Reland: [cfe] Embed and use allowed experiments in CFE

This CL embeds the sdk_nnbd/lib/_internal/allowed_experiments.json
into the CFE and uses this to allow experiments enabled on a
per library basis. The file is embedded through generated code to
avoid reliance on access to the file itself.

A presubmit check is also added to ensure that the json file and
the generated code are in sync.

This work is in preparation for https://github.com/dart-lang/sdk/issues/41538

This was reverted in https://dart-review.googlesource.com/c/sdk/+/149620
because flutter wasn't prepared for auto-enabling nnbd in dart:* libraries.
This has now been fixed in https://github.com/flutter/engine/pull/18714

Closes #42162

Change-Id: I686ed6feaef8ee066b426068fe2a0f5080bf1713
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149588
Reviewed-by: Jens Johansen <jensj@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/_fe_analyzer_shared/lib/src/sdk/allowed_experiments.dart

@@ -27,7 +27,7 @@ class AllowedExperiments {
   /// are enabled for all files of this package.
   final Map<String, List<String>> packageExperiments;
 
-  const AllowedExperiments({
+  AllowedExperiments({
     @required this.sdkDefaultExperiments,
     @required this.sdkLibraryExperiments,
     @required this.packageExperiments,

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

@@ -16,6 +16,7 @@ import '../base/nnbd_mode.dart';
 
 import 'experimental_flags.dart'
     show
+        AllowedExperimentalFlags,
         defaultExperimentalFlags,
         ExperimentalFlag,
         expiredExperimentalFlags,
@@ -129,6 +130,8 @@ class CompilerOptions {
   /// Features not mentioned in the map will have their default value.
   Map<ExperimentalFlag, bool> experimentalFlags = <ExperimentalFlag, bool>{};
 
+  AllowedExperimentalFlags allowedExperimentalFlags;
+
   /// Environment map used when evaluating `bool.fromEnvironment`,
   /// `int.fromEnvironment` and `String.fromEnvironment` during constant
   /// evaluation. If the map is `null`, all environment constants will be left

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

@@ -1,86 +1,117 @@
-// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2020, 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.
 
-// NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
-//
-// Instead modify 'tools/experimental_features.yaml' and run
-// 'dart pkg/front_end/tool/fasta.dart generate-experimental-flags' to update.
-
-import 'package:_fe_analyzer_shared/src/sdk/allowed_experiments.dart';
 import 'package:kernel/kernel.dart' show Version;
 
-enum ExperimentalFlag {
-  constantUpdate2018,
-  controlFlowCollections,
-  extensionMethods,
-  nonNullable,
-  nonfunctionTypeAliases,
-  setLiterals,
-  spreadCollections,
-  tripleShift,
-  variance,
-}
+part 'experimental_flags_generated.dart';
 
-const Version enableConstantUpdate2018Version = const Version(2, 4);
-const Version enableControlFlowCollectionsVersion = const Version(2, 2);
-const Version enableExtensionMethodsVersion = const Version(2, 6);
-const Version enableNonNullableVersion = const Version(2, 9);
-const Version enableNonfunctionTypeAliasesVersion = const Version(2, 9);
-const Version enableSetLiteralsVersion = const Version(2, 2);
-const Version enableSpreadCollectionsVersion = const Version(2, 2);
-const Version enableTripleShiftVersion = const Version(2, 9);
-const Version enableVarianceVersion = const Version(2, 9);
+/// 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`.
+class AllowedExperimentalFlags {
+  /// The set of experiments that are enabled for all SDK libraries other than
+  /// for those which are specified in [sdkLibraryExperiments].
+  final Set<ExperimentalFlag> sdkDefaultExperiments;
 
-ExperimentalFlag parseExperimentalFlag(String flag) {
-  switch (flag) {
-    case "constant-update-2018":
-      return ExperimentalFlag.constantUpdate2018;
-    case "control-flow-collections":
-      return ExperimentalFlag.controlFlowCollections;
-    case "extension-methods":
-      return ExperimentalFlag.extensionMethods;
-    case "non-nullable":
-      return ExperimentalFlag.nonNullable;
-    case "nonfunction-type-aliases":
-      return ExperimentalFlag.nonfunctionTypeAliases;
-    case "set-literals":
-      return ExperimentalFlag.setLiterals;
-    case "spread-collections":
-      return ExperimentalFlag.spreadCollections;
-    case "triple-shift":
-      return ExperimentalFlag.tripleShift;
-    case "variance":
-      return ExperimentalFlag.variance;
+  /// Mapping from individual SDK libraries, e.g. 'core', to the set of
+  /// experiments that are enabled for this library.
+  final Map<String, Set<ExperimentalFlag>> sdkLibraryExperiments;
+
+  /// Mapping from package names, e.g. 'path', to the set of experiments that
+  /// are enabled for all files of this package.
+  final Map<String, Set<ExperimentalFlag>> packageExperiments;
+
+  const AllowedExperimentalFlags({
+    this.sdkDefaultExperiments: const {},
+    this.sdkLibraryExperiments: const {},
+    this.packageExperiments: const {},
+  });
+
+  /// Return the set of enabled experiments for the package with the [name],
+  /// e.g. "path", possibly `null`.
+  Set<ExperimentalFlag> forPackage(String name) {
+    return packageExperiments[name];
+  }
+
+  /// Return the set of enabled experiments for the library with the [name],
+  /// e.g. "core".
+  Set<ExperimentalFlag> forSdkLibrary(String name) {
+    return sdkLibraryExperiments[name] ?? sdkDefaultExperiments;
   }
-  return null;
 }
 
