(#)', jsIterator, awaitValue);
     } catch (e, s) {
       addError(e, s);
-      return null;
+      return;
     }
 
     if (JS('!', '#.done', iterResult)) {
       close();
-      return null;
+      return;
     }
 
     // If we're suspended at a yield/yield*, we're done for now.
-    if (isSuspendedAtYield || isSuspendedAtYieldStar) return null;
+    if (isSuspendedAtYield || isSuspendedAtYieldStar) return;
 
     // Handle `await`: if we get a value passed to `yield` it means we are
     // waiting on this Future. Make sure to prevent scheduling, and pass the
@@ -350,10 +348,10 @@ class _AsyncStarImpl<T> {
     // TODO(jmesserly): is the timing here correct? The assumption here is
     // that we should schedule `await` in `async*` the same as in `async`.
     isSuspendedAtAwait = true;
-    FutureOr<Object> value = JS('', '#.value', iterResult);
+    FutureOr<Object?> value = JS('', '#.value', iterResult);
 
     // TODO(jmesserly): this logic was copied from `async` function impl.
-    _Future f;
+    _Future<Object?> f;
     if (value is _Future) {
       f = value;
     } else if (value is Future) {
@@ -362,7 +360,7 @@ class _AsyncStarImpl<T> {
     } else {
       f = _Future.value(value);
     }
-    f._thenAwait(_runBodyCallback, handleError);
+    f._thenAwait(_runBodyCallback!, handleError);
   }
 
   /// Adds element to [stream] and returns true if the caller should terminate
@@ -417,10 +415,11 @@ class _AsyncStarImpl<T> {
 
   void addError(Object error, StackTrace stackTrace) {
     ArgumentError.checkNotNull(error, "error");
-    if (cancellationCompleter != null && !cancellationCompleter.isCompleted) {
+    var completer = cancellationCompleter;
+    if (completer != null && !completer.isCompleted) {
       // If the stream has been cancelled, complete the cancellation future
       // with the error.
-      cancellationCompleter.completeError(error, stackTrace);
+      completer.completeError(error, stackTrace);
     } else if (controller.hasListener) {
       controller.addError(error, stackTrace);
     }
@@ -432,10 +431,11 @@ class _AsyncStarImpl<T> {
   }
 
   void close() {
-    if (cancellationCompleter != null && !cancellationCompleter.isCompleted) {
+    var completer = cancellationCompleter;
+    if (completer != null && !completer.isCompleted) {
       // If the stream has been cancelled, complete the cancellation future
       // with the error.
-      cancellationCompleter.complete();
+      completer.complete();
     }
     controller.close();
   }
@@ -465,7 +465,7 @@ class _AsyncStarImpl<T> {
         scheduleGenerator();
       }
     }
-    return cancellationCompleter.future;
+    return cancellationCompleter!.future;
   }
 
   _fatal(String message) => throw StateError(message);

sdk/lib/_internal/js_dev_runtime/patch/collection_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS, JSExportName;
 import 'dart:_runtime' as dart;
@@ -26,9 +24,9 @@ import 'dart:_js_helper'
 class HashMap<K, V> {
   @patch
   factory HashMap(
-      {bool equals(K key1, K key2),
-      int hashCode(K key),
-      bool isValidKey(Object potentialKey)}) {
+      {bool Function(K, K)? equals,
+      int Function(K)? hashCode,
+      bool Function(dynamic)? isValidKey}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -56,9 +54,9 @@ class HashMap<K, V> {
 class LinkedHashMap<K, V> {
   @patch
   factory LinkedHashMap(
-      {bool equals(K key1, K key2),
-      int hashCode(K key),
-      bool isValidKey(Object potentialKey)}) {
+      {bool Function(K, K)? equals,
+      int Function(K)? hashCode,
+      bool Function(dynamic)? isValidKey}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -86,9 +84,9 @@ class LinkedHashMap<K, V> {
 class HashSet<E> {
   @patch
   factory HashSet(
-      {bool equals(E e1, E e2),
-      int hashCode(E e),
-      bool isValidKey(Object potentialKey)}) {
+      {bool Function(E, E)? equals,
+      int Function(E)? hashCode,
+      bool Function(dynamic)? isValidKey}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -97,7 +95,6 @@ class HashSet<E> {
           }
           return _HashSet<E>();
         }
-        hashCode = dart.hashCode;
       } else if (identical(identityHashCode, hashCode) &&
           identical(identical, equals)) {
         return _IdentityHashSet<E>();
@@ -117,9 +114,9 @@ class HashSet<E> {
 class LinkedHashSet<E> {
   @patch
   factory LinkedHashSet(
-      {bool equals(E e1, E e2),
-      int hashCode(E e),
-      bool isValidKey(Object potentialKey)}) {
+      {bool Function(E, E)? equals,
+      int Function(E)? hashCode,
+      bool Function(dynamic)? isValidKey}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -133,8 +130,7 @@ class LinkedHashSet<E> {
           identical(identical, equals)) {
         return _IdentityHashSet<E>();
       }
-      return _CustomHashSet<E>(
-          equals ?? dart.equals, hashCode ?? dart.hashCode);
+      return _CustomHashSet<E>(equals ?? dart.equals, hashCode);
     }
     return _CustomKeyHashSet<E>(
         equals ?? dart.equals, hashCode ?? dart.hashCode, isValidKey);
@@ -180,13 +176,14 @@ class _HashSet<E> extends _InternalSet<E>
 
   Set<R> _newSimilarSet<R>() => _HashSet<R>();
 
-  bool contains(Object key) {
+  bool contains(Object? key) {
     if (key == null) {
+      // Convert undefined to null, if needed.
       key = null;
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       @notNull
-      var k = key;
+      Object? k = key;
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, k.hashCode);
       if (buckets != null) {
         for (int i = 0, n = JS('!', '#.length', buckets); i < n; i++) {
@@ -199,12 +196,12 @@ class _HashSet<E> extends _InternalSet<E>
     return JS<bool>('!', '#.has(#)', _map, key);
   }
 
-  E lookup(Object key) {
+  E? lookup(Object? key) {
     if (key == null) return null;
     if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       @notNull
-      var k = key;
+      Object? k = key;
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, k.hashCode);
       if (buckets != null) {
         for (int i = 0, n = JS('!', '#.length', buckets); i < n; i++) {
@@ -221,7 +218,8 @@ class _HashSet<E> extends _InternalSet<E>
     var map = _map;
     if (key == null) {
       if (JS('', '#.has(null)', map)) return false;
-      key = null;
+      // Convert undefined to null, if needed.
+      JS('', '# = null', key);
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       var keyMap = _keyMap;
@@ -251,7 +249,8 @@ class _HashSet<E> extends _InternalSet<E>
     int length = JS('', '#.size', map);
     for (E key in objects) {
       if (key == null) {
-        key = null; // converts undefined to null, if needed.
+        // Convert undefined to null, if needed.
+        JS('', '# = null', key);
       } else if (JS<bool>('!', '#[#] !== #', key,
           dart.extensionSymbol('_equals'), dart.identityEquals)) {
         key = putLinkedMapKey(key, _keyMap);
@@ -263,13 +262,14 @@ class _HashSet<E> extends _InternalSet<E>
     }
   }
 
-  bool remove(Object key) {
+  bool remove(Object? key) {
     if (key == null) {
+      // Convert undefined to null, if needed.
       key = null;
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       @notNull
-      var k = key;
+      Object? k = key;
       int hash = JS('!', '# & 0x3ffffff', k.hashCode);
       var buckets = JS('', '#.get(#)', _keyMap, hash);
       if (buckets == null) return false; // not found
@@ -311,7 +311,8 @@ class _ImmutableSet<E> extends _HashSet<E> {
     var map = _map;
     for (Object key in entries) {
       if (key == null) {
-        key = null; // converts undefined to null, if needed.
+        // Convert undefined to null, if needed.
+        JS('', '# = null', key);
       } else if (JS<bool>('!', '#[#] !== #', key,
           dart.extensionSymbol('_equals'), dart.identityEquals)) {
         key = putLinkedMapKey(key, _keyMap);
@@ -320,10 +321,10 @@ class _ImmutableSet<E> extends _HashSet<E> {
     }
   }
 
-  bool add(Object other) => throw _unsupported();
-  void addAll(Object other) => throw _unsupported();
+  bool add(E value) => throw _unsupported();
+  void addAll(Iterable<E> elements) => throw _unsupported();
   void clear() => throw _unsupported();
-  bool remove(Object key) => throw _unsupported();
+  bool remove(Object? value) => throw _unsupported();
 
   static Error _unsupported() =>
       UnsupportedError("Cannot modify unmodifiable set");
@@ -344,12 +345,14 @@ class _IdentityHashSet<E> extends _InternalSet<E>
 
   Set<R> _newSimilarSet<R>() => _IdentityHashSet<R>();
 
-  bool contains(Object element) {
-    return JS('', '#.has(#)', _map, element);
+  bool contains(Object? element) {
+    return JS<bool>('!', '#.has(#)', _map, element);
   }
 
-  E lookup(Object element) {
-    return JS('', '#.has(#)', _map, element) ? element : null;
+  E? lookup(Object? element) {
+    return element is E && JS<bool>('!', '#.has(#)', _map, element)
+        ? element
+        : null;
   }
 
   bool add(E element) {
@@ -371,7 +374,7 @@ class _IdentityHashSet<E> extends _InternalSet<E>
     }
   }
 
-  bool remove(Object element) {
+  bool remove(Object? element) {
     if (JS<bool>('!', '#.delete(#)', _map, element)) {
       _modifications = (_modifications + 1) & 0x3ffffff;
       return true;
@@ -389,7 +392,7 @@ class _IdentityHashSet<E> extends _InternalSet<E>
 }
 
 class _CustomKeyHashSet<E> extends _CustomHashSet<E> {
-  _Predicate<Object> _validKey;
+  _Predicate<Object?> _validKey;
   _CustomKeyHashSet(_Equality<E> equals, _Hasher<E> hashCode, this._validKey)
       : super(equals, hashCode);
 
@@ -397,7 +400,7 @@ class _CustomKeyHashSet<E> extends _CustomHashSet<E> {
 
   Set<R> _newSimilarSet<R>() => _HashSet<R>();
 
-  bool contains(Object element) {
+  bool contains(Object? element) {
     // TODO(jmesserly): there is a subtle difference here compared to Dart 1.
     // See the comment on CustomKeyHashMap.containsKey for more information.
     // Treatment of `null` is different due to strong mode's requirement to
@@ -406,12 +409,12 @@ class _CustomKeyHashSet<E> extends _CustomHashSet<E> {
     return super.contains(element);
   }
 
-  E lookup(Object element) {
+  E? lookup(Object? element) {
     if (!_validKey(element)) return null;
     return super.lookup(element);
   }
 
-  bool remove(Object element) {
+  bool remove(Object? element) {
     if (!_validKey(element)) return false;
     return super.remove(element);
   }
@@ -447,7 +450,7 @@ class _CustomHashSet<E> extends _InternalSet<E>
   Set<E> _newSet() => _CustomHashSet<E>(_equals, _hashCode);
   Set<R> _newSimilarSet<R>() => _HashSet<R>();
 
-  bool contains(Object key) {
+  bool contains(Object? key) {
     if (key is E) {
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, _hashCode(key));
       if (buckets != null) {
@@ -461,7 +464,7 @@ class _CustomHashSet<E> extends _InternalSet<E>
     return false;
   }
 
-  E lookup(Object key) {
+  E? lookup(Object? key) {
     if (key is E) {
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, _hashCode(key));
       if (buckets != null) {
@@ -499,7 +502,7 @@ class _CustomHashSet<E> extends _InternalSet<E>
     for (E element in objects) add(element);
   }
 
-  bool remove(Object key) {
+  bool remove(Object? key) {
     if (key is E) {
       var hash = JS<int>('!', '# & 0x3ffffff', _hashCode(key));
       var keyMap = _keyMap;
@@ -575,30 +578,3 @@ abstract class _InternalSet<E> extends _SetBase<E> {
         iterator);
   }
 }
-
-@patch
-abstract class _SplayTree<K, Node extends _SplayTreeNode<K>> {
-  @patch
-  Node _splayMin(Node node) {
-    Node current = node;
-    while (current.left != null) {
-      Node left = current.left;
-      current.left = left.right;
-      left.right = current;
-      current = left;
-    }
-    return current;
-  }
-
-  @patch
-  Node _splayMax(Node node) {
-    Node current = node;
-    while (current.right != null) {
-      Node right = current.right;
-      current.right = right.left;
-      right.left = current;
-      current = right;
-    }
-    return current;
-  }
-}

sdk/lib/_internal/js_dev_runtime/patch/convert_patch.dart

@@ -2,15 +2,13 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:convert library.
 
 import 'dart:_js_helper' show argumentErrorValue, patch;
 import 'dart:_foreign_helper' show JS;
 import 'dart:_interceptors' show JSExtendableArray;
 import 'dart:_internal' show MappedIterable, ListIterable;
-import 'dart:collection' show Maps, LinkedHashMap, MapBase;
+import 'dart:collection' show LinkedHashMap, MapBase;
 import 'dart:_native_typed_data' show NativeUint8List;
 
 /**
@@ -30,7 +28,7 @@ import 'dart:_native_typed_data' show NativeUint8List;
  * Throws [FormatException] if the input is not valid JSON text.
  */
 @patch
-_parseJson(String source, reviver(Object key, Object value)) {
+_parseJson(String source, reviver(key, value)?) {
   if (source is! String) throw argumentErrorValue(source);
 
   var parsed;
@@ -53,8 +51,7 @@ _parseJson(String source, reviver(Object key, Object value)) {
  * Maps. [json] is expected to be freshly allocated so elements can be replaced
  * in-place.
  */
-_convertJsonToDart(json, reviver(Object key, Object value)) {
-  assert(reviver != null);
+_convertJsonToDart(json, reviver(Object? key, Object? value)) {
   walk(e) {
     // JavaScript null, string, number, bool are in the correct representation.
     if (JS<bool>('!', '# == null', e) ||
@@ -214,7 +211,7 @@ class _JsonMap extends MapBase<String, dynamic> {
     return value;
   }
 
-  remove(Object key) {
+  remove(Object? key) {
     if (!_isUpgraded && !containsKey(key)) return null;
     return _upgrade().remove(key);
   }
@@ -275,7 +272,7 @@ class _JsonMap extends MapBase<String, dynamic> {
 
   List<String> _computeKeys() {
     assert(!_isUpgraded);
-    List keys = _data;
+    List? keys = _data;
     if (keys == null) {
       keys = _data = _getPropertyNames(_original);
     }
@@ -298,7 +295,7 @@ class _JsonMap extends MapBase<String, dynamic> {
     // safely force a concurrent modification error in case
     // someone is iterating over the map here.
     if (keys.isEmpty) {
-      keys.add(null);
+      keys.add("");
     } else {
       keys.clear();
     }
@@ -357,13 +354,13 @@ class _JsonMapKeyIterable extends ListIterable<String> {
 
   /// Delegate to [parent.containsKey] to ensure the performance expected
   /// from [Map.keys.containsKey].
-  bool contains(Object key) => _parent.containsKey(key);
+  bool contains(Object? key) => _parent.containsKey(key);
 }
 
 @patch
 class JsonDecoder {
   @patch
-  StringConversionSink startChunkedConversion(Sink<Object> sink) {
+  StringConversionSink startChunkedConversion(Sink<Object?> sink) {
     return _JsonDecoderSink(_reviver, sink);
   }
 }
@@ -375,18 +372,17 @@ class JsonDecoder {
  * The sink only creates one object, but its input can be chunked.
  */
 // TODO(floitsch): don't accumulate everything before starting to decode.
-class _JsonDecoderSink extends _StringSinkConversionSink {
-  final Function(Object key, Object value) _reviver;
-  final Sink<Object> _sink;
+class _JsonDecoderSink extends _StringSinkConversionSink<StringBuffer> {
+  final Object? Function(Object? key, Object? value)? _reviver;
+  final Sink<Object?> _sink;
 
   _JsonDecoderSink(this._reviver, this._sink) : super(StringBuffer(''));
 
   void close() {
     super.close();
-    StringBuffer buffer = _stringSink;
-    String accumulated = buffer.toString();
-    buffer.clear();
-    Object decoded = _parseJson(accumulated, _reviver);
+    String accumulated = _stringSink.toString();
+    _stringSink.clear();
+    Object? decoded = _parseJson(accumulated, _reviver);
     _sink.add(decoded);
     _sink.close();
   }
@@ -405,8 +401,8 @@ class Utf8Decoder {
 
   // Currently not intercepting UTF8 decoding.
   @patch
-  static String _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int end) {
+  static String? _convertIntercepted(
+      bool allowMalformed, List<int> codeUnits, int start, int? end) {
     // Test `codeUnits is NativeUint8List`. Dart's NativeUint8List is
     // implemented by JavaScript's Uint8Array.
     if (JS<bool>('!', '# instanceof Uint8Array', codeUnits)) {
@@ -417,7 +413,7 @@ class Utf8Decoder {
       if (end - start < _shortInputThreshold) {
         return null;
       }
-      String result =
+      String? result =
           _convertInterceptedUint8List(allowMalformed, casted, start, end);
       if (result != null && allowMalformed) {
         // In principle, TextDecoder should have provided the correct result
@@ -433,7 +429,7 @@ class Utf8Decoder {
     return null; // This call was not intercepted.
   }
 
-  static String _convertInterceptedUint8List(
+  static String? _convertInterceptedUint8List(
       bool allowMalformed, NativeUint8List codeUnits, int start, int end) {
     final decoder = allowMalformed ? _decoderNonfatal : _decoder;
     if (decoder == null) return null;
@@ -448,7 +444,7 @@ class Utf8Decoder {
         JS<NativeUint8List>('!', '#.subarray(#, #)', codeUnits, start, end));
   }
 
-  static String _useTextDecoder(decoder, NativeUint8List codeUnits) {
+  static String? _useTextDecoder(decoder, NativeUint8List codeUnits) {
     // If the input is malformed, catch the exception and return `null` to fall
     // back on unintercepted decoder. The fallback will either succeed in
     // decoding, or report the problem better than TextDecoder.
@@ -480,12 +476,12 @@ class _Utf8Decoder {
   _Utf8Decoder(this.allowMalformed) : _state = beforeBom;
 
   @patch
-  String convertSingle(List<int> codeUnits, int start, int maybeEnd) {
+  String convertSingle(List<int> codeUnits, int start, int? maybeEnd) {
     return convertGeneral(codeUnits, start, maybeEnd, true);
   }
 
   @patch
-  String convertChunked(List<int> codeUnits, int start, int maybeEnd) {
+  String convertChunked(List<int> codeUnits, int start, int? maybeEnd) {
     return convertGeneral(codeUnits, start, maybeEnd, false);
   }
 }

sdk/lib/_internal/js_dev_runtime/patch/core_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:core classes.
 import "dart:_internal" as _symbol_dev;
 import 'dart:_interceptors';
@@ -30,14 +28,14 @@ import 'dart:typed_data' show Endian, Uint8List, Uint16List;
 
 String _symbolToString(Symbol symbol) => symbol is PrivateSymbol
     ? PrivateSymbol.getName(symbol)
-    : _symbol_dev.Symbol.getName(symbol);
+    : _symbol_dev.Symbol.getName(symbol as _symbol_dev.Symbol);
 
 @patch
-int identityHashCode(Object object) {
+int identityHashCode(Object? object) {
   if (object == null) return 0;
   // Note: this works for primitives because we define the `identityHashCode`
   // for them to be equivalent to their computed hashCode function.
-  int hash = JS('int|Null', r'#[#]', object, dart.identityHashCode_);
+  int? hash = JS<int?>('int|Null', r'#[#]', object, dart.identityHashCode_);
   if (hash == null) {
     hash = JS<int>('!', '(Math.random() * 0x3fffffff) | 0');
     JS('void', r'#[#] = #', object, dart.identityHashCode_, hash);
@@ -49,7 +47,7 @@ int identityHashCode(Object object) {
 @patch
 class Object {
   @patch
-  bool operator ==(other) => identical(this, other);
+  bool operator ==(Object other) => identical(this, other);
 
   @patch
   int get hashCode => identityHashCode(this);
@@ -59,7 +57,7 @@ class Object {
       "Instance of '${dart.typeName(dart.getReifiedType(this))}'";
 
   @patch
-  noSuchMethod(Invocation invocation) {
+  dynamic noSuchMethod(Invocation invocation) {
     return dart.defaultNoSuchMethod(this, invocation);
   }
 
@@ -68,10 +66,11 @@ class Object {
 
   // Everything is an Object.
   @JSExportName('is')
-  static bool _is_Object(Object o) => true;
+  static bool _is_Object(Object? o) => o != null;
 
   @JSExportName('as')
-  static Object _as_Object(Object o) => o;
+  static Object? _as_Object(Object? o) =>
+      o == null ? dart.cast(o, dart.unwrapType(Object)) : o;
 }
 
 @patch
@@ -80,10 +79,10 @@ class Null {
   int get hashCode => super.hashCode;
 
   @JSExportName('is')
-  static bool _is_Null(Object o) => o == null;
+  static bool _is_Null(Object? o) => o == null;
 
   @JSExportName('as')
-  static Object _as_Null(Object o) {
+  static Object? _as_Null(Object? o) {
     // Avoid extra function call to core.Null.is() by manually inlining.
     if (o == null) return o;
     return dart.cast(o, dart.unwrapType(Null));
@@ -94,8 +93,8 @@ class Null {
 @patch
 class Function {
   @patch
-  static apply(Function f, List positionalArguments,
-      [Map<Symbol, dynamic> namedArguments]) {
+  static apply(Function function, List<dynamic>? positionalArguments,
+      [Map<Symbol, dynamic>? namedArguments]) {
     positionalArguments ??= [];
     // dcall expects the namedArguments as a JS map in the last slot.
     if (namedArguments != null && namedArguments.isNotEmpty) {
@@ -103,9 +102,9 @@ class Function {
       namedArguments.forEach((symbol, arg) {
         JS('', '#[#] = #', map, _symbolToString(symbol), arg);
       });
-      return dart.dcall(f, positionalArguments, map);
+      return dart.dcall(function, positionalArguments, map);
     }
-    return dart.dcall(f, positionalArguments);
+    return dart.dcall(function, positionalArguments);
   }
 
   static Map<String, dynamic> _toMangledNames(
@@ -118,13 +117,13 @@ class Function {
   }
 
   @JSExportName('is')
-  static bool _is_Function(Object o) =>
+  static bool _is_Function(Object? o) =>
       JS<bool>('!', 'typeof $o == "function"');
 
   @JSExportName('as')
-  static Object _as_Function(Object o) {
+  static Object? _as_Function(Object? o) {
     // Avoid extra function call to core.Function.is() by manually inlining.
-    if (JS<Object>('!', 'typeof $o == "function"') || o == null) return o;
+    if (JS<bool>('!', 'typeof $o == "function"')) return o;
     return dart.cast(o, dart.unwrapType(Function));
   }
 }
@@ -132,18 +131,20 @@ class Function {
 // TODO(jmesserly): switch to WeakMap
 // Patch for Expando implementation.
 @patch
-class Expando<T> {
+class Expando<T extends Object> {
   @patch
-  Expando([String name]) : this.name = name;
+  Expando([String? name]) : this.name = name;
 
   @patch
-  T operator [](Object object) {
+  T? operator [](Object object) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
-    return (values == null) ? null : Primitives.getProperty(values, _getKey());
+    return (values == null)
+        ? null
+        : Primitives.getProperty(values, _getKey()) as T?;
   }
 
   @patch
-  void operator []=(Object object, T value) {
+  void operator []=(Object object, T? value) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
     if (values == null) {
       values = Object();
@@ -153,7 +154,7 @@ class Expando<T> {
   }
 
   String _getKey() {
-    String key = Primitives.getProperty(this, _KEY_PROPERTY_NAME);
+    var key = Primitives.getProperty(this, _KEY_PROPERTY_NAME) as String?;
     if (key == null) {
       key = "expando\$key\$${_keyCount++}";
       Primitives.setProperty(this, _KEY_PROPERTY_NAME, key);
@@ -170,7 +171,7 @@ class Expando<T> {
 class int {
   @patch
   static int parse(String source,
-      {int radix, @deprecated int onError(String source)}) {
+      {int? radix, @deprecated int onError(String source)?}) {
     var value = tryParse(source, radix: radix);
     if (value != null) return value;
     if (onError != null) return onError(source);
@@ -178,7 +179,7 @@ class int {
   }
 
   @patch
-  static int tryParse(String source, {int radix}) {
+  static int? tryParse(String source, {int? radix}) {
     return Primitives.parseInt(source, radix);
   }
 
@@ -190,15 +191,14 @@ class int {
   }
 
   @JSExportName('is')
-  static bool _is_int(Object o) {
+  static bool _is_int(Object? o) {
     return JS<bool>('!', 'typeof $o == "number" && Math.floor($o) == $o');
   }
 
   @JSExportName('as')
-  static Object _as_int(Object o) {
+  static Object? _as_int(Object? o) {
     // Avoid extra function call to core.int.is() by manually inlining.
-    if (JS<bool>('!', '(typeof $o == "number" && Math.floor($o) == $o)') ||
-        o == null) {
+    if (JS<bool>('!', '(typeof $o == "number" && Math.floor($o) == $o)')) {
       return o;
     }
     return dart.cast(o, dart.unwrapType(int));
@@ -209,7 +209,7 @@ class int {
 class double {
   @patch
   static double parse(String source,
-      [@deprecated double onError(String source)]) {
+      [@deprecated double onError(String source)?]) {
     var value = tryParse(source);
     if (value != null) return value;
     if (onError != null) return onError(source);
@@ -217,19 +217,19 @@ class double {
   }
 
   @patch
-  static double tryParse(String source) {
+  static double? tryParse(String source) {
     return Primitives.parseDouble(source);
   }
 
   @JSExportName('is')
-  static bool _is_double(o) {
+  static bool _is_double(Object? o) {
     return JS<bool>('!', 'typeof $o == "number"');
   }
 
   @JSExportName('as')
-  static Object _as_double(o) {
+  static Object? _as_double(Object? o) {
     // Avoid extra function call to core.double.is() by manually inlining.
-    if (JS<bool>('!', 'typeof $o == "number"') || o == null) return o;
+    if (JS<bool>('!', 'typeof $o == "number"')) return o;
     return dart.cast(o, dart.unwrapType(double));
   }
 }
@@ -237,14 +237,14 @@ class double {
 @patch
 abstract class num implements Comparable<num> {
   @JSExportName('is')
-  static bool _is_num(o) {
+  static bool _is_num(Object? o) {
     return JS<bool>('!', 'typeof $o == "number"');
   }
 
   @JSExportName('as')
-  static Object _as_num(o) {
+  static Object? _as_num(Object? o) {
     // Avoid extra function call to core.num.is() by manually inlining.
-    if (JS<bool>('!', 'typeof $o == "number"') || o == null) return o;
+    if (JS<bool>('!', 'typeof $o == "number"')) return o;
     return dart.cast(o, dart.unwrapType(num));
   }
 }
@@ -259,11 +259,11 @@ class BigInt implements Comparable<BigInt> {
   static BigInt get two => _BigIntImpl.two;
 
   @patch
-  static BigInt parse(String source, {int radix}) =>
+  static BigInt parse(String source, {int? radix}) =>
       _BigIntImpl.parse(source, radix: radix);
 
   @patch
-  static BigInt tryParse(String source, {int radix}) =>
+  static BigInt? tryParse(String source, {int? radix}) =>
       _BigIntImpl._tryParse(source, radix: radix);
 
   @patch
@@ -283,7 +283,7 @@ class Error {
   }
 
   @patch
-  StackTrace get stackTrace => dart.stackTraceForError(this);
+  StackTrace? get stackTrace => dart.stackTraceForError(this);
 }
 
 @patch
@@ -319,10 +319,7 @@ class DateTime {
   @patch
   DateTime._internal(int year, int month, int day, int hour, int minute,
       int second, int millisecond, int microsecond, bool isUtc)
-      // checkBool is manually inlined here because dart2js doesn't inline it
-      // and [isUtc] is usually a constant.
-      : this.isUtc =
-            isUtc is bool ? isUtc : throw ArgumentError.value(isUtc, 'isUtc'),
+      : isUtc = isUtc,
         _value = checkInt(Primitives.valueFromDecomposedDate(
             year,
             month,
@@ -346,7 +343,7 @@ class DateTime {
   }
 
   @patch
-  static int _brokenDownDateToValue(int year, int month, int day, int hour,
+  static int? _brokenDownDateToValue(int year, int month, int day, int hour,
       int minute, int second, int millisecond, int microsecond, bool isUtc) {
     return Primitives.valueFromDecomposedDate(
         year,
@@ -367,7 +364,7 @@ class DateTime {
 
   @patch
   Duration get timeZoneOffset {
-    if (isUtc) return Duration();
+    if (isUtc) return Duration.zero;
     return Duration(minutes: Primitives.getTimeZoneOffsetInMinutes(this));
   }
 
@@ -420,7 +417,7 @@ class DateTime {
   int get weekday => Primitives.getWeekday(this);
 
   @patch
-  bool operator ==(dynamic other) =>
+  bool operator ==(Object other) =>
       other is DateTime &&
       _value == other.millisecondsSinceEpoch &&
       isUtc == other.isUtc;
@@ -444,9 +441,9 @@ class DateTime {
 @patch
 class Stopwatch {
   @patch
-  static void _initTicker() {
+  static int _initTicker() {
     Primitives.initTicker();
-    _frequency = Primitives.timerFrequency;
+    return Primitives.timerFrequency;
   }
 
   @patch
@@ -473,22 +470,29 @@ class Stopwatch {
 @patch
 class List<E> {
   @patch
-  factory List([@undefined int _length]) {
+  factory List([@undefined int? length]) {
     dynamic list;
-    if (JS<bool>('!', '# === void 0', _length)) {
+    if (JS<bool>('!', '# === void 0', length)) {
       list = JS('', '[]');
     } else {
-      int length = JS('!', '#', _length);
-      if (_length == null || length < 0) {
+      int _length = JS('!', '#', length);
+      if (length == null || _length < 0) {
         throw ArgumentError("Length must be a non-negative integer: $_length");
       }
-      list = JS('', 'new Array(#)', length);
+      list = JS('', 'new Array(#)', _length);
       JS('', '#.fill(null)', list);
       JSArray.markFixedList(list);
     }
     return JSArray<E>.of(list);
   }
 
+  @patch
+  factory List.empty({bool growable = false}) {
+    var list = JSArray<E>.of(JS('', 'new Array()'));
+    if (!growable) JSArray.markFixedList(list);
+    return list;
+  }
+
   @patch
   factory List.filled(@nullCheck int length, E fill, {bool growable = false}) {
     var list = JSArray<E>.of(JS('', 'new Array(#)', length));
@@ -521,6 +525,17 @@ class List<E> {
     return List.from(elements, growable: growable);
   }
 
+  @patch
+  factory List.generate(int length, E generator(int index),
+      {bool growable = true}) {
+    final result = JSArray<E>.of(JS('', 'new Array(#)', length));
+    if (!growable) JSArray.markFixedList(result);
+    for (int i = 0; i < length; i++) {
+      result[i] = generator(i);
+    }
+    return result;
+  }
+
   @patch
   factory List.unmodifiable(Iterable elements) {
     var list = List<E>.from(elements);
@@ -532,7 +547,7 @@ class List<E> {
 @patch
 class Map<K, V> {
   @patch
-  factory Map.unmodifiable(Map other) {
+  factory Map.unmodifiable(Map<dynamic, dynamic> other) {
     return UnmodifiableMapView<K, V>(Map<K, V>.from(other));
   }
 
@@ -544,7 +559,7 @@ class Map<K, V> {
 class String {
   @patch
   factory String.fromCharCodes(Iterable<int> charCodes,
-      [int start = 0, int end]) {
+      [int start = 0, int? end]) {
     if (charCodes is JSArray) {
       return _stringFromJSArray(charCodes, start, end);
     }
@@ -569,7 +584,7 @@ class String {
   static String _stringFromJSArray(
       /*=JSArray<int>*/ list,
       int start,
-      int endOrNull) {
+      int? endOrNull) {
     int len = list.length;
     int end = RangeError.checkValidRange(start, endOrNull, len);
     if (start > 0 || end < len) {
@@ -579,14 +594,14 @@ class String {
   }
 
   static String _stringFromUint8List(
-      NativeUint8List charCodes, int start, int endOrNull) {
+      NativeUint8List charCodes, int start, int? endOrNull) {
     int len = charCodes.length;
     int end = RangeError.checkValidRange(start, endOrNull, len);
     return Primitives.stringFromNativeUint8List(charCodes, start, end);
   }
 
   static String _stringFromIterable(
-      Iterable<int> charCodes, int start, int end) {
+      Iterable<int> charCodes, int start, int? end) {
     if (start < 0) throw RangeError.range(start, 0, charCodes.length);
     if (end != null && end < start) {
       throw RangeError.range(end, start, charCodes.length);
@@ -597,7 +612,7 @@ class String {
         throw RangeError.range(start, 0, i);
       }
     }
-    var list = <int>[];
+    var list = JSArray<int>.of(JS('', 'new Array()'));
     if (end == null) {
       while (it.moveNext()) list.add(it.current);
     } else {
@@ -612,14 +627,14 @@ class String {
   }
 
   @JSExportName('is')
-  static bool _is_String(Object o) {
+  static bool _is_String(Object? o) {
     return JS<bool>('!', 'typeof $o == "string"');
   }
 
   @JSExportName('as')
-  static Object _as_String(Object o) {
+  static Object? _as_String(Object? o) {
     // Avoid extra function call to core.String.is() by manually inlining.
-    if (JS<bool>('!', 'typeof $o == "string"') || o == null) return o;
+    if (JS<bool>('!', 'typeof $o == "string"')) return o;
     return dart.cast(o, dart.unwrapType(String));
   }
 }
@@ -644,13 +659,13 @@ class bool {
   int get hashCode => super.hashCode;
 
   @JSExportName('is')
-  static bool _is_bool(Object o) =>
+  static bool _is_bool(Object? o) =>
       JS<bool>('!', '$o === true || $o === false');
 
   @JSExportName('as')
-  static Object _as_bool(Object o) {
+  static Object? _as_bool(Object? o) {
     // Avoid extra function call to core.bool.is() by manually inlining.
-    if (JS<bool>("!", '$o === true || $o === false') || o == null) return o;
+    if (JS<bool>("!", '$o === true || $o === false')) return o;
     return dart.cast(o, dart.unwrapType(bool));
   }
 }
@@ -675,7 +690,7 @@ class RegExp {
 
 // Patch for 'identical' function.
 @patch
-bool identical(Object a, Object b) {
+bool identical(Object? a, Object? b) {
   return JS<bool>('!', '(# == null ? # == null : # === #)', a, b, a, b);
 }
 
@@ -690,7 +705,7 @@ class StringBuffer {
   int get length => _contents.length;
 
   @patch
-  void write(Object obj) {
+  void write(Object? obj) {
     _writeString('$obj');
   }
 
@@ -700,12 +715,12 @@ class StringBuffer {
   }
 
   @patch
-  void writeAll(Iterable objects, [String separator = ""]) {
+  void writeAll(Iterable<dynamic> objects, [String separator = ""]) {
     _contents = _writeAll(_contents, objects, separator);
   }
 
   @patch
-  void writeln([Object obj = ""]) {
+  void writeln([Object? obj = ""]) {
     _writeString('$obj\n');
   }
 
@@ -717,7 +732,7 @@ class StringBuffer {
   @patch
   String toString() => Primitives.flattenString(_contents);
 
-  void _writeString(str) {
+  void _writeString(String str) {
     _contents = Primitives.stringConcatUnchecked(_contents, str);
   }
 
@@ -738,7 +753,7 @@ class StringBuffer {
     return string;
   }
 
-  static String _writeOne(String string, Object obj) {
+  static String _writeOne(String string, Object? obj) {
     return Primitives.stringConcatUnchecked(string, '$obj');
   }
 }
@@ -752,46 +767,44 @@ class _CompileTimeError extends Error {
 
 @patch
 class NoSuchMethodError {
-  final Object _receiver;
+  final Object? _receiver;
   final Symbol _memberName;
-  final List _arguments;
-  final Map<Symbol, dynamic> _namedArguments;
-  final List _existingArgumentNames;
-  final Invocation _invocation;
+  final List? _arguments;
+  final Map<Symbol, dynamic>? _namedArguments;
+  final Invocation? _invocation;
 
   @patch
-  NoSuchMethodError(Object receiver, Symbol memberName,
-      List positionalArguments, Map<Symbol, dynamic> namedArguments,
-      [List existingArgumentNames = null])
+  NoSuchMethodError(Object? receiver, Symbol memberName,
+      List? positionalArguments, Map<Symbol, dynamic>? namedArguments)
       : _receiver = receiver,
         _memberName = memberName,
         _arguments = positionalArguments,
         _namedArguments = namedArguments,
-        _existingArgumentNames = existingArgumentNames,
         _invocation = null;
 
   @patch
-  NoSuchMethodError.withInvocation(Object receiver, Invocation invocation)
+  NoSuchMethodError.withInvocation(Object? receiver, Invocation invocation)
       : _receiver = receiver,
         _memberName = invocation.memberName,
         _arguments = invocation.positionalArguments,
         _namedArguments = invocation.namedArguments,
-        _existingArgumentNames = null,
         _invocation = invocation;
 
   @patch
   String toString() {
     StringBuffer sb = StringBuffer('');
     String comma = '';
-    if (_arguments != null) {
-      for (var argument in _arguments) {
+    var arguments = _arguments;
+    if (arguments != null) {
+      for (var argument in arguments) {
         sb.write(comma);
         sb.write(Error.safeToString(argument));
         comma = ', ';
       }
     }
-    if (_namedArguments != null) {
-      _namedArguments.forEach((Symbol key, var value) {
+    var namedArguments = _namedArguments;
+    if (namedArguments != null) {
+      namedArguments.forEach((Symbol key, var value) {
         sb.write(comma);
         sb.write(_symbolToString(key));
         sb.write(": ");
@@ -802,22 +815,14 @@ class NoSuchMethodError {
     String memberName = _symbolToString(_memberName);
     String receiverText = Error.safeToString(_receiver);
     String actualParameters = '$sb';
-    var failureMessage = (_invocation is dart.InvocationImpl)
-        ? (_invocation as dart.InvocationImpl).failureMessage
+    var invocation = _invocation;
+    var failureMessage = (invocation is dart.InvocationImpl)
+        ? invocation.failureMessage
         : 'method not found';
-    if (_existingArgumentNames == null) {
-      return "NoSuchMethodError: '$memberName'\n"
-          "$failureMessage\n"
-          "Receiver: ${receiverText}\n"
-          "Arguments: [$actualParameters]";
-    } else {
-      String formalParameters = _existingArgumentNames.join(', ');
-      return "NoSuchMethodError: incorrect number of arguments passed to "
-          "method named '$memberName'\n"
-          "Receiver: ${receiverText}\n"
-          "Tried calling: $memberName($actualParameters)\n"
-          "Found: $memberName($formalParameters)";
-    }
+    return "NoSuchMethodError: '$memberName'\n"
+        "$failureMessage\n"
+        "Receiver: ${receiverText}\n"
+        "Arguments: [$actualParameters]";
   }
 }
 
@@ -973,14 +978,14 @@ class _BigIntImpl implements BigInt {
 
   // Result cache for last _divRem call.
   // Result cache for last _divRem call.
-  static Uint16List _lastDividendDigits;
-  static int _lastDividendUsed;
-  static Uint16List _lastDivisorDigits;
-  static int _lastDivisorUsed;
-  static Uint16List _lastQuoRemDigits;
-  static int _lastQuoRemUsed;
-  static int _lastRemUsed;
-  static int _lastRem_nsh;
+  static Uint16List? _lastDividendDigits;
+  static int? _lastDividendUsed;
+  static Uint16List? _lastDivisorDigits;
+  static int? _lastDivisorUsed;
+  static Uint16List? _lastQuoRemDigits;
+  static int? _lastQuoRemUsed;
+  static int? _lastRemUsed;
+  static int? _lastRem_nsh;
 
   /// Whether this bigint is negative.
   final bool _isNegative;
@@ -1021,7 +1026,7 @@ class _BigIntImpl implements BigInt {
    * Throws a [FormatException] if the [source] is not a valid integer literal,
    * optionally prefixed by a sign.
    */
-  static _BigIntImpl parse(String source, {int radix}) {
+  static _BigIntImpl parse(String source, {int? radix}) {
     var result = _tryParse(source, radix: radix);
     if (result == null) {
       throw FormatException("Could not parse BigInt", source);
@@ -1040,7 +1045,7 @@ class _BigIntImpl implements BigInt {
     // Read in the source 4 digits at a time.
     // The first part may have a few leading virtual '0's to make the remaining
     // parts all have exactly 4 digits.
-    int digitInPartCount = 4 - source.length.remainder(4);
+    var digitInPartCount = 4 - source.length.remainder(4);
     if (digitInPartCount == 4) digitInPartCount = 0;
     for (int i = 0; i < source.length; i++) {
       part = part * 10 + source.codeUnitAt(i) - _0;
@@ -1082,7 +1087,7 @@ class _BigIntImpl implements BigInt {
   /// If [isNegative] is true, negates the result before returning it.
   ///
   /// The [source] (substring) must be a valid hex literal.
-  static _BigIntImpl _parseHex(String source, int startPos, bool isNegative) {
+  static _BigIntImpl? _parseHex(String source, int startPos, bool isNegative) {
     int hexDigitsPerChunk = _digitBits ~/ 4;
     int sourceLength = source.length - startPos;
     int chunkCount = (sourceLength / hexDigitsPerChunk).ceil();
@@ -1116,7 +1121,7 @@ class _BigIntImpl implements BigInt {
   ///
   /// The [source] will be checked for invalid characters. If it is invalid,
   /// this function returns `null`.
-  static _BigIntImpl _parseRadix(String source, int radix, bool isNegative) {
+  static _BigIntImpl? _parseRadix(String source, int radix, bool isNegative) {
     var result = zero;
     var base = _BigIntImpl._fromInt(radix);
     for (int i = 0; i < source.length; i++) {
@@ -1133,7 +1138,7 @@ class _BigIntImpl implements BigInt {
   /// Returns the parsed big integer, or `null` if it failed.
   ///
   /// If the [radix] is `null` accepts decimal literals or `0x` hex literals.
-  static _BigIntImpl _tryParse(String source, {int radix}) {
+  static _BigIntImpl? _tryParse(String source, {int? radix}) {
     if (source == "") return null;
 
     var match = _parseRE.firstMatch(source);
@@ -1145,9 +1150,9 @@ class _BigIntImpl implements BigInt {
 
     bool isNegative = match[signIndex] == "-";
 
-    String decimalMatch = match[decimalIndex];
-    String hexMatch = match[hexIndex];
-    String nonDecimalMatch = match[nonDecimalHexIndex];
+    String? decimalMatch = match[decimalIndex];
+    String? hexMatch = match[hexIndex];
+    String? nonDecimalMatch = match[nonDecimalHexIndex];
 
     if (radix == null) {
       if (decimalMatch != null) {
@@ -1168,11 +1173,11 @@ class _BigIntImpl implements BigInt {
       return _parseDecimal(decimalMatch, isNegative);
     }
     if (radix == 16 && (decimalMatch != null || nonDecimalMatch != null)) {
-      return _parseHex(decimalMatch ?? nonDecimalMatch, 0, isNegative);
+      return _parseHex(decimalMatch ?? nonDecimalMatch!, 0, isNegative);
     }
 
     return _parseRadix(
-        decimalMatch ?? nonDecimalMatch ?? hexMatch, radix, isNegative);
+        decimalMatch ?? nonDecimalMatch ?? hexMatch!, radix, isNegative);
   }
 
   static RegExp _parseRE = RegExp(
@@ -1220,7 +1225,7 @@ class _BigIntImpl implements BigInt {
     // then use the bit-manipulating `_fromDouble` for all other values.
     if (value.abs() < 0x100000000) return _BigIntImpl._fromInt(value.toInt());
     if (value is double) return _BigIntImpl._fromDouble(value);
-    return _BigIntImpl._fromInt(value);
+    return _BigIntImpl._fromInt(value as int);
   }
 
   factory _BigIntImpl._fromInt(int value) {
@@ -1984,9 +1989,9 @@ class _BigIntImpl implements BigInt {
     _divRem(other);
     // Return quotient, i.e.
     // _lastQuoRem_digits[_lastRem_used.._lastQuoRem_used-1] with proper sign.
-    var lastQuo_used = _lastQuoRemUsed - _lastRemUsed;
+    var lastQuo_used = _lastQuoRemUsed! - _lastRemUsed!;
     var quo_digits = _cloneDigits(
-        _lastQuoRemDigits, _lastRemUsed, _lastQuoRemUsed, lastQuo_used);
+        _lastQuoRemDigits!, _lastRemUsed!, _lastQuoRemUsed!, lastQuo_used);
     var quo = _BigIntImpl._(false, lastQuo_used, quo_digits);
     if ((_isNegative != other._isNegative) && (quo._used > 0)) {
       quo = -quo;
@@ -2004,10 +2009,10 @@ class _BigIntImpl implements BigInt {
     // Return remainder, i.e.
     // denormalized _lastQuoRem_digits[0.._lastRem_used-1] with proper sign.
     var remDigits =
-        _cloneDigits(_lastQuoRemDigits, 0, _lastRemUsed, _lastRemUsed);
-    var rem = _BigIntImpl._(false, _lastRemUsed, remDigits);
-    if (_lastRem_nsh > 0) {
-      rem = rem >> _lastRem_nsh; // Denormalize remainder.
+        _cloneDigits(_lastQuoRemDigits!, 0, _lastRemUsed!, _lastRemUsed!);
+    var rem = _BigIntImpl._(false, _lastRemUsed!, remDigits);
+    if (_lastRem_nsh! > 0) {
+      rem = rem >> _lastRem_nsh!; // Denormalize remainder.
     }
     if (_isNegative && (rem._used > 0)) {
       rem = -rem;

sdk/lib/_internal/js_dev_runtime/patch/developer_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:developer library.
 
 import 'dart:_js_helper' show patch, ForceInline, ReifyFunctionTypes;
@@ -15,7 +13,7 @@ import 'dart:isolate';
 
 @patch
 @ForceInline()
-bool debugger({bool when = true, String message}) {
+bool debugger({bool when = true, String? message}) {
   if (when) {
     JS('', 'debugger');
   }
@@ -23,7 +21,7 @@ bool debugger({bool when = true, String message}) {
 }
 
 @patch
-Object inspect(Object object) {
+Object? inspect(Object? object) {
   // Note: this log level does not show up by default in Chrome.
   // This is used for communication with the debugger service.
   JS('', 'console.debug("dart.developer.inspect", #)', object);
@@ -32,13 +30,13 @@ Object inspect(Object object) {
 
 @patch
 void log(String message,
-    {DateTime time,
-    int sequenceNumber,
+    {DateTime? time,
+    int? sequenceNumber,
     int level = 0,
     String name = '',
-    Zone zone,
-    Object error,
-    StackTrace stackTrace}) {
+    Zone? zone,
+    Object? error,
+    StackTrace? stackTrace}) {
   Object items =
       JS('!', '{ message: #, name: #, level: # }', message, name, level);
   if (time != null) JS('', '#.time = #', items, time);
@@ -52,10 +50,10 @@ void log(String message,
   JS('', 'console.debug("dart.developer.log", #)', items);
 }
 
-final _extensions = Map<String, ServiceExtensionHandler>();
+final _extensions = <String, ServiceExtensionHandler>{};
 
 @patch
-ServiceExtensionHandler _lookupExtension(String method) {
+ServiceExtensionHandler? _lookupExtension(String method) {
   return _extensions[method];
 }
 
@@ -81,7 +79,7 @@ _invokeExtension(String methodName, String encodedJson) {
   return JS('', 'new #.Promise(#)', dart.global_,
       (Function(Object) resolve, Function(Object) reject) async {
     try {
-      var method = _lookupExtension(methodName);
+      var method = _lookupExtension(methodName)!;
       var parameters = (json.decode(encodedJson) as Map).cast<String, String>();
       var result = await method(methodName, parameters);
       resolve(result._toString());
@@ -154,7 +152,7 @@ void _webServerControl(SendPort sendPort, bool enable) {
 }
 
 @patch
-String _getIsolateIDFromSendPort(SendPort sendPort) {
+String? _getIsolateIDFromSendPort(SendPort sendPort) {
   return null;
 }
 
@@ -168,7 +166,7 @@ class UserTag {
 }
 
 class _FakeUserTag implements UserTag {
-  static Map _instances = {};
+  static final _instances = <String, _FakeUserTag>{};
 
   _FakeUserTag.real(this.label);
 
@@ -183,10 +181,7 @@ class _FakeUserTag implements UserTag {
       throw UnsupportedError(
           'UserTag instance limit (${UserTag.MAX_USER_TAGS}) reached.');
     }
-    // Create a new instance and add it to the instance map.
-    var instance = _FakeUserTag.real(label);
-    _instances[label] = instance;
-    return instance;
+    return _instances[label] = _FakeUserTag.real(label);
   }
 
   final String label;

sdk/lib/_internal/js_dev_runtime/patch/internal_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 import 'dart:core' hide Symbol;
 import 'dart:core' as core show Symbol;
 import 'dart:_js_primitives' show printString;
@@ -12,6 +10,9 @@ import 'dart:_interceptors' show JSArray;
 import 'dart:_foreign_helper' show JS;
 import 'dart:_runtime' as dart;
 
+@patch
+bool typeAcceptsNull<T>() => !dart.strictNullSafety || null is T;
+
 @patch
 class Symbol implements core.Symbol {
   @patch
@@ -19,7 +20,7 @@ class Symbol implements core.Symbol {
 
   @patch
   int get hashCode {
-    int hash = JS('int|Null', '#._hashCode', this);
+    int? hash = JS('int|Null', '#._hashCode', this);
     if (hash != null) return hash;
     const arbitraryPrime = 664597;
     hash = 0x1fffffff & (arbitraryPrime * _name.hashCode);
@@ -40,17 +41,17 @@ void printToConsole(String line) {
 }
 
 @patch
-List<E> makeListFixedLength<E>(List<E> growableList) {
+List<T> makeListFixedLength<T>(List<T> growableList) {
   JSArray.markFixedList(growableList);
   return growableList;
 }
 
 @patch
-List<E> makeFixedListUnmodifiable<E>(List<E> fixedLengthList) {
+List<T> makeFixedListUnmodifiable<T>(List<T> fixedLengthList) {
   JSArray.markUnmodifiableList(fixedLengthList);
   return fixedLengthList;
 }
 
 @patch
-Object extractTypeArguments<T>(T instance, Function extract) =>
+Object? extractTypeArguments<T>(T instance, Function extract) =>
     dart.extractTypeArguments<T>(instance, extract);

sdk/lib/_internal/js_dev_runtime/patch/io_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 import 'dart:_js_helper' show patch;
 import 'dart:async';
 import 'dart:convert';
@@ -75,7 +73,7 @@ class _AsyncDirectoryListerOps {
 @patch
 class _EventHandler {
   @patch
-  static void _sendData(Object sender, SendPort sendPort, int data) {
+  static void _sendData(Object? sender, SendPort sendPort, int data) {
     throw UnsupportedError("EventHandler._sendData");
   }
 }
@@ -305,7 +303,7 @@ class _Platform {
 @patch
 class _ProcessUtils {
   @patch
-  static void _exit(int status) {
+  static Never _exit(int status) {
     throw UnsupportedError("ProcessUtils._exit");
   }
 
@@ -325,7 +323,7 @@ class _ProcessUtils {
   }
 
   @patch
-  static int _pid(Process process) {
+  static int _pid(Process? process) {
     throw UnsupportedError("ProcessUtils._pid");
   }
 
@@ -352,8 +350,8 @@ class ProcessInfo {
 class Process {
   @patch
   static Future<Process> start(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment = true,
       bool runInShell = false,
       ProcessStartMode mode = ProcessStartMode.normal}) {
@@ -362,8 +360,8 @@ class Process {
 
   @patch
   static Future<ProcessResult> run(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment = true,
       bool runInShell = false,
       Encoding stdoutEncoding = systemEncoding,
@@ -373,8 +371,8 @@ class Process {
 
   @patch
   static ProcessResult runSync(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment = true,
       bool runInShell = false,
       Encoding stdoutEncoding = systemEncoding,
@@ -411,13 +409,13 @@ class InternetAddress {
   }
 
   @patch
-  factory InternetAddress(String address, {InternetAddressType type}) {
+  factory InternetAddress(String address, {InternetAddressType? type}) {
     throw UnsupportedError("InternetAddress");
   }
 
   @patch
   factory InternetAddress.fromRawAddress(Uint8List rawAddress,
-      {InternetAddressType type}) {
+      {InternetAddressType? type}) {
     throw new UnsupportedError("InternetAddress.fromRawAddress");
   }
 
@@ -434,7 +432,7 @@ class InternetAddress {
   }
 
   @patch
-  static InternetAddress tryParse(String address) {
+  static InternetAddress? tryParse(String address) {
     throw UnsupportedError("InternetAddress.tryParse");
   }
 }
@@ -476,14 +474,14 @@ class ServerSocket {
 @patch
 class RawSocket {
   @patch
-  static Future<RawSocket> connect(host, int port,
-      {sourceAddress, Duration timeout}) {
+  static Future<RawSocket> connect(dynamic host, int port,
+      {dynamic sourceAddress, Duration? timeout}) {
     throw UnsupportedError("RawSocket constructor");
   }
 
   @patch
-  static Future<ConnectionTask<RawSocket>> startConnect(host, int port,
-      {sourceAddress}) {
+  static Future<ConnectionTask<RawSocket>> startConnect(dynamic host, int port,
+      {dynamic sourceAddress}) {
     throw UnsupportedError("RawSocket constructor");
   }
 }
@@ -491,14 +489,14 @@ class RawSocket {
 @patch
 class Socket {
   @patch
-  static Future<Socket> _connect(host, int port,
-      {sourceAddress, Duration timeout}) {
+  static Future<Socket> _connect(dynamic host, int port,
+      {dynamic sourceAddress, Duration? timeout}) {
     throw UnsupportedError("Socket constructor");
   }
 
   @patch
-  static Future<ConnectionTask<Socket>> _startConnect(host, int port,
-      {sourceAddress}) {
+  static Future<ConnectionTask<Socket>> _startConnect(dynamic host, int port,
+      {dynamic sourceAddress}) {
     throw UnsupportedError("Socket constructor");
   }
 }
@@ -514,7 +512,7 @@ class SecureSocket {
 @patch
 class RawSynchronousSocket {
   @patch
-  static RawSynchronousSocket connectSync(host, int port) {
+  static RawSynchronousSocket connectSync(dynamic host, int port) {
     throw UnsupportedError("RawSynchronousSocket.connectSync");
   }
 }
@@ -556,7 +554,7 @@ class X509Certificate {
 @patch
 class RawDatagramSocket {
   @patch
-  static Future<RawDatagramSocket> bind(host, int port,
+  static Future<RawDatagramSocket> bind(dynamic host, int port,
       {bool reuseAddress = true, bool reusePort = false, int ttl = 1}) {
     throw UnsupportedError("RawDatagramSocket.bind");
   }
@@ -618,14 +616,14 @@ class RawZLibFilter {
       int windowBits,
       int memLevel,
       int strategy,
-      List<int> dictionary,
+      List<int>? dictionary,
       bool raw) {
     throw UnsupportedError("_newZLibDeflateFilter");
   }
 
   @patch
   static RawZLibFilter _makeZLibInflateFilter(
-      int windowBits, List<int> dictionary, bool raw) {
+      int windowBits, List<int>? dictionary, bool raw) {
     throw UnsupportedError("_newZLibInflateFilter");
   }
 }

sdk/lib/_internal/js_dev_runtime/patch/isolate_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for the dart:isolate library.
 
 import 'dart:_js_helper' show patch, NoReifyGeneric;
@@ -18,36 +16,37 @@ class Isolate {
   static Isolate get current => _unsupported();
 
   @patch
-  String get debugName => _unsupported();
+  String? get debugName => _unsupported();
 
   @patch
-  static Future<Uri> get packageRoot => _unsupported();
+  static Future<Uri?> get packageRoot => _unsupported();
 
   @patch
-  static Future<Uri> get packageConfig => _unsupported();
+  static Future<Uri?> get packageConfig => _unsupported();
 
   @patch
-  static Future<Uri> resolvePackageUri(Uri packageUri) => _unsupported();
+  static Future<Uri?> resolvePackageUri(Uri packageUri) => _unsupported();
 
   @patch
   static Future<Isolate> spawn<T>(void entryPoint(T message), T message,
           {bool paused = false,
-          bool errorsAreFatal,
-          SendPort onExit,
-          SendPort onError}) =>
+          bool errorsAreFatal = true,
+          SendPort? onExit,
+          SendPort? onError}) =>
       _unsupported();
 
   @patch
   static Future<Isolate> spawnUri(Uri uri, List<String> args, var message,
           {bool paused = false,
-          SendPort onExit,
-          SendPort onError,
-          bool errorsAreFatal,
-          bool checked,
-          Map<String, String> environment,
-          Uri packageRoot,
-          Uri packageConfig,
-          bool automaticPackageResolution = false}) =>
+          SendPort? onExit,
+          SendPort? onError,
+          bool errorsAreFatal = true,
+          bool? checked,
+          Map<String, String>? environment,
+          Uri? packageRoot,
+          Uri? packageConfig,
+          bool automaticPackageResolution = false,
+          String? debugName}) =>
       _unsupported();
 
   @patch
@@ -57,7 +56,7 @@ class Isolate {
   void resume(Capability resumeCapability) => _unsupported();
 
   @patch
-  void addOnExitListener(SendPort responsePort, {Object response}) =>
+  void addOnExitListener(SendPort responsePort, {Object? response}) =>
       _unsupported();
 
   @patch
@@ -70,7 +69,7 @@ class Isolate {
   void kill({int priority = beforeNextEvent}) => _unsupported();
   @patch
   void ping(SendPort responsePort,
-          {Object response, int priority = immediate}) =>
+          {Object? response, int priority = immediate}) =>
       _unsupported();
 
   @patch
@@ -99,13 +98,17 @@ class _ReceivePort extends Stream implements ReceivePort {
 
   get sendPort => _unsupported();
 
-  listen(onData, {onError, onDone, cancelOnError}) => _unsupported();
+  StreamSubscription listen(void Function(dynamic)? onData,
+          {Function? onError,
+          void Function()? onDone,
+          bool? cancelOnError = true}) =>
+      _unsupported();
 }
 
 @patch
 class RawReceivePort {
   @patch
-  factory RawReceivePort([void handler(event)]) => _unsupported();
+  factory RawReceivePort([Function? handler]) => _unsupported();
 }
 
 @patch

sdk/lib/_internal/js_dev_runtime/patch/js_patch.dart

@@ -2,14 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:js library.
 library dart.js;
 
 import 'dart:collection' show HashMap, ListMixin;
 
-import 'dart:_js_helper' show patch, Primitives;
+import 'dart:_js_helper' show patch, NoReifyGeneric, Primitives;
 import 'dart:_foreign_helper' show JS;
 import 'dart:_runtime' as dart;
 
@@ -21,7 +19,7 @@ final JsObject _context = _wrapToDart(dart.global_);
 @patch
 class JsObject {
   // The wrapped JS object.
-  final dynamic _jsObject;
+  final Object _jsObject;
 
   // This should only be called from _wrapToDart
   JsObject._fromJs(this._jsObject) {
@@ -29,7 +27,7 @@ class JsObject {
   }
 
   @patch
-  factory JsObject(JsFunction constructor, [List arguments]) {
+  factory JsObject(JsFunction constructor, [List? arguments]) {
     var ctor = constructor._jsObject;
     if (arguments == null) {
       return _wrapToDart(JS('', 'new #()', ctor));
@@ -39,25 +37,25 @@ class JsObject {
   }
 
   @patch
-  factory JsObject.fromBrowserObject(object) {
+  factory JsObject.fromBrowserObject(Object object) {
     if (object is num || object is String || object is bool || object == null) {
       throw ArgumentError("object cannot be a num, string, bool, or null");
     }
-    return _wrapToDart(_convertToJS(object));
+    return _wrapToDart(_convertToJS(object)!);
   }
 
   @patch
-  factory JsObject.jsify(object) {
+  factory JsObject.jsify(Object object) {
     if ((object is! Map) && (object is! Iterable)) {
       throw ArgumentError("object must be a Map or Iterable");
     }
     return _wrapToDart(_convertDataTree(object));
   }
 
-  static _convertDataTree(data) {
+  static _convertDataTree(Object data) {
     var _convertedObjects = HashMap.identity();
 
-    _convert(o) {
+    _convert(Object? o) {
       if (_convertedObjects.containsKey(o)) {
         return _convertedObjects[o];
       }
@@ -90,7 +88,7 @@ class JsObject {
   }
 
   @patch
-  void operator []=(Object property, value) {
+  void operator []=(Object property, Object? value) {
     if (property is! String && property is! num) {
       throw ArgumentError("property is not a String or num");
     }
@@ -98,11 +96,11 @@ class JsObject {
   }
 
   @patch
-  bool operator ==(other) =>
+  bool operator ==(Object other) =>
       other is JsObject && JS<bool>('!', '# === #', _jsObject, other._jsObject);
 
   @patch
-  bool hasProperty(property) {
+  bool hasProperty(Object property) {
     if (property is! String && property is! num) {
       throw ArgumentError("property is not a String or num");
     }
@@ -110,7 +108,7 @@ class JsObject {
   }
 
   @patch
-  void deleteProperty(property) {
+  void deleteProperty(Object property) {
     if (property is! String && property is! num) {
       throw ArgumentError("property is not a String or num");
     }
@@ -132,14 +130,14 @@ class JsObject {
   }
 
   @patch
-  dynamic callMethod(method, [List args]) {
+  dynamic callMethod(Object method, [List? args]) {
     if (method is! String && method is! num) {
       throw ArgumentError("method is not a String or num");
     }
     if (args != null) args = List.from(args.map(_convertToJS));
     var fn = JS('', '#[#]', _jsObject, method);
     if (JS<bool>('!', 'typeof(#) !== "function"', fn)) {
-      throw NoSuchMethodError(_jsObject, Symbol(method), args, {});
+      throw NoSuchMethodError(_jsObject, Symbol('$method'), args, {});
     }
     return _convertToDart(JS('', '#.apply(#, #)', fn, _jsObject, args));
   }
@@ -164,7 +162,7 @@ class JsFunction extends JsObject {
         f));
   }
 
-  JsFunction._fromJs(jsObject) : super._fromJs(jsObject);
+  JsFunction._fromJs(Object jsObject) : super._fromJs(jsObject);
 
   @patch
   dynamic apply(List args, {thisArg}) => _convertToDart(JS(
@@ -185,16 +183,16 @@ class JsArray<E> extends JsObject with ListMixin<E> {
   factory JsArray.from(Iterable<E> other) =>
       JsArray<E>._fromJs([]..addAll(other.map(_convertToJS)));
 
-  JsArray._fromJs(jsObject) : super._fromJs(jsObject);
+  JsArray._fromJs(Object jsObject) : super._fromJs(jsObject);
 
   _checkIndex(int index) {
-    if (index is int && (index < 0 || index >= length)) {
+    if (index < 0 || index >= length) {
       throw RangeError.range(index, 0, length);
     }
   }
 
   _checkInsertIndex(int index) {
-    if (index is int && (index < 0 || index >= length + 1)) {
+    if (index < 0 || index >= length + 1) {
       throw RangeError.range(index, 0, length);
     }
   }
@@ -210,9 +208,7 @@ class JsArray<E> extends JsObject with ListMixin<E> {
 
   @patch
   E operator [](Object index) {
-    // TODO(justinfagnani): fix the semantics for non-ints
-    // dartbug.com/14605
-    if (index is num && index == index.toInt()) {
+    if (index is int) {
       _checkIndex(index);
     }
     return super[index] as E;
@@ -220,9 +216,7 @@ class JsArray<E> extends JsObject with ListMixin<E> {
 
   @patch
   void operator []=(Object index, value) {
-    // TODO(justinfagnani): fix the semantics for non-ints
-    // dartbug.com/14605
-    if (index is num && index == index.toInt()) {
+    if (index is int) {
       _checkIndex(index);
     }
     super[index] = value;
@@ -253,7 +247,7 @@ class JsArray<E> extends JsObject with ListMixin<E> {
   @patch
   void addAll(Iterable<E> iterable) {
     var list = (JS<bool>('!', '# instanceof Array', iterable))
-        ? iterable
+        ? JS<List>('', '#', iterable)
         : List.from(iterable);
     callMethod('push', list);
   }
@@ -288,13 +282,13 @@ class JsArray<E> extends JsObject with ListMixin<E> {
     int length = end - start;
     if (length == 0) return;
     if (skipCount < 0) throw ArgumentError(skipCount);
-    var args = <Object>[start, length]
+    var args = <Object?>[start, length]
       ..addAll(iterable.skip(skipCount).take(length));
     callMethod('splice', args);
   }
 
   @patch
-  void sort([int compare(E a, E b)]) {
+  void sort([int compare(E a, E b)?]) {
     // Note: arr.sort(null) is a type error in FF
     callMethod('sort', compare == null ? [] : [compare]);
   }
@@ -304,7 +298,7 @@ class JsArray<E> extends JsObject with ListMixin<E> {
 // We include the instanceof Object test to filter out cross frame objects
 // on FireFox. Surprisingly on FireFox the instanceof Window test succeeds for
 // cross frame windows while the instanceof Object test fails.
-bool _isBrowserType(o) => JS(
+bool _isBrowserType(Object o) => JS(
     'bool',
     '# instanceof Object && ('
         '# instanceof Blob || '
@@ -329,11 +323,11 @@ bool _isBrowserType(o) => JS(
     o);
 
 class _DartObject {
-  final _dartObj;
+  final Object _dartObj;
   _DartObject(this._dartObj);
 }
 
-dynamic _convertToJS(dynamic o) {
+Object? _convertToJS(Object? o) {
   if (o == null || o is String || o is num || o is bool || _isBrowserType(o)) {
     return o;
   } else if (o is DateTime) {
@@ -349,8 +343,8 @@ dynamic _convertToJS(dynamic o) {
   }
 }
 
-dynamic _wrapDartFunction(f) {
-  var wrapper = JS(
+Object _wrapDartFunction(Object f) {
+  var wrapper = JS<Object>(
       '',
       'function(/*...arguments*/) {'
           '  let args = Array.prototype.map.call(arguments, #);'
@@ -366,11 +360,11 @@ dynamic _wrapDartFunction(f) {
 
 // converts a Dart object to a reference to a native JS object
 // which might be a DartObject JS->Dart proxy
-Object _convertToDart(o) {
+Object? _convertToDart(Object? o) {
   if (o == null || o is String || o is num || o is bool || _isBrowserType(o)) {
     return o;
   } else if (JS('!', '# instanceof Date', o)) {
-    num ms = JS('!', '#.getTime()', o);
+    int ms = JS('!', '#.getTime()', o);
     return DateTime.fromMillisecondsSinceEpoch(ms);
   } else if (o is _DartObject &&
       !identical(dart.getReifiedType(o), dart.jsobject)) {
@@ -380,9 +374,10 @@ Object _convertToDart(o) {
   }
 }
 