-const Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
-  ExperimentalFlag.constantUpdate2018: true,
-  ExperimentalFlag.controlFlowCollections: true,
-  ExperimentalFlag.extensionMethods: true,
-  ExperimentalFlag.nonNullable: false,
-  ExperimentalFlag.nonfunctionTypeAliases: false,
-  ExperimentalFlag.setLiterals: true,
-  ExperimentalFlag.spreadCollections: true,
-  ExperimentalFlag.tripleShift: false,
-  ExperimentalFlag.variance: false,
-};
+/// Returns `true` if [flag] is enabled using global [experimentalFlags].
+///
+/// If [experimentalFlags] is `null` or doesn't contain [flag], the default
+/// value from [defaultExperimentalFlags] is returned.
+///
+/// If [flag] is marked as expired in [expiredExperimentalFlags], the value from
+/// [defaultExperimentalFlags] is always returned.
+bool isExperimentEnabled(ExperimentalFlag flag,
+    {Map<ExperimentalFlag, bool> experimentalFlags}) {
+  assert(defaultExperimentalFlags.containsKey(flag),
+      "No default value for $flag.");
+  assert(expiredExperimentalFlags.containsKey(flag),
+      "No expired value for $flag.");
+  if (expiredExperimentalFlags[flag]) {
+    return defaultExperimentalFlags[flag];
+  }
+  bool enabled;
+  if (experimentalFlags != null) {
+    enabled = experimentalFlags[flag];
+  }
+  enabled ??= defaultExperimentalFlags[flag];
+  return enabled;
+}
 
-const Map<ExperimentalFlag, bool> expiredExperimentalFlags = {
-  ExperimentalFlag.constantUpdate2018: true,
-  ExperimentalFlag.controlFlowCollections: true,
-  ExperimentalFlag.extensionMethods: false,
-  ExperimentalFlag.nonNullable: false,
-  ExperimentalFlag.nonfunctionTypeAliases: false,
-  ExperimentalFlag.setLiterals: true,
-  ExperimentalFlag.spreadCollections: true,
-  ExperimentalFlag.tripleShift: false,
-  ExperimentalFlag.variance: false,
-};
-
-const AllowedExperiments allowedExperiments =
-    const AllowedExperiments(sdkDefaultExperiments: [
-  "non-nullable",
-], sdkLibraryExperiments: {}, packageExperiments: {});
+/// Returns `true` if [flag] is enabled in the library with the [canonicalUri]
+/// either globally using [experimentalFlags] or per library using
+/// [allowedExperimentalFlags].
+///
+/// If [experimentalFlags] is `null` or doesn't contain [flag], the default
+/// value from [defaultExperimentalFlags] used as the global flag state.
+///
+/// If [allowedExperimentalFlags] is `null` [defaultAllowedExperimentalFlags] is
+/// used for the per library flag state.
+///
+/// If [flag] is marked as expired in [expiredExperimentalFlags], the value from
+/// [defaultExperimentalFlags] is always returned.
+///
+/// The canonical uri, also known as the import uri, is the absolute uri that
+/// defines the identity of a library, for instance `dart:core`, `package:foo`,
+/// or `file:///path/dir/file.dart`.
+bool isExperimentEnabledInLibrary(ExperimentalFlag flag, Uri canonicalUri,
+    {Map<ExperimentalFlag, bool> experimentalFlags,
+    AllowedExperimentalFlags allowedExperimentalFlags}) {
+  assert(defaultExperimentalFlags.containsKey(flag),
+      "No default value for $flag.");
+  assert(expiredExperimentalFlags.containsKey(flag),
+      "No expired value for $flag.");
+  if (expiredExperimentalFlags[flag]) {
+    return defaultExperimentalFlags[flag];
+  }
+  bool enabled;
+  if (experimentalFlags != null) {
+    enabled = experimentalFlags[flag];
+  }
+  enabled ??= defaultExperimentalFlags[flag];
+  if (!enabled) {
+    allowedExperimentalFlags ??= defaultAllowedExperimentalFlags;
+    Set<ExperimentalFlag> allowedFlags;
+    if (canonicalUri.scheme == 'dart') {
+      allowedFlags = allowedExperimentalFlags.forSdkLibrary(canonicalUri.path);
+    } else if (canonicalUri.scheme == 'package') {
+      int index = canonicalUri.path.indexOf('/');
+      if (index >= 0) {
+        String packageName = canonicalUri.path.substring(0, index);
+        allowedFlags = allowedExperimentalFlags.forPackage(packageName);
+      }
+    }
+    if (allowedFlags != null) {
+      enabled = allowedFlags.contains(flag);
+    }
+  }
+  return enabled;
+}

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

@@ -0,0 +1,85 @@
+// Copyright (c) 2020, 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.
+
+// NOTE: THIS FILE IS GENERATED. DO NOT EDIT.
+//
+// Instead modify 'tools/experimental_features.yaml' and run
+// 'dart pkg/front_end/tool/fasta.dart generate-experimental-flags' to update.
+
+part of 'experimental_flags.dart';
+
+enum ExperimentalFlag {
+  constantUpdate2018,
+  controlFlowCollections,
+  extensionMethods,
+  nonNullable,
+  nonfunctionTypeAliases,
+  setLiterals,
+  spreadCollections,
+  tripleShift,
+  variance,
+}
+
+const Version enableConstantUpdate2018Version = const Version(2, 4);
+const Version enableControlFlowCollectionsVersion = const Version(2, 2);
+const Version enableExtensionMethodsVersion = const Version(2, 6);
+const Version enableNonNullableVersion = const Version(2, 9);
+const Version enableNonfunctionTypeAliasesVersion = const Version(2, 9);
+const Version enableSetLiteralsVersion = const Version(2, 2);
+const Version enableSpreadCollectionsVersion = const Version(2, 2);
+const Version enableTripleShiftVersion = const Version(2, 9);
+const Version enableVarianceVersion = const Version(2, 9);
+
+ExperimentalFlag parseExperimentalFlag(String flag) {
+  switch (flag) {
+    case "constant-update-2018":
+      return ExperimentalFlag.constantUpdate2018;
+    case "control-flow-collections":
+      return ExperimentalFlag.controlFlowCollections;
+    case "extension-methods":
+      return ExperimentalFlag.extensionMethods;
+    case "non-nullable":
+      return ExperimentalFlag.nonNullable;
+    case "nonfunction-type-aliases":
+      return ExperimentalFlag.nonfunctionTypeAliases;
+    case "set-literals":
+      return ExperimentalFlag.setLiterals;
+    case "spread-collections":
+      return ExperimentalFlag.spreadCollections;
+    case "triple-shift":
+      return ExperimentalFlag.tripleShift;
+    case "variance":
+      return ExperimentalFlag.variance;
+  }
+  return null;
+}
+
+const Map<ExperimentalFlag, bool> defaultExperimentalFlags = {
+  ExperimentalFlag.constantUpdate2018: true,
+  ExperimentalFlag.controlFlowCollections: true,
+  ExperimentalFlag.extensionMethods: true,
+  ExperimentalFlag.nonNullable: false,
+  ExperimentalFlag.nonfunctionTypeAliases: false,
+  ExperimentalFlag.setLiterals: true,
+  ExperimentalFlag.spreadCollections: true,
+  ExperimentalFlag.tripleShift: false,
+  ExperimentalFlag.variance: false,
+};
+
+const Map<ExperimentalFlag, bool> expiredExperimentalFlags = {
+  ExperimentalFlag.constantUpdate2018: true,
+  ExperimentalFlag.controlFlowCollections: true,
+  ExperimentalFlag.extensionMethods: false,
+  ExperimentalFlag.nonNullable: false,
+  ExperimentalFlag.nonfunctionTypeAliases: false,
+  ExperimentalFlag.setLiterals: true,
+  ExperimentalFlag.spreadCollections: true,
+  ExperimentalFlag.tripleShift: false,
+  ExperimentalFlag.variance: false,
+};
+
+const AllowedExperimentalFlags defaultAllowedExperimentalFlags =
+    const AllowedExperimentalFlags(sdkDefaultExperiments: {
+  ExperimentalFlag.nonNullable,
+}, sdkLibraryExperiments: {}, packageExperiments: {});

pkg/front_end/lib/src/base/processed_options.dart

@@ -22,8 +22,7 @@ import 'package:package_config/package_config.dart';
 import '../api_prototype/compiler_options.dart'
     show CompilerOptions, DiagnosticMessage;
 
-import '../api_prototype/experimental_flags.dart'
-    show defaultExperimentalFlags, ExperimentalFlag, expiredExperimentalFlags;
+import '../api_prototype/experimental_flags.dart' as flags;
 
 import '../api_prototype/file_system.dart'
     show FileSystem, FileSystemEntity, FileSystemException;
@@ -325,15 +324,27 @@ class ProcessedOptions {
   Target get target =>
       _target ??= _raw.target ?? new NoneTarget(new TargetFlags());
 
-  bool isExperimentEnabled(ExperimentalFlag flag) {
-    assert(defaultExperimentalFlags.containsKey(flag),
-        "No default value for $flag.");
-    assert(expiredExperimentalFlags.containsKey(flag),
-        "No expired value for $flag.");
-    if (expiredExperimentalFlags[flag]) {
-      return defaultExperimentalFlags[flag];
-    }
-    return _raw.experimentalFlags[flag] ?? defaultExperimentalFlags[flag];
+  /// Returns `true` if the [flag] is enabled globally.
+  ///
+  /// This is `true` either if the [flag] is passed through an explicit
+  /// `--enable-experiment` option or if the [flag] is expired and on by
+  /// default.
+  bool isExperimentEnabledGlobally(flags.ExperimentalFlag flag) {
+    return flags.isExperimentEnabled(flag,
+        experimentalFlags: _raw.experimentalFlags);
+  }
+
+  /// Returns `true` if the [flag] is enabled in the library with the given
+  /// [importUri].
+  ///
+  /// This is `true` either if the [flag] is enabled globally as defined
+  /// by [isExperimentEnabledGlobally] or is explicitly enabled through
+  /// the 'allowed_experiments.json' file for this library.
+  bool isExperimentEnabledInLibrary(
+      flags.ExperimentalFlag flag, Uri importUri) {
+    return flags.isExperimentEnabledInLibrary(flag, importUri,
+        experimentalFlags: _raw.experimentalFlags,
+        allowedExperimentalFlags: _raw.allowedExperimentalFlags);
   }
 