-Object _wrapToDart(o) => _putIfAbsent(_dartProxies, o, _wrapToDartHelper);
+JsObject _wrapToDart(Object o) =>
+    _putIfAbsent(_dartProxies, o, _wrapToDartHelper);
 
-Object _wrapToDartHelper(o) {
+JsObject _wrapToDartHelper(Object o) {
   if (JS<bool>('!', 'typeof # == "function"', o)) {
     return JsFunction._fromJs(o);
   }
@@ -392,16 +387,18 @@ Object _wrapToDartHelper(o) {
   return JsObject._fromJs(o);
 }
 
-final _dartProxies = JS('', 'new WeakMap()');
-final _jsProxies = JS('', 'new WeakMap()');
+final Object _dartProxies = JS('', 'new WeakMap()');
+final Object _jsProxies = JS('', 'new WeakMap()');
 
-Object _putIfAbsent(weakMap, o, getValue(o)) {
-  var value = JS('', '#.get(#)', weakMap, o);
+@NoReifyGeneric()
+T _putIfAbsent<T>(Object weakMap, Object o, T getValue(Object o)) {
+  T? value = JS('', '#.get(#)', weakMap, o);
   if (value == null) {
     value = getValue(o);
     JS('', '#.set(#, #)', weakMap, o, value);
   }
-  return value;
+  // TODO(vsm): Static cast.  Unnecessary?
+  return JS('', '#', value);
 }
 
 Expando<Function> _interopExpando = Expando<Function>();
@@ -409,9 +406,9 @@ Expando<Function> _interopExpando = Expando<Function>();
 @patch
 F allowInterop<F extends Function>(F f) {
   if (!dart.isDartFunction(f)) return f;
-  var ret = _interopExpando[f];
+  var ret = _interopExpando[f] as F?;
   if (ret == null) {
-    ret = JS(
+    ret = JS<F>(
         '',
         'function (...args) {'
             ' return #(#, args);'
@@ -430,7 +427,7 @@ Function allowInteropCaptureThis(Function f) {
   if (!dart.isDartFunction(f)) return f;
   var ret = _interopCaptureThisExpando[f];
   if (ret == null) {
-    ret = JS(
+    ret = JS<Function>(
         '',
         'function(...arguments) {'
             '  let args = [this];'

sdk/lib/_internal/js_dev_runtime/patch/math_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:math library.
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper' show patch, nullCheck, notNull;
@@ -12,53 +10,53 @@ import 'dart:typed_data' show ByteData;
 @patch
 @notNull
 T min<T extends num>(@nullCheck T a, @nullCheck T b) =>
-    JS('-dynamic', r'Math.min(#, #)', a, b);
+    JS<T>('-dynamic', r'Math.min(#, #)', a, b);
 
 @patch
 @notNull
 T max<T extends num>(@nullCheck T a, @nullCheck T b) =>
-    JS('-dynamic', r'Math.max(#, #)', a, b);
+    JS<T>('-dynamic', r'Math.max(#, #)', a, b);
 
 @patch
 @notNull
-double sqrt(@nullCheck num x) => JS<num>('!', r'Math.sqrt(#)', x);
+double sqrt(@nullCheck num x) => JS<double>('!', r'Math.sqrt(#)', x);
 
 @patch
 @notNull
-double sin(@nullCheck num radians) => JS<num>('!', r'Math.sin(#)', radians);
+double sin(@nullCheck num radians) => JS<double>('!', r'Math.sin(#)', radians);
 
 @patch
 @notNull
-double cos(@nullCheck num radians) => JS<num>('!', r'Math.cos(#)', radians);
+double cos(@nullCheck num radians) => JS<double>('!', r'Math.cos(#)', radians);
 
 @patch
 @notNull
-double tan(@nullCheck num radians) => JS<num>('!', r'Math.tan(#)', radians);
+double tan(@nullCheck num radians) => JS<double>('!', r'Math.tan(#)', radians);
 
 @patch
 @notNull
-double acos(@nullCheck num x) => JS<num>('!', r'Math.acos(#)', x);
+double acos(@nullCheck num x) => JS<double>('!', r'Math.acos(#)', x);
 
 @patch
 @notNull
-double asin(@nullCheck num x) => JS<num>('!', r'Math.asin(#)', x);
+double asin(@nullCheck num x) => JS<double>('!', r'Math.asin(#)', x);
 
 @patch
 @notNull
-double atan(@nullCheck num x) => JS<num>('!', r'Math.atan(#)', x);
+double atan(@nullCheck num x) => JS<double>('!', r'Math.atan(#)', x);
 
 @patch
 @notNull
 double atan2(@nullCheck num a, @nullCheck num b) =>
-    JS<num>('!', r'Math.atan2(#, #)', a, b);
+    JS<double>('!', r'Math.atan2(#, #)', a, b);
 
 @patch
 @notNull
-double exp(@nullCheck num x) => JS<num>('!', r'Math.exp(#)', x);
+double exp(@nullCheck num x) => JS<double>('!', r'Math.exp(#)', x);
 
 @patch
 @notNull
-double log(@nullCheck num x) => JS<num>('!', r'Math.log(#)', x);
+double log(@nullCheck num x) => JS<double>('!', r'Math.log(#)', x);
 
 @patch
 @notNull
@@ -69,10 +67,10 @@ const int _POW2_32 = 0x100000000;
 
 @patch
 class Random {
-  static Random _secureRandom;
+  static Random? _secureRandom;
 
   @patch
-  factory Random([int seed]) =>
+  factory Random([int? seed]) =>
       (seed == null) ? const _JSRandom() : _Random(seed);
 
   @patch
@@ -88,7 +86,7 @@ class _JSRandom implements Random {
     if (max <= 0 || max > _POW2_32) {
       throw RangeError("max must be in range 0 < max ≤ 2^32, was $max");
     }
-    return JS("int", "(Math.random() * #) >>> 0", max);
+    return JS<int>("int", "(Math.random() * #) >>> 0", max);
   }
 
   /**
@@ -96,13 +94,13 @@ class _JSRandom implements Random {
    * the range from 0.0, inclusive, to 1.0, exclusive.
    */
   @notNull
-  double nextDouble() => JS("double", "Math.random()");
+  double nextDouble() => JS<double>("double", "Math.random()");
 
   /**
    * Generates a random boolean value.
    */
   @notNull
-  bool nextBool() => JS("bool", "Math.random() < 0.5");
+  bool nextBool() => JS<bool>("bool", "Math.random() < 0.5");
 }
 
 class _Random implements Random {
@@ -240,7 +238,7 @@ class _Random implements Random {
     do {
       _nextState();
       rnd32 = _lo;
-      result = rnd32.remainder(max); // % max;
+      result = rnd32.remainder(max).toInt(); // % max;
     } while ((rnd32 - result + max) >= _POW2_32);
     return result;
   }
@@ -327,7 +325,7 @@ class _JSSecureRandom implements Random {
     }
     _buffer.setUint32(0, 0);
     int start = 4 - byteCount;
-    int randomLimit = pow(256, byteCount);
+    int randomLimit = pow(256, byteCount).toInt();
     while (true) {
       _getRandomBytes(start, byteCount);
       // The getUint32 method is big-endian as default.
@@ -336,7 +334,7 @@ class _JSSecureRandom implements Random {
         // Max is power of 2.
         return random & (max - 1);
       }
-      int result = random.remainder(max);
+      int result = random.remainder(max).toInt();
       // Ensure results have equal probability by rejecting values in the
       // last range of k*max .. 256**byteCount.
       // TODO: Consider picking a higher byte count if the last range is a

sdk/lib/_internal/js_dev_runtime/patch/typed_data_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 import 'dart:_js_helper' show patch;
 import 'dart:_native_typed_data';
 

sdk/lib/_internal/js_dev_runtime/private/annotations.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 /// Tells the optimizing compiler to always inline the annotated method.
@@ -83,7 +81,7 @@ class JsPeerInterface {
   /// Used for classes where Dart subclasses should be callable from JavaScript
   /// matching the JavaScript calling conventions.
   final String name;
-  const JsPeerInterface({this.name});
+  const JsPeerInterface({required this.name});
 }
 
 /// A Dart interface may only be implemented by a native JavaScript object

sdk/lib/_internal/js_dev_runtime/private/custom_hash_map.dart

@@ -2,30 +2,28 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 class CustomKeyHashMap<K, V> extends CustomHashMap<K, V> {
-  final _Predicate<Object> _validKey;
+  final _Predicate<Object?> _validKey;
   CustomKeyHashMap(_Equality<K> equals, _Hasher<K> hashCode, this._validKey)
       : super(equals, hashCode);
 
   @override
   @notNull
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (!_validKey(key)) return false;
     return super.containsKey(key);
   }
 
   @override
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (!_validKey(key)) return null;
     return super[key];
   }
 
   @override
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (!_validKey(key)) return null;
     return super.remove(key);
   }
@@ -69,7 +67,7 @@ class CustomHashMap<K, V> extends InternalMap<K, V> {
   Iterable<V> get values => _JSMapIterable<V>(this, false);
 
   @notNull
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (key is K) {
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, _hashCode(key));
       if (buckets != null) {
@@ -83,7 +81,7 @@ class CustomHashMap<K, V> extends InternalMap<K, V> {
     return false;
   }
 
-  bool containsValue(Object value) {
+  bool containsValue(Object? value) {
     for (var v in JS('', '#.values()', _map)) {
       if (value == v) return true;
     }
@@ -96,7 +94,7 @@ class CustomHashMap<K, V> extends InternalMap<K, V> {
     });
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (key is K) {
       var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, _hashCode(key));
       if (buckets != null) {
@@ -152,13 +150,13 @@ class CustomHashMap<K, V> extends InternalMap<K, V> {
       JS('', '#.push(#)', buckets, key);
     }
     V value = ifAbsent();
-    if (value == null) value = null; // coerce undefined to null.
+    if (value == null) JS('', '# = null', value); // coerce undefined to null.
     JS('', '#.set(#, #)', _map, key, value);
     _modifications = (_modifications + 1) & 0x3ffffff;
     return value;
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (key is K) {
       int hash = JS('!', '# & 0x3ffffff', _hashCode(key));
       var keyMap = _keyMap;

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/classes.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// This library defines the operations that define and manipulate Dart
 /// classes.  Included in this are:
 ///   - Generics
@@ -109,7 +107,7 @@ final mixinOn = JS('', 'Symbol("mixinOn")');
 @JSExportName('implements')
 final implements_ = JS('', 'Symbol("implements")');
 
-List Function() getImplements(clazz) => JS(
+List? Function() getImplements(clazz) => JS(
     '',
     'Object.hasOwnProperty.call(#, #) ? #[#] : null',
     clazz,
@@ -229,11 +227,11 @@ getGenericClass(type) => safeGetOwnProperty(type, _originalDeclaration);
 
 // TODO(markzipan): Make this non-nullable if we can ensure this returns
 // an empty list or if null and the empty list are semantically the same.
-List getGenericArgs(type) =>
+List? getGenericArgs(type) =>
     JS<List>('', '#', safeGetOwnProperty(type, _typeArguments));
 
-List getGenericArgVariances(type) =>
-    JS<List>('', '#', safeGetOwnProperty(type, _variances));
+List? getGenericArgVariances(type) =>
+    JS<List?>('', '#', safeGetOwnProperty(type, _variances));
 
 void setGenericArgVariances(f, variances) =>
     JS('', '#[#] = #', f, _variances, variances);

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._runtime;
 
 // We need to set these properties while the sdk is only partially initialized
@@ -21,15 +19,15 @@ throwUnimplementedError(String message) {
 
 // TODO(nshahan) Cleanup embeded strings and extract file location at runtime
 // from the stacktrace.
-assertFailed(String message,
-    [String fileUri, int line, int column, String conditionSource]) {
+assertFailed(String? message,
+    [String? fileUri, int? line, int? column, String? conditionSource]) {
   throw AssertionErrorImpl(message, fileUri, line, column, conditionSource);
 }
 
 final _nullFailedSet = JS('!', 'new Set()');
 // Run-time null safety assertion per:
 // https://github.com/dart-lang/language/blob/master/accepted/future-releases/nnbd/feature-specification.md#automatic-debug-assertion-insertion
-nullFailed(String fileUri, int line, int column, String variable) {
+nullFailed(String? fileUri, int? line, int? column, String? variable) {
   if (strictNullSafety) {
     throw AssertionErrorImpl(
         'A null value was passed into a non-nullable parameter $variable',
@@ -47,7 +45,7 @@ nullFailed(String fileUri, int line, int column, String variable) {
   }
 }
 
-throwCyclicInitializationError([String field]) {
+throwCyclicInitializationError([String? field]) {
   throw CyclicInitializationError(field);
 }
 
@@ -101,7 +99,7 @@ final Object _jsError = JS('', 'Symbol("_jsError")');
 ///
 /// If the throw originated in JavaScript, then there is not a corresponding
 /// Dart value, so we just return the error object.
-Object getThrown(Object error) {
+Object? getThrown(Object? error) {
   if (error != null) {
     // Get the Dart thrown value, if any.
     var value = JS('', '#[#]', error, _thrownValue);
@@ -123,7 +121,7 @@ final _stackTrace = JS('', 'Symbol("_stackTrace")');
 /// the corresponding stack trace the same way we do for Dart throws. If the
 /// throw object was not an Error, then we don't have a JS trace, so we create
 /// one here.
-StackTrace stackTrace(Object error) {
+StackTrace stackTrace(Object? error) {
   if (JS<bool>('!', '!(# instanceof Error)', error)) {
     // We caught something that isn't a JS Error.
     //
@@ -133,7 +131,7 @@ StackTrace stackTrace(Object error) {
   }
 
   // If we've already created the Dart stack trace object, return it.
-  StackTrace trace = JS('', '#[#]', error, _stackTrace);
+  StackTrace? trace = JS('', '#[#]', error, _stackTrace);
   if (trace != null) return trace;
 
   // Otherwise create the Dart stack trace (by parsing the JS stack), and
@@ -210,7 +208,7 @@ final Object RethrownDartError = JS(
 /// Implements `throw` of [exception], allowing for throw in an expression
 /// context, and capturing the current stack trace.
 @JSExportName('throw')
-void throw_(Object exception) {
+void throw_(Object? exception) {
   /// Wrap the object so we capture a new stack trace, and so it will print
   /// nicely from JS, as if it were a normal JS error.
   JS('', 'throw new #(#)', DartError, exception);
@@ -233,7 +231,7 @@ void throw_(Object exception) {
 /// If the stack trace is null, this will preserve the original stack trace
 /// on the exception, if available, otherwise it will capture the current stack
 /// trace.
-Object createErrorWithStack(Object exception, StackTrace trace) {
+Object? createErrorWithStack(Object exception, StackTrace? trace) {
   if (trace == null) {
     var error = JS('', '#[#]', exception, _jsError);
     return error != null ? error : JS('', 'new #(#)', DartError, exception);
@@ -257,18 +255,18 @@ void stackPrint(Object error) {
 }
 
 class _StackTrace implements StackTrace {
-  final Object _jsError;
-  final Object _jsObjectMissingTrace;
-  String _trace;
+  final Object? _jsError;
+  final Object? _jsObjectMissingTrace;
+  String? _trace;
 
   _StackTrace(this._jsError) : _jsObjectMissingTrace = null;
 
-  _StackTrace.missing(Object caughtObj)
+  _StackTrace.missing(Object? caughtObj)
       : _jsObjectMissingTrace = caughtObj != null ? caughtObj : 'null',
         _jsError = JS('', 'Error()');
 
   String toString() {
-    if (_trace != null) return _trace;
+    if (_trace != null) return _trace!;
 
     var e = _jsError;
     String trace = '';

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// This library defines runtime operations on objects used by the code
 /// generator.
 part of dart._runtime;
@@ -19,7 +17,7 @@ class InvocationImpl extends Invocation {
   final bool isSetter;
   final String failureMessage;
 
-  InvocationImpl(memberName, List<Object> positionalArguments,
+  InvocationImpl(memberName, List<Object?> positionalArguments,
       {namedArguments,
       List typeArguments = const [],
       this.isMethod = false,
@@ -146,7 +144,7 @@ dput(obj, field, value) {
 /// [actuals] and [namedActuals].
 ///
 /// Returns `null` if all checks pass.
-String _argumentErrors(FunctionType type, List actuals, namedActuals) {
+String? _argumentErrors(FunctionType type, List actuals, namedActuals) {
   // Check for too few required arguments.
   int actualsCount = JS('!', '#.length', actuals);
   var required = type.args;
@@ -165,7 +163,7 @@ String _argumentErrors(FunctionType type, List actuals, namedActuals) {
   }
 
   // Check if we have invalid named arguments.
-  Iterable names;
+  Iterable? names;
   var named = type.named;
   var requiredNamed = type.requiredNamed;
   if (namedActuals != null) {
@@ -444,7 +442,7 @@ cast(obj, type) {
   return castError(obj, type);
 }
 
-bool test(bool obj) {
+bool test(bool? obj) {
   if (obj == null) throw BooleanConversionAssertionError();
   return obj;
 }
@@ -513,11 +511,11 @@ final constantMaps = JS<Object>('!', 'new Map()');
 // Keeping the paths is probably expensive.  It would probably
 // be more space efficient to just use a direct hash table with
 // an appropriately defined structural equality function.
-Object _lookupNonTerminal(Object map, Object key) {
+Object _lookupNonTerminal(Object map, Object? key) {
   var result = JS('', '#.get(#)', map, key);
   if (result != null) return result;
   JS('', '#.set(#, # = new Map())', map, key, result);
-  return result;
+  return result!;
 }
 
 Map<K, V> constMap<K, V>(JSArray elements) {
@@ -527,7 +525,7 @@ Map<K, V> constMap<K, V>(JSArray elements) {
     map = _lookupNonTerminal(map, JS('', '#[#]', elements, i));
   }
   map = _lookupNonTerminal(map, K);
-  Map<K, V> result = JS('', '#.get(#)', map, V);
+  Map<K, V>? result = JS('', '#.get(#)', map, V);
   if (result != null) return result;
   result = ImmutableMap<K, V>.from(elements);
   JS('', '#.set(#, #)', map, V, result);
@@ -550,7 +548,7 @@ Set<E> constSet<E>(JSArray<E> elements) {
   for (var i = 0; i < count; i++) {
     map = _lookupNonTerminal(map, JS('', '#[#]', elements, i));
   }
-  Set<E> result = JS('', '#.get(#)', map, E);
+  Set<E>? result = JS('', '#.get(#)', map, E);
   if (result != null) return result;
   result = _createImmutableSet<E>(elements);
   JS('', '#.set(#, #)', map, E, result);

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/rtti.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// This library defines the association between runtime objects and
 /// runtime types.
 part of dart._runtime;
@@ -116,7 +114,7 @@ getReifiedType(obj) {
 }
 
 /// Return the module name for a raw library object.
-String getModuleName(Object module) => JS('', '#[#]', module, _moduleName);
+String? getModuleName(Object module) => JS('', '#[#]', module, _moduleName);
 
 final _loadedModules = JS('', 'new Map()');
 final _loadedPartMaps = JS('', 'new Map()');
@@ -126,7 +124,7 @@ List<String> getModuleNames() {
   return JS<List<String>>('', 'Array.from(#.keys())', _loadedModules);
 }
 
-String getSourceMap(String moduleName) {
+String? getSourceMap(String moduleName) {
   return JS('!', '#.get(#)', _loadedSourceMaps, moduleName);
 }
 
@@ -143,7 +141,7 @@ getModulePartMap(String name) => JS('', '#.get(#)', _loadedPartMaps, name);
 
 /// Track all libraries
 void trackLibraries(
-    String moduleName, Object libraries, Object parts, String sourceMap) {
+    String moduleName, Object libraries, Object parts, String? sourceMap) {
   if (parts is String) {
     // Added for backwards compatibility.
     // package:build_web_compilers currently invokes this without [parts]
@@ -159,9 +157,9 @@ void trackLibraries(
   _parts = null;
 }
 
-List<String> _libraries;
-Map<String, Object> _libraryObjects;
-Map<String, List<String>> _parts;
+List<String>? _libraries;
+Map<String, Object?>? _libraryObjects;
+Map<String, List<String>?>? _parts;
 
 _computeLibraryMetadata() {
   _libraries = [];
@@ -174,16 +172,16 @@ _computeLibraryMetadata() {
     // TODO(nshahan) Can we optimize this cast and the one below to use
     // JsArray.of() to be more efficient?
     var libraries = getOwnPropertyNames(module).cast<String>();
-    _libraries.addAll(libraries);
+    _libraries!.addAll(libraries);
     for (var library in libraries) {
-      _libraryObjects[library] = JS('', '#.#', module, library);
+      _libraryObjects![library] = JS('', '#.#', module, library);
     }
 
     // Add parts from each module.
     var partMap = getModulePartMap(name);
     libraries = getOwnPropertyNames(partMap).cast<String>();
     for (var library in libraries) {
-      _parts[library] = List.from(JS('List', '#.#', partMap, library));
+      _parts![library] = List.from(JS('List', '#.#', partMap, library));
     }
   }
 }
@@ -191,11 +189,11 @@ _computeLibraryMetadata() {
 /// Returns the JS library object for a given library [uri] or
 /// undefined / null if it isn't loaded.  Top-level types and
 /// methods are available on this object.
-Object getLibrary(String uri) {
+Object? getLibrary(String uri) {
   if (_libraryObjects == null) {
     _computeLibraryMetadata();
   }
-  return _libraryObjects[uri];
+  return _libraryObjects![uri];
 }
 
 /// Returns a JSArray of library uris (e.g,
@@ -205,7 +203,7 @@ List<String> getLibraries() {
   if (_libraries == null) {
     _computeLibraryMetadata();
   }
-  return _libraries;
+  return _libraries!;
 }
 
 /// Returns a JSArray of part uris for a given [libraryUri].
@@ -225,5 +223,5 @@ List<String> getParts(String libraryUri) {
   if (_parts == null) {
     _computeLibraryMetadata();
   }
-  return _parts[libraryUri] ?? [];
+  return _parts![libraryUri] ?? [];
 }

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/runtime.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 @ReifyFunctionTypes(false)
 library dart._runtime;
 

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/types.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// This library defines the representation of runtime types.
 part of dart._runtime;
 
@@ -118,7 +116,7 @@ class DynamicType extends DartType {
   bool is_T(object) => true;
 
   @JSExportName('as')
-  Object as_T(Object object) => object;
+  Object? as_T(Object? object) => object;
 }
 
 @notNull
@@ -144,7 +142,7 @@ bool isDartFunction(obj) =>
 Expando<Function> _assertInteropExpando = Expando<Function>();
 
 @NoReifyGeneric()
-F tearoffInterop<F extends Function>(F f) {
+F tearoffInterop<F extends Function?>(F f) {
   // Wrap a JS function with a closure that ensures all function arguments are
   // native JS functions.
   if (!_isJsObject(f) || f == null) return f;
@@ -171,10 +169,10 @@ F tearoffInterop<F extends Function>(F f) {
 /// we disable type checks for in these cases, and allow any JS object to work
 /// as if it were an instance of this JS type.
 class LazyJSType extends DartType {
-  Function() _getRawJSTypeFn;
+  Function()? _getRawJSTypeFn;
   @notNull
   final String _dartName;
-  Object _rawJSType;
+  Object? _rawJSType;
 
   LazyJSType(this._getRawJSTypeFn, this._dartName);
 
@@ -183,7 +181,7 @@ class LazyJSType extends DartType {
     return raw != null ? typeName(raw) : "JSObject<$_dartName>";
   }
 
-  Object _getRawJSType() {
+  Object? _getRawJSType() {
     var raw = _rawJSType;
     if (raw != null) return raw;
 
@@ -193,7 +191,7 @@ class LazyJSType extends DartType {
     // overhead, especially if exceptions are being thrown. Also it means the
     // behavior of a given type check can change later on.
     try {
-      raw = _getRawJSTypeFn();
+      raw = _getRawJSTypeFn!();
     } catch (e) {}
 
     if (raw == null) {
@@ -434,7 +432,7 @@ class VoidType extends DartType {
   bool is_T(object) => true;
 
   @JSExportName('as')
-  Object as_T(Object object) => object;
+  Object? as_T(Object? object) => object;
 }
 
 @JSExportName('void')
@@ -685,7 +683,7 @@ class FunctionType extends AbstractFunctionType {
   // Named arguments native JS Object of the form { namedArgName: namedArgType }
   final named;
   final requiredNamed;
-  String _stringValue;
+  String? _stringValue;
 
   /// Construct a function type.
   ///
@@ -743,7 +741,7 @@ class FunctionType extends AbstractFunctionType {
   }
 
   /// Maps argument names to their canonicalized type.
-  Map<String, Object> _createNameMap(List<Object> names) {
+  Map<String, Object> _createNameMap(List<Object?> names) {
     var result = <String, Object>{};
     // TODO: Remove this sort if ordering can be conserved.
     JS('', '#.sort()', names);
@@ -763,7 +761,7 @@ class FunctionType extends AbstractFunctionType {
       _createNameMap(getOwnPropertyNames(requiredNamed).toList());
 
   get name {
-    if (_stringValue != null) return _stringValue;
+    if (_stringValue != null) return _stringValue!;
     var buffer = '(';
     for (var i = 0; JS<bool>('!', '# < #.length', i, args); ++i) {
       if (i > 0) {
@@ -858,7 +856,7 @@ class GenericFunctionTypeIdentifier extends AbstractFunctionType {
   final typeFormals;
   final typeBounds;
   final FunctionType function;
-  String _stringValue;
+  String? _stringValue;
 
   GenericFunctionTypeIdentifier(
       this.typeFormals, this.typeBounds, this.function);
@@ -869,7 +867,7 @@ class GenericFunctionTypeIdentifier extends AbstractFunctionType {
   /// Type formal names may not correspond to those of the originating type.
   /// We should consider auto-generating these to avoid confusion.
   toString() {
-    if (_stringValue != null) return _stringValue;
+    if (_stringValue != null) return _stringValue!;
     String s = "<";
     var typeFormals = this.typeFormals;
     var typeBounds = this.typeBounds;
@@ -994,7 +992,7 @@ class GenericFunctionType extends AbstractFunctionType {
     // formal if known, or it will be the original TypeVariable if we are still
     // solving for it. This array is passed to `instantiateToBounds` as we are
     // progressively solving for type variables.
-    var defaults = List<Object>.filled(typeFormals.length, null);
+    var defaults = List<Object?>.filled(typeFormals.length, null);
     // not ground
     var partials = Map<TypeVariable, Object>.identity();
 
@@ -1037,9 +1035,9 @@ class GenericFunctionType extends AbstractFunctionType {
     while (hasProgress) {
       hasProgress = false;
       for (var typeFormal in partials.keys) {
-        var partialBound = partials[typeFormal];
+        var partialBound = partials[typeFormal]!;
         if (!hasFreeFormal(partialBound)) {
-          int index = all[typeFormal];
+          int index = all[typeFormal]!;
           defaults[index] = instantiateTypeBounds(defaults)[index];
           partials.remove(typeFormal);
           hasProgress = true;
@@ -1079,7 +1077,7 @@ class GenericFunctionType extends AbstractFunctionType {
   }
 }
 
-List<TypeVariable> _typeFormalsFromFunction(Object typeConstructor) {
+List<TypeVariable> _typeFormalsFromFunction(Object? typeConstructor) {
   // Extract parameter names from the function parameters.
   //
   // This is not robust in general for user-defined JS functions, but it
@@ -1610,7 +1608,7 @@ bool _isInterfaceSubtype(t1, t2, @notNull bool strictMode) => JS('', '''(() => {
   return false;
 })()''');
 
-Object extractTypeArguments<T>(T instance, Function f) {
+Object? extractTypeArguments<T>(T instance, Function f) {
   if (instance == null) {
     throw ArgumentError('Cannot extract type of null instance.');
   }
@@ -1622,7 +1620,7 @@ Object extractTypeArguments<T>(T instance, Function f) {
     throw ArgumentError('Cannot extract from non-class type ($type).');
   }
   var typeArguments = getGenericArgs(type);
-  if (typeArguments.isEmpty) {
+  if (typeArguments!.isEmpty) {
     throw ArgumentError('Cannot extract from non-generic type ($type).');
   }
   var supertype = _getMatchingSupertype(getReifiedType(instance), type);
@@ -1646,14 +1644,14 @@ class _TypeInferrer {
             typeVariables, typeVariables.map((_) => TypeConstraint()));
 
   /// Returns the inferred types based on the current constraints.
-  List<Object> getInferredTypes() {
+  List<Object>? getInferredTypes() {
     var result = <Object>[];
     for (var constraint in _typeVariables.values) {
       // Prefer the known bound, if any.
       if (constraint.lower != null) {
-        result.add(constraint.lower);
+        result.add(constraint.lower!);
       } else if (constraint.upper != null) {
-        result.add(constraint.upper);
+        result.add(constraint.upper!);
       } else {
         return null;
       }
@@ -1670,11 +1668,11 @@ class _TypeInferrer {
       _isSubtypeMatch(subtype, supertype);
 
   void _constrainLower(TypeVariable parameter, Object lower) {
-    _typeVariables[parameter]._constrainLower(lower);
+    _typeVariables[parameter]!._constrainLower(lower);
   }
 
   void _constrainUpper(TypeVariable parameter, Object upper) {
-    _typeVariables[parameter]._constrainUpper(upper);
+    _typeVariables[parameter]!._constrainUpper(upper);
   }
 
   bool _isFunctionSubtypeMatch(FunctionType subtype, FunctionType supertype) {
@@ -1740,13 +1738,13 @@ class _TypeInferrer {
     for (var name in supertypeNamed.keys) {
       var subtypeParamType = subtypeNamed[name];
       if (subtypeParamType == null) return false;
-      if (!_isSubtypeMatch(supertypeNamed[name], subtypeParamType)) {
+      if (!_isSubtypeMatch(supertypeNamed[name]!, subtypeParamType)) {
         return false;
       }
     }
     for (var name in supertypeRequiredNamed.keys) {
-      var subtypeParamType = subtypeRequiredNamed[name] ?? subtypeNamed[name];
-      if (!_isSubtypeMatch(supertypeRequiredNamed[name], subtypeParamType)) {
+      var subtypeParamType = subtypeRequiredNamed[name] ?? subtypeNamed[name]!;
+      if (!_isSubtypeMatch(supertypeRequiredNamed[name]!, subtypeParamType)) {
         return false;
       }
     }
@@ -1777,8 +1775,8 @@ class _TypeInferrer {
     var matchingSupertype = _getMatchingSupertype(subtype, supertype);
     if (matchingSupertype == null) return false;
 
-    var matchingTypeArgs = getGenericArgs(matchingSupertype);
-    var supertypeTypeArgs = getGenericArgs(supertype);
+    var matchingTypeArgs = getGenericArgs(matchingSupertype)!;
+    var supertypeTypeArgs = getGenericArgs(supertype)!;
     for (int i = 0; i < supertypeTypeArgs.length; i++) {
       if (!_isSubtypeMatch(matchingTypeArgs[i], supertypeTypeArgs[i])) {
         return false;
@@ -1824,13 +1822,13 @@ class _TypeInferrer {
 
     // Handle FutureOr<T> union type.
     if (_isFutureOr(subtype)) {
-      var subtypeArg = getGenericArgs(subtype)[0];
+      var subtypeArg = getGenericArgs(subtype)![0];
       if (_isFutureOr(supertype)) {
         // `FutureOr<P>` is a subtype match for `FutureOr<Q>` with respect to `L`
         // under constraints `C`:
         // - If `P` is a subtype match for `Q` with respect to `L` under constraints
         //   `C`.
-        var supertypeArg = getGenericArgs(supertype)[0];
+        var supertypeArg = getGenericArgs(supertype)![0];
         return _isSubtypeMatch(subtypeArg, supertypeArg);
       }
 
@@ -1843,7 +1841,7 @@ class _TypeInferrer {
       var subtypeFuture =
           JS<Object>('!', '#(#)', getGenericClass(Future), subtypeArg);
       return _isSubtypeMatch(subtypeFuture, supertype) &&
-          _isSubtypeMatch(subtypeArg, supertype);
+          _isSubtypeMatch(subtypeArg!, supertype);
     }
 
     if (_isFutureOr(supertype)) {
@@ -1855,7 +1853,7 @@ class _TypeInferrer {
       //   constraints `C`
       //   - And `P` is a subtype match for `Q` with respect to `L` under
       //     constraints `C`
-      var supertypeArg = getGenericArgs(supertype)[0];
+      var supertypeArg = getGenericArgs(supertype)![0];
       var supertypeFuture =
           JS<Object>('!', '#(#)', getGenericClass(Future), supertypeArg);
       return _isSubtypeMatch(subtype, supertypeFuture) ||
@@ -1950,11 +1948,11 @@ class _TypeInferrer {
 class TypeConstraint {
   /// The lower bound of the type being constrained.  This bound must be a
   /// subtype of the type being constrained.
-  Object lower;
+  Object? lower;
 
   /// The upper bound of the type being constrained.  The type being constrained
   /// must be a subtype of this bound.
-  Object upper;
+  Object? upper;
 
   void _constrainLower(Object type) {
     var _lower = lower;
@@ -1991,7 +1989,7 @@ class TypeConstraint {
 
 /// Finds a supertype of [subtype] that matches the class [supertype], but may
 /// contain different generic type arguments.
-Object _getMatchingSupertype(Object subtype, Object supertype) {
+Object? _getMatchingSupertype(Object? subtype, Object supertype) {
   if (identical(subtype, supertype)) return supertype;
   if (subtype == null || _equalType(subtype, Object)) return null;
 