   /// Get an outline component that summarizes the SDK, if any.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -5518,7 +5518,7 @@ class BodyBuilder extends ScopeListener<JumpTarget>
     TypeVariableBuilder variable = typeVariables[index];
     variable.bound = bound?.builder;
     if (variance != null) {
-      if (!libraryBuilder.loader.target.enableVariance) {
+      if (!libraryBuilder.enableVarianceInLibrary) {
         reportVarianceModifierNotEnabled(variance);
       }
       variable.variance = Variance.fromString(variance.lexeme);

pkg/front_end/lib/src/fasta/kernel/kernel_target.dart

@@ -6,6 +6,7 @@ library fasta.kernel_target;
 
 import 'dart:async' show Future;
 
+import 'package:front_end/src/api_prototype/experimental_flags.dart';
 import 'package:kernel/ast.dart'
     show
         Arguments,
@@ -251,9 +252,8 @@ class KernelTarget extends TargetImplementation {
     if (dillTarget.isLoaded) {
       LibraryBuilder builder = dillTarget.loader.builders[uri];
       if (builder != null) {
-        if (enableNonNullable &&
-            (loader.nnbdMode == NnbdMode.Strong ||
-                loader.nnbdMode == NnbdMode.Agnostic)) {
+        if (loader.nnbdMode == NnbdMode.Strong ||
+            loader.nnbdMode == NnbdMode.Agnostic) {
           if (!builder.isNonNullableByDefault) {
             loader.addProblem(messageStrongModeNNBDButOptOut, -1, 1, fileUri);
           }
@@ -400,7 +400,7 @@ class KernelTarget extends TargetImplementation {
         nameRoot: nameRoot, libraries: libraries, uriToSource: uriToSource));
 
     NonNullableByDefaultCompiledMode compiledMode = null;
-    if (enableNonNullable) {
+    if (isExperimentEnabledGlobally(ExperimentalFlag.nonNullable)) {
       switch (loader.nnbdMode) {
         case NnbdMode.Weak:
           compiledMode = NonNullableByDefaultCompiledMode.Weak;
@@ -1099,7 +1099,8 @@ class KernelTarget extends TargetImplementation {
     // because the SDK might be agnostic and therefore needs to be weakened
     // for legacy mode.
     assert(
-        enableNonNullable || loader.nnbdMode == NnbdMode.Weak,
+        isExperimentEnabledGlobally(ExperimentalFlag.nonNullable) ||
+            loader.nnbdMode == NnbdMode.Weak,
         "Non-weak nnbd mode found without experiment enabled: "
         "${loader.nnbdMode}.");
     switch (loader.nnbdMode) {
@@ -1122,7 +1123,8 @@ class KernelTarget extends TargetImplementation {
         new KernelConstantErrorReporter(loader),
         evaluationMode,
         desugarSets: !backendTarget.supportsSetLiterals,
-        enableTripleShift: enableTripleShift,
+        enableTripleShift:
+            isExperimentEnabledGlobally(ExperimentalFlag.tripleShift),
         errorOnUnevaluatedConstant: errorOnUnevaluatedConstant);
     ticker.logMs("Evaluated constants");
 

pkg/front_end/lib/src/fasta/source/outline_builder.dart

@@ -1636,10 +1636,10 @@ class OutlineBuilder extends StackListenerImpl {
         return;
       }
       if (type is FunctionTypeBuilder &&
-          !libraryBuilder.loader.target.enableNonfunctionTypeAliases) {
+          !libraryBuilder.enableNonfunctionTypeAliasesInLibrary) {
         if (type.nullabilityBuilder.build(libraryBuilder) ==
                 Nullability.nullable &&
-            libraryBuilder.loader.target.enableNonNullable) {
+            libraryBuilder.enableNonNullableInLibrary) {
           // The error is reported when the non-nullable experiment is enabled.
           // Otherwise, the attempt to use a nullable type will be reported
           // elsewhere.
@@ -1653,7 +1653,7 @@ class OutlineBuilder extends StackListenerImpl {
           // of a generic function).
           aliasedType = type;
         }
-      } else if (libraryBuilder.loader.target.enableNonfunctionTypeAliases) {
+      } else if (libraryBuilder.enableNonfunctionTypeAliasesInLibrary) {
         if (type is TypeBuilder) {
           aliasedType = type;
         } else {
@@ -1797,7 +1797,7 @@ class OutlineBuilder extends StackListenerImpl {
     if (typeParameters != null) {
       typeParameters[index].bound = bound;
       if (variance != null) {
-        if (!libraryBuilder.loader.target.enableVariance) {
+        if (!libraryBuilder.enableVarianceInLibrary) {
           reportVarianceModifierNotEnabled(variance);
         }
         typeParameters[index].variance = Variance.fromString(variance.lexeme);

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

@@ -73,6 +73,7 @@ import 'package:kernel/type_algebra.dart' show substitute;
 import 'package:kernel/type_environment.dart'
     show SubtypeCheckMode, TypeEnvironment;
 
+import '../../api_prototype/experimental_flags.dart';
 import '../../base/nnbd_mode.dart';
 
 import '../builder/builder.dart';
@@ -166,9 +167,6 @@ import 'source_extension_builder.dart' show SourceExtensionBuilder;
 
 import 'source_loader.dart' show SourceLoader;
 
-import '../../api_prototype/experimental_flags.dart'
-    show enableNonNullableVersion;
-
 class SourceLibraryBuilder extends LibraryBuilderImpl {
   static const String MALFORMED_URI_SCHEME = "org-dartlang-malformed-uri";
 
@@ -319,9 +317,36 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
     updateLibraryNNBDSettings();
   }
 
+  bool _enableVarianceInLibrary;
+  bool _enableNonfunctionTypeAliasesInLibrary;
+  bool _enableNonNullableInLibrary;
+  bool _enableTripleShiftInLibrary;
+  bool _enableExtensionMethodsInLibrary;
+
+  bool get enableVarianceInLibrary => _enableVarianceInLibrary ??= loader.target
+      .isExperimentEnabledInLibrary(ExperimentalFlag.variance, importUri);
+
+  bool get enableNonfunctionTypeAliasesInLibrary =>
+      _enableNonfunctionTypeAliasesInLibrary ??= loader.target
+          .isExperimentEnabledInLibrary(
+              ExperimentalFlag.nonfunctionTypeAliases, importUri);
+
+  bool get enableNonNullableInLibrary => _enableNonNullableInLibrary ??= loader
+      .target
+      .isExperimentEnabledInLibrary(ExperimentalFlag.nonNullable, importUri);
+
+  bool get enableTripleShiftInLibrary => _enableTripleShiftInLibrary ??= loader
+      .target
+      .isExperimentEnabledInLibrary(ExperimentalFlag.tripleShift, importUri);
+
+  bool get enableExtensionMethodsInLibrary =>
+      _enableExtensionMethodsInLibrary ??= loader.target
+          .isExperimentEnabledInLibrary(
+              ExperimentalFlag.extensionMethods, importUri);
+
   void updateLibraryNNBDSettings() {
     library.isNonNullableByDefault = isNonNullableByDefault;
-    if (loader.target.enableNonNullable) {
+    if (enableNonNullableInLibrary) {
       switch (loader.nnbdMode) {
         case NnbdMode.Weak:
           library.nonNullableByDefaultCompiledMode =
@@ -382,7 +407,7 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
 
   @override
   bool get isNonNullableByDefault =>
-      loader.target.enableNonNullable &&
+      enableNonNullableInLibrary &&
       languageVersion.version >= enableNonNullableVersion &&
       !isOptOutTest(library.importUri);
 
@@ -449,7 +474,7 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
         new LanguageVersion(version, fileUri, offset, length, explicit);
     library.setLanguageVersion(version);
 
-    if (loader.target.enableNonNullable &&
+    if (enableNonNullableInLibrary &&
         (loader.nnbdMode == NnbdMode.Strong ||
             loader.nnbdMode == NnbdMode.Agnostic)) {
       // In strong and agnostic mode, the language version is not allowed to
@@ -3031,7 +3056,7 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
                 isNonNullableByDefault),
             fieldBuilder.charOffset,
             fieldBuilder.name.length,
-            fileUri);
+            fieldBuilder.fileUri);
       }
     }
   }

pkg/front_end/lib/src/fasta/source/source_loader.dart

@@ -256,16 +256,16 @@ class SourceLoader extends Loader {
     ScannerResult result = scan(bytes,
         includeComments: includeComments,
         configuration: new ScannerConfiguration(
-            enableTripleShift: target.enableTripleShift,
-            enableExtensionMethods: target.enableExtensionMethods,
+            enableTripleShift: library.enableTripleShiftInLibrary,
+            enableExtensionMethods: library.enableExtensionMethodsInLibrary,
             enableNonNullable: library.isNonNullableByDefault),
         languageVersionChanged:
             (Scanner scanner, LanguageVersionToken version) {
       library.setLanguageVersion(new Version(version.major, version.minor),
           offset: version.offset, length: version.length, explicit: true);
       scanner.configuration = new ScannerConfiguration(
-          enableTripleShift: target.enableTripleShift,
-          enableExtensionMethods: target.enableExtensionMethods,
+          enableTripleShift: library.enableTripleShiftInLibrary,
+          enableExtensionMethods: library.enableExtensionMethodsInLibrary,
           enableNonNullable: library.isNonNullableByDefault);
     });
     Token token = result.tokens;

pkg/front_end/lib/src/fasta/source/stack_listener_impl.dart

@@ -68,7 +68,7 @@ abstract class StackListenerImpl extends StackListener {
   void reportMissingNonNullableSupport(Token token) {
     assert(!libraryBuilder.isNonNullableByDefault);
     assert(token != null);
-    if (libraryBuilder.loader.target.enableNonNullable) {
+    if (libraryBuilder.enableNonNullableInLibrary) {
       if (libraryBuilder.languageVersion.isExplicit) {
         addProblem(messageNonNullableOptOut, token.charOffset, token.charCount,
             context: <LocatedMessage>[

pkg/front_end/lib/src/fasta/target_implementation.dart

@@ -48,28 +48,23 @@ abstract class TargetImplementation extends Target {
   MemberBuilder cachedDuplicatedFieldInitializerError;
   MemberBuilder cachedNativeAnnotation;
 
-  bool enableExtensionMethods;
-  bool enableNonNullable;
-  bool enableTripleShift;
-  bool enableVariance;
-  bool enableNonfunctionTypeAliases;
+  final ProcessedOptions _options;
 