@@ -2014,7 +2012,7 @@ Object _getMatchingSupertype(Object subtype, Object supertype) {
   // Check interfaces.
   var getInterfaces = getImplements(subtype);
   if (getInterfaces != null) {
-    for (var iface in getInterfaces()) {
+    for (var iface in getInterfaces()!) {
       result = _getMatchingSupertype(iface, supertype);
       if (result != null) return result;
     }

sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/utils.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._runtime;
 
 /// This library defines a set of general javascript utilities for us
@@ -19,11 +17,11 @@ defineValue(obj, name, value) {
 }
 
 final Function(Object, Object,
-    {Object get,
-    Object set,
-    Object value,
-    bool configurable,
-    bool writable}) defineAccessor = JS('', 'Object.defineProperty');
+    {Object? get,
+    Object? set,
+    Object? value,
+    bool? configurable,
+    bool? writable}) defineAccessor = JS('', 'Object.defineProperty');
 
 final dynamic Function(Object, Object) getOwnPropertyDescriptor =
     JS('', 'Object.getOwnPropertyDescriptor');

sdk/lib/_internal/js_dev_runtime/private/debugger.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._debugger;
 
 import 'dart:_foreign_helper' show JS;
@@ -171,7 +169,7 @@ bool hasMethod(object, String name) {
 /// [JsonMLFormatter] consumes [NameValuePair] objects and
 class NameValuePair {
   NameValuePair(
-      {this.name,
+      {this.name = '',
       this.value,
       this.config = JsonMLConfig.none,
       this.hideName = false});
@@ -187,7 +185,7 @@ class NameValuePair {
   int get hashCode => name.hashCode;
 
   final String name;
-  final Object value;
+  final Object? value;
   final JsonMLConfig config;
   final bool hideName;
 
@@ -197,8 +195,8 @@ class NameValuePair {
 class MapEntry {
   MapEntry({this.key, this.value});
 
-  final Object key;
-  final Object value;
+  final Object? key;
+  final Object? value;
 }
 
 class IterableSpan {
@@ -216,7 +214,7 @@ class IterableSpan {
   /// 10000-length subset and 1 1-length subset.
   int get maxPowerOfSubsetSize =>
       (log(length - .5) / log(_maxSpanLength)).truncate();
-  int get subsetSize => pow(_maxSpanLength, maxPowerOfSubsetSize);
+  int get subsetSize => pow(_maxSpanLength, maxPowerOfSubsetSize).toInt();
 
   Map<int, dynamic> asMap() =>
       iterable.skip(start).take(length).toList().asMap();
@@ -284,7 +282,7 @@ safeProperties(object) => Map.fromIterable(
 /// Devtools Formatter API.
 class JsonMLElement {
   dynamic _attributes;
-  List _jsonML;
+  late List _jsonML;
 
   JsonMLElement(tagName) {
     _attributes = JS('', '{}');
@@ -408,7 +406,7 @@ class JsonMLFormatter {
       // The value is indented when it is on a different line from the name
       // by setting right padding of the name to -13px and the padding of the
       // value to 13px.
-      JsonMLElement nameSpan;
+      JsonMLElement? nameSpan;
       var valueStyle = '';
       if (!child.hideName) {
         nameSpan = JsonMLElement('span')
@@ -444,38 +442,36 @@ class JsonMLFormatter {
 
 abstract class Formatter {
   bool accept(object, config);
-  String preview(object);
+  String? preview(object);
   bool hasChildren(object);
-  List<NameValuePair> children(object);
+  List<NameValuePair>? children(object);
 }
 
 class DartFormatter {
-  List<Formatter> _formatters;
+  final List<Formatter> _formatters;
 
-  DartFormatter() {
-    // The order of formatters matters as formatters earlier in the list take
-    // precedence.
-    _formatters = [
-      ObjectInternalsFormatter(),
-      ClassFormatter(),
-      TypeFormatter(),
-      NamedConstructorFormatter(),
-      MapFormatter(),
-      MapOverviewFormatter(),
-      IterableFormatter(),
-      IterableSpanFormatter(),
-      MapEntryFormatter(),
-      StackTraceFormatter(),
-      ErrorAndExceptionFormatter(),
-      FunctionFormatter(),
-      HeritageClauseFormatter(),
-      LibraryModuleFormatter(),
-      LibraryFormatter(),
-      ObjectFormatter(),
-    ];
-  }
+  DartFormatter()
+      : _formatters = [
+          // Formatters earlier in the list take precedence.
+          ObjectInternalsFormatter(),
+          ClassFormatter(),
+          TypeFormatter(),
+          NamedConstructorFormatter(),
+          MapFormatter(),
+          MapOverviewFormatter(),
+          IterableFormatter(),
+          IterableSpanFormatter(),
+          MapEntryFormatter(),
+          StackTraceFormatter(),
+          ErrorAndExceptionFormatter(),
+          FunctionFormatter(),
+          HeritageClauseFormatter(),
+          LibraryModuleFormatter(),
+          LibraryFormatter(),
+          ObjectFormatter(),
+        ];
 
-  String preview(object, config) {
+  String? preview(object, config) {
     try {
       if (object == null ||
           object is num ||
@@ -509,7 +505,7 @@ class DartFormatter {
     return false;
   }
 
-  List<NameValuePair> children(object, config) {
+  List<NameValuePair>? children(object, config) {
     try {
       if (object != null) {
         for (var formatter in _formatters) {
@@ -558,7 +554,7 @@ class ObjectFormatter extends Formatter {
 
   bool hasChildren(object) => true;
 
-  List<NameValuePair> children(object) {
+  children(object) {
     var type = dart.getType(object);
     var ret = LinkedHashSet<NameValuePair>();
     // We use a Set rather than a List to avoid duplicates.
@@ -591,12 +587,12 @@ class ObjectInternalsFormatter extends ObjectFormatter {
 
 /// Formatter for module Dart Library objects.
 class LibraryModuleFormatter implements Formatter {
-  accept(object, config) => dart.getModuleName(object) != null;
+  bool accept(object, config) => dart.getModuleName(object) != null;
 
   bool hasChildren(object) => true;
 
   String preview(object) {
-    var libraryNames = dart.getModuleName(object).split('/');
+    var libraryNames = dart.getModuleName(object)!.split('/');
     // Library names are received with a repeat directory name, so strip the
     // last directory entry here to make the path cleaner. For example, the
     // library "third_party/dart/utf/utf" shoud display as
@@ -622,7 +618,7 @@ class LibraryModuleFormatter implements Formatter {
 class LibraryFormatter implements Formatter {
   var genericParameters = HashMap<String, String>();
 
-  accept(object, config) => object is Library;
+  bool accept(object, config) => object is Library;
 
   bool hasChildren(object) => true;
 
@@ -657,7 +653,7 @@ class LibraryFormatter implements Formatter {
 /// we can distinguish them based on whether they have been tagged with
 /// runtime type information.
 class FunctionFormatter implements Formatter {
-  accept(object, config) {
+  bool accept(object, config) {
     if (_typeof(object) != 'function') return false;
     return dart.getReifiedType(object) != null;
   }
@@ -690,7 +686,7 @@ class FunctionFormatter implements Formatter {
 class MapOverviewFormatter implements Formatter {
   // Because this comes after MapFormatter in the list, internal
   // maps will be picked up by that formatter.
-  accept(object, config) => object is Map;
+  bool accept(object, config) => object is Map;
 
   bool hasChildren(object) => true;
 
@@ -718,7 +714,7 @@ class MapOverviewFormatter implements Formatter {
 /// This is only used for internal maps, or when shown as [[entries]]
 /// from MapOverViewFormatter.
 class MapFormatter implements Formatter {
-  accept(object, config) =>
+  bool accept(object, config) =>
       object is InternalMap || config == JsonMLConfig.asMap;
 
   bool hasChildren(object) => true;
@@ -779,7 +775,7 @@ class IterableFormatter implements Formatter {
 }
 
 class NamedConstructorFormatter implements Formatter {
-  accept(object, config) => object is NamedConstructor;
+  bool accept(object, config) => object is NamedConstructor;
 
   // TODO(bmilligan): Display the signature of the named constructor as the
   // preview.
@@ -798,7 +794,7 @@ class NamedConstructorFormatter implements Formatter {
 /// Formatter for synthetic MapEntry objects used to display contents of a Map
 /// cleanly.
 class MapEntryFormatter implements Formatter {
-  accept(object, config) => object is MapEntry;
+  bool accept(object, config) => object is MapEntry;
 
   String preview(object) {
     MapEntry entry = object;
@@ -839,7 +835,7 @@ class HeritageClauseFormatter implements Formatter {
 /// Formatter for synthetic IterableSpan objects used to display contents of
 /// an Iterable cleanly.
 class IterableSpanFormatter implements Formatter {
-  accept(object, config) => object is IterableSpan;
+  bool accept(object, config) => object is IterableSpan;
 
   String preview(object) {
     return '[${object.start}...${object.end - 1}]';
@@ -854,7 +850,7 @@ class IterableSpanFormatter implements Formatter {
 class ErrorAndExceptionFormatter extends ObjectFormatter {
   static final RegExp _pattern = RegExp(r'\d+\:\d+');
 
-  accept(object, config) => object is Error || object is Exception;
+  bool accept(object, config) => object is Error || object is Exception;
 
   bool hasChildren(object) => true;
 
@@ -867,8 +863,8 @@ class ErrorAndExceptionFormatter extends ObjectFormatter {
             l.contains(_pattern) &&
             !l.contains('dart:sdk') &&
             !l.contains('dart_sdk'),
-        orElse: () => null);
-    return line != null ? '${object} at ${line}' : '${object}';
+        orElse: () => '');
+    return line != '' ? '${object} at ${line}' : '${object}';
   }
 
   List<NameValuePair> children(object) {
@@ -890,7 +886,7 @@ class ErrorAndExceptionFormatter extends ObjectFormatter {
 }
 
 class StackTraceFormatter implements Formatter {
-  accept(object, config) => object is StackTrace;
+  bool accept(object, config) => object is StackTrace;
 
   String preview(object) => 'StackTrace';
 
@@ -908,13 +904,13 @@ class StackTraceFormatter implements Formatter {
 }
 
 class ClassFormatter implements Formatter {
-  accept(object, config) => config == JsonMLConfig.asClass;
+  bool accept(object, config) => config == JsonMLConfig.asClass;
 
   String preview(type) {
-    var implements = dart.getImplements(type);
+    var implements = dart.getImplements(type)();
     var typeName = getTypeName(type);
     if (implements != null) {
-      var typeNames = implements().map(getTypeName);
+      var typeNames = implements.map(getTypeName);
       return '${typeName} implements ${typeNames.join(", ")}';
     } else {
       return typeName;
@@ -979,7 +975,7 @@ class ClassFormatter implements Formatter {
 }
 
 class TypeFormatter implements Formatter {
-  accept(object, config) => object is Type;
+  bool accept(object, config) => object is Type;
 
   String preview(object) => object.toString();
 
@@ -995,7 +991,7 @@ typedef String StackTraceMapper(String stackTrace);
 ///
 /// Raw JS stack traces are used if $dartStackTraceUtility has not been
 /// specified.
-StackTraceMapper get stackTraceMapper {
+StackTraceMapper? get stackTraceMapper {
   var _util = JS('', r'#.$dartStackTraceUtility', dart.global_);
   return _util != null ? JS('!', '#.mapper', _util) : null;
 }

sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._foreign_helper;
 
 /**
@@ -108,7 +106,7 @@ library dart._foreign_helper;
  */
 // Add additional optional arguments if needed. The method is treated internally
 // as a variable argument method.
-T JS<T extends Object>(String typeDescription, String codeTemplate,
+external T JS<T extends Object?>(String typeDescription, String codeTemplate,
     [arg0,
     arg1,
     arg2,
@@ -128,7 +126,7 @@ T JS<T extends Object>(String typeDescription, String codeTemplate,
     arg16,
     arg17,
     arg18,
-    arg19]) {}
+    arg19]);
 
 /// Annotates the compiled Js name for fields and methods.
 /// Similar behaviour to `JS` from `package:js/js.dart` (but usable from runtime
@@ -161,73 +159,73 @@ JS_INTERCEPTOR_CONSTANT(Type type) {}
 /**
  * Returns the prefix used for generated is checks on classes.
  */
-String JS_OPERATOR_IS_PREFIX() {}
+external String JS_OPERATOR_IS_PREFIX();
 
 /**
  * Returns the prefix used for generated type argument substitutions on classes.
  */
-String JS_OPERATOR_AS_PREFIX() {}
+external String JS_OPERATOR_AS_PREFIX();
 
 /// Returns the name of the class `Object` in the generated code.
-String JS_OBJECT_CLASS_NAME() {}
+external String JS_OBJECT_CLASS_NAME();
 
 /// Returns the name of the class `Null` in the generated code.
-String JS_NULL_CLASS_NAME() {}
+external String JS_NULL_CLASS_NAME();
 
 /// Returns the name of the class `Function` in the generated code.
-String JS_FUNCTION_CLASS_NAME() {}
+external String JS_FUNCTION_CLASS_NAME();
 
 /**
  * Returns the field name used for determining if an object or its
  * interceptor has JavaScript indexing behavior.
  */
-String JS_IS_INDEXABLE_FIELD_NAME() {}
+external String JS_IS_INDEXABLE_FIELD_NAME();
 
 /// Returns the name used for generated function types on classes and methods.
-String JS_SIGNATURE_NAME() {}
+external String JS_SIGNATURE_NAME();
 
 /// Returns the name used to tag typedefs.
-String JS_TYPEDEF_TAG() {}
+external String JS_TYPEDEF_TAG();
 
 /// Returns the name used to tag function type representations in JavaScript.
-String JS_FUNCTION_TYPE_TAG() {}
+external String JS_FUNCTION_TYPE_TAG();
 
 /**
  * Returns the name used to tag void return in function type representations
  * in JavaScript.
  */
-String JS_FUNCTION_TYPE_VOID_RETURN_TAG() {}
+external String JS_FUNCTION_TYPE_VOID_RETURN_TAG();
 
 /**
  * Returns the name used to tag return types in function type representations
  * in JavaScript.
  */
-String JS_FUNCTION_TYPE_RETURN_TYPE_TAG() {}
+external String JS_FUNCTION_TYPE_RETURN_TYPE_TAG();
 
 /**
  * Returns the name used to tag required parameters in function type
  * representations in JavaScript.
  */
-String JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG() {}
+external String JS_FUNCTION_TYPE_REQUIRED_PARAMETERS_TAG();
 
 /**
  * Returns the name used to tag optional parameters in function type
  * representations in JavaScript.
  */
-String JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG() {}
+external String JS_FUNCTION_TYPE_OPTIONAL_PARAMETERS_TAG();
 
 /**
  * Returns the name used to tag named parameters in function type
  * representations in JavaScript.
  */
-String JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG() {}
+external String JS_FUNCTION_TYPE_NAMED_PARAMETERS_TAG();
 
 /// Returns the JS name for [name] from the Namer.
-String JS_GET_NAME(String name) {}
+external String JS_GET_NAME(String name);
 
 /// Returns the state of a flag that is determined by the state of the compiler
 /// when the program has been analyzed.
-bool JS_GET_FLAG(String name) {}
+external bool JS_GET_FLAG(String name);
 
 /**
  * Pretend [code] is executed.  Generates no executable code.  This is used to

sdk/lib/_internal/js_dev_runtime/private/identity_hash_map.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 class IdentityMap<K, V> extends InternalMap<K, V> {
@@ -35,11 +33,11 @@ class IdentityMap<K, V> extends InternalMap<K, V> {
   Iterable<K> get keys => _JSMapIterable<K>(this, true);
   Iterable<V> get values => _JSMapIterable<V>(this, false);
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     return JS<bool>('!', '#.has(#)', _map, key);
   }
 
-  bool containsValue(Object value) {
+  bool containsValue(Object? value) {
     for (var v in JS('', '#.values()', _map)) {
       if (v == value) return true;
     }
@@ -56,7 +54,7 @@ class IdentityMap<K, V> extends InternalMap<K, V> {
     }
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     V value = JS('', '#.get(#)', _map, key);
     return value == null ? null : value; // coerce undefined to null.
   }
@@ -75,13 +73,13 @@ class IdentityMap<K, V> extends InternalMap<K, V> {
       return JS('', '#.get(#)', _map, key);
     }
     V value = ifAbsent();
-    if (value == null) value = null; // coerce undefined to null.
+    if (value == null) JS('', '# = null', value);
     JS('', '#.set(#, #)', _map, key, value);
     _modifications = (_modifications + 1) & 0x3ffffff;
     return value;
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     V value = JS('', '#.get(#)', _map, key);
     if (JS<bool>('!', '#.delete(#)', _map, key)) {
       _modifications = (_modifications + 1) & 0x3ffffff;
@@ -130,10 +128,10 @@ class _JSMapIterable<E> extends EfficientLengthIterable<E> {
 
   Iterator<E> get iterator => DartIterator<E>(_jsIterator());
 
-  bool contains(Object element) =>
+  bool contains(Object? element) =>
       _isKeys ? _map.containsKey(element) : _map.containsValue(element);
 
-  void forEach(void f(E element)) {
+  void forEach(void Function(E) f) {
     for (var entry in this) f(entry);
   }
 }

sdk/lib/_internal/js_dev_runtime/private/interceptors.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._interceptors;
 
 import 'dart:collection';
@@ -122,15 +120,15 @@ class JSNoSuchMethodError extends NativeError implements NoSuchMethodError {
   static final _extensionName = RegExp(r"^Symbol\(dartx\.(.+)\)$");
   static final _privateName = RegExp(r"^Symbol\((_.+)\)$");
 
-  String _fieldName(String message) {
-    var match = _nullError.firstMatch(message);
+  String? _fieldName(String message) {
+    RegExpMatch? match = _nullError.firstMatch(message);
     if (match == null) return null;
-    var name = match[1];
+    String name = match[1]!;
     match = _extensionName.firstMatch(name) ?? _privateName.firstMatch(name);
     return match != null ? match[1] : name;
   }
 
-  String _functionCallTarget(String message) {
+  String? _functionCallTarget(String message) {
     var match = _notAFunction.firstMatch(message);
     return match != null ? match[1] : null;
   }
@@ -180,7 +178,7 @@ class JSFunction extends Interceptor {
   // TODO(jmesserly): remove these once we canonicalize tearoffs.
   operator ==(other) {
     if (other == null) return false;
-    var boundObj = JS<Object>('', '#._boundObject', this);
+    var boundObj = JS<Object?>('', '#._boundObject', this);
     if (boundObj == null) return JS<bool>('!', '# === #', this, other);
     return JS(
         'bool',
@@ -192,7 +190,7 @@ class JSFunction extends Interceptor {
   }
 
   get hashCode {
-    var boundObj = JS<Object>('', '#._boundObject', this);
+    var boundObj = JS<Object?>('', '#._boundObject', this);
     if (boundObj == null) return identityHashCode(this);
 
     var boundMethod = JS<Object>('!', '#._boundMethod', this);
@@ -229,7 +227,7 @@ class JSRangeError extends Interceptor implements ArgumentError {
 // Warning: calls to these methods need to be removed before custom elements
 // and cross-frame dom objects behave correctly in ddc.
 // See https://github.com/dart-lang/sdk/issues/28326
-findInterceptorConstructorForType(Type type) {}
-findConstructorForNativeSubclassType(Type type, String name) {}
+findInterceptorConstructorForType(Type? type) {}
+findConstructorForNativeSubclassType(Type? type, String name) {}
 getNativeInterceptor(object) {}
 setDispatchProperty(object, value) {}

sdk/lib/_internal/js_dev_runtime/private/isolate_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._isolate_helper;
 
 import 'dart:_runtime' as dart;
@@ -36,7 +34,7 @@ final global = dart.global_;
 
 class TimerImpl implements Timer {
   final bool _once;
-  int _handle;
+  int? _handle;
   int _tick = 0;
 
   TimerImpl(int milliseconds, void callback()) : _once = true {

sdk/lib/_internal/js_dev_runtime/private/js_array.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._interceptors;
 
 /**
@@ -120,7 +118,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return JS('var', r'#.pop()', this);
   }
 
-  bool remove(Object element) {
+  bool remove(Object? element) {
     checkGrowable('remove');
     var length = this.length;
     for (int i = 0; i < length; i++) {
@@ -135,17 +133,17 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
   /**
    * Removes elements matching [test] from [this] List.
    */
-  void removeWhere(bool test(E element)) {
+  void removeWhere(bool Function(E) test) {
     checkGrowable('removeWhere');
     _removeWhere(test, true);
   }
 
-  void retainWhere(bool test(E element)) {
+  void retainWhere(bool Function(E) test) {
     checkGrowable('retainWhere');
     _removeWhere(test, false);
   }
 
-  void _removeWhere(bool test(E element), bool removeMatching) {
+  void _removeWhere(bool Function(E) test, bool removeMatching) {
     // Performed in two steps, to avoid exposing an inconsistent state
     // to the [test] function. First the elements to retain are found, and then
     // the original list is updated to contain those elements.
@@ -156,8 +154,6 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     List retained = [];
     int end = this.length;
     for (int i = 0; i < end; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       // !test() ensures bool conversion in checked mode.
       if (!test(element) == removeMatching) {
@@ -174,11 +170,11 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     }
   }
 
-  Iterable<E> where(bool f(E element)) {
+  Iterable<E> where(bool Function(E) f) {
     return WhereIterable<E>(this, f);
   }
 
-  Iterable<T> expand<T>(Iterable<T> f(E element)) {
+  Iterable<T> expand<T>(Iterable<T> Function(E) f) {
     return ExpandIterable<E, T>(this, f);
   }
 
@@ -196,24 +192,22 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     length = 0;
   }
 
-  void forEach(void f(E element)) {
+  void forEach(void Function(E) f) {
     int end = this.length;
     for (int i = 0; i < end; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       f(element);
       if (this.length != end) throw ConcurrentModificationError(this);
     }
   }
 
-  Iterable<T> map<T>(T f(E element)) {
+  Iterable<T> map<T>(T Function(E) f) {
     return MappedListIterable<E, T>(this, f);
   }
 
   String join([String separator = ""]) {
     var length = this.length;
-    var list = List(length);
+    var list = List<String>.filled(length, "");
     for (int i = 0; i < length; i++) {
       list[i] = "${this[i]}";
     }
@@ -232,7 +226,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return SubListIterable<E>(this, n, null);
   }
 
-  Iterable<E> skipWhile(bool test(E value)) {
+  Iterable<E> skipWhile(bool Function(E) test) {
     return SkipWhileIterable<E>(this, test);
   }
 
@@ -241,8 +235,6 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     if (length == 0) throw IterableElementError.noElement();
     E value = this[0];
     for (int i = 1; i < length; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       value = combine(value, element);
       if (length != this.length) throw ConcurrentModificationError(this);
@@ -250,12 +242,10 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return value;
   }
 
-  T fold<T>(T initialValue, T combine(T previousValue, E element)) {
+  T fold<T>(T initialValue, T Function(T previousValue, E element) combine) {
     var value = initialValue;
     int length = this.length;
     for (int i = 0; i < length; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       value = combine(value, element);
       if (this.length != length) throw ConcurrentModificationError(this);
@@ -263,11 +253,9 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return value;
   }
 
-  E firstWhere(bool test(E value), {E orElse()}) {
+  E firstWhere(bool Function(E) test, {E Function()? orElse}) {
     int end = this.length;
     for (int i = 0; i < end; ++i) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       if (test(element)) return element;
       if (this.length != end) throw ConcurrentModificationError(this);
@@ -276,11 +264,9 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     throw IterableElementError.noElement();
   }
 
-  E lastWhere(bool test(E element), {E orElse()}) {
+  E lastWhere(bool Function(E) test, {E Function()? orElse}) {
     int length = this.length;
     for (int i = length - 1; i >= 0; i--) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       if (test(element)) return element;
       if (length != this.length) {
@@ -291,13 +277,11 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     throw IterableElementError.noElement();
   }
 
-  E singleWhere(bool test(E element), {E orElse()}) {
+  E singleWhere(bool Function(E) test, {E Function()? orElse}) {
     int length = this.length;
-    E match = null;
+    E? match = null;
     bool matchFound = false;
     for (int i = 0; i < length; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       if (test(element)) {
         if (matchFound) {
@@ -310,7 +294,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
         throw ConcurrentModificationError(this);
       }
     }
-    if (matchFound) return match;
+    if (matchFound) return match as E;
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
   }
@@ -319,7 +303,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return this[index];
   }
 
-  List<E> sublist(@nullCheck int start, [int end]) {
+  List<E> sublist(@nullCheck int start, [int? end]) {
     if (start < 0 || start > length) {
       throw RangeError.range(start, 0, length, "start");
     }
@@ -373,7 +357,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     if (length == 0) return;
     RangeError.checkNotNegative(skipCount, "skipCount");
 
-    List<E> otherList;
+    var otherList = <E>[];
     int otherStart = 0;
     // TODO(floitsch): Make this accept more.
     if (iterable is List<E>) {
@@ -405,12 +389,12 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     }
   }
 
-  void fillRange(@nullCheck int start, @nullCheck int end, [E fillValue]) {
+  void fillRange(@nullCheck int start, @nullCheck int end, [E? fillValue]) {
     checkMutable('fill range');
     RangeError.checkValidRange(start, end, this.length);
+    E checkedFillValue = fillValue as E;
     for (int i = start; i < end; i++) {
-      // Store is safe since [fillValue] type has been checked as parameter.
-      JS('', '#[#] = #', this, i, fillValue);
+      JS('', '#[#] = #', this, i, checkedFillValue);
     }
   }
 
@@ -443,11 +427,9 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     }
   }
 
-  bool any(bool test(E element)) {
+  bool any(bool Function(E) test) {
     int end = this.length;
     for (int i = 0; i < end; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       if (test(element)) return true;
       if (this.length != end) throw ConcurrentModificationError(this);
@@ -455,11 +437,9 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return false;
   }
 
-  bool every(bool test(E element)) {
+  bool every(bool Function(E) test) {
     int end = this.length;
     for (int i = 0; i < end; i++) {
-      // TODO(22407): Improve bounds check elimination to allow this JS code to
-      // be replaced by indexing.
       var element = JS<E>('', '#[#]', this, i);
       if (!test(element)) return false;
       if (this.length != end) throw ConcurrentModificationError(this);
@@ -469,16 +449,17 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
 
   Iterable<E> get reversed => ReversedListIterable<E>(this);
 
-  void sort([int compare(E a, E b)]) {
+  void sort([int Function(E, E)? compare]) {
     checkMutable('sort');
     if (compare == null) {
-      Sort.sort(this, (a, b) => Comparable.compare(a, b));
+      Sort.sort(
+          this, (a, b) => Comparable.compare(a as Comparable, b as Comparable));
     } else {
       Sort.sort(this, compare);
     }
   }
 
-  void shuffle([Random random]) {
+  void shuffle([Random? random]) {
     checkMutable('shuffle');
     if (random == null) random = Random();
     int length = this.length;
@@ -491,7 +472,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     }
   }
 
-  int indexOf(Object element, [@nullCheck int start = 0]) {
+  int indexOf(Object? element, [@nullCheck int start = 0]) {
     int length = this.length;
     if (start >= length) {
       return -1;
@@ -507,15 +488,15 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return -1;
   }
 
-  int lastIndexOf(Object element, [int _startIndex]) {
+  int lastIndexOf(Object? element, [int? startIndex]) {
     @notNull
-    int startIndex = _startIndex ?? this.length - 1;
-    if (startIndex >= this.length) {
-      startIndex = this.length - 1;
-    } else if (startIndex < 0) {
+    int start = startIndex ?? this.length - 1;
+    if (start >= this.length) {
+      start = this.length - 1;
+    } else if (start < 0) {
       return -1;
     }
-    for (int i = startIndex; i >= 0; i--) {
+    for (int i = start; i >= 0; i--) {
       if (this[i] == element) {
         return i;
       }
@@ -523,7 +504,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return -1;
   }
 
-  bool contains(Object other) {
+  bool contains(Object? other) {
     var length = this.length;
     for (int i = 0; i < length; i++) {
       var element = JS<E>('', '#[#]', this, i);
@@ -601,15 +582,9 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
 
   Iterable<T> whereType<T>() => new WhereTypeIterable<T>(this);
 
-  List<E> operator +(List<E> other) {
-    int totalLength = this.length + other.length;
-    return <E>[]
-      ..length = totalLength
-      ..setRange(0, this.length, this)
-      ..setRange(this.length, totalLength, other);
-  }
+  List<E> operator +(List<E> other) => [...this, ...other];
 
-  int indexWhere(bool test(E element), [int start = 0]) {
+  int indexWhere(bool Function(E) test, [int start = 0]) {
     if (start >= this.length) return -1;
     if (start < 0) start = 0;
     for (int i = start; i < this.length; i++) {
@@ -618,7 +593,7 @@ class JSArray<E> implements List<E>, JSIndexable<E> {
     return -1;
   }
 
-  int lastIndexWhere(bool test(E element), [int start]) {
+  int lastIndexWhere(bool Function(E) test, [int? start]) {
     if (start == null) start = this.length - 1;
     if (start < 0) return -1;
     for (int i = start; i >= 0; i--) {
@@ -665,14 +640,14 @@ class ArrayIterator<E> implements Iterator<E> {
   final int _length;
   @notNull
   int _index;
-  E _current;
+  E? _current;
 
   ArrayIterator(JSArray<E> iterable)
       : _iterable = iterable,
         _length = iterable.length,
         _index = 0;
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     @notNull

sdk/lib/_internal/js_dev_runtime/private/js_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library dart._js_helper;
 
 import 'dart:collection';
@@ -45,11 +43,11 @@ const _Patch patch = _Patch();
 // https://github.com/dart-lang/sdk/issues/28320
 class DartIterator<E> implements Iterator<E> {
   final _jsIterator;
-  E _current;
+  E? _current;
 
   DartIterator(this._jsIterator);
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     final ret = JS('', '#.next()', _jsIterator);
@@ -70,11 +68,11 @@ class SyncIterable<E> extends IterableBase<E> {
 }
 
 class Primitives {
-  static int parseInt(@nullCheck String source, int _radix) {
+  static int? parseInt(@nullCheck String source, int? _radix) {
     var re = JS('', r'/^\s*[+-]?((0x[a-f0-9]+)|(\d+)|([a-z0-9]+))\s*$/i');
     // TODO(jmesserly): this isn't reified List<String>, but it's safe to use as
     // long as we use it locally and don't expose it to user code.
-    List<String> match = JS('', '#.exec(#)', re, source);
+    List<String>? match = JS('', '#.exec(#)', re, source);
     int digitsIndex = 1;
     int hexIndex = 2;
     int decimalIndex = 3;
@@ -84,7 +82,7 @@ class Primitives {
       // again.
       return null;
     }
-    String decimalMatch = match[decimalIndex];
+    String? decimalMatch = match[decimalIndex];
     if (_radix == null) {
       if (decimalMatch != null) {
         // Cannot fail because we know that the digits are all decimal.
@@ -140,7 +138,7 @@ class Primitives {
     return JS<int>('!', r'parseInt(#, #)', source, radix);
   }
 
-  static double parseDouble(@nullCheck String source) {
+  static double? parseDouble(@nullCheck String source) {
     // Notice that JS parseFloat accepts garbage at the end of the string.
     // Accept only:
     // - [+/-]NaN
@@ -171,10 +169,9 @@ class Primitives {
   static int dateNow() => JS<int>('!', r'Date.now()');
 
   static void initTicker() {
-    if (timerFrequency != null) return;
+    if (timerFrequency != 0) return;
     // Start with low-resolution. We overwrite the fields if we find better.
     timerFrequency = 1000;
-    timerTicks = dateNow;
     if (JS<bool>('!', 'typeof window == "undefined"')) return;
     var jsWindow = JS('var', 'window');
     if (jsWindow == null) return;
@@ -185,8 +182,9 @@ class Primitives {
     timerTicks = () => (1000 * JS<num>('!', '#.now()', performance)).floor();
   }
 
-  static int timerFrequency;
-  static num Function() timerTicks;
+  /// 0 frequency indicates the default uninitialized state.
+  static int timerFrequency = 0;
+  static int Function() timerTicks = dateNow; // Low-resolution version.
 
   static bool get isD8 {
     return JS(
@@ -310,7 +308,7 @@ class Primitives {
     // Example: "Wed May 16 2012 21:13:00 GMT+0200 (CEST)".
     // We extract this name using a regexp.
     var d = lazyAsJsDate(receiver);
-    List match = JS('JSArray|Null', r'/\((.*)\)/.exec(#.toString())', d);
+    List? match = JS('JSArray|Null', r'/\((.*)\)/.exec(#.toString())', d);
     if (match != null) return match[1];
 
     // Internet Explorer 10+ emits the zone name without parenthesis:
@@ -345,7 +343,7 @@ class Primitives {
     return -JS<int>('!', r'#.getTimezoneOffset()', lazyAsJsDate(receiver));
   }
 
-  static num valueFromDecomposedDate(
+  static int? valueFromDecomposedDate(
       @nullCheck int years,
       @nullCheck int month,
       @nullCheck int day,
@@ -356,12 +354,12 @@ class Primitives {
       @nullCheck bool isUtc) {
     final int MAX_MILLISECONDS_SINCE_EPOCH = 8640000000000000;
     var jsMonth = month - 1;
-    num value;
+    int value;
     if (isUtc) {
-      value = JS('!', r'Date.UTC(#, #, #, #, #, #, #)', years, jsMonth, day,
-          hours, minutes, seconds, milliseconds);
+      value = JS<int>('!', r'Date.UTC(#, #, #, #, #, #, #)', years, jsMonth,
+          day, hours, minutes, seconds, milliseconds);
     } else {
-      value = JS('!', r'new Date(#, #, #, #, #, #, #).valueOf()', years,
+      value = JS<int>('!', r'new Date(#, #, #, #, #, #, #).valueOf()', years,
           jsMonth, day, hours, minutes, seconds, milliseconds);
     }
     if (value.isNaN ||
@@ -373,14 +371,14 @@ class Primitives {
     return value;
   }
 