   TargetImplementation(Ticker ticker, this.uriTranslator, this.backendTarget)
       : assert(ticker != null),
         assert(uriTranslator != null),
         assert(backendTarget != null),
-        enableExtensionMethods = CompilerContext.current.options
-            .isExperimentEnabled(ExperimentalFlag.extensionMethods),
-        enableNonNullable = CompilerContext.current.options
-            .isExperimentEnabled(ExperimentalFlag.nonNullable),
-        enableTripleShift = CompilerContext.current.options
-            .isExperimentEnabled(ExperimentalFlag.tripleShift),
-        enableVariance = CompilerContext.current.options
-            .isExperimentEnabled(ExperimentalFlag.variance),
-        enableNonfunctionTypeAliases = CompilerContext.current.options
-            .isExperimentEnabled(ExperimentalFlag.nonfunctionTypeAliases),
+        _options = CompilerContext.current.options,
         super(ticker);
 
+  bool isExperimentEnabledInLibrary(ExperimentalFlag flag, Uri importUri) {
+    return _options.isExperimentEnabledInLibrary(flag, importUri);
+  }
+
+  bool isExperimentEnabledGlobally(ExperimentalFlag flag) {
+    return _options.isExperimentEnabledGlobally(flag);
+  }
+
   /// Creates a [LibraryBuilder] corresponding to [uri], if one doesn't exist
   /// already.
   ///

pkg/front_end/lib/src/testing/id_testing_helper.dart

@@ -11,7 +11,8 @@ import 'package:kernel/ast.dart';
 import 'package:kernel/target/targets.dart';
 import '../api_prototype/compiler_options.dart'
     show CompilerOptions, DiagnosticMessage;
-import '../api_prototype/experimental_flags.dart' show ExperimentalFlag;
+import '../api_prototype/experimental_flags.dart'
+    show AllowedExperimentalFlags, ExperimentalFlag;
 import '../api_prototype/terminal_color_support.dart'
     show printDiagnosticMessage;
 import '../base/common.dart';
@@ -43,6 +44,7 @@ class TestConfig {
   final String marker;
   final String name;
   final Map<ExperimentalFlag, bool> experimentalFlags;
+  final AllowedExperimentalFlags allowedExperimentalFlags;
   final Uri librariesSpecificationUri;
   // TODO(johnniwinther): Tailor support to redefine selected platform
   // classes/members only.
@@ -52,6 +54,7 @@ class TestConfig {
 
   const TestConfig(this.marker, this.name,
       {this.experimentalFlags = const {},
+      this.allowedExperimentalFlags,
       this.librariesSpecificationUri,
       this.compileSdk: false,
       this.targetFlags: const TargetFlags(),
@@ -298,6 +301,7 @@ Future<TestResult<T>> runTestForConfig<T>(
   options.debugDump = printCode;
   options.target = new NoneTarget(config.targetFlags);
   options.experimentalFlags.addAll(config.experimentalFlags);
+  options.allowedExperimentalFlags = config.allowedExperimentalFlags;
   options.nnbdMode = config.nnbdMode;
   if (config.librariesSpecificationUri != null) {
     Set<Uri> testFiles =

pkg/front_end/test/extensions/extensions_test.dart

@@ -5,6 +5,7 @@
 import 'dart:io' show Directory, Platform;
 import 'package:_fe_analyzer_shared/src/testing/id.dart';
 import 'package:_fe_analyzer_shared/src/testing/id_testing.dart';
+import 'package:front_end/src/api_prototype/experimental_flags.dart';
 
 import 'package:front_end/src/fasta/builder/class_builder.dart';
 import 'package:front_end/src/fasta/builder/extension_builder.dart';
@@ -28,7 +29,8 @@ main(List<String> args) async {
       onFailure: onFailure,
       runTest: runTestFor(const ExtensionsDataComputer(), [
         new TestConfig(cfeMarker, 'cfe',
-            librariesSpecificationUri: createUriForFileName('libraries.json'))
+            librariesSpecificationUri: createUriForFileName('libraries.json'),
+            allowedExperimentalFlags: const AllowedExperimentalFlags())
       ]));
 }
 

pkg/front_end/test/fasta/expression_suite.dart

@@ -14,6 +14,7 @@ import 'package:_fe_analyzer_shared/src/util/colors.dart' as colors;
 
 import "package:front_end/src/api_prototype/compiler_options.dart"
     show CompilerOptions, DiagnosticMessage;
+import 'package:front_end/src/api_prototype/experimental_flags.dart';
 
 import "package:front_end/src/api_prototype/memory_file_system.dart"
     show MemoryFileSystem;
@@ -409,7 +410,8 @@ Future<Context> createContext(
       printDiagnosticMessage(message, print);
       errors.add(message);
     }
-    ..environmentDefines = const {};
+    ..environmentDefines = const {}
+    ..allowedExperimentalFlags = const AllowedExperimentalFlags();
 
   final ProcessedOptions options =
       new ProcessedOptions(options: optionBuilder, inputs: [entryPoint]);

pkg/front_end/test/fasta/testing/suite.dart

@@ -23,7 +23,7 @@ import 'package:front_end/src/api_prototype/compiler_options.dart'
     show CompilerOptions, DiagnosticMessage;
 
 import 'package:front_end/src/api_prototype/experimental_flags.dart'
-    show ExperimentalFlag, defaultExperimentalFlags;
+    show ExperimentalFlag, defaultExperimentalFlags, isExperimentEnabled;
 
 import 'package:front_end/src/api_prototype/standard_file_system.dart'
     show StandardFileSystem;
@@ -618,7 +618,8 @@ class Outline extends Step<TestDescription, ComponentResult, FastaContext> {
     Map<ExperimentalFlag, bool> experimentalFlags =
         testOptions.computeExperimentalFlags(context.experimentalFlags);
     NnbdMode nnbdMode = context.weak ||
-            !experimentalFlags[ExperimentalFlag.nonNullable]
+            !isExperimentEnabled(ExperimentalFlag.nonNullable,
+                experimentalFlags: experimentalFlags)
         ? NnbdMode.Weak
         : (testOptions.nnbdAgnosticMode ? NnbdMode.Agnostic : NnbdMode.Strong);
     List<Uri> inputs = <Uri>[description.uri];

pkg/front_end/test/patching/patching_test.dart

@@ -28,11 +28,13 @@ main(List<String> args) async {
       runTest: runTestFor(const PatchingDataComputer(), [
         new TestConfigWithLanguageVersion(
             cfeMarker, 'cfe with libraries specification',
-            librariesSpecificationUri: createUriForFileName('libraries.json')),
+            librariesSpecificationUri: createUriForFileName('libraries.json'),
+            allowedExperimentalFlags: const AllowedExperimentalFlags()),
         new TestConfigWithLanguageVersion(cfeWithNnbdMarker,
             'cfe with libraries specification and non-nullable',
             librariesSpecificationUri: createUriForFileName('libraries.json'),
-            experimentalFlags: {ExperimentalFlag.nonNullable: true})
+            experimentalFlags: {ExperimentalFlag.nonNullable: true},
+            allowedExperimentalFlags: const AllowedExperimentalFlags())
       ]),
       skipMap: {
         cfeMarker: [
@@ -47,10 +49,12 @@ main(List<String> args) async {
 class TestConfigWithLanguageVersion extends TestConfig {
   TestConfigWithLanguageVersion(String marker, String name,
       {Uri librariesSpecificationUri,
-      Map<ExperimentalFlag, bool> experimentalFlags = const {}})
+      Map<ExperimentalFlag, bool> experimentalFlags = const {},
+      AllowedExperimentalFlags allowedExperimentalFlags})
       : super(marker, name,
             librariesSpecificationUri: librariesSpecificationUri,
-            experimentalFlags: experimentalFlags);
+            experimentalFlags: experimentalFlags,
+            allowedExperimentalFlags: allowedExperimentalFlags);
 
   @override
   void customizeCompilerOptions(CompilerOptions options, TestData testData) {

pkg/front_end/test/spell_checking_list_tests.txt

@@ -181,6 +181,7 @@ epoch
 err
 everytime
 evicting
+exceed
 excess
 exe
 execute

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/libraries.json

@@ -3,7 +3,8 @@
     "libraries": {
       "test": {
         "patches": [
-          "patch_lib.dart"
+          "patch_lib.dart",
+          "patch_lib2.dart"
         ],
         "uri": "origin_lib.dart"
       }

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/main.dart.outline.expect

@@ -7,6 +7,13 @@ static method main() → dynamic
   ;
 
 library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:32:14: Error: Field 'staticField' should be initialized because its type 'int' doesn't allow null.
+//   static int staticField;
+//              ^^^^^^^^^^^
+//
 import self as self2;
 import "dart:_internal" as _in;
 import "dart:core" as core;
@@ -15,13 +22,14 @@ import "dart:_internal";
 
 @_in::patch
 class Class1 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
+  static field core::int staticField /* from org-dartlang-testcase:///patch_lib2.dart */;
   synthetic constructor •() → self2::Class1
     ;
 }
 @_in::patch
 class Class2 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
   constructor constructor2(core::int field) → self2::Class2
     ;
   constructor constructor1() → self2::Class2

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/main.dart.strong.expect

@@ -13,11 +13,15 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:10:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:32:14: Error: Field 'staticField' should be initialized because its type 'int' doesn't allow null.
+//   static int staticField;
+//              ^^^^^^^^^^^
+//
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:30:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:15:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:37:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
@@ -29,14 +33,15 @@ import "dart:_internal";
 
 @#C1
 class Class1 extends core::Object {
-  field core::int field = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field = null /* from org-dartlang-testcase:///patch_lib2.dart */;
+  static field core::int staticField = null /* from org-dartlang-testcase:///patch_lib2.dart */;
   synthetic constructor •() → test::Class1
     : super core::Object::•()
     ;
 }
 @#C1
 class Class2 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
   constructor constructor2(core::int field) → test::Class2
     : test::Class2::field = field, super core::Object::•()
     ;

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/main.dart.strong.transformed.expect

@@ -13,11 +13,15 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:10:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:32:14: Error: Field 'staticField' should be initialized because its type 'int' doesn't allow null.
+//   static int staticField;
+//              ^^^^^^^^^^^
+//
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:30:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:15:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:37:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
@@ -29,14 +33,15 @@ import "dart:_internal";
 
 @#C1
 class Class1 extends core::Object {
-  field core::int field = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field = null /* from org-dartlang-testcase:///patch_lib2.dart */;
+  static field core::int staticField = null /* from org-dartlang-testcase:///patch_lib2.dart */;
   synthetic constructor •() → test::Class1
     : super core::Object::•()
     ;
 }
 @#C1
 class Class2 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
   constructor constructor2(core::int field) → test::Class2
     : test::Class2::field = field, super core::Object::•()
     ;

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/main.dart.weak.expect

@@ -13,11 +13,15 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:10:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:32:14: Error: Field 'staticField' should be initialized because its type 'int' doesn't allow null.
+//   static int staticField;
+//              ^^^^^^^^^^^
+//
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:30:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:15:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:37:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
@@ -29,14 +33,15 @@ import "dart:_internal";
 