-  static num patchUpY2K(value, years, isUtc) {
-    var date = JS('', r'new Date(#)', value);
+  static int patchUpY2K(value, years, isUtc) {
+    var date = JS<int>('!', r'new Date(#)', value);
     if (isUtc) {
-      JS('', r'#.setUTCFullYear(#)', date, years);
+      JS<int>('!', r'#.setUTCFullYear(#)', date, years);
     } else {
-      JS('', r'#.setFullYear(#)', date, years);
+      JS<int>('!', r'#.setFullYear(#)', date, years);
     }
-    return JS('!', r'#.valueOf()', date);
+    return JS<int>('!', r'#.valueOf()', date);
   }
 
   // Lazily keep a JS Date stored in the JS object.
@@ -453,7 +451,7 @@ class Primitives {
     return value;
   }
 
-  static getProperty(object, key) {
+  static Object? getProperty(Object? object, Object key) {
     if (object == null || object is bool || object is num || object is String) {
       throw argumentErrorValue(object);
     }
@@ -489,7 +487,7 @@ Error diagnoseIndexError(indexable, int index) {
  * describes the problem.
  */
 @NoInline()
-Error diagnoseRangeError(int start, int end, int length) {
+Error diagnoseRangeError(int? start, int? end, int length) {
   if (start == null) {
     return ArgumentError.value(start, 'start');
   }
@@ -538,9 +536,9 @@ throwConcurrentModificationError(collection) {
 }
 
 class JsNoSuchMethodError extends Error implements NoSuchMethodError {
-  final String _message;
-  final String _method;
-  final String _receiver;
+  final String? _message;
+  final String? _method;
+  final String? _receiver;
 
   JsNoSuchMethodError(this._message, match)
       : _method = match == null ? null : JS('String|Null', '#.method', match),
@@ -582,11 +580,11 @@ fillLiteralMap(keyValuePairs, Map result) {
   return result;
 }
 
-bool jsHasOwnProperty(var jsObject, String property) {
+bool jsHasOwnProperty(jsObject, String property) {
   return JS<bool>('!', r'#.hasOwnProperty(#)', jsObject, property);
 }
 
-jsPropertyAccess(var jsObject, String property) {
+jsPropertyAccess(jsObject, String property) {
   return JS('var', r'#[#]', jsObject, property);
 }
 
@@ -720,12 +718,12 @@ class RuntimeError extends Error {
 
 /// Error thrown by DDC when an `assert()` fails (with or without a message).
 class AssertionErrorImpl extends AssertionError {
-  final String _fileUri;
-  final int _line;
-  final int _column;
-  final String _conditionSource;
+  final String? _fileUri;
+  final int? _line;
+  final int? _column;
+  final String? _conditionSource;
 
-  AssertionErrorImpl(Object message,
+  AssertionErrorImpl(Object? message,
       [this._fileUri, this._line, this._column, this._conditionSource])
       : super(message);
 
@@ -791,7 +789,7 @@ class PrivateSymbol implements Symbol {
 
   static String getName(Symbol symbol) => (symbol as PrivateSymbol)._name;
 
-  static Object getNativeSymbol(Symbol symbol) {
+  static Object? getNativeSymbol(Symbol symbol) {
     if (symbol is PrivateSymbol) return symbol._nativeSymbol;
     return null;
   }

sdk/lib/_internal/js_dev_runtime/private/js_number.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._interceptors;
 
 /**
@@ -55,14 +53,14 @@ class JSNumber extends Interceptor implements int, double {
 
   @notNull
   JSNumber remainder(@nullCheck num b) {
-    return JS<num>('!', r'# % #', this, b);
+    return JS<JSNumber>('!', r'# % #', this, b);
   }
 
   @notNull
-  JSNumber abs() => JS<num>('!', r'Math.abs(#)', this);
+  JSNumber abs() => JS<JSNumber>('!', r'Math.abs(#)', this);
 
   @notNull
-  JSNumber get sign => this > 0 ? 1 : this < 0 ? -1 : this;
+  JSNumber get sign => (this > 0 ? 1 : this < 0 ? -1 : this) as JSNumber;
 
   @notNull
   static const int _MIN_INT32 = -0x80000000;
@@ -112,17 +110,17 @@ class JSNumber extends Interceptor implements int, double {
   }
 
   @notNull
-  double ceilToDouble() => JS<num>('!', r'Math.ceil(#)', this);
+  double ceilToDouble() => JS<double>('!', r'Math.ceil(#)', this);
 
   @notNull
-  double floorToDouble() => JS<num>('!', r'Math.floor(#)', this);
+  double floorToDouble() => JS<double>('!', r'Math.floor(#)', this);
 
   @notNull
   double roundToDouble() {
     if (this < 0) {
-      return JS<num>('!', r'-Math.round(-#)', this);
+      return JS<double>('!', r'-Math.round(-#)', this);
     } else {
-      return JS<num>('!', r'Math.round(#)', this);
+      return JS<double>('!', r'Math.round(#)', this);
     }
   }
 
@@ -153,7 +151,7 @@ class JSNumber extends Interceptor implements int, double {
   }
 
   @notNull
-  String toStringAsExponential([int fractionDigits]) {
+  String toStringAsExponential([int? fractionDigits]) {
     String result;
     if (fractionDigits != null) {
       @notNull
@@ -196,7 +194,7 @@ class JSNumber extends Interceptor implements int, double {
   static String _handleIEtoString(String result) {
     // Result is probably IE's untraditional format for large numbers,
     // e.g., "8.0000000000008(e+15)" for 0x8000000000000800.toString(16).
-    var match = JS<List>(
+    var match = JS<List?>(
         '', r'/^([\da-z]+)(?:\.([\da-z]+))?\(e\+(\d+)\)$/.exec(#)', result);
     if (match == null) {
       // Then we don't know how to handle it at all.
@@ -258,38 +256,38 @@ class JSNumber extends Interceptor implements int, double {
   }
 
   @notNull
-  JSNumber operator -() => JS<num>('!', r'-#', this);
+  JSNumber operator -() => JS<JSNumber>('!', r'-#', this);
 
   @notNull
   JSNumber operator +(@nullCheck num other) {
-    return JS<num>('!', '# + #', this, other);
+    return JS<JSNumber>('!', '# + #', this, other);
   }
 
   @notNull
   JSNumber operator -(@nullCheck num other) {
-    return JS<num>('!', '# - #', this, other);
+    return JS<JSNumber>('!', '# - #', this, other);
   }
 
   @notNull
   double operator /(@nullCheck num other) {
-    return JS<num>('!', '# / #', this, other);
+    return JS<double>('!', '# / #', this, other);
   }
 
   @notNull
   JSNumber operator *(@nullCheck num other) {
-    return JS<num>('!', '# * #', this, other);
+    return JS<JSNumber>('!', '# * #', this, other);
   }
 
   @notNull
   JSNumber operator %(@nullCheck num other) {
     // Euclidean Modulo.
-    num result = JS<num>('!', r'# % #', this, other);
+    JSNumber result = JS<JSNumber>('!', r'# % #', this, other);
     if (result == 0) return (0 as JSNumber); // Make sure we don't return -0.0.
     if (result > 0) return result;
-    if (JS<num>('!', '#', other) < 0) {
-      return result - JS<num>('!', '#', other);
+    if (JS<JSNumber>('!', '#', other) < 0) {
+      return result - JS<JSNumber>('!', '#', other);
     } else {
-      return result + JS<num>('!', '#', other);
+      return result + JS<JSNumber>('!', '#', other);
     }
   }
 
@@ -308,7 +306,7 @@ class JSNumber extends Interceptor implements int, double {
 
   @notNull
   int _tdivSlow(num other) {
-    return (JS<num>('!', r'# / #', this, other)).toInt();
+    return JS<num>('!', r'# / #', this, other).toInt();
   }
 
   // TODO(ngeoffray): Move the bit operations below to [JSInt] and

sdk/lib/_internal/js_dev_runtime/private/js_primitives.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// dart2js "primitives", that is, features that cannot be implemented without
 /// access to JavaScript features.
 library dart2js._js_primitives;

sdk/lib/_internal/js_dev_runtime/private/js_rti.dart

@@ -2,28 +2,26 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 // TODO(leafp): Maybe get rid of this?  Currently used by the interceptors
 // library, but that should probably be culled as well.
-Type getRuntimeType(var object) =>
+Type? getRuntimeType(object) =>
     JS('Type|null', 'dart.getReifiedType(#)', object);
 
 /// Returns the property [index] of the JavaScript array [array].
-getIndex(var array, int index) {
+getIndex(array, int index) {
   assert(isJsArray(array));
   return JS('var', r'#[#]', array, index);
 }
 
 /// Returns the length of the JavaScript array [array].
-int getLength(var array) {
+int getLength(array) {
   assert(isJsArray(array));
   return JS<int>('!', r'#.length', array);
 }
 
 /// Returns whether [value] is a JavaScript array.
-bool isJsArray(var value) {
+bool isJsArray(value) {
   return value is JSArray;
 }

sdk/lib/_internal/js_dev_runtime/private/js_string.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._interceptors;
 
 /**
@@ -37,7 +35,7 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
     return allMatchesInStringUnchecked(this, string, start);
   }
 
-  Match matchAsPrefix(@nullCheck String string, [@nullCheck int start = 0]) {
+  Match? matchAsPrefix(@nullCheck String string, [@nullCheck int start = 0]) {
     int stringLength = JS('!', '#.length', string);
     if (start < 0 || start > stringLength) {
       throw RangeError.range(start, 0, stringLength);
@@ -71,13 +69,13 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
   }
 
   @notNull
-  String replaceAllMapped(Pattern from, String convert(Match match)) {
+  String replaceAllMapped(Pattern from, String Function(Match) convert) {
     return this.splitMapJoin(from, onMatch: convert);
   }
 
   @notNull
   String splitMapJoin(Pattern from,
-      {String onMatch(Match match), String onNonMatch(String nonMatch)}) {
+      {String Function(Match)? onMatch, String Function(String)? onNonMatch}) {
     return stringReplaceAllFuncUnchecked(this, from, onMatch, onNonMatch);
   }
 
@@ -110,9 +108,9 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
 
   @notNull
   String replaceRange(
-      @nullCheck int start, int end, @nullCheck String replacement) {
-    end = RangeError.checkValidRange(start, end, this.length);
-    return stringReplaceRangeUnchecked(this, start, end, replacement);
+      @nullCheck int start, int? end, @nullCheck String replacement) {
+    var e = RangeError.checkValidRange(start, end, this.length);
+    return stringReplaceRangeUnchecked(this, start, e, replacement);
   }
 
   @notNull
@@ -166,7 +164,7 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
   }
 
   @notNull
-  String substring(@nullCheck int startIndex, [int _endIndex]) {
+  String substring(@nullCheck int startIndex, [int? _endIndex]) {
     var length = this.length;
     final endIndex = _endIndex ?? length;
     if (startIndex < 0) throw RangeError.value(startIndex);
@@ -418,7 +416,7 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
     }
     if (pattern is JSSyntaxRegExp) {
       JSSyntaxRegExp re = pattern;
-      Match match = firstMatchAfter(re, this, start);
+      Match? match = firstMatchAfter(re, this, start);
       return (match == null) ? -1 : match.start;
     }
     var length = this.length;
@@ -429,7 +427,7 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
   }
 
   @notNull
-  int lastIndexOf(@nullCheck Pattern pattern, [int _start]) {
+  int lastIndexOf(@nullCheck Pattern pattern, [int? _start]) {
     var length = this.length;
     var start = _start ?? length;
     if (start < 0 || start > length) {
@@ -497,7 +495,7 @@ class JSString extends Interceptor implements String, JSIndexable<String> {
   Type get runtimeType => String;
 
   @notNull
-  final int length;
+  int get length native;
 
   @notNull
   String operator [](@nullCheck int index) {

sdk/lib/_internal/js_dev_runtime/private/linked_hash_map.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Efficient JavaScript based implementation of a linked hash map used as a
 // backing map for constant maps and the [LinkedHashMap] patch
 
@@ -74,7 +72,7 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
       K key = JS('', '#[#]', entries, i);
       V value = JS('', '#[#]', entries, i + 1);
       if (key == null) {
-        key = null;
+        key = JS('', 'null');
       } else if (JS<bool>('!', '#[#] !== #', key,
           dart.extensionSymbol('_equals'), dart.identityEquals)) {
         key = putLinkedMapKey(key, keyMap);
@@ -96,17 +94,15 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
   Iterable<V> get values => _JSMapIterable<V>(this, false);
 
   @notNull
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (key == null) {
-      key = null;
+      key = JS('', 'null');
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
-      @notNull
-      var k = key;
-      var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, k.hashCode);
+      var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, key.hashCode);
       if (buckets != null) {
         for (int i = 0, n = JS('!', '#.length', buckets); i < n; i++) {
-          k = JS('', '#[#]', buckets, i);
+          K k = JS('', '#[#]', buckets, i);
           if (k == key) return true;
         }
       }
@@ -115,7 +111,7 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
     return JS<bool>('!', '#.has(#)', _map, key);
   }
 
-  bool containsValue(Object value) {
+  bool containsValue(Object? value) {
     for (var v in JS('', '#.values()', _map)) {
       if (v == value) return true;
     }
@@ -127,7 +123,7 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
     int length = JS('', '#.size', map);
     other.forEach((K key, V value) {
       if (key == null) {
-        key = null;
+        key = JS('', 'null');
       } else if (JS<bool>('!', '#[#] !== #', key,
           dart.extensionSymbol('_equals'), dart.identityEquals)) {
         key = putLinkedMapKey(key, _keyMap);
@@ -139,17 +135,15 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
     }
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (key == null) {
-      key = null;
+      key = JS('', 'null');
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
-      @notNull
-      var k = key;
-      var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, k.hashCode);
+      var buckets = JS('', '#.get(# & 0x3ffffff)', _keyMap, key.hashCode);
       if (buckets != null) {
         for (int i = 0, n = JS('!', '#.length', buckets); i < n; i++) {
-          k = JS('', '#[#]', buckets, i);
+          K k = JS('', '#[#]', buckets, i);
           if (k == key) return JS('', '#.get(#)', _map, k);
         }
       }
@@ -161,7 +155,7 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
 
   void operator []=(K key, V value) {
     if (key == null) {
-      key = null;
+      key = JS('', 'null');
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       key = putLinkedMapKey(key, _keyMap);
@@ -177,7 +171,7 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
   V putIfAbsent(K key, V ifAbsent()) {
     var map = _map;
     if (key == null) {
-      key = null;
+      key = JS('', 'null');
       if (JS<bool>('!', '#.has(null)', map)) return JS('', '#.get(null)', map);
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
@@ -198,24 +192,25 @@ class LinkedMap<K, V> extends InternalMap<K, V> {
       return JS('', '#.get(#)', map, key);
     }
     V value = ifAbsent();
-    if (value == null) value = null; // coerce undefined to null.
+    if (value == null) {
+      value = JS('', 'null');
+    }
     JS('', '#.set(#, #)', map, key, value);
     _modifications = (_modifications + 1) & 0x3ffffff;
     return value;
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (key == null) {
-      key = null;
+      key = JS('', 'null');
     } else if (JS<bool>('!', '#[#] !== #', key, dart.extensionSymbol('_equals'),
         dart.identityEquals)) {
       @notNull
-      var k = key;
-      var hash = JS<int>('!', '# & 0x3ffffff', k.hashCode);
+      var hash = JS<int>('!', '# & 0x3ffffff', key.hashCode);
       var buckets = JS('', '#.get(#)', _keyMap, hash);
       if (buckets == null) return null; // not found
       for (int i = 0, n = JS('!', '#.length', buckets);;) {
-        k = JS('', '#[#]', buckets, i);
+        K k = JS('', '#[#]', buckets, i);
         if (k == key) {
           key = k;
           if (n == 1) {
@@ -266,14 +261,14 @@ K putLinkedMapKey<K>(@notNull K key, keyMap) {
 class ImmutableMap<K, V> extends LinkedMap<K, V> {
   ImmutableMap.from(JSArray entries) : super.from(entries);
 
-  void operator []=(Object key, Object value) {
+  void operator []=(K key, V value) {
     throw _unsupported();
   }
 
   void addAll(Object other) => throw _unsupported();
   void clear() => throw _unsupported();
-  V remove(Object key) => throw _unsupported();
-  V putIfAbsent(Object key, Object ifAbsent()) => throw _unsupported();
+  V? remove(Object? key) => throw _unsupported();
+  V putIfAbsent(K key, V ifAbsent()) => throw _unsupported();
 
   static Error _unsupported() =>
       UnsupportedError("Cannot modify unmodifiable map");

sdk/lib/_internal/js_dev_runtime/private/mirror_helper.dart

@@ -1,7 +1,6 @@
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
-// @dart = 2.6
 
 /**
  * Helps dealing with reflection in the case that the source code has been

sdk/lib/_internal/js_dev_runtime/private/native_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 // Obsolete in dart dev compiler. Added only so that the same version of

sdk/lib/_internal/js_dev_runtime/private/native_typed_data.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// Specialized integers and floating point numbers,
 /// with SIMD support and efficient lists.
 library dart.typed_data.implementation;
@@ -32,69 +30,69 @@ class NativeByteBuffer implements ByteBuffer {
 
   Type get runtimeType => ByteBuffer;
 
-  Uint8List asUint8List([int offsetInBytes = 0, int length]) {
+  Uint8List asUint8List([int offsetInBytes = 0, int? length]) {
     return NativeUint8List.view(this, offsetInBytes, length);
   }
 
-  Int8List asInt8List([int offsetInBytes = 0, int length]) {
+  Int8List asInt8List([int offsetInBytes = 0, int? length]) {
     return NativeInt8List.view(this, offsetInBytes, length);
   }
 
-  Uint8ClampedList asUint8ClampedList([int offsetInBytes = 0, int length]) {
+  Uint8ClampedList asUint8ClampedList([int offsetInBytes = 0, int? length]) {
     return NativeUint8ClampedList.view(this, offsetInBytes, length);
   }
 
-  Uint16List asUint16List([int offsetInBytes = 0, int length]) {
+  Uint16List asUint16List([int offsetInBytes = 0, int? length]) {
     return NativeUint16List.view(this, offsetInBytes, length);
   }
 
-  Int16List asInt16List([int offsetInBytes = 0, int length]) {
+  Int16List asInt16List([int offsetInBytes = 0, int? length]) {
     return NativeInt16List.view(this, offsetInBytes, length);
   }
 
-  Uint32List asUint32List([int offsetInBytes = 0, int length]) {
+  Uint32List asUint32List([int offsetInBytes = 0, int? length]) {
     return NativeUint32List.view(this, offsetInBytes, length);
   }
 
-  Int32List asInt32List([int offsetInBytes = 0, int length]) {
+  Int32List asInt32List([int offsetInBytes = 0, int? length]) {
     return NativeInt32List.view(this, offsetInBytes, length);
   }
 
-  Uint64List asUint64List([int offsetInBytes = 0, int length]) {
+  Uint64List asUint64List([int offsetInBytes = 0, int? length]) {
     throw UnsupportedError("Uint64List not supported by dart2js.");
   }
 
-  Int64List asInt64List([int offsetInBytes = 0, int length]) {
+  Int64List asInt64List([int offsetInBytes = 0, int? length]) {
     throw UnsupportedError("Int64List not supported by dart2js.");
   }
 
-  Int32x4List asInt32x4List([int offsetInBytes = 0, int length]) {
-    NativeInt32List storage =
+  Int32x4List asInt32x4List([int offsetInBytes = 0, int? length]) {
+    var storage =
         this.asInt32List(offsetInBytes, length != null ? length * 4 : null);
     return NativeInt32x4List._externalStorage(storage);
   }
 
-  Float32List asFloat32List([int offsetInBytes = 0, int length]) {
+  Float32List asFloat32List([int offsetInBytes = 0, int? length]) {
     return NativeFloat32List.view(this, offsetInBytes, length);
   }
 
-  Float64List asFloat64List([int offsetInBytes = 0, int length]) {
+  Float64List asFloat64List([int offsetInBytes = 0, int? length]) {
     return NativeFloat64List.view(this, offsetInBytes, length);
   }
 
-  Float32x4List asFloat32x4List([int offsetInBytes = 0, int length]) {
-    NativeFloat32List storage =
+  Float32x4List asFloat32x4List([int offsetInBytes = 0, int? length]) {
+    var storage =
         this.asFloat32List(offsetInBytes, length != null ? length * 4 : null);
     return NativeFloat32x4List._externalStorage(storage);
   }
 
-  Float64x2List asFloat64x2List([int offsetInBytes = 0, int length]) {
-    NativeFloat64List storage =
+  Float64x2List asFloat64x2List([int offsetInBytes = 0, int? length]) {
+    var storage =
         this.asFloat64List(offsetInBytes, length != null ? length * 2 : null);
     return NativeFloat64x2List._externalStorage(storage);
   }
 
-  ByteData asByteData([int offsetInBytes = 0, int length]) {
+  ByteData asByteData([int offsetInBytes = 0, int? length]) {
     return NativeByteData.view(this, offsetInBytes, length);
   }
 }
@@ -105,7 +103,7 @@ class NativeByteBuffer implements ByteBuffer {
 class NativeFloat32x4List extends Object
     with ListMixin<Float32x4>, FixedLengthListMixin<Float32x4>
     implements Float32x4List {
-  final NativeFloat32List _storage;
+  final Float32List _storage;
 
   /// Creates a [Float32x4List] of the specified length (in elements),
   /// all of whose elements are initially zero.
@@ -164,10 +162,10 @@ class NativeFloat32x4List extends Object
     _storage[(index * 4) + 3] = value.w;
   }
 
-  Float32x4List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Float32x4List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     return NativeFloat32x4List._externalStorage(
-        _storage.sublist(start * 4, end * 4));
+        _storage.sublist(start * 4, stop * 4));
   }
 }
 
@@ -236,10 +234,10 @@ class NativeInt32x4List extends Object
     _storage[(index * 4) + 3] = value.w;
   }
 
-  Int32x4List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Int32x4List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     return NativeInt32x4List._externalStorage(
-        _storage.sublist(start * 4, end * 4));
+        _storage.sublist(start * 4, stop * 4));
   }
 }
 
@@ -249,7 +247,7 @@ class NativeInt32x4List extends Object
 class NativeFloat64x2List extends Object
     with ListMixin<Float64x2>, FixedLengthListMixin<Float64x2>
     implements Float64x2List {
-  final NativeFloat64List _storage;
+  final Float64List _storage;
 
   /// Creates a [Float64x2List] of the specified length (in elements),
   /// all of whose elements are initially zero.
@@ -302,10 +300,10 @@ class NativeFloat64x2List extends Object
     _storage[(index * 2) + 1] = value.y;
   }
 
-  Float64x2List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Float64x2List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     return NativeFloat64x2List._externalStorage(
-        _storage.sublist(start * 2, end * 2));
+        _storage.sublist(start * 2, stop * 2));
   }
 }
 
@@ -313,8 +311,7 @@ class NativeFloat64x2List extends Object
 class NativeTypedData implements TypedData {
   /// Returns the byte buffer associated with this object.
   @Creates('NativeByteBuffer')
-  // May be Null for IE's CanvasPixelArray.
-  @Returns('NativeByteBuffer|Null')
+  @Returns('NativeByteBuffer')
   external ByteBuffer get buffer;
 
   /// Returns the length of this view, in bytes.
@@ -366,7 +363,7 @@ void _checkViewArguments(buffer, offsetInBytes, length) {
   if (offsetInBytes is! int) {
     throw ArgumentError('Invalid view offsetInBytes $offsetInBytes');
   }
-  if (length != null && length is! int) {
+  if (length is! int?) {
     throw ArgumentError('Invalid view length $length');
   }
 }
@@ -375,7 +372,7 @@ void _checkViewArguments(buffer, offsetInBytes, length) {
 // returns a copy of the list.
 List _ensureNativeList(List list) {
   if (list is JSIndexable) return list;
-  List result = List(list.length);
+  List result = List.filled(list.length, null);
   for (int i = 0; i < list.length; i++) {
     result[i] = list[i];
   }
@@ -399,7 +396,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
   /// if [offsetInBytes] + ([length] * elementSizeInBytes) is greater than
   /// the length of [buffer].
   factory NativeByteData.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -421,7 +418,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getFloat32')
   @Returns('double')
-  double _getFloat32(int byteOffset, [bool littleEndian]) native;
+  double _getFloat32(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the floating point number represented by the eight bytes at
   /// the specified [byteOffset] in this object, in IEEE 754
@@ -434,7 +431,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getFloat64')
   @Returns('double')
-  double _getFloat64(int byteOffset, [bool littleEndian]) native;
+  double _getFloat64(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the (possibly negative) integer represented by the two bytes at
   /// the specified [byteOffset] in this object, in two's complement binary
@@ -449,7 +446,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getInt16')
   @Returns('int')
-  int _getInt16(int byteOffset, [bool littleEndian]) native;
+  int _getInt16(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the (possibly negative) integer represented by the four bytes at
   /// the specified [byteOffset] in this object, in two's complement binary
@@ -464,7 +461,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getInt32')
   @Returns('int')
-  int _getInt32(int byteOffset, [bool littleEndian]) native;
+  int _getInt32(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the (possibly negative) integer represented by the eight bytes at
   /// the specified [byteOffset] in this object, in two's complement binary
@@ -498,7 +495,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getUint16')
   @Returns('int')
-  int _getUint16(int byteOffset, [bool littleEndian]) native;
+  int _getUint16(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the positive integer represented by the four bytes starting
   /// at the specified [byteOffset] in this object, in unsigned binary
@@ -512,7 +509,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
 
   @JSName('getUint32')
   @Returns('int')
-  int _getUint32(int byteOffset, [bool littleEndian]) native;
+  int _getUint32(int byteOffset, [bool? littleEndian]) native;
 
   /// Returns the positive integer represented by the eight bytes starting
   /// at the specified [byteOffset] in this object, in unsigned binary
@@ -552,7 +549,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setFloat32(byteOffset, value, Endian.little == endian);
 
   @JSName('setFloat32')
-  void _setFloat32(int byteOffset, num value, [bool littleEndian]) native;
+  void _setFloat32(int byteOffset, num value, [bool? littleEndian]) native;
 
   /// Sets the eight bytes starting at the specified [byteOffset] in this
   /// object to the IEEE 754 double-precision binary floating-point
@@ -564,7 +561,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setFloat64(byteOffset, value, Endian.little == endian);
 
   @JSName('setFloat64')
-  void _setFloat64(int byteOffset, num value, [bool littleEndian]) native;
+  void _setFloat64(int byteOffset, num value, [bool? littleEndian]) native;
 
   /// Sets the two bytes starting at the specified [byteOffset] in this
   /// object to the two's complement binary representation of the specified
@@ -577,7 +574,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setInt16(byteOffset, value, Endian.little == endian);
 
   @JSName('setInt16')
-  void _setInt16(int byteOffset, int value, [bool littleEndian]) native;
+  void _setInt16(int byteOffset, int value, [bool? littleEndian]) native;
 
   /// Sets the four bytes starting at the specified [byteOffset] in this
   /// object to the two's complement binary representation of the specified
@@ -590,7 +587,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setInt32(byteOffset, value, Endian.little == endian);
 
   @JSName('setInt32')
-  void _setInt32(int byteOffset, int value, [bool littleEndian]) native;
+  void _setInt32(int byteOffset, int value, [bool? littleEndian]) native;
 
   /// Sets the eight bytes starting at the specified [byteOffset] in this
   /// object to the two's complement binary representation of the specified
@@ -623,7 +620,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setUint16(byteOffset, value, Endian.little == endian);
 
   @JSName('setUint16')
-  void _setUint16(int byteOffset, int value, [bool littleEndian]) native;
+  void _setUint16(int byteOffset, int value, [bool? littleEndian]) native;
 
   /// Sets the four bytes starting at the specified [byteOffset] in this object
   /// to the unsigned binary representation of the specified [value],
@@ -636,7 +633,7 @@ class NativeByteData extends NativeTypedData implements ByteData {
       _setUint32(byteOffset, value, Endian.little == endian);
 
   @JSName('setUint32')
-  void _setUint32(int byteOffset, int value, [bool littleEndian]) native;
+  void _setUint32(int byteOffset, int value, [bool? littleEndian]) native;
 
   /// Sets the eight bytes starting at the specified [byteOffset] in this object
   /// to the unsigned binary representation of the specified [value],
@@ -751,7 +748,7 @@ class NativeFloat32List extends NativeTypedArrayOfDouble
       _create1(_ensureNativeList(elements));
 
   factory NativeFloat32List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -760,10 +757,10 @@ class NativeFloat32List extends NativeTypedArrayOfDouble
 
   Type get runtimeType => Float32List;
 
-  Float32List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Float32List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     var source =
-        JS<NativeFloat32List>('!', '#.subarray(#, #)', this, start, end);
+        JS<NativeFloat32List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -786,7 +783,7 @@ class NativeFloat64List extends NativeTypedArrayOfDouble
       _create1(_ensureNativeList(elements));
 
   factory NativeFloat64List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -795,9 +792,9 @@ class NativeFloat64List extends NativeTypedArrayOfDouble
 
   Type get runtimeType => Float64List;
 
-  Float64List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
-    var source = JS('NativeFloat64List', '#.subarray(#, #)', this, start, end);
+  Float64List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
+    var source = JS('NativeFloat64List', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -819,7 +816,7 @@ class NativeInt16List extends NativeTypedArrayOfInt implements Int16List {
       _create1(_ensureNativeList(elements));
 
   factory NativeInt16List.view(
-      NativeByteBuffer buffer, int offsetInBytes, int length) {
+      NativeByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -833,9 +830,9 @@ class NativeInt16List extends NativeTypedArrayOfInt implements Int16List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Int16List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
-    var source = JS('NativeInt16List', '#.subarray(#, #)', this, start, end);
+  Int16List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
+    var source = JS('NativeInt16List', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -857,7 +854,7 @@ class NativeInt32List extends NativeTypedArrayOfInt implements Int32List {
       _create1(_ensureNativeList(elements));
 
   factory NativeInt32List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -871,9 +868,10 @@ class NativeInt32List extends NativeTypedArrayOfInt implements Int32List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Int32List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
-    var source = JS<NativeInt32List>('!', '#.subarray(#, #)', this, start, end);
+  Int32List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
+    var source =
+        JS<NativeInt32List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -895,7 +893,7 @@ class NativeInt8List extends NativeTypedArrayOfInt implements Int8List {
       _create1(_ensureNativeList(elements));
 
   factory NativeInt8List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -909,9 +907,9 @@ class NativeInt8List extends NativeTypedArrayOfInt implements Int8List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Int8List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
-    var source = JS<NativeInt8List>('!', '#.subarray(#, #)', this, start, end);
+  Int8List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
+    var source = JS<NativeInt8List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -921,7 +919,7 @@ class NativeInt8List extends NativeTypedArrayOfInt implements Int8List {
   static NativeInt8List _create2(arg1, arg2) =>
       JS<NativeInt8List>('!', 'new Int8Array(#, #)', arg1, arg2);
 
-  static Int8List _create3(arg1, arg2, arg3) =>
+  static NativeInt8List _create3(arg1, arg2, arg3) =>
       JS<NativeInt8List>('!', 'new Int8Array(#, #, #)', arg1, arg2, arg3);
 }
 
@@ -933,7 +931,7 @@ class NativeUint16List extends NativeTypedArrayOfInt implements Uint16List {
       _create1(_ensureNativeList(list));
 
   factory NativeUint16List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -947,10 +945,10 @@ class NativeUint16List extends NativeTypedArrayOfInt implements Uint16List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Uint16List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Uint16List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     var source =
-        JS<NativeUint16List>('!', '#.subarray(#, #)', this, start, end);
+        JS<NativeUint16List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -972,7 +970,7 @@ class NativeUint32List extends NativeTypedArrayOfInt implements Uint32List {
       _create1(_ensureNativeList(elements));
 
   factory NativeUint32List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -986,10 +984,10 @@ class NativeUint32List extends NativeTypedArrayOfInt implements Uint32List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Uint32List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Uint32List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     var source =
-        JS<NativeUint32List>('!', '#.subarray(#, #)', this, start, end);
+        JS<NativeUint32List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -1012,7 +1010,7 @@ class NativeUint8ClampedList extends NativeTypedArrayOfInt
       _create1(_ensureNativeList(elements));
 
   factory NativeUint8ClampedList.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -1028,10 +1026,10 @@ class NativeUint8ClampedList extends NativeTypedArrayOfInt
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Uint8ClampedList sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
+  Uint8ClampedList sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
     var source =
-        JS<NativeUint8ClampedList>('!', '#.subarray(#, #)', this, start, end);
+        JS<NativeUint8ClampedList>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -1062,7 +1060,7 @@ class NativeUint8List extends NativeTypedArrayOfInt implements Uint8List {
       _create1(_ensureNativeList(elements));
 
   factory NativeUint8List.view(
-      ByteBuffer buffer, int offsetInBytes, int length) {
+      ByteBuffer buffer, int offsetInBytes, int? length) {
     _checkViewArguments(buffer, offsetInBytes, length);
     return length == null
         ? _create2(buffer, offsetInBytes)
@@ -1078,9 +1076,10 @@ class NativeUint8List extends NativeTypedArrayOfInt implements Uint8List {
     return JS<int>('!', '#[#]', this, index);
   }
 
-  Uint8List sublist(int start, [int end]) {
-    end = _checkValidRange(start, end, this.length);
-    var source = JS<NativeUint8List>('!', '#.subarray(#, #)', this, start, end);
+  Uint8List sublist(int start, [int? end]) {
+    var stop = _checkValidRange(start, end, this.length);
+    var source =
+        JS<NativeUint8List>('!', '#.subarray(#, #)', this, start, stop);
     return _create1(source);
   }
 
@@ -1466,7 +1465,7 @@ class NativeInt32x4 implements Int32x4 {
     floatList[1] = f.y;
     floatList[2] = f.z;
     floatList[3] = f.w;
-    NativeInt32List view = floatList.buffer.asInt32List();
+    Int32List view = floatList.buffer.asInt32List();
     return NativeInt32x4._truncated(view[0], view[1], view[2], view[3]);
   }
 
@@ -1684,7 +1683,7 @@ class NativeFloat64x2 implements Float64x2 {
   final double y;
 
   static NativeFloat64List _list = NativeFloat64List(2);
-  static NativeUint32List _uint32View = _list.buffer.asUint32List();
+  static Uint32List _uint32View = _list.buffer.asUint32List();
 
   NativeFloat64x2(this.x, this.y) {
     if (x is! num) throw ArgumentError(x);
@@ -1815,7 +1814,7 @@ void _checkValidIndex(int index, List list, int length) {
 ///
 /// Returns the actual value of `end`, which is `length` if `end` is `null`, and
 /// the original value of `end` otherwise.
-int _checkValidRange(int start, int end, int length) {
+int _checkValidRange(int start, int? end, int length) {
   if (_isInvalidArrayIndex(start) || // Ensures start is non-negative int.
       ((end == null)
           ? start > length

sdk/lib/_internal/js_dev_runtime/private/profile.dart

@@ -2,19 +2,15 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 /// This file supports profiling dynamic calls.
 part of dart._debugger;
 
 class _MethodStats {
   final String typeName;
   final String frame;
-  double count;
+  double count = 0.0;
 
-  _MethodStats(this.typeName, this.frame) {
-    count = 0.0;
-  }
+  _MethodStats(this.typeName, this.frame);
 }
 
 class _CallMethodRecord {
@@ -29,7 +25,7 @@ int _callRecordSampleSize = 5000;
 
 /// If the number of dynamic calls exceeds [_callRecordSampleSize] this list
 /// will represent a random sample of the dynamic calls made.
-List<_CallMethodRecord> _callMethodRecords = List();
+var _callMethodRecords = <_CallMethodRecord>[];
 
 /// If the number of dynamic calls exceeds [_callRecordSampleSize] this value
 /// will be greater than [_callMethodRecords.length].
@@ -45,7 +41,7 @@ num _minCount = 2;
 /// speedup lookup of source map frames when running the profiler.
 /// The number of source map entries looked up makes caching more important
 /// in this case than for typical source map use cases.
-Map<String, String> _frameMappingCache = Map();
+var _frameMappingCache = <String, String>{};
 
 List<List<Object>> getDynamicStats() {
   // Process the accumulated method stats. This may be quite slow as processing
@@ -56,7 +52,7 @@ List<List<Object>> getDynamicStats() {
   // raw number of dynamic calls so that the magnitude of the dynamic call
   // performance hit is clear to users.
 