 @#C1
 class Class1 extends core::Object {
-  field core::int field = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field = null /* from org-dartlang-testcase:///patch_lib2.dart */;
+  static field core::int staticField = null /* from org-dartlang-testcase:///patch_lib2.dart */;
   synthetic constructor •() → test::Class1
     : super core::Object::•()
     ;
 }
 @#C1
 class Class2 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
   constructor constructor2(core::int field) → test::Class2
     : test::Class2::field = field, super core::Object::•()
     ;

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/main.dart.weak.transformed.expect

@@ -13,11 +13,15 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:10:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:32:14: Error: Field 'staticField' should be initialized because its type 'int' doesn't allow null.
+//   static int staticField;
+//              ^^^^^^^^^^^
+//
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:30:7: Error: Field 'field' should be initialized because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
-// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart:15:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart:37:7: Error: This constructor should initialize field 'field' because its type 'int' doesn't allow null.
 //   int field;
 //       ^^^^^
 //
@@ -29,14 +33,15 @@ import "dart:_internal";
 
 @#C1
 class Class1 extends core::Object {
-  field core::int field = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field = null /* from org-dartlang-testcase:///patch_lib2.dart */;
+  static field core::int staticField = null /* from org-dartlang-testcase:///patch_lib2.dart */;
   synthetic constructor •() → test::Class1
     : super core::Object::•()
     ;
 }
 @#C1
 class Class2 extends core::Object {
-  field core::int field /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::int field /* from org-dartlang-testcase:///patch_lib2.dart */;
   constructor constructor2(core::int field) → test::Class2
     : test::Class2::field = field, super core::Object::•()
     ;

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib.dart

@@ -4,15 +4,3 @@
 
 // ignore: import_internal_library
 import 'dart:_internal';
-
-@patch
-class Class1 {
-  int field;
-}
-
-@patch
-class Class2 {
-  int field;
-
-  Class2.constructor2(this.field);
-}

pkg/front_end/testcases/nnbd/platform_nonnullable_fields/patch_lib2.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2020, 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.
+
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+// Comment to make offset in patch_lib2.dart exceed the range of patch_lib.dart.
+
+@patch
+class Class1 {
+  int field;
+
+  static int staticField;
+}
+
+@patch
+class Class2 {
+  int field;
+
+  Class2.constructor2(this.field);
+}

pkg/front_end/tool/_fasta/generate_experimental_flags.dart

@@ -22,7 +22,7 @@ main(List<String> arguments) {
 
 Uri computeCfeGeneratedFile() {
   return Platform.script
-      .resolve("../../lib/src/api_prototype/experimental_flags.dart");
+      .resolve("../../lib/src/api_prototype/experimental_flags_generated.dart");
 }
 
 Uri computeKernelGeneratedFile() {
@@ -91,7 +91,7 @@ String generateCfeFile() {
   StringBuffer sb = new StringBuffer();
 
   sb.write('''
-// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2020, 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.
 
@@ -100,8 +100,7 @@ String generateCfeFile() {
 // Instead modify 'tools/experimental_features.yaml' and run
 // 'dart pkg/front_end/tool/fasta.dart generate-experimental-flags' to update.
 
-import 'package:_fe_analyzer_shared/src/sdk/allowed_experiments.dart';
-import 'package:kernel/kernel.dart' show Version;
+part of 'experimental_flags.dart';
 ''');
 
   Map<dynamic, dynamic> features = yaml['features'];
@@ -182,32 +181,33 @@ const Map<ExperimentalFlag, bool> expiredExperimentalFlags = {
       new File.fromUri(allowListFile).readAsStringSync());
 
   sb.write('''
-const AllowedExperiments allowedExperiments = const AllowedExperiments(
+const AllowedExperimentalFlags defaultAllowedExperimentalFlags =
+    const AllowedExperimentalFlags(
 ''');
-  sb.writeln('sdkDefaultExperiments: [');
+  sb.writeln('sdkDefaultExperiments: {');
   for (String sdkDefaultExperiment
       in allowedExperiments.sdkDefaultExperiments) {
-    sb.writeln('"$sdkDefaultExperiment",');
+    sb.writeln('ExperimentalFlag.${keyToIdentifier(sdkDefaultExperiment)},');
   }
-  sb.writeln('],');
+  sb.writeln('},');
   sb.writeln('sdkLibraryExperiments: {');
   allowedExperiments.sdkLibraryExperiments
       .forEach((String library, List<String> experiments) {
-    sb.writeln('"$library": [');
+    sb.writeln('"$library": {');
     for (String experiment in experiments) {
-      sb.writeln('"$experiment",');
+      sb.writeln('ExperimentalFlag.${keyToIdentifier(experiment)},');
     }
-    sb.writeln('],');
+    sb.writeln('},');
   });
   sb.writeln('},');
   sb.writeln('packageExperiments: {');
   allowedExperiments.packageExperiments
       .forEach((String package, List<String> experiments) {
-    sb.writeln('"$package": [');
+    sb.writeln('"$package": {');
     for (String experiment in experiments) {
-      sb.writeln('"$experiment",');
+      sb.writeln('ExperimentalFlag.${keyToIdentifier(experiment)},');
     }
-    sb.writeln('],');
+    sb.writeln('},');
   });
   sb.writeln('});');