-  Map<String, _MethodStats> callMethodStats = Map();
+  var callMethodStats = <String, _MethodStats>{};
   if (_callMethodRecords.length > 0) {
     // Ratio between total record count and sampled records count.
     var recordRatio = _totalCallRecords / _callMethodRecords.length;
@@ -67,8 +63,8 @@ List<List<Object>> getDynamicStats() {
       // runtime.
       var src = frames
           .skip(2)
-          .map((f) =>
-              _frameMappingCache.putIfAbsent(f, () => stackTraceMapper('\n$f')))
+          .map((f) => _frameMappingCache.putIfAbsent(
+              f, () => stackTraceMapper!('\n$f')))
           .firstWhere((f) => !f.startsWith('dart:'), orElse: () => '');
 
       var actualTypeName = dart.typeName(record.type);
@@ -83,7 +79,7 @@ List<List<Object>> getDynamicStats() {
     // complete profile.
     if (_totalCallRecords != _callMethodRecords.length) {
       for (var k in callMethodStats.keys.toList()) {
-        var stats = callMethodStats[k];
+        var stats = callMethodStats[k]!;
         var threshold = _minCount * recordRatio;
         if (stats.count + 0.001 < threshold) {
           callMethodStats.remove(k);
@@ -94,12 +90,11 @@ List<List<Object>> getDynamicStats() {
   _callMethodRecords.clear();
   _totalCallRecords = 0;
   var keys = callMethodStats.keys.toList();
-
   keys.sort(
-      (a, b) => callMethodStats[b].count.compareTo(callMethodStats[a].count));
-  List<List<Object>> ret = [];
+      (a, b) => callMethodStats[b]!.count.compareTo(callMethodStats[a]!.count));
+  var ret = <List<Object>>[];
   for (var key in keys) {
-    var stats = callMethodStats[key];
+    var stats = callMethodStats[key]!;
     ret.add([stats.typeName, stats.frame, stats.count.round()]);
   }
   return ret;

sdk/lib/_internal/js_dev_runtime/private/regexp_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 // Helper method used by internal libraries.
@@ -117,10 +115,11 @@ class JSSyntaxRegExp implements RegExp {
     throw FormatException("Illegal RegExp pattern: $source, $errorMessage");
   }
 
-  RegExpMatch firstMatch(@nullCheck String string) {
-    List m = JS('JSExtendableArray|Null', r'#.exec(#)', _nativeRegExp, string);
+  RegExpMatch? firstMatch(@nullCheck String string) {
+    List<String>? m =
+        JS('JSExtendableArray|Null', r'#.exec(#)', _nativeRegExp, string);
     if (m == null) return null;
-    return _MatchImplementation(this, JSArray<String>.of(m));
+    return _MatchImplementation(this, m);
   }
 
   @notNull
@@ -128,7 +127,7 @@ class JSSyntaxRegExp implements RegExp {
     return JS<bool>('!', r'#.test(#)', _nativeRegExp, string);
   }
 
-  String stringMatch(String string) {
+  String? stringMatch(String string) {
     var match = firstMatch(string);
     if (match != null) return match.group(0);
     return null;
@@ -142,27 +141,29 @@ class JSSyntaxRegExp implements RegExp {
     return _AllMatchesIterable(this, string, start);
   }
 
-  RegExpMatch _execGlobal(String string, int start) {
+  RegExpMatch? _execGlobal(String string, int start) {
     Object regexp = _nativeGlobalVersion;
     JS("void", "#.lastIndex = #", regexp, start);
-    List match = JS("JSExtendableArray|Null", "#.exec(#)", regexp, string);
+    List<String>? match =
+        JS("JSExtendableArray|Null", "#.exec(#)", regexp, string);
     if (match == null) return null;
-    return _MatchImplementation(this, JSArray<String>.of(match));
+    return _MatchImplementation(this, match);
   }
 
-  RegExpMatch _execAnchored(String string, int start) {
+  RegExpMatch? _execAnchored(String string, int start) {
     Object regexp = _nativeAnchoredVersion;
     JS("void", "#.lastIndex = #", regexp, start);
-    List match = JS("JSExtendableArray|Null", "#.exec(#)", regexp, string);
+    List<String>? match =
+        JS("JSExtendableArray|Null", "#.exec(#)", regexp, string);
     if (match == null) return null;
     // If the last capture group participated, the original regexp did not
     // match at the start position.
     if (match[match.length - 1] != null) return null;
     match.length -= 1;
-    return _MatchImplementation(this, JSArray<String>.of(match));
+    return _MatchImplementation(this, match);
   }
 
-  RegExpMatch matchAsPrefix(String string, [int start = 0]) {
+  Match? matchAsPrefix(String string, [int start = 0]) {
     if (start < 0 || start > string.length) {
       throw RangeError.range(start, 0, string.length);
     }
@@ -190,22 +191,22 @@ class _MatchImplementation implements RegExpMatch {
   int get start => JS("int", "#.index", _match);
   int get end => start + _match[0].length;
 
-  String group(int index) => _match[index];
-  String operator [](int index) => group(index);
+  String? group(int index) => _match[index];
+  String? operator [](int index) => group(index);
   int get groupCount => _match.length - 1;
 
-  List<String> groups(List<int> groups) {
-    List<String> out = [];
+  List<String?> groups(List<int> groups) {
+    List<String?> out = [];
     for (int i in groups) {
       out.add(group(i));
     }
     return out;
   }
 
-  String namedGroup(String name) {
-    var groups = JS('Object|Null', '#.groups', _match);
+  String? namedGroup(String name) {
+    var groups = JS<Object?>('Object|Null', '#.groups', _match);
     if (groups != null) {
-      var result = JS('String|Null', '#[#]', groups, name);
+      var result = JS<String?>('', '#[#]', groups, name);
       if (result != null || JS<bool>('!', '# in #', name, groups)) {
         return result;
       }
@@ -214,7 +215,7 @@ class _MatchImplementation implements RegExpMatch {
   }
 
   Iterable<String> get groupNames {
-    var groups = JS('Object|Null', '#.groups', _match);
+    var groups = JS<Object?>('Object|Null', '#.groups', _match);
     if (groups != null) {
       var keys = JSArray<String>.of(JS('', 'Object.keys(#)', groups));
       return SubListIterable(keys, 0, null);
@@ -236,13 +237,13 @@ class _AllMatchesIterable extends IterableBase<RegExpMatch> {
 
 class _AllMatchesIterator implements Iterator<RegExpMatch> {
   final JSSyntaxRegExp _regExp;
-  String _string;
+  String? _string;
   int _nextIndex;
-  RegExpMatch _current;
+  RegExpMatch? _current;
 
   _AllMatchesIterator(this._regExp, this._string, this._nextIndex);
 
-  RegExpMatch get current => _current;
+  RegExpMatch get current => _current as RegExpMatch;
 
   static bool _isLeadSurrogate(int c) {
     return c >= 0xd800 && c <= 0xdbff;
@@ -253,9 +254,10 @@ class _AllMatchesIterator implements Iterator<RegExpMatch> {
   }
 
   bool moveNext() {
-    if (_string == null) return false;
-    if (_nextIndex <= _string.length) {
-      var match = _regExp._execGlobal(_string, _nextIndex);
+    var string = _string;
+    if (string == null) return false;
+    if (_nextIndex <= string.length) {
+      var match = _regExp._execGlobal(string, _nextIndex);
       if (match != null) {
         _current = match;
         int nextIndex = match.end;
@@ -264,9 +266,9 @@ class _AllMatchesIterator implements Iterator<RegExpMatch> {
           // is in unicode mode and it would put us within a surrogate
           // pair. In that case, advance past the code point as a whole.
           if (_regExp.isUnicode &&
-              _nextIndex + 1 < _string.length &&
-              _isLeadSurrogate(_string.codeUnitAt(_nextIndex)) &&
-              _isTrailSurrogate(_string.codeUnitAt(_nextIndex + 1))) {
+              _nextIndex + 1 < string.length &&
+              _isLeadSurrogate(string.codeUnitAt(_nextIndex)) &&
+              _isTrailSurrogate(string.codeUnitAt(_nextIndex + 1))) {
             nextIndex++;
           }
           nextIndex++;
@@ -282,6 +284,6 @@ class _AllMatchesIterator implements Iterator<RegExpMatch> {
 }
 
 /** Find the first match of [regExp] in [string] at or after [start]. */
-RegExpMatch firstMatchAfter(JSSyntaxRegExp regExp, String string, int start) {
+RegExpMatch? firstMatchAfter(JSSyntaxRegExp regExp, String string, int start) {
   return regExp._execGlobal(string, start);
 }

sdk/lib/_internal/js_dev_runtime/private/string_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of dart._js_helper;
 
 @notNull
@@ -41,7 +39,7 @@ class StringMatch implements Match {
   }
 
   List<String> groups(List<int> groups_) {
-    List<String> result = List<String>();
+    List<String> result = <String>[];
     for (int g in groups_) {
       result.add(group(g));
     }
@@ -81,7 +79,7 @@ class _StringAllMatchesIterator implements Iterator<Match> {
   final String _input;
   final String _pattern;
   int _index;
-  Match _current;
+  Match? _current;
 
   _StringAllMatchesIterator(this._input, this._pattern, this._index);
 
@@ -104,7 +102,7 @@ class _StringAllMatchesIterator implements Iterator<Match> {
     return true;
   }
 
-  Match get current => _current;
+  Match get current => _current!;
 }
 
 @notNull
@@ -176,15 +174,15 @@ String stringReplaceAllUnchecked(@notNull String receiver,
   }
 }
 
-String _matchString(Match match) => match[0];
+String _matchString(Match match) => match[0]!;
 String _stringIdentity(String string) => string;
 
 @notNull
 String stringReplaceAllFuncUnchecked(
     String receiver,
     @nullCheck Pattern pattern,
-    String onMatch(Match match),
-    String onNonMatch(String nonMatch)) {
+    String Function(Match)? onMatch,
+    String Function(String)? onNonMatch) {
   if (onMatch == null) onMatch = _matchString;
   if (onNonMatch == null) onNonMatch = _stringIdentity;
   if (pattern is String) {

sdk/lib/_internal/js_runtime/lib/annotations.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of _js_helper;
 
 /// Marks a class as native and defines its JavaScript name(s).

sdk/lib/_internal/js_runtime/lib/async_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for the dart:async library.
 
 import 'dart:_js_helper'
@@ -122,7 +120,7 @@ class Timer {
 
 class _TimerImpl implements Timer {
   final bool _once;
-  int _handle;
+  int? _handle;
   int _tick = 0;
 
   _TimerImpl(int milliseconds, void callback()) : _once = true {
@@ -197,15 +195,24 @@ class _AsyncAwaitCompleter<T> implements Completer<T> {
 
   _AsyncAwaitCompleter() : isSync = false;
 
-  void complete([FutureOr<T> value]) {
-    if (!isSync || value is Future<T>) {
+  void complete([FutureOr<T>? value]) {
+    // All paths require that if value is null, null as T succeeds.
+    value = (value == null) ? value as T : value;
+    if (!isSync) {
       _future._asyncComplete(value);
+    } else if (value is Future<T>) {
+      assert(!_future._isComplete);
+      _future._chainFuture(value);
     } else {
-      _future._completeWithValue(value);
+      // TODO(40014): Remove cast when type promotion works.
+      // This would normally be `as T` but we use `as dynamic` to make the
+      // unneeded check be implict to match dart2js unsound optimizations in the
+      // user code.
+      _future._completeWithValue(value as dynamic);
     }
   }
 
-  void completeError(Object e, [StackTrace st]) {
+  void completeError(Object e, [StackTrace? st]) {
     st ??= AsyncError.defaultStackTrace(e);
     if (isSync) {
       _future._completeError(e, st);
@@ -280,7 +287,7 @@ dynamic _asyncRethrow(dynamic object, Completer completer) {
 /// The [bodyFunction] argument is the continuation that should be invoked
 /// when the future completes.
 void _awaitOnObject(object, _WrappedAsyncBody bodyFunction) {
-  Function thenCallback =
+  FutureOr<dynamic> Function(dynamic) thenCallback =
       (result) => bodyFunction(async_error_codes.SUCCESS, result);
 
   Function errorCallback = (dynamic error, StackTrace stackTrace) {
@@ -377,7 +384,7 @@ void _asyncStarHelper(
   if (identical(bodyFunctionOrErrorCode, async_error_codes.SUCCESS)) {
     // This happens on return from the async* function.
     if (controller.isCanceled) {
-      controller.cancelationFuture._completeWithValue(null);
+      controller.cancelationFuture!._completeWithValue(null);
     } else {
       controller.close();
     }
@@ -385,7 +392,7 @@ void _asyncStarHelper(
   } else if (identical(bodyFunctionOrErrorCode, async_error_codes.ERROR)) {
     // The error is a js-error.
     if (controller.isCanceled) {
-      controller.cancelationFuture._completeError(
+      controller.cancelationFuture!._completeError(
           unwrapException(object), getTraceFromException(object));
     } else {
       controller.addError(
@@ -451,7 +458,7 @@ Stream _streamOfController(_AsyncStarStreamController controller) {
 /// If yielding while the subscription is paused it will become suspended. And
 /// only resume after the subscription is resumed or canceled.
 class _AsyncStarStreamController<T> {
-  StreamController<T> controller;
+  late StreamController<T> controller;
   Stream get stream => controller.stream;
 
   /// True when the async* function has yielded while being paused.
@@ -461,7 +468,7 @@ class _AsyncStarStreamController<T> {
 
   bool get isPaused => controller.isPaused;
 
-  _Future cancelationFuture = null;
+  _Future? cancelationFuture = null;
 
   /// True after the StreamSubscription has been cancelled.
   /// When this is true, errors thrown from the async* body should go to the
@@ -565,22 +572,21 @@ class _SyncStarIterator<T> implements Iterator<T> {
   dynamic _body;
 
   // The current value, unless iterating a non-sync* nested iterator.
-  T _current = null;
+  T? _current = null;
 
   // This is the nested iterator when iterating a yield* of a non-sync iterator.
-  // TODO(32956): In strong-mode, yield* takes an Iterable<T> (possibly checked
-  // with an implicit downcast), so change type to Iterator<T>.
-  Iterator _nestedIterator = null;
+  Iterator<T>? _nestedIterator = null;
 
   // Stack of suspended state machines when iterating a yield* of a sync*
   // iterator.
-  List _suspendedBodies = null;
+  List? _suspendedBodies = null;
 
   _SyncStarIterator(this._body);
 
   T get current {
-    if (_nestedIterator == null) return _current;
-    return _nestedIterator.current;
+    var nested = _nestedIterator;
+    if (nested == null) return _current as dynamic; // implicit: as T;
+    return nested.current;
   }
 
   _runBody() {
@@ -611,7 +617,7 @@ class _SyncStarIterator<T> implements Iterator<T> {
   bool moveNext() {
     while (true) {
       if (_nestedIterator != null) {
-        if (_nestedIterator.moveNext()) {
+        if (_nestedIterator!.moveNext()) {
           return true;
         } else {
           _nestedIterator = null;
@@ -621,13 +627,14 @@ class _SyncStarIterator<T> implements Iterator<T> {
       if (value is _IterationMarker) {
         int state = value.state;
         if (state == _IterationMarker.ITERATION_ENDED) {
-          if (_suspendedBodies == null || _suspendedBodies.isEmpty) {
+          var suspendedBodies = _suspendedBodies;
+          if (suspendedBodies == null || suspendedBodies.isEmpty) {
             _current = null;
             // Rely on [_body] to repeatedly return `ITERATION_ENDED`.
             return false;
           }
           // Resume the innermost suspended iterator.
-          _body = _suspendedBodies.removeLast();
+          _body = suspendedBodies.removeLast();
           continue;
         } else if (state == _IterationMarker.UNCAUGHT_ERROR) {
           // Rely on [_body] to repeatedly return `UNCAUGHT_ERROR`.
@@ -636,8 +643,12 @@ class _SyncStarIterator<T> implements Iterator<T> {
           JS('', 'throw #', value.value);
         } else {
           assert(state == _IterationMarker.YIELD_STAR);
-          Iterator inner = value.value.iterator;
+          Iterator<T> inner = value.value.iterator;
           if (inner is _SyncStarIterator) {
+            // The test needs to be 'is _SyncStarIterator<T>' for promotion to
+            // work. However, that test is much more expensive, so we use an
+            // unsafe cast.
+            _SyncStarIterator<T> innerSyncStarIterator = JS('', '#', inner);
             // Suspend the current state machine and start acting on behalf of
             // the nested state machine.
             //
@@ -645,7 +656,7 @@ class _SyncStarIterator<T> implements Iterator<T> {
             // suspending the current body when all it will do is step without
             // effect to ITERATION_ENDED.
             (_suspendedBodies ??= []).add(_body);
-            _body = inner._body;
+            _body = innerSyncStarIterator._body;
             continue;
           } else {
             _nestedIterator = inner;

sdk/lib/_internal/js_runtime/lib/collection_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper'
@@ -30,9 +28,9 @@ const int _mask30 = 0x3fffffff; // Low 30 bits.
 class HashMap<K, V> {
   @patch
   factory HashMap(
-      {bool equals(K key1, K key2),
-      int hashCode(K key),
-      bool isValidKey(potentialKey)}) {
+      {bool equals(K key1, K key2)?,
+      int hashCode(K key)?,
+      bool isValidKey(potentialKey)?}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -82,7 +80,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
   // list of all the keys. We cache that on the instance and clear the
   // the cache whenever the key set changes. This is also used to
   // guard against concurrent modifications.
-  List _keys;
+  List? _keys;
 
   _HashMap();
 
@@ -95,10 +93,10 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
   }
 
   Iterable<V> get values {
-    return new MappedIterable<K, V>(keys, (each) => this[each]);
+    return new MappedIterable<K, V>(keys, (each) => this[each] as V);
   }
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (_isStringKey(key)) {
       var strings = _strings;
       return (strings == null) ? false : _hasTableEntry(strings, key);
@@ -110,14 +108,14 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     }
   }
 
-  bool _containsKey(Object key) {
+  bool _containsKey(Object? key) {
     var rest = _rest;
     if (rest == null) return false;
     var bucket = _getBucket(rest, key);
     return _findBucketIndex(bucket, key) >= 0;
   }
 
-  bool containsValue(Object value) {
+  bool containsValue(Object? value) {
     return _computeKeys().any((each) => this[each] == value);
   }
 
@@ -127,7 +125,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     });
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (_isStringKey(key)) {
       var strings = _strings;
       return JS('', '#', strings == null ? null : _getTableEntry(strings, key));
@@ -139,7 +137,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     }
   }
 
-  V _get(Object key) {
+  V? _get(Object? key) {
     var rest = _rest;
     if (rest == null) return null;
     var bucket = _getBucket(rest, key);
@@ -183,13 +181,13 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
-    if (containsKey(key)) return this[key];
+    if (containsKey(key)) return this[key] as V;
     V value = ifAbsent();
     this[key] = value;
     return value;
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (_isStringKey(key)) {
       return _removeHashTableEntry(_strings, key);
     } else if (_isNumericKey(key)) {
@@ -199,7 +197,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     }
   }
 
-  V _remove(Object key) {
+  V? _remove(Object? key) {
     var rest = _rest;
     if (rest == null) return null;
     var hash = _computeHashCode(key);
@@ -228,7 +226,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     List keys = _computeKeys();
     for (int i = 0, length = keys.length; i < length; i++) {
       var key = JS('var', '#[#]', keys, i);
-      action(key, this[key]);
+      action(key, this[key] as V);
       if (JS('bool', '# !== #', keys, _keys)) {
         throw new ConcurrentModificationError(this);
       }
@@ -236,8 +234,9 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
   }
 
   List _computeKeys() {
-    if (_keys != null) return _keys;
-    List result = new List(_length);
+    var result = _keys;
+    if (result != null) return result;
+    result = List.filled(_length, null);
     int index = 0;
 
     // Add all string keys to the list.
@@ -283,7 +282,8 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
       }
     }
     assert(index == _length);
-    return _keys = result;
+    _keys = result;
+    return result;
   }
 
   void _addHashTableEntry(var table, K key, V value) {
@@ -294,7 +294,7 @@ class _HashMap<K, V> extends MapBase<K, V> implements HashMap<K, V> {
     _setTableEntry(table, key, value);
   }
 
-  V _removeHashTableEntry(var table, Object key) {
+  V? _removeHashTableEntry(var table, Object? key) {
     if (table != null && _hasTableEntry(table, key)) {
       V value = _getTableEntry(table, key);
       _deleteTableEntry(table, key);
@@ -408,10 +408,10 @@ class _CustomHashMap<K, V> extends _HashMap<K, V> {
   final _Hasher<K> _hashCode;
   final _Predicate _validKey;
 
-  _CustomHashMap(this._equals, this._hashCode, bool validKey(potentialKey))
+  _CustomHashMap(this._equals, this._hashCode, bool validKey(potentialKey)?)
       : _validKey = (validKey != null) ? validKey : ((v) => v is K);
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (!_validKey(key)) return null;
     return super._get(key);
   }
@@ -420,12 +420,12 @@ class _CustomHashMap<K, V> extends _HashMap<K, V> {
     super._set(key, value);
   }
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (!_validKey(key)) return false;
     return super._containsKey(key);
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (!_validKey(key)) return null;
     return super._remove(key);
   }
@@ -458,7 +458,7 @@ class _HashMapKeyIterable<E> extends EfficientLengthIterable<E> {
     return new _HashMapKeyIterator<E>(_map, _map._computeKeys());
   }
 
-  bool contains(Object element) {
+  bool contains(Object? element) {
     return _map.containsKey(element);
   }
 
@@ -477,11 +477,11 @@ class _HashMapKeyIterator<E> implements Iterator<E> {
   final _map;
   final List _keys;
   int _offset = 0;
-  E _current;
+  E? _current;
 
   _HashMapKeyIterator(this._map, this._keys);
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     var keys = _keys;
@@ -506,9 +506,9 @@ class _HashMapKeyIterator<E> implements Iterator<E> {
 class LinkedHashMap<K, V> {
   @patch
   factory LinkedHashMap(
-      {bool equals(K key1, K key2),
-      int hashCode(K key),
-      bool isValidKey(potentialKey)}) {
+      {bool equals(K key1, K key2)?,
+      int hashCode(K key)?,
+      bool isValidKey(potentialKey)?}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -613,11 +613,11 @@ class _Es6LinkedIdentityHashMap<K, V> extends _LinkedIdentityHashMap<K, V>
 
   Iterable<V> get values => new _Es6MapIterable<V>(this, false);
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     return JS('bool', '#.has(#)', _map, key);
   }
 
-  bool containsValue(Object value) {
+  bool containsValue(Object? value) {
     return values.any((each) => each == value);
   }
 
@@ -627,7 +627,7 @@ class _Es6LinkedIdentityHashMap<K, V> extends _LinkedIdentityHashMap<K, V>
     });
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     return JS('var', '#.get(#)', _map, key);
   }
 
@@ -637,14 +637,14 @@ class _Es6LinkedIdentityHashMap<K, V> extends _LinkedIdentityHashMap<K, V>
   }
 
   V putIfAbsent(K key, V ifAbsent()) {
-    if (containsKey(key)) return this[key];
+    if (containsKey(key)) return this[key] as V;
     V value = ifAbsent();
     this[key] = value;
     return value;
   }
 
-  V remove(Object key) {
-    V value = this[key];
+  V? remove(Object? key) {
+    V? value = this[key];
     JS('bool', '#.delete(#)', _map, key);
     _modified();
     return value;
@@ -693,7 +693,7 @@ class _Es6MapIterable<E> extends EfficientLengthIterable<E> {
   Iterator<E> get iterator =>
       new _Es6MapIterator<E>(_map, _map._modifications, _isKeys);
 
-  bool contains(Object element) => _map.containsKey(element);
+  bool contains(Object? element) => _map.containsKey(element);
 
   void forEach(void f(E element)) {
     var jsIterator;
@@ -722,8 +722,8 @@ class _Es6MapIterator<E> implements Iterator<E> {
   final bool _isKeys;
   var _jsIterator;
   var _next;
-  E _current;
-  bool _done;
+  E? _current;
+  bool _done = false;
 
   _Es6MapIterator(this._map, this._modifications, this._isKeys) {
     if (_isKeys) {
@@ -731,10 +731,9 @@ class _Es6MapIterator<E> implements Iterator<E> {
     } else {
       _jsIterator = JS('var', '#.values()', _map._map);
     }
-    _done = false;
   }
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     if (_modifications != _map._modifications) {
@@ -761,10 +760,10 @@ class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
   final _Predicate _validKey;
 
   _LinkedCustomHashMap(
-      this._equals, this._hashCode, bool validKey(potentialKey))
+      this._equals, this._hashCode, bool validKey(potentialKey)?)
       : _validKey = (validKey != null) ? validKey : ((v) => v is K);
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (!_validKey(key)) return null;
     return super.internalGet(key);
   }
@@ -773,12 +772,12 @@ class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
     super.internalSet(key, value);
   }
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (!_validKey(key)) return false;
     return super.internalContainsKey(key);
   }
 
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (!_validKey(key)) return null;
     return super.internalRemove(key);
   }
@@ -805,9 +804,9 @@ class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
 class HashSet<E> {
   @patch
   factory HashSet(
-      {bool equals(E e1, E e2),
-      int hashCode(E e),
-      bool isValidKey(potentialKey)}) {
+      {bool equals(E e1, E e2)?,
+      int hashCode(E e)?,
+      bool isValidKey(potentialKey)?}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -858,7 +857,7 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
   // list of all the elements. We cache that on the instance and clear
   // the cache whenever the set changes. This is also used to
   // guard against concurrent modifications.
-  List _elements;
+  List? _elements;
 
   _HashSet();
 
@@ -874,7 +873,7 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
   bool get isEmpty => _length == 0;
   bool get isNotEmpty => !isEmpty;
 
-  bool contains(Object object) {
+  bool contains(Object? object) {
     if (_isStringElement(object)) {
       var strings = _strings;
       return (strings == null) ? false : _hasTableEntry(strings, object);
@@ -886,21 +885,21 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
     }
   }
 
-  bool _contains(Object object) {
+  bool _contains(Object? object) {
     var rest = _rest;
     if (rest == null) return false;
     var bucket = _getBucket(rest, object);
     return _findBucketIndex(bucket, object) >= 0;
   }
 
-  E lookup(Object object) {
+  E? lookup(Object? object) {
     if (_isStringElement(object) || _isNumericElement(object)) {
-      return this.contains(object) ? object : null;
+      return this.contains(object) ? object as E : null;
     }
     return _lookup(object);
   }
 
-  E _lookup(Object object) {
+  E? _lookup(Object? object) {
     var rest = _rest;
     if (rest == null) return null;
     var bucket = _getBucket(rest, object);
@@ -947,7 +946,7 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
     }
   }
 
-  bool remove(Object object) {
+  bool remove(Object? object) {
     if (_isStringElement(object)) {
       return _removeHashTableEntry(_strings, object);
     } else if (_isNumericElement(object)) {
@@ -957,7 +956,7 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
     }
   }
 
-  bool _remove(Object object) {
+  bool _remove(Object? object) {
     var rest = _rest;
     if (rest == null) return false;
     var hash = _computeHashCode(object);
@@ -985,8 +984,9 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
   }
 
   List _computeElements() {
-    if (_elements != null) return _elements;
-    List result = new List(_length);
+    var result = _elements;
+    if (result != null) return result;
+    result = List.filled(_length, null);
     int index = 0;
 
     // Add all string elements to the list.
@@ -1031,7 +1031,8 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
       }
     }
     assert(index == _length);
-    return _elements = result;
+    _elements = result;
+    return result;
   }
 
   bool _addHashTableEntry(var table, E element) {
@@ -1042,7 +1043,7 @@ class _HashSet<E> extends _SetBase<E> implements HashSet<E> {
     return true;
   }
 
-  bool _removeHashTableEntry(var table, Object element) {
+  bool _removeHashTableEntry(var table, Object? element) {
     if (table != null && _hasTableEntry(table, element)) {
       _deleteTableEntry(table, element);
       _length--;
@@ -1143,7 +1144,7 @@ class _CustomHashSet<E> extends _HashSet<E> {
   _Equality<E> _equality;
   _Hasher<E> _hasher;
   _Predicate _validKey;
-  _CustomHashSet(this._equality, this._hasher, bool validKey(potentialKey))
+  _CustomHashSet(this._equality, this._hasher, bool validKey(potentialKey)?)
       : _validKey = (validKey != null) ? validKey : ((x) => x is E);
 
   Set<E> _newSet() => new _CustomHashSet<E>(_equality, _hasher, _validKey);
@@ -1168,17 +1169,17 @@ class _CustomHashSet<E> extends _HashSet<E> {
 
   bool add(E object) => super._add(object);
 
-  bool contains(Object object) {
+  bool contains(Object? object) {
     if (!_validKey(object)) return false;
     return super._contains(object);
   }
 
-  E lookup(Object object) {
+  E? lookup(Object? object) {
     if (!_validKey(object)) return null;
     return super._lookup(object);
   }
 
-  bool remove(Object object) {
+  bool remove(Object? object) {
     if (!_validKey(object)) return false;
     return super._remove(object);
   }
@@ -1189,11 +1190,11 @@ class _HashSetIterator<E> implements Iterator<E> {
   final _set;
   final List _elements;
   int _offset = 0;
-  E _current;
+  E? _current;
 
   _HashSetIterator(this._set, this._elements);
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     var elements = _elements;
@@ -1218,9 +1219,9 @@ class _HashSetIterator<E> implements Iterator<E> {
 class LinkedHashSet<E> {
   @patch
   factory LinkedHashSet(
-      {bool equals(E e1, E e2),
-      int hashCode(E e),
-      bool isValidKey(potentialKey)}) {
+      {bool equals(E e1, E e2)?,
+      int hashCode(E e)?,
+      bool isValidKey(potentialKey)?}) {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
@@ -1293,8 +1294,8 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
 
   // The elements are stored in cells that are linked together
   // to form a double linked list.
-  _LinkedHashSetCell _first;
-  _LinkedHashSetCell _last;
+  _LinkedHashSetCell? _first;
+  _LinkedHashSetCell? _last;
 
   // We track the number of modifications done to the element set to
   // be able to throw when the set is modified while being iterated
@@ -1319,38 +1320,38 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
   bool get isEmpty => _length == 0;
   bool get isNotEmpty => !isEmpty;
 
-  bool contains(Object object) {
+  bool contains(Object? object) {
     if (_isStringElement(object)) {
       var strings = _strings;
       if (strings == null) return false;
-      _LinkedHashSetCell cell = _getTableEntry(strings, object);
+      _LinkedHashSetCell? cell = _getTableEntry(strings, object);
       return cell != null;
     } else if (_isNumericElement(object)) {
       var nums = _nums;
       if (nums == null) return false;
-      _LinkedHashSetCell cell = _getTableEntry(nums, object);
+      _LinkedHashSetCell? cell = _getTableEntry(nums, object);
       return cell != null;
     } else {
       return _contains(object);
     }
   }
 
-  bool _contains(Object object) {
+  bool _contains(Object? object) {
     var rest = _rest;
     if (rest == null) return false;
     var bucket = _getBucket(rest, object);
     return _findBucketIndex(bucket, object) >= 0;
   }
 
-  E lookup(Object object) {
+  E? lookup(Object? object) {
     if (_isStringElement(object) || _isNumericElement(object)) {
-      return this.contains(object) ? object : null;
+      return this.contains(object) ? object as E : null;
     } else {
       return _lookup(object);
     }
   }
 
-  E _lookup(Object object) {
+  E? _lookup(Object? object) {
     var rest = _rest;
     if (rest == null) return null;
     var bucket = _getBucket(rest, object);
@@ -1360,7 +1361,7 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
   }
 
   void forEach(void action(E element)) {
-    _LinkedHashSetCell cell = _first;
+    _LinkedHashSetCell? cell = _first;
     int modifications = _modifications;
     while (cell != null) {
       action(cell._element);
@@ -1372,13 +1373,15 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
   }
 
   E get first {
-    if (_first == null) throw new StateError("No elements");
-    return _first._element;
+    var first = _first;
+    if (first == null) throw new StateError("No elements");
+    return first._element;
   }
 
   E get last {
-    if (_last == null) throw new StateError("No elements");
-    return _last._element;
+    var last = _last;
+    if (last == null) throw new StateError("No elements");
+    return last._element;
   }
 
   // Collection.
@@ -1413,7 +1416,7 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
     return true;
   }
 
-  bool remove(Object object) {
+  bool remove(Object? object) {
     if (_isStringElement(object)) {
       return _removeHashTableEntry(_strings, object);
     } else if (_isNumericElement(object)) {
@@ -1423,7 +1426,7 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
     }
   }
 
-  bool _remove(Object object) {
+  bool _remove(Object? object) {
     var rest = _rest;
     if (rest == null) return false;
     var hash = _computeHashCode(object);
@@ -1448,10 +1451,10 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
   }
 
   void _filterWhere(bool test(E element), bool removeMatching) {
-    _LinkedHashSetCell cell = _first;
+    _LinkedHashSetCell? cell = _first;
     while (cell != null) {
       E element = cell._element;
-      _LinkedHashSetCell next = cell._next;
+      _LinkedHashSetCell? next = cell._next;
       int modifications = _modifications;
       bool shouldRemove = (removeMatching == test(element));
       if (modifications != _modifications) {
@@ -1471,15 +1474,15 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
   }
 
   bool _addHashTableEntry(var table, E element) {
-    _LinkedHashSetCell cell = _getTableEntry(table, element);
+    _LinkedHashSetCell? cell = _getTableEntry(table, element);
     if (cell != null) return false;
     _setTableEntry(table, element, _newLinkedCell(element));
     return true;
   }
 
-  bool _removeHashTableEntry(var table, Object element) {
+  bool _removeHashTableEntry(var table, Object? element) {
     if (table == null) return false;
-    _LinkedHashSetCell cell = _getTableEntry(table, element);
+    _LinkedHashSetCell? cell = _getTableEntry(table, element);
     if (cell == null) return false;
     _unlinkCell(cell);
     _deleteTableEntry(table, element);
@@ -1499,7 +1502,7 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
     if (_first == null) {
       _first = _last = cell;
     } else {
-      _LinkedHashSetCell last = _last;
+      _LinkedHashSetCell last = _last!;
       cell._previous = last;
       _last = last._next = cell;
     }
@@ -1510,8 +1513,8 @@ class _LinkedHashSet<E> extends _SetBase<E> implements LinkedHashSet<E> {
 
   // Unlink the given cell from the linked list of cells.
   void _unlinkCell(_LinkedHashSetCell cell) {
-    _LinkedHashSetCell previous = cell._previous;
-    _LinkedHashSetCell next = cell._next;
+    _LinkedHashSetCell? previous = cell._previous;
+    _LinkedHashSetCell? next = cell._next;
     if (previous == null) {
       assert(cell == _first);
       _first = next;
@@ -1617,7 +1620,7 @@ class _LinkedCustomHashSet<E> extends _LinkedHashSet<E> {
   _Hasher<E> _hasher;
   _Predicate _validKey;
   _LinkedCustomHashSet(
-      this._equality, this._hasher, bool validKey(potentialKey))
+      this._equality, this._hasher, bool validKey(potentialKey)?)
       : _validKey = (validKey != null) ? validKey : ((x) => x is E);
 
   Set<E> _newSet() =>
@@ -1644,30 +1647,30 @@ class _LinkedCustomHashSet<E> extends _LinkedHashSet<E> {
 
   bool add(E element) => super._add(element);
 
-  bool contains(Object object) {
+  bool contains(Object? object) {
     if (!_validKey(object)) return false;
     return super._contains(object);
   }
 
-  E lookup(Object object) {
+  E? lookup(Object? object) {
     if (!_validKey(object)) return null;
     return super._lookup(object);
   }
 
-  bool remove(Object object) {
+  bool remove(Object? object) {
     if (!_validKey(object)) return false;
     return super._remove(object);
   }
 
-  bool containsAll(Iterable<Object> elements) {
-    for (Object element in elements) {
+  bool containsAll(Iterable<Object?> elements) {
+    for (Object? element in elements) {
       if (!_validKey(element) || !this.contains(element)) return false;
     }
     return true;
   }
 
-  void removeAll(Iterable<Object> elements) {
-    for (Object element in elements) {
+  void removeAll(Iterable<Object?> elements) {
+    for (Object? element in elements) {
       if (_validKey(element)) {
         super._remove(element);
       }
@@ -1678,8 +1681,8 @@ class _LinkedCustomHashSet<E> extends _LinkedHashSet<E> {
 class _LinkedHashSetCell {
   final _element;
 
-  _LinkedHashSetCell _next;
-  _LinkedHashSetCell _previous;
+  _LinkedHashSetCell? _next;
+  _LinkedHashSetCell? _previous;
 
   _LinkedHashSetCell(this._element);
 }
@@ -1688,52 +1691,26 @@ class _LinkedHashSetCell {
 class _LinkedHashSetIterator<E> implements Iterator<E> {
   final _set;
   final int _modifications;
-  _LinkedHashSetCell _cell;
-  E _current;
+  _LinkedHashSetCell? _cell;
+  E? _current;
 
   _LinkedHashSetIterator(this._set, this._modifications) {
     _cell = _set._first;
   }
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
+    var cell = _cell;
     if (_modifications != _set._modifications) {
       throw new ConcurrentModificationError(_set);
-    } else if (_cell == null) {
+    } else if (cell == null) {
       _current = null;
       return false;
     } else {
-      _current = _cell._element;
-      _cell = _cell._next;
+      _current = cell._element;
+      _cell = cell._next;
       return true;
     }
   }
 }
-
-@patch
-abstract class _SplayTree<K, Node extends _SplayTreeNode<K>> {
-  @patch
-  Node _splayMin(Node node) {
-    Node current = node;
-    while (current.left != null) {
-      Node left = current.left;
-      current.left = left.right;
-      left.right = current;
-      current = left;
-    }
-    return current;
-  }
-
-  @patch
-  Node _splayMax(Node node) {
-    Node current = node;
-    while (current.right != null) {
-      Node right = current.right;
-      current.right = right.left;
-      right.left = current;
-      current = right;
-    }
-    return current;
-  }
-}

sdk/lib/_internal/js_runtime/lib/constant_map.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of _js_helper;
 
 class ConstantMapView<K, V> extends UnmodifiableMapView<K, V>
@@ -14,7 +12,7 @@ class ConstantMapView<K, V> extends UnmodifiableMapView<K, V>
 abstract class ConstantMap<K, V> implements Map<K, V> {
   // Used to create unmodifiable maps from other maps.
   factory ConstantMap.from(Map other) {
-    List keys = new List<K>.from(other.keys);
+    var keys = new List<K>.from(other.keys);
     bool allStrings = true;
     for (var k in keys) {
       if (k is! String) {
@@ -30,7 +28,7 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
       for (var k in keys) {
         V v = other[k];
         if (k != '__proto__') {
-          if (!jsHasOwnProperty(object, k)) length++;
+          if (!jsHasOwnProperty(object, k as String)) length++;
           JS('void', '#[#] = #', object, k, v);
         } else {
           containsProto = true;
@@ -56,18 +54,27 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
 
   String toString() => MapBase.mapToString(this);
 
-  static Null _throwUnmodifiable() {
+  static Never _throwUnmodifiable() {
     throw new UnsupportedError('Cannot modify unmodifiable Map');
   }
 
-  void operator []=(K key, V val) => _throwUnmodifiable();
-  V putIfAbsent(K key, V ifAbsent()) => _throwUnmodifiable();
-  V remove(Object key) => _throwUnmodifiable();
+  void operator []=(K key, V val) {
+    _throwUnmodifiable();
+  }
+
+  V putIfAbsent(K key, V ifAbsent()) {
+    _throwUnmodifiable();
+  }
+
+  V? remove(Object? key) {
+    _throwUnmodifiable();
+  }
+
   void clear() => _throwUnmodifiable();
   void addAll(Map<K, V> other) => _throwUnmodifiable();
 
   Iterable<MapEntry<K, V>> get entries sync* {
-    for (var key in keys) yield new MapEntry<K, V>(key, this[key]);
+    for (var key in keys) yield new MapEntry<K, V>(key, this[key]!);
   }
 
   void addEntries(Iterable<MapEntry<K, V>> entries) {
@@ -83,7 +90,7 @@ abstract class ConstantMap<K, V> implements Map<K, V> {
     return result;
   }
 
-  V update(K key, V update(V value), {V ifAbsent()}) {
+  V update(K key, V update(V value), {V ifAbsent()?}) {
     _throwUnmodifiable();
   }
 
@@ -111,17 +118,17 @@ class ConstantStringMap<K, V> extends ConstantMap<K, V> {
   int get length => JS('JSUInt31', '#', _length);
   List<K> get _keysArray => JS('JSUnmodifiableArray', '#', _keys);
 
-  bool containsValue(Object needle) {
+  bool containsValue(Object? needle) {
     return values.any((V value) => value == needle);
   }
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (key is! String) return false;
     if ('__proto__' == key) return false;
     return jsHasOwnProperty(_jsObject, key);
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     if (!containsKey(key)) return null;
     return JS('', '#', _fetch(key));
   }
@@ -157,7 +164,7 @@ class ConstantProtoMap<K, V> extends ConstantStringMap<K, V> {
 
   final V _protoValue;
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     if (key is! String) return false;
     if ('__proto__' == key) return true;
     return jsHasOwnProperty(_jsObject, key);
@@ -187,7 +194,7 @@ class GeneralConstantMap<K, V> extends ConstantMap<K, V> {
   // We cannot create the backing map on creation since hashCode interceptors
   // have not been defined when constants are created.
   Map<K, V> _getMap() {
-    LinkedHashMap<K, V> backingMap = JS('LinkedHashMap|Null', r'#.$map', this);
+    LinkedHashMap<K, V>? backingMap = JS('LinkedHashMap|Null', r'#.$map', this);
     if (backingMap == null) {
       backingMap = new JsLinkedHashMap<K, V>();
       fillLiteralMap(_jsData, backingMap);
@@ -196,15 +203,15 @@ class GeneralConstantMap<K, V> extends ConstantMap<K, V> {
     return backingMap;
   }
 
-  bool containsValue(Object needle) {
+  bool containsValue(Object? needle) {
     return _getMap().containsValue(needle);
   }
 
-  bool containsKey(Object key) {
+  bool containsKey(Object? key) {
     return _getMap().containsKey(key);
   }
 
-  V operator [](Object key) {
+  V? operator [](Object? key) {
     return _getMap()[key];
   }
 

sdk/lib/_internal/js_runtime/lib/convert_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:convert library.
 
 import 'dart:_js_helper' show argumentErrorValue, patch;
@@ -28,7 +26,7 @@ import 'dart:_native_typed_data' show NativeUint8List;
 ///
 /// Throws [FormatException] if the input is not valid JSON text.
 @patch
-_parseJson(String source, reviver(key, value)) {
+_parseJson(String source, reviver(key, value)?) {
   if (source is! String) throw argumentErrorValue(source);
 
   var parsed;
@@ -36,7 +34,7 @@ _parseJson(String source, reviver(key, value)) {
     parsed = JS('=Object|JSExtendableArray|Null|bool|num|String',
         'JSON.parse(#)', source);
   } catch (e) {
-    throw new FormatException(JS('String', 'String(#)', e));
+    throw FormatException(JS<String>('String', 'String(#)', e));
   }
 
   if (reviver == null) {
@@ -49,20 +47,20 @@ _parseJson(String source, reviver(key, value)) {
 /// Walks the raw JavaScript value [json], replacing JavaScript Objects with
 /// Maps. [json] is expected to be freshly allocated so elements can be replaced
 /// in-place.
-_convertJsonToDart(json, reviver(key, value)) {
-  assert(reviver != null);
+_convertJsonToDart(json, reviver(Object? key, Object? value)) {
   walk(e) {
     // JavaScript null, string, number, bool are in the correct representation.
-    if (JS('bool', '# == null', e) || JS('bool', 'typeof # != "object"', e)) {
+    if (JS<bool>('bool', '# == null', e) ||
+        JS<bool>('bool', 'typeof # != "object"', e)) {
       return e;
     }
 
     // This test is needed to avoid identifying '{"__proto__":[]}' as an Array.
     // TODO(sra): Replace this test with cheaper '#.constructor === Array' when
     // bug 621 below is fixed.
-    if (JS('bool', 'Object.getPrototypeOf(#) === Array.prototype', e)) {
+    if (JS<bool>('bool', 'Object.getPrototypeOf(#) === Array.prototype', e)) {
       // In-place update of the elements since JS Array is a Dart List.
-      for (int i = 0; i < JS('int', '#.length', e); i++) {
+      for (int i = 0; i < JS<int>('int', '#.length', e); i++) {
         // Use JS indexing to avoid range checks.  We know this is the only
         // reference to the list, but the compiler will likely never be able to
         // tell that this instance of the list cannot have its length changed by
@@ -76,7 +74,7 @@ _convertJsonToDart(json, reviver(key, value)) {
 
     // Otherwise it is a plain object, so copy to a JSON map, so we process
     // and revive all entries recursively.
-    _JsonMap map = new _JsonMap(e);
+    _JsonMap map = _JsonMap(e);
     var processed = map._processed;
     List<String> keys = map._computeKeys();
     for (int i = 0; i < keys.length; i++) {
@@ -98,19 +96,20 @@ _convertJsonToDartLazy(object) {
   if (object == null) return null;
 
   // JavaScript string, number, bool already has the correct representation.
-  if (JS('bool', 'typeof # != "object"', object)) {
+  if (JS<bool>('bool', 'typeof # != "object"', object)) {
     return object;
   }
 
   // This test is needed to avoid identifying '{"__proto__":[]}' as an array.
   // TODO(sra): Replace this test with cheaper '#.constructor === Array' when
   // bug https://code.google.com/p/v8/issues/detail?id=621 is fixed.
-  if (JS('bool', 'Object.getPrototypeOf(#) !== Array.prototype', object)) {
-    return new _JsonMap(object);
+  if (JS<bool>(
+      'bool', 'Object.getPrototypeOf(#) !== Array.prototype', object)) {
+    return _JsonMap(object);
   }
 
   // Update the elements in place since JS arrays are Dart lists.
-  for (int i = 0; i < JS('int', '#.length', object); i++) {
+  for (int i = 0; i < JS<int>('int', '#.length', object); i++) {
     // Use JS indexing to avoid range checks.  We know this is the only
     // reference to the list, but the compiler will likely never be able to
     // tell that this instance of the list cannot have its length changed by
@@ -157,12 +156,12 @@ class _JsonMap extends MapBase<String, dynamic> {
 
   Iterable<String> get keys {
     if (_isUpgraded) return _upgradedMap.keys;
-    return new _JsonMapKeyIterable(this);
+    return _JsonMapKeyIterable(this);
   }
 
   Iterable get values {
     if (_isUpgraded) return _upgradedMap.values;
-    return new MappedIterable(_computeKeys(), (each) => this[each]);
+    return MappedIterable(_computeKeys(), (each) => this[each]);
   }
 
   operator []=(key, value) {
@@ -209,7 +208,7 @@ class _JsonMap extends MapBase<String, dynamic> {
     return value;
   }
 
-  remove(Object key) {
+  remove(Object? key) {
     if (!_isUpgraded && !containsKey(key)) return null;
     return _upgrade().remove(key);
   }
@@ -249,7 +248,7 @@ class _JsonMap extends MapBase<String, dynamic> {
       // Check if invoking the callback function changed
       // the key set. If so, throw an exception.
       if (!identical(keys, _data)) {
-        throw new ConcurrentModificationError(this);
+        throw ConcurrentModificationError(this);
       }
     }
   }
@@ -270,7 +269,7 @@ class _JsonMap extends MapBase<String, dynamic> {
 
   List<String> _computeKeys() {
     assert(!_isUpgraded);
-    List keys = _data;
+    List? keys = _data;
     if (keys == null) {
       keys = _data = new JSArray<String>.typed(_getPropertyNames(_original));
     }
@@ -293,7 +292,7 @@ class _JsonMap extends MapBase<String, dynamic> {
     // safely force a concurrent modification error in case
     // someone is iterating over the map here.
     if (keys.isEmpty) {
-      keys.add(null);
+      keys.add("");
     } else {
       keys.clear();
     }
@@ -316,15 +315,15 @@ class _JsonMap extends MapBase<String, dynamic> {
   // Private JavaScript helper methods.
   // ------------------------------------------
 
-  static bool _hasProperty(object, String key) =>
-      JS('bool', 'Object.prototype.hasOwnProperty.call(#,#)', object, key);
+  static bool _hasProperty(object, String key) => JS<bool>(
+      'bool', 'Object.prototype.hasOwnProperty.call(#,#)', object, key);
   static _getProperty(object, String key) => JS('', '#[#]', object, key);
   static _setProperty(object, String key, value) =>
       JS('', '#[#]=#', object, key, value);
   static List _getPropertyNames(object) =>
       JS('JSExtendableArray', 'Object.keys(#)', object);
   static bool _isUnprocessed(object) =>
-      JS('bool', 'typeof(#)=="undefined"', object);
+      JS<bool>('bool', 'typeof(#)=="undefined"', object);
   static _newJavaScriptObject() => JS('=Object', 'Object.create(null)');
 }
 
@@ -352,14 +351,14 @@ class _JsonMapKeyIterable extends ListIterable<String> {
 
   /// Delegate to [parent.containsKey] to ensure the performance expected
   /// from [Map.keys.containsKey].
-  bool contains(Object key) => _parent.containsKey(key);
+  bool contains(Object? key) => _parent.containsKey(key);
 }
 
 @patch
 class JsonDecoder {
   @patch
-  StringConversionSink startChunkedConversion(Sink<Object> sink) {
-    return new _JsonDecoderSink(_reviver, sink);
+  StringConversionSink startChunkedConversion(Sink<Object?> sink) {
+    return _JsonDecoderSink(_reviver, sink);
   }
 }
 
@@ -368,18 +367,17 @@ class JsonDecoder {
 ///
 /// The sink only creates one object, but its input can be chunked.
 // TODO(floitsch): don't accumulate everything before starting to decode.
-class _JsonDecoderSink extends _StringSinkConversionSink {
-  final Function(Object key, Object value) _reviver;
-  final Sink<Object> _sink;
+class _JsonDecoderSink extends _StringSinkConversionSink<StringBuffer> {
+  final Object? Function(Object? key, Object? value)? _reviver;
+  final Sink<Object?> _sink;
 
-  _JsonDecoderSink(this._reviver, this._sink) : super(new StringBuffer(''));
+  _JsonDecoderSink(this._reviver, this._sink) : super(StringBuffer(''));
 
   void close() {
     super.close();
-    StringBuffer buffer = _stringSink;
-    String accumulated = buffer.toString();
-    buffer.clear();
-    Object decoded = _parseJson(accumulated, _reviver);
+    String accumulated = _stringSink.toString();
+    _stringSink.clear();
+    Object? decoded = _parseJson(accumulated, _reviver);
     _sink.add(decoded);
     _sink.close();
   }
@@ -397,19 +395,20 @@ class Utf8Decoder {
   }
 
   @patch
-  static String _convertIntercepted(
-      bool allowMalformed, List<int> codeUnits, int start, int end) {
+  static String? _convertIntercepted(
+      bool allowMalformed, List<int> codeUnits, int start, int? end) {
     // Test `codeUnits is NativeUint8List`. Dart's NativeUint8List is
     // implemented by JavaScript's Uint8Array.
-    if (JS('bool', '# instanceof Uint8Array', codeUnits)) {
+    if (JS<bool>('bool', '# instanceof Uint8Array', codeUnits)) {
       // JS 'cast' to avoid a downcast equivalent to the is-check we hand-coded.
-      NativeUint8List casted = JS('NativeUint8List', '#', codeUnits);
+      NativeUint8List casted =
+          JS<NativeUint8List>('NativeUint8List', '#', codeUnits);
       // Always use Dart implementation for short strings.
       end ??= casted.length;
       if (end - start < _shortInputThreshold) {
         return null;
       }
-      String result =
+      String? result =
           _convertInterceptedUint8List(allowMalformed, casted, start, end);
       if (result != null && allowMalformed) {
         // In principle, TextDecoder should have provided the correct result
@@ -425,7 +424,7 @@ class Utf8Decoder {
     return null; // This call was not intercepted.
   }
 
-  static String _convertInterceptedUint8List(
+  static String? _convertInterceptedUint8List(
       bool allowMalformed, NativeUint8List codeUnits, int start, int end) {
     final decoder = allowMalformed ? _decoderNonfatal : _decoder;
     if (decoder == null) return null;
@@ -436,16 +435,18 @@ class Utf8Decoder {
     int length = codeUnits.length;
     end = RangeError.checkValidRange(start, end, length);
 
-    return _useTextDecoder(decoder,
-        JS('NativeUint8List', '#.subarray(#, #)', codeUnits, start, end));
+    return _useTextDecoder(
+        decoder,
+        JS<NativeUint8List>(
+            'NativeUint8List', '#.subarray(#, #)', codeUnits, start, end));
   }
 
-  static String _useTextDecoder(decoder, NativeUint8List codeUnits) {
+  static String? _useTextDecoder(decoder, NativeUint8List codeUnits) {
     // If the input is malformed, catch the exception and return `null` to fall
     // back on unintercepted decoder. The fallback will either succeed in
     // decoding, or report the problem better than TextDecoder.
     try {
-      return JS('String', '#.decode(#)', decoder, codeUnits);
+      return JS<String>('String', '#.decode(#)', decoder, codeUnits);
     } catch (e) {}
     return null;
   }
@@ -472,12 +473,12 @@ class _Utf8Decoder {
   _Utf8Decoder(this.allowMalformed) : _state = beforeBom;
 
   @patch
-  String convertSingle(List<int> codeUnits, int start, int maybeEnd) {
+  String convertSingle(List<int> codeUnits, int start, int? maybeEnd) {
     return convertGeneral(codeUnits, start, maybeEnd, true);
   }
 
   @patch
-  String convertChunked(List<int> codeUnits, int start, int maybeEnd) {
+  String convertChunked(List<int> codeUnits, int start, int? maybeEnd) {
     return convertGeneral(codeUnits, start, maybeEnd, false);
   }
 }

sdk/lib/_internal/js_runtime/lib/core_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:core classes.
 import "dart:_internal" hide Symbol, LinkedList, LinkedListEntry;
 import "dart:_internal" as _symbol_dev;
@@ -34,9 +32,10 @@ import "dart:convert" show Encoding, utf8;
 
 import 'dart:typed_data' show Endian, Uint8List, Uint16List;
 
-String _symbolToString(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);
+String _symbolToString(Symbol symbol) =>
+    _symbol_dev.Symbol.getName(symbol as _symbol_dev.Symbol);
 
-Map<String, dynamic> _symbolMapToStringMap(Map<Symbol, dynamic> map) {
+Map<String, dynamic>? _symbolMapToStringMap(Map<Symbol, dynamic>? map) {
   if (map == null) return null;
   var result = new Map<String, dynamic>();
   map.forEach((Symbol key, value) {
@@ -46,13 +45,13 @@ Map<String, dynamic> _symbolMapToStringMap(Map<Symbol, dynamic> map) {
 }
 
 @patch
-int identityHashCode(Object object) => objectHashCode(object);
+int identityHashCode(Object? object) => objectHashCode(object);
 
 // Patch for Object implementation.
 @patch
 class Object {
   @patch
-  bool operator ==(other) => identical(this, other);
+  bool operator ==(Object other) => identical(this, other);
 
   @patch
   int get hashCode => Primitives.objectHashCode(this);
@@ -80,8 +79,8 @@ class Null {
 @patch
 class Function {
   @patch
-  static apply(Function function, List positionalArguments,
-      [Map<Symbol, dynamic> namedArguments]) {
+  static apply(Function function, List<dynamic>? positionalArguments,
+      [Map<Symbol, dynamic>? namedArguments]) {
     return Primitives.applyFunction(
         function,
         positionalArguments,
@@ -103,27 +102,27 @@ class Expando<T> {
   final Object _jsWeakMapOrKey;
 
   @patch
-  Expando([String name])
+  Expando([String? name])
       : this.name = name,
         _jsWeakMapOrKey = JS('bool', 'typeof WeakMap == "function"')
             ? JS('=Object', 'new WeakMap()')
             : _createKey();
 
   @patch
-  T operator [](Object object) {
+  T? operator [](Object object) {
     if (_jsWeakMapOrKey is! String) {
       _checkType(object); // WeakMap doesn't check on reading, only writing.
       return JS('', '#.get(#)', _jsWeakMapOrKey, object);
     }
-    return _getFromObject(_jsWeakMapOrKey, object);
+    return _getFromObject(_jsWeakMapOrKey as String, object) as T?;
   }
 
   @patch
-  void operator []=(Object object, T value) {
+  void operator []=(Object object, T? value) {
     if (_jsWeakMapOrKey is! String) {
       JS('void', '#.set(#, #)', _jsWeakMapOrKey, object, value);
     } else {
-      _setOnObject(_jsWeakMapOrKey, object, value);
+      _setOnObject(_jsWeakMapOrKey as String, object, value);
     }
   }
 
@@ -132,7 +131,7 @@ class Expando<T> {
     return (values == null) ? null : Primitives.getProperty(values, key);
   }
 
-  static void _setOnObject(String key, Object object, Object value) {
+  static void _setOnObject(String key, Object object, Object? value) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
     if (values == null) {
       values = new Object();
@@ -155,15 +154,15 @@ class Expando<T> {
 class int {
   @patch
   static int parse(String source,
-      {int radix, @deprecated int onError(String source)}) {
-    int value = tryParse(source, radix: radix);
+      {int? radix, @deprecated int onError(String source)?}) {
+    int? value = tryParse(source, radix: radix);
     if (value != null) return value;
     if (onError != null) return onError(source);
     throw new FormatException(source);
   }
 
   @patch
-  static int tryParse(String source, {int radix}) {
+  static int? tryParse(String source, {int? radix}) {
     return Primitives.parseInt(source, radix);
   }
 }
@@ -172,15 +171,15 @@ class int {
 class double {
   @patch
   static double parse(String source,
-      [@deprecated double onError(String source)]) {
-    double value = tryParse(source);
+      [@deprecated double onError(String source)?]) {
+    double? value = tryParse(source);
     if (value != null) return value;
     if (onError != null) return onError(source);
     throw new FormatException('Invalid double', source);
   }
 
   @patch
-  static double tryParse(String source) {
+  static double? tryParse(String source) {
     return Primitives.parseDouble(source);
   }
 }
@@ -195,11 +194,11 @@ class BigInt implements Comparable<BigInt> {
   static BigInt get two => _BigIntImpl.two;
 
   @patch
-  static BigInt parse(String source, {int radix}) =>
+  static BigInt parse(String source, {int? radix}) =>
       _BigIntImpl.parse(source, radix: radix);
 
   @patch
-  static BigInt tryParse(String source, {int radix}) =>
+  static BigInt? tryParse(String source, {int? radix}) =>
       _BigIntImpl._tryParse(source, radix: radix);
 
   @patch
@@ -221,7 +220,7 @@ class Error {
   }
 
   @patch
-  StackTrace get stackTrace => Primitives.extractStackTrace(this);
+  StackTrace? get stackTrace => Primitives.extractStackTrace(this);
 }
 
 @patch
@@ -286,7 +285,7 @@ class DateTime {
   }
 
   @patch
-  static int _brokenDownDateToValue(int year, int month, int day, int hour,
+  static int? _brokenDownDateToValue(int year, int month, int day, int hour,
       int minute, int second, int millisecond, int microsecond, bool isUtc) {
     return Primitives.valueFromDecomposedDate(
         year,
@@ -362,7 +361,7 @@ class DateTime {
   int get weekday => Primitives.getWeekday(this);
 
   @patch
-  bool operator ==(dynamic other) =>
+  bool operator ==(Object other) =>
       other is DateTime &&
       _value == other.millisecondsSinceEpoch &&
       isUtc == other.isUtc;
@@ -386,9 +385,9 @@ class DateTime {
 @patch
 class Stopwatch {
   @patch
-  static void _initTicker() {
+  static int _initTicker() {
     Primitives.initTicker();
-    _frequency = Primitives.timerFrequency;
+    return Primitives.timerFrequency;
   }
 
   @patch
@@ -415,11 +414,11 @@ class Stopwatch {
 @patch
 class List<E> {
   @patch
-  factory List([int length]) = JSArray<E>.list;
+  factory List([int? length]) = JSArray<E>.list;
 
   @patch
   factory List.filled(int length, E fill, {bool growable: false}) {
-    List result = growable
+    var result = growable
         ? new JSArray<E>.growable(length)
         : new JSArray<E>.fixed(length);
     if (length != 0 && fill != null) {
@@ -433,6 +432,11 @@ class List<E> {
     return result;
   }
 
+  @patch
+  factory List.empty({bool growable: false}) {
+    return growable ? new JSArray<E>.growable(0) : new JSArray<E>.fixed(0);
+  }
+
   @patch
   factory List.from(Iterable elements, {bool growable: true}) {
     List<E> list = <E>[];
@@ -449,9 +453,21 @@ class List<E> {
     return List.from(elements, growable: growable);
   }
 
+  @patch
+  factory List.generate(int length, E generator(int index),
+      {bool growable = true}) {
+    final result = growable
+        ? new JSArray<E>.growable(length)
+        : new JSArray<E>.fixed(length);
+    for (int i = 0; i < length; i++) {
+      result[i] = generator(i);
+    }
+    return result;
+  }
+
   @patch
   factory List.unmodifiable(Iterable elements) {
-    List result = new List<E>.from(elements, growable: false);
+    var result = List<E>.from(elements, growable: false);
     return makeFixedListUnmodifiable(result);
   }
 }
@@ -469,9 +485,12 @@ class Map<K, V> {
 class String {
   @patch
   factory String.fromCharCodes(Iterable<int> charCodes,
-      [int start = 0, int end]) {
+      [int start = 0, int? end]) {
     if (charCodes is JSArray) {
-      JSArray<int> array = charCodes;
+      // Type promotion doesn't work unless the check is `is JSArray<int>`,
+      // which is more expensive.
+      // TODO(41383): Optimize `is JSArray<int>` rather than do weird 'casts'.
+      JSArray array = JS('JSArray', '#', charCodes);
       return _stringFromJSArray(array, start, end);
     }
     if (charCodes is NativeUint8List) {
@@ -485,24 +504,24 @@ class String {
     return Primitives.stringFromCharCode(charCode);
   }
 
-  static String _stringFromJSArray(List list, int start, int endOrNull) {
+  static String _stringFromJSArray(JSArray list, int start, int? endOrNull) {
     int len = list.length;
     int end = RangeError.checkValidRange(start, endOrNull, len);
     if (start > 0 || end < len) {
-      list = list.sublist(start, end);
+      list = JS('JSArray', '#.slice(#, #)', list, start, end);
     }
     return Primitives.stringFromCharCodes(list);
   }
 
   static String _stringFromUint8List(
-      NativeUint8List charCodes, int start, int endOrNull) {
+      NativeUint8List charCodes, int start, int? endOrNull) {
     int len = charCodes.length;
     int end = RangeError.checkValidRange(start, endOrNull, len);
     return Primitives.stringFromNativeUint8List(charCodes, start, end);
   }
 
   static String _stringFromIterable(
-      Iterable<int> charCodes, int start, int end) {
+      Iterable<int> charCodes, int start, int? end) {
     if (start < 0) throw new RangeError.range(start, 0, charCodes.length);
     if (end != null && end < start) {
       throw new RangeError.range(end, start, charCodes.length);
@@ -557,7 +576,7 @@ class RegExp {
 @pragma(
     'dart2js:noInline') // No inlining since we recognize the call in optimizer.
 @patch
-bool identical(Object a, Object b) {
+bool identical(Object? a, Object? b) {
   return JS('bool', '(# == null ? # == null : # === #)', a, b, a, b);
 }
 
@@ -572,7 +591,7 @@ class StringBuffer {
   int get length => _contents.length;
 
   @patch
-  void write(Object obj) {
+  void write(Object? obj) {
     _writeString('$obj');
   }
 
@@ -582,12 +601,12 @@ class StringBuffer {
   }
 
   @patch
-  void writeAll(Iterable objects, [String separator = ""]) {
+  void writeAll(Iterable<dynamic> objects, [String separator = ""]) {
     _contents = _writeAll(_contents, objects, separator);
   }
 
   @patch
-  void writeln([Object obj = ""]) {
+  void writeln([Object? obj = ""]) {
     _writeString('$obj\n');
   }
 
@@ -599,7 +618,7 @@ class StringBuffer {
   @patch
   String toString() => Primitives.flattenString(_contents);
 
-  void _writeString(str) {
+  void _writeString(String str) {
     _contents = Primitives.stringConcatUnchecked(_contents, str);
   }
 
@@ -620,28 +639,28 @@ class StringBuffer {
     return string;
   }
 
-  static String _writeOne(String string, Object obj) {
+  static String _writeOne(String string, Object? obj) {
     return Primitives.stringConcatUnchecked(string, '$obj');
   }
 }
 
 @patch
 class NoSuchMethodError {
-  final Object _receiver;
+  final Object? _receiver;
   final Symbol _memberName;
-  final List _arguments;
-  final Map<Symbol, dynamic> _namedArguments;
-  final List _existingArgumentNames;
+  final List? _arguments;
+  final Map<Symbol, dynamic>? _namedArguments;
+  final List? _existingArgumentNames;
 
   @patch
-  NoSuchMethodError.withInvocation(Object receiver, Invocation invocation)
+  NoSuchMethodError.withInvocation(Object? receiver, Invocation invocation)
       : this(receiver, invocation.memberName, invocation.positionalArguments,
             invocation.namedArguments);
 
   @patch
-  NoSuchMethodError(Object receiver, Symbol memberName,
-      List positionalArguments, Map<Symbol, dynamic> namedArguments,
-      [List existingArgumentNames = null])
+  NoSuchMethodError(Object? receiver, Symbol memberName,
+      List? positionalArguments, Map<Symbol, dynamic>? namedArguments,
+      [List? existingArgumentNames = null])
       : _receiver = receiver,
         _memberName = memberName,
         _arguments = positionalArguments,
@@ -650,17 +669,19 @@ class NoSuchMethodError {
 
   @patch
   String toString() {
-    StringBuffer sb = new StringBuffer('');
+    StringBuffer sb = StringBuffer('');
     String comma = '';
-    if (_arguments != null) {
-      for (var argument in _arguments) {
+    var arguments = _arguments;
+    if (arguments != null) {
+      for (var argument in arguments) {
         sb.write(comma);
         sb.write(Error.safeToString(argument));
         comma = ', ';
       }
     }
-    if (_namedArguments != null) {
-      _namedArguments.forEach((Symbol key, var value) {
+    var namedArguments = _namedArguments;
+    if (namedArguments != null) {
+      namedArguments.forEach((Symbol key, var value) {
         sb.write(comma);
         sb.write(_symbolToString(key));
         sb.write(": ");
@@ -671,12 +692,13 @@ class NoSuchMethodError {
     String memberName = _symbolToString(_memberName);
     String receiverText = Error.safeToString(_receiver);
     String actualParameters = '$sb';
-    if (_existingArgumentNames == null) {
+    var existingArgumentNames = _existingArgumentNames;
+    if (existingArgumentNames == null) {
       return "NoSuchMethodError: method not found: '$memberName'\n"
           "Receiver: ${receiverText}\n"
           "Arguments: [$actualParameters]";
     } else {
-      String formalParameters = _existingArgumentNames.join(', ');
+      String formalParameters = existingArgumentNames.join(', ');
       return "NoSuchMethodError: incorrect number of arguments passed to "
           "method named '$memberName'\n"
           "Receiver: ${receiverText}\n"
@@ -697,7 +719,7 @@ class _CompileTimeError extends Error {
 class Uri {
   @patch
   static Uri get base {
-    String uri = Primitives.currentUri();
+    String? uri = Primitives.currentUri();
     if (uri != null) return Uri.parse(uri);
     throw new UnsupportedError("'Uri.base' is not supported");
   }
@@ -924,14 +946,14 @@ class _BigIntImpl implements BigInt {
 
   // Result cache for last _divRem call.
   // Result cache for last _divRem call.
-  static Uint16List _lastDividendDigits;
-  static int _lastDividendUsed;
-  static Uint16List _lastDivisorDigits;
-  static int _lastDivisorUsed;
-  static Uint16List _lastQuoRemDigits;
-  static int _lastQuoRemUsed;
-  static int _lastRemUsed;
-  static int _lastRem_nsh;
+  static Uint16List? _lastDividendDigits;
+  static int? _lastDividendUsed;
+  static Uint16List? _lastDivisorDigits;
+  static int? _lastDivisorUsed;
+  static late Uint16List _lastQuoRemDigits;
+  static late int _lastQuoRemUsed;
+  static late int _lastRemUsed;
+  static late int _lastRem_nsh;
 
   /// Whether this bigint is negative.
   final bool _isNegative;
@@ -970,7 +992,7 @@ class _BigIntImpl implements BigInt {
   ///
   /// Throws a [FormatException] if the [source] is not a valid integer literal,
   /// optionally prefixed by a sign.
-  static _BigIntImpl parse(String source, {int radix}) {
+  static _BigIntImpl parse(String source, {int? radix}) {
     var result = _tryParse(source, radix: radix);
     if (result == null) {
       throw new FormatException("Could not parse BigInt", source);
@@ -989,7 +1011,7 @@ class _BigIntImpl implements BigInt {
     // Read in the source 4 digits at a time.
     // The first part may have a few leading virtual '0's to make the remaining
     // parts all have exactly 4 digits.
-    int digitInPartCount = 4 - source.length.remainder(4);
+    var digitInPartCount = 4 - source.length.remainder(4);
     if (digitInPartCount == 4) digitInPartCount = 0;
     for (int i = 0; i < source.length; i++) {
       part = part * 10 + source.codeUnitAt(i) - _0;
@@ -1031,7 +1053,7 @@ class _BigIntImpl implements BigInt {
   /// If [isNegative] is true, negates the result before returning it.
   ///
   /// The [source] (substring) must be a valid hex literal.
-  static _BigIntImpl _parseHex(String source, int startPos, bool isNegative) {
+  static _BigIntImpl? _parseHex(String source, int startPos, bool isNegative) {
     int hexDigitsPerChunk = _digitBits ~/ 4;
     int sourceLength = source.length - startPos;
     int chunkCount = (sourceLength / hexDigitsPerChunk).ceil();
@@ -1065,7 +1087,7 @@ class _BigIntImpl implements BigInt {
   ///
   /// The [source] will be checked for invalid characters. If it is invalid,
   /// this function returns `null`.
-  static _BigIntImpl _parseRadix(String source, int radix, bool isNegative) {
+  static _BigIntImpl? _parseRadix(String source, int radix, bool isNegative) {
     var result = zero;
     var base = new _BigIntImpl._fromInt(radix);
     for (int i = 0; i < source.length; i++) {
@@ -1082,7 +1104,7 @@ class _BigIntImpl implements BigInt {
   /// Returns the parsed big integer, or `null` if it failed.
   ///
   /// If the [radix] is `null` accepts decimal literals or `0x` hex literals.
-  static _BigIntImpl _tryParse(String source, {int radix}) {
+  static _BigIntImpl? _tryParse(String source, {int? radix}) {
     if (source == "") return null;
 
     var match = _parseRE.firstMatch(source);
@@ -1094,9 +1116,9 @@ class _BigIntImpl implements BigInt {
 
     bool isNegative = match[signIndex] == "-";
 
-    String decimalMatch = match[decimalIndex];
-    String hexMatch = match[hexIndex];
-    String nonDecimalMatch = match[nonDecimalHexIndex];
+    String? decimalMatch = match[decimalIndex];
+    String? hexMatch = match[hexIndex];
+    String? nonDecimalMatch = match[nonDecimalHexIndex];
 
     if (radix == null) {
       if (decimalMatch != null) {
@@ -1120,11 +1142,11 @@ class _BigIntImpl implements BigInt {
       return _parseDecimal(decimalMatch, isNegative);
     }
     if (radix == 16 && (decimalMatch != null || nonDecimalMatch != null)) {
-      return _parseHex(decimalMatch ?? nonDecimalMatch, 0, isNegative);
+      return _parseHex(decimalMatch ?? nonDecimalMatch!, 0, isNegative);
     }
 
     return _parseRadix(
-        decimalMatch ?? nonDecimalMatch ?? hexMatch, radix, isNegative);
+        decimalMatch ?? nonDecimalMatch ?? hexMatch!, radix, isNegative);
   }
 
   static RegExp _parseRE = RegExp(
@@ -1173,7 +1195,7 @@ class _BigIntImpl implements BigInt {
     if (value.abs() < 0x100000000)
       return new _BigIntImpl._fromInt(value.toInt());
     if (value is double) return new _BigIntImpl._fromDouble(value);
-    return new _BigIntImpl._fromInt(value);
+    return new _BigIntImpl._fromInt(value as int);
   }
 
   factory _BigIntImpl._fromInt(int value) {

sdk/lib/_internal/js_runtime/lib/developer_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for dart:developer library.
 
 import 'dart:_js_helper' show patch, ForceInline;
@@ -13,7 +11,7 @@ import 'dart:isolate';
 
 @patch
 @pragma('dart2js:tryInline')
-bool debugger({bool when: true, String message}) {
+bool debugger({bool when = true, String? message}) {
   if (when) {
     JS('', 'debugger');
   }
@@ -21,26 +19,26 @@ bool debugger({bool when: true, String message}) {
 }
 
 @patch
-Object inspect(Object object) {
+Object? inspect(Object? object) {
   return object;
 }
 
 @patch
 void log(String message,
-    {DateTime time,
-    int sequenceNumber,
-    int level: 0,
-    String name: '',
-    Zone zone,
-    Object error,
-    StackTrace stackTrace}) {
+    {DateTime? time,
+    int? sequenceNumber,
+    int level = 0,
+    String name = '',
+    Zone? zone,
+    Object? error,
+    StackTrace? stackTrace}) {
   // TODO.
 }
 
-final _extensions = new Map<String, ServiceExtensionHandler>();
+final _extensions = <String, ServiceExtensionHandler>{};
 
 @patch
-ServiceExtensionHandler _lookupExtension(String method) {
+ServiceExtensionHandler? _lookupExtension(String method) {
   return _extensions[method];
 }
 
@@ -110,7 +108,7 @@ void _webServerControl(SendPort sendPort, bool enable) {
 }
 
 @patch
-String _getIsolateIDFromSendPort(SendPort sendPort) {
+String? _getIsolateIDFromSendPort(SendPort sendPort) {
   return null;
 }
 
@@ -124,7 +122,7 @@ class UserTag {
 }
 
 class _FakeUserTag implements UserTag {
-  static Map _instances = {};
+  static final _instances = <String, _FakeUserTag>{};
 
   _FakeUserTag.real(this.label);
 
@@ -136,13 +134,10 @@ class _FakeUserTag implements UserTag {
     }
     // Throw an exception if we've reached the maximum number of user tags.
     if (_instances.length == UserTag.MAX_USER_TAGS) {
-      throw new UnsupportedError(
+      throw UnsupportedError(
           'UserTag instance limit (${UserTag.MAX_USER_TAGS}) reached.');
     }
-    // Create a new instance and add it to the instance map.
-    var instance = new _FakeUserTag.real(label);
-    _instances[label] = instance;
-    return instance;
+    return _instances[label] = _FakeUserTag.real(label);
   }
 
   final String label;

sdk/lib/_internal/js_runtime/lib/foreign_helper.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library _foreign_helper;
 
 import 'dart:_js_embedded_names' show JsGetName, JsBuiltin;

sdk/lib/_internal/js_runtime/lib/instantiation.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of _js_helper;
 
 /// Support class for generic function type instantiation (binding of types).

sdk/lib/_internal/js_runtime/lib/interceptors.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 library _interceptors;
 
 import 'dart:_js_embedded_names'
@@ -63,17 +61,6 @@ part 'js_string.dart';
 final String DART_CLOSURE_PROPERTY_NAME =
     getIsolateAffinityTag(r'_$dart_dartClosure');
 
-String _symbolToString(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);
-
-_symbolMapToStringMap(Map<Symbol, dynamic> map) {
-  if (map == null) return null;
-  var result = new Map<String, dynamic>();
-  map.forEach((Symbol key, value) {
-    result[_symbolToString(key)] = value;
-  });
-  return result;
-}
-
 getDispatchProperty(object) {
   return JS(
       '', '#[#]', object, JS_EMBEDDED_GLOBAL('String', DISPATCH_PROPERTY_NAME));
@@ -123,7 +110,7 @@ makeDispatchRecord(interceptor, proto, extension, indexability) {
 dispatchRecordInterceptor(record) => JS('', '#.i', record);
 dispatchRecordProto(record) => JS('', '#.p', record);
 dispatchRecordExtension(record) => JS('', '#.e', record);
-dispatchRecordIndexability(record) => JS('bool|Null', '#.x', record);
+bool? dispatchRecordIndexability(record) => JS('bool|Null', '#.x', record);
 
 /// Returns the interceptor for a native class instance. Used by
 /// [getInterceptor].
@@ -197,7 +184,10 @@ getNativeInterceptor(object) {
 }
 
 // A JS String or Symbol.
-final JS_INTEROP_INTERCEPTOR_TAG = getIsolateAffinityTag(r'_$dart_js');
+dynamic _JS_INTEROP_INTERCEPTOR_TAG = null;
+get JS_INTEROP_INTERCEPTOR_TAG {
+  return _JS_INTEROP_INTERCEPTOR_TAG ??= getIsolateAffinityTag(r'_$dart_js');
+}
 
 lookupInterceptorByConstructor(constructor) {
   return constructor == null
@@ -236,7 +226,7 @@ get typeToInterceptorMap {
   return JS_EMBEDDED_GLOBAL('', TYPE_TO_INTERCEPTOR_MAP);
 }
 
-int findIndexForNativeSubclassType(Type type) {
+int? findIndexForNativeSubclassType(Type? type) {
   if (JS('bool', '# == null', typeToInterceptorMap)) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
   for (int i = 0; i + 1 < map.length; i += 3) {
@@ -247,7 +237,7 @@ int findIndexForNativeSubclassType(Type type) {
   return null;
 }
 
-findInterceptorConstructorForType(Type type) {
+findInterceptorConstructorForType(Type? type) {
   var index = findIndexForNativeSubclassType(type);
   if (index == null) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
@@ -258,7 +248,7 @@ findInterceptorConstructorForType(Type type) {
 /// `null` if there is no such constructor.
 ///
 /// The returned function takes one argument, the web component object.
-findConstructorForNativeSubclassType(Type type, String name) {
+findConstructorForNativeSubclassType(Type? type, String name) {
   var index = findIndexForNativeSubclassType(type);
   if (index == null) return null;
   List map = JS('JSFixedArray', '#', typeToInterceptorMap);
@@ -267,7 +257,7 @@ findConstructorForNativeSubclassType(Type type, String name) {
   return constructorFn;
 }
 
-findInterceptorForType(Type type) {
+findInterceptorForType(Type? type) {
   var constructor = findInterceptorConstructorForType(type);
   if (constructor == null) return null;
   return JS('', '#.prototype', constructor);

sdk/lib/_internal/js_runtime/lib/internal_patch.dart

@@ -2,15 +2,20 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 import 'dart:core' hide Symbol;
-import 'dart:core' as core;
+import 'dart:core' as core show Symbol;
 import 'dart:_js_primitives' show printString;
-import 'dart:_js_helper' show patch, NoInline;
+import 'dart:_js_helper' show patch;
 import 'dart:_interceptors' show JSArray;
 import 'dart:_foreign_helper' show JS, JS_GET_FLAG;
 
+@patch
+@pragma('dart2js:tryInline')
+bool typeAcceptsNull<T>() {
+  bool isLegacySubtyping = JS_GET_FLAG('LEGACY');
+  return isLegacySubtyping || null is T;
+}
+
 @patch
 class Symbol implements core.Symbol {
   @patch
@@ -18,7 +23,7 @@ class Symbol implements core.Symbol {
 
   @patch
   int get hashCode {
-    int hash = JS('int|Null', '#._hashCode', this);
+    int? hash = JS('int|Null', '#._hashCode', this);
     if (hash != null) return hash;
     const arbitraryPrime = 664597;
     hash = 0x1fffffff & (arbitraryPrime * _name.hashCode);

sdk/lib/_internal/js_runtime/lib/io_patch.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 import 'dart:_js_helper' show patch;
 import 'dart:_internal' hide Symbol;
 import 'dart:async';
@@ -75,7 +73,7 @@ class _AsyncDirectoryListerOps {
 @patch
 class _EventHandler {
   @patch
-  static void _sendData(Object sender, SendPort sendPort, int data) {
+  static void _sendData(Object? sender, SendPort sendPort, int data) {
     throw new UnsupportedError("EventHandler._sendData");
   }
 }
@@ -305,7 +303,7 @@ class _Platform {
 @patch
 class _ProcessUtils {
   @patch
-  static void _exit(int status) {
+  static Never _exit(int status) {
     throw new UnsupportedError("ProcessUtils._exit");
   }
 
@@ -325,7 +323,7 @@ class _ProcessUtils {
   }
 
   @patch
-  static int _pid(Process process) {
+  static int _pid(Process? process) {
     throw new UnsupportedError("ProcessUtils._pid");
   }
 
@@ -352,8 +350,8 @@ class ProcessInfo {
 class Process {
   @patch
   static Future<Process> start(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment: true,
       bool runInShell: false,
       ProcessStartMode mode: ProcessStartMode.normal}) {
@@ -362,8 +360,8 @@ class Process {
 
   @patch
   static Future<ProcessResult> run(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment: true,
       bool runInShell: false,
       Encoding stdoutEncoding: systemEncoding,
@@ -373,8 +371,8 @@ class Process {
 
   @patch
   static ProcessResult runSync(String executable, List<String> arguments,
-      {String workingDirectory,
-      Map<String, String> environment,
+      {String? workingDirectory,
+      Map<String, String>? environment,
       bool includeParentEnvironment: true,
       bool runInShell: false,
       Encoding stdoutEncoding: systemEncoding,
@@ -411,13 +409,13 @@ class InternetAddress {
   }
 
   @patch
-  factory InternetAddress(String address, {InternetAddressType type}) {
+  factory InternetAddress(String address, {InternetAddressType? type}) {
     throw new UnsupportedError("InternetAddress");
   }
 
   @patch
   factory InternetAddress.fromRawAddress(Uint8List rawAddress,
-      {InternetAddressType type}) {
+      {InternetAddressType? type}) {
     throw new UnsupportedError("InternetAddress.fromRawAddress");
   }
 
@@ -434,8 +432,8 @@ class InternetAddress {
   }
 
   @patch
-  static InternetAddress tryParse(String address) {
-    throw new UnsupportedError("InternetAddress.tryParse");
+  static InternetAddress? tryParse(String address) {
+    throw UnsupportedError("InternetAddress.tryParse");
   }
 }
 
@@ -476,14 +474,14 @@ class ServerSocket {
 @patch
 class RawSocket {
   @patch
-  static Future<RawSocket> connect(host, int port,
-      {sourceAddress, Duration timeout}) {
+  static Future<RawSocket> connect(dynamic host, int port,
+      {dynamic sourceAddress, Duration? timeout}) {
     throw new UnsupportedError("RawSocket constructor");
   }
 
   @patch
-  static Future<ConnectionTask<RawSocket>> startConnect(host, int port,
-      {sourceAddress}) {
+  static Future<ConnectionTask<RawSocket>> startConnect(dynamic host, int port,
+      {dynamic sourceAddress}) {
     throw new UnsupportedError("RawSocket constructor");
   }
 }
@@ -491,14 +489,14 @@ class RawSocket {
 @patch
 class Socket {
   @patch
-  static Future<Socket> _connect(host, int port,
-      {sourceAddress, Duration timeout}) {
+  static Future<Socket> _connect(dynamic host, int port,
+      {dynamic sourceAddress, Duration? timeout}) {
     throw new UnsupportedError("Socket constructor");
   }
 
   @patch
-  static Future<ConnectionTask<Socket>> _startConnect(host, int port,
-      {sourceAddress}) {
+  static Future<ConnectionTask<Socket>> _startConnect(dynamic host, int port,
+      {dynamic sourceAddress}) {
     throw new UnsupportedError("Socket constructor");
   }
 }
@@ -514,7 +512,7 @@ class SecureSocket {
 @patch
 class RawSynchronousSocket {
   @patch
-  static RawSynchronousSocket connectSync(host, int port) {
+  static RawSynchronousSocket connectSync(dynamic host, int port) {
     throw new UnsupportedError("RawSynchronousSocket.connectSync");
   }
 }
@@ -556,7 +554,7 @@ class X509Certificate {
 @patch
 class RawDatagramSocket {
   @patch
-  static Future<RawDatagramSocket> bind(host, int port,
+  static Future<RawDatagramSocket> bind(dynamic host, int port,
       {bool reuseAddress: true, bool reusePort: false, int ttl: 1}) {
     throw new UnsupportedError("RawDatagramSocket.bind");
   }
@@ -618,14 +616,14 @@ class RawZLibFilter {
       int windowBits,
       int memLevel,
       int strategy,
-      List<int> dictionary,
+      List<int>? dictionary,
       bool raw) {
     throw new UnsupportedError("_newZLibDeflateFilter");
   }
 
   @patch
   static RawZLibFilter _makeZLibInflateFilter(
-      int windowBits, List<int> dictionary, bool raw) {
+      int windowBits, List<int>? dictionary, bool raw) {
     throw new UnsupportedError("_newZLibInflateFilter");
   }
 }

sdk/lib/_internal/js_runtime/lib/isolate_patch.dart

@@ -2,14 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 // Patch file for the dart:isolate library.
 
 import "dart:async";
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper' show patch;
-import "dart:typed_data" show ByteData, TypedData, Uint8List;
+import "dart:typed_data" show TypedData;
 
 @patch
 class Isolate {
@@ -19,45 +17,46 @@ class Isolate {
   }
 
   @patch
-  String get debugName {
+  String? get debugName {
     throw new UnsupportedError("Isolate.debugName");
   }
 
   @patch
-  static Future<Uri> get packageRoot {
+  static Future<Uri?> get packageRoot {
     throw new UnsupportedError("Isolate.packageRoot");
   }
 
   @patch
-  static Future<Uri> get packageConfig {
+  static Future<Uri?> get packageConfig {
     throw new UnsupportedError("Isolate.packageConfig");
   }
 
   @patch
-  static Future<Uri> resolvePackageUri(Uri packageUri) {
+  static Future<Uri?> resolvePackageUri(Uri packageUri) {
     throw new UnsupportedError("Isolate.resolvePackageUri");
   }
 
   @patch
   static Future<Isolate> spawn<T>(void entryPoint(T message), T message,
-      {bool paused: false,
-      bool errorsAreFatal,
-      SendPort onExit,
-      SendPort onError}) {
+      {bool paused = false,
+      bool errorsAreFatal = true,
+      SendPort? onExit,
+      SendPort? onError}) {
     throw new UnsupportedError("Isolate.spawn");
   }
 
   @patch
   static Future<Isolate> spawnUri(Uri uri, List<String> args, var message,
-      {bool paused: false,
-      SendPort onExit,
-      SendPort onError,
-      bool errorsAreFatal,
-      bool checked,
-      Map<String, String> environment,
-      Uri packageRoot,
-      Uri packageConfig,
-      bool automaticPackageResolution: false}) {
+      {bool paused = false,
+      SendPort? onExit,
+      SendPort? onError,
+      bool errorsAreFatal = true,
+      bool? checked,
+      Map<String, String>? environment,
+      Uri? packageRoot,
+      Uri? packageConfig,
+      bool automaticPackageResolution = false,
+      String? debugName}) {
     throw new UnsupportedError("Isolate.spawnUri");
   }
 
@@ -72,7 +71,7 @@ class Isolate {
   }
 
   @patch
-  void addOnExitListener(SendPort responsePort, {Object response}) {
+  void addOnExitListener(SendPort responsePort, {Object? response}) {
     throw new UnsupportedError("Isolate.addOnExitListener");
   }
 
@@ -87,12 +86,13 @@ class Isolate {
   }
 
   @patch
-  void kill({int priority: beforeNextEvent}) {
+  void kill({int priority = beforeNextEvent}) {
     throw new UnsupportedError("Isolate.kill");
   }
 
   @patch
-  void ping(SendPort responsePort, {Object response, int priority: immediate}) {
+  void ping(SendPort responsePort,
+      {Object? response, int priority = immediate}) {
     throw new UnsupportedError("Isolate.ping");
   }
 
@@ -119,8 +119,10 @@ class ReceivePort {
 }
 
 class _ReceivePortImpl extends Stream implements ReceivePort {
-  StreamSubscription listen(void onData(var event),
-      {Function onError, void onDone(), bool cancelOnError}) {
+  StreamSubscription listen(void Function(dynamic)? onData,
+      {Function? onError,
+      void Function()? onDone,
+      bool? cancelOnError = true}) {
     throw new UnsupportedError("ReceivePort.listen");
   }
 
@@ -132,7 +134,7 @@ class _ReceivePortImpl extends Stream implements ReceivePort {
 @patch
 class RawReceivePort {
   @patch
-  factory RawReceivePort([Function handler]) {
+  factory RawReceivePort([Function? handler]) {
     throw new UnsupportedError('new RawReceivePort');
   }
 }

sdk/lib/_internal/js_runtime/lib/js_array.dart

@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.6
-
 part of _interceptors;
 
 class _Growable {
@@ -16,7 +14,7 @@ const _ListConstructorSentinel = const _Growable();
 /// class as an interceptor, and changes references to [:this:] to
 /// actually use the receiver of the method, which is generated as an extra
 /// argument added to each member.
-class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
+class JSArray<E> extends Interceptor implements List<E>, JSIndexable<E> {
   const JSArray();
 
   // This factory constructor is the redirection target of the List() factory
@@ -82,7 +80,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
   factory JSArray.markGrowable(allocation) =>
       JS('JSExtendableArray', '#', new JSArray<E>.typed(allocation));
 
-  static List markFixedList(List list) {
+  static List<T> markFixedList<T>(List<T> list) {
     // Functions are stored in the hidden class and not as properties in
     // the object. We never actually look at the value, but only want
     // to know if the property exists.
@@ -90,7 +88,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return JS('JSFixedArray', '#', list);
   }
 
-  static List markUnmodifiableList(List list) {
+  static List<T> markUnmodifiableList<T>(List list) {
     // Functions are stored in the hidden class and not as properties in
     // the object. We never actually look at the value, but only want
     // to know if the property exists.
@@ -178,7 +176,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return JS('', r'#.pop()', this);
   }
 
-  bool remove(Object element) {
+  bool remove(Object? element) {
     checkGrowable('remove');
     for (int i = 0; i < this.length; i++) {
       if (this[i] == element) {
@@ -266,7 +264,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
   }
 
   String join([String separator = '']) {
-    var list = new List(this.length);
+    var list = List.filled(this.length, "");
     for (int i = 0; i < this.length; i++) {
       list[i] = '${this[i]}';
     }
@@ -316,7 +314,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return value;
   }
 
-  E firstWhere(bool test(E value), {E orElse()}) {
+  E firstWhere(bool Function(E) test, {E Function()? orElse}) {
     var end = this.length;
     for (int i = 0; i < end; ++i) {
       // TODO(22407): Improve bounds check elimination to allow this JS code to
@@ -329,7 +327,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     throw IterableElementError.noElement();
   }
 
-  E lastWhere(bool test(E element), {E orElse()}) {
+  E lastWhere(bool Function(E) test, {E Function()? orElse}) {
     int length = this.length;
     for (int i = length - 1; i >= 0; i--) {
       // TODO(22407): Improve bounds check elimination to allow this JS code to
@@ -344,9 +342,9 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     throw IterableElementError.noElement();
   }
 
-  E singleWhere(bool test(E element), {E orElse()}) {
+  E singleWhere(bool Function(E) test, {E Function()? orElse}) {
     int length = this.length;
-    E match = null;
+    E? match = null;
     bool matchFound = false;
     for (int i = 0; i < length; i++) {
       // TODO(22407): Improve bounds check elimination to allow this JS code to
@@ -363,7 +361,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
         throw new ConcurrentModificationError(this);
       }
     }
-    if (matchFound) return match;
+    if (matchFound) return match as E;
     if (orElse != null) return orElse();
     throw IterableElementError.noElement();
   }
@@ -372,7 +370,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return this[index];
   }
 
-  List<E> sublist(int start, [int end]) {
+  List<E> sublist(int start, [int? end]) {
     checkNull(start); // TODO(ahe): This is not specified but co19 tests it.
     if (start is! int) throw argumentErrorValue(start);
     if (start < 0 || start > length) {
@@ -431,7 +429,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     int otherStart;
     // TODO(floitsch): Make this accept more.
     if (iterable is List) {
-      otherList = iterable;
+      otherList = JS<List<E>>('', '#', iterable);
       otherStart = skipCount;
     } else {
       otherList = iterable.skip(skipCount).toList(growable: false);
@@ -459,12 +457,14 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     }
   }
 
-  void fillRange(int start, int end, [E fillValue]) {
+  void fillRange(int start, int end, [E? fillValue]) {
     checkMutable('fill range');
     RangeError.checkValidRange(start, end, this.length);
+    E checkedFillValue = fillValue as E;
     for (int i = start; i < end; i++) {
-      // Store is safe since [fillValue] type has been checked as parameter.
-      JS('', '#[#] = #', this, i, fillValue);
+      // Store is safe since [checkedFillValue] type has been checked as
+      // parameter and for null.
+      JS('', '#[#] = #', this, i, checkedFillValue);
     }
   }
 
@@ -521,18 +521,16 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
 
   Iterable<E> get reversed => new ReversedListIterable<E>(this);
 
-  void sort([int compare(E a, E b)]) {
+  void sort([int Function(E, E)? compare]) {
     checkMutable('sort');
     Sort.sort(this, compare ?? _compareAny);
   }
 
   static int _compareAny(a, b) {
-    // In strong mode Comparable.compare requires an implicit cast to ensure
-    // `a` and `b` are Comparable.
     return Comparable.compare(a, b);
   }
 
-  void shuffle([Random random]) {
+  void shuffle([Random? random]) {
     checkMutable('shuffle');
     if (random == null) random = new Random();
     int length = this.length;
@@ -545,14 +543,15 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     }
   }
 
-  int indexOf(Object element, [int start = 0]) {
-    if (start >= this.length) {
+  int indexOf(Object? element, [int start = 0]) {
+    int length = this.length;
+    if (start >= length) {
       return -1;
     }
     if (start < 0) {
       start = 0;
     }
-    for (int i = start; i < this.length; i++) {
+    for (int i = start; i < length; i++) {
       if (this[i] == element) {
         return i;
       }
@@ -560,18 +559,15 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return -1;
   }
 
-  int lastIndexOf(Object element, [int startIndex]) {
-    if (startIndex == null) {
-      startIndex = this.length - 1;
-    } else {
-      if (startIndex < 0) {
-        return -1;
-      }
-      if (startIndex >= this.length) {
-        startIndex = this.length - 1;
-      }
+  int lastIndexOf(Object? element, [int? startIndex]) {
+    int start = startIndex ?? this.length - 1;
+    if (start < 0) {
+      return -1;
     }
-    for (int i = startIndex; i >= 0; i--) {
+    if (start >= this.length) {
+      start = this.length - 1;
+    }
+    for (int i = start; i >= 0; i--) {
       if (this[i] == element) {
         return i;
       }
@@ -579,9 +575,10 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return -1;
   }
 
-  bool contains(Object other) {
+  bool contains(Object? other) {
     for (int i = 0; i < length; i++) {
-      if (this[i] == other) return true;
+      E element = JS('', '#[#]', this, i);
+      if (element == other) return true;
     }
     return false;
   }
@@ -646,13 +643,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
 
   Iterable<T> whereType<T>() => new WhereTypeIterable<T>(this);
 
-  List<E> operator +(List<E> other) {
-    int totalLength = this.length + other.length;
-    return <E>[]
-      ..length = totalLength
-      ..setRange(0, this.length, this)
-      ..setRange(this.length, totalLength, other);
-  }
+  List<E> operator +(List<E> other) => [...this, ...other];
 
   int indexWhere(bool test(E element), [int start = 0]) {
     if (start >= this.length) return -1;
@@ -663,7 +654,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
     return -1;
   }
 
-  int lastIndexWhere(bool test(E element), [int start]) {
+  int lastIndexWhere(bool test(E element), [int? start]) {
     if (start == null) start = this.length - 1;
     if (start < 0) return -1;
     for (int i = start; i >= 0; i--) {
@@ -692,7 +683,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable {
 /// 'isGrowable' and 'isMutable' checks into the getInterceptor implementation
 /// so these classes can have specialized implementations. Doing so will
 /// challenge many assumptions in the JS backend.
-class JSMutableArray<E> extends JSArray<E> implements JSMutableIndexable {}
+class JSMutableArray<E> extends JSArray<E> implements JSMutableIndexable<E> {}
 
 class JSFixedArray<E> extends JSMutableArray<E> {}
 
@@ -706,14 +697,14 @@ class ArrayIterator<E> implements Iterator<E> {
   final JSArray<E> _iterable;
   final int _length;
   int _index;
-  E _current;
+  E? _current;
 
   ArrayIterator(JSArray<E> iterable)
       : _iterable = iterable,
         _length = iterable.length,
         _index = 0;
 
-  E get current => _current;
+  E get current => _current as E;
 
   bool moveNext() {
     int length = _iterable.length;