[VM/Libraries] Fix all errors reported by CFE when the option

performNnbdChecks is turned on.

Bug:40424
Change-Id: I97a283c4a2d54f570def04d938baa9a4ced08667
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137250
Commit-Queue: Siva Annamalai <asiva@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

pkg/dev_compiler/tool/dart2js_nnbd_sdk_error_golden.txt

@@ -6,21 +6,16 @@ ERROR|COMPILE_TIME_ERROR|INCONSISTENT_INHERITANCE|lib/_internal/js_runtime/lib/i
 ERROR|COMPILE_TIME_ERROR|INCONSISTENT_INHERITANCE|lib/_internal/js_runtime/lib/interceptors.dart|1637|7|5|Superinterfaces don't have a valid override for '>>': int.>> (int Function(int)), JSNumber.>> (num Function(num)).
 ERROR|COMPILE_TIME_ERROR|INCONSISTENT_INHERITANCE|lib/_internal/js_runtime/lib/interceptors.dart|1637|7|5|Superinterfaces don't have a valid override for '\|': int.\| (int Function(int)), JSNumber.\| (num Function(num)).
 ERROR|COMPILE_TIME_ERROR|INCONSISTENT_INHERITANCE|lib/_internal/js_runtime/lib/interceptors.dart|1637|7|5|Superinterfaces don't have a valid override for '^': int.^ (int Function(int)), JSNumber.^ (num Function(num)).
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1003|10|5|Non-nullable instance field 'value' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1004|10|5|Non-nullable instance field 'value' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1029|8|6|Non-nullable instance field 'secure' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1030|8|6|Non-nullable instance field 'secure' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1035|8|8|Non-nullable instance field 'httpOnly' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1036|8|8|Non-nullable instance field 'httpOnly' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1491|12|11|Non-nullable instance field 'idleTimeout' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1493|12|11|Non-nullable instance field 'idleTimeout' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1541|8|14|Non-nullable instance field 'autoUncompress' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1543|8|14|Non-nullable instance field 'autoUncompress' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|171|8|12|Non-nullable instance field 'autoCompress' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|172|8|12|Non-nullable instance field 'autoCompress' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|990|10|4|Non-nullable instance field 'name' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|991|10|4|Non-nullable instance field 'name' must be initialized.
 ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/io/io.dart|5589|12|8|Non-nullable instance field 'encoding' must be initialized.
 ERROR|STATIC_TYPE_WARNING|UNDEFINED_OPERATOR|lib/_internal/js_runtime/lib/interceptors.dart|1654|28|1|The operator '&' isn't defined for the type 'JSInt'.
 ERROR|STATIC_TYPE_WARNING|UNDEFINED_OPERATOR|lib/_internal/js_runtime/lib/interceptors.dart|1656|27|1|The operator '&' isn't defined for the type 'JSInt'.
 ERROR|STATIC_TYPE_WARNING|UNDEFINED_OPERATOR|lib/_internal/js_runtime/lib/interceptors.dart|1659|17|1|The operator '&' isn't defined for the type 'JSInt'.
 ERROR|STATIC_TYPE_WARNING|UNDEFINED_OPERATOR|lib/_internal/js_runtime/lib/interceptors.dart|1664|18|1|The operator '&' isn't defined for the type 'JSInt'.
 ERROR|STATIC_TYPE_WARNING|UNDEFINED_OPERATOR|lib/_internal/js_runtime/lib/interceptors.dart|1664|44|1|The operator '&' isn't defined for the type 'JSInt'.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|1476|39|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|8384|60|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|9311|54|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/developer/developer.dart|315|25|23|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/io/io.dart|9188|16|1|The left operand can't be null, so the right operand is never executed.

pkg/dev_compiler/tool/dartdevc_nnbd_sdk_error_golden.txt

@@ -15,16 +15,11 @@ ERROR|COMPILE_TIME_ERROR|BODY_MIGHT_COMPLETE_NORMALLY|lib/_internal/js_dev_runti
 ERROR|COMPILE_TIME_ERROR|BODY_MIGHT_COMPLETE_NORMALLY|lib/_internal/js_dev_runtime/private/foreign_helper.dart|221|8|37|The body might complete normally, which would cause 'null' to be returned, but the return type is a potentially non-nullable type.
 ERROR|COMPILE_TIME_ERROR|BODY_MIGHT_COMPLETE_NORMALLY|lib/_internal/js_dev_runtime/private/foreign_helper.dart|224|8|11|The body might complete normally, which would cause 'null' to be returned, but the return type is a potentially non-nullable type.
 ERROR|COMPILE_TIME_ERROR|BODY_MIGHT_COMPLETE_NORMALLY|lib/_internal/js_dev_runtime/private/foreign_helper.dart|228|6|11|The body might complete normally, which would cause 'null' to be returned, but the return type is a potentially non-nullable type.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1003|10|5|Non-nullable instance field 'value' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1004|10|5|Non-nullable instance field 'value' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1029|8|6|Non-nullable instance field 'secure' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1030|8|6|Non-nullable instance field 'secure' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1035|8|8|Non-nullable instance field 'httpOnly' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1036|8|8|Non-nullable instance field 'httpOnly' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1491|12|11|Non-nullable instance field 'idleTimeout' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1493|12|11|Non-nullable instance field 'idleTimeout' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1541|8|14|Non-nullable instance field 'autoUncompress' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|1543|8|14|Non-nullable instance field 'autoUncompress' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|171|8|12|Non-nullable instance field 'autoCompress' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|172|8|12|Non-nullable instance field 'autoCompress' must be initialized.
-ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|990|10|4|Non-nullable instance field 'name' must be initialized.
+ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/_http/http.dart|991|10|4|Non-nullable instance field 'name' must be initialized.
 ERROR|COMPILE_TIME_ERROR|NOT_INITIALIZED_NON_NULLABLE_INSTANCE_FIELD|lib/io/io.dart|5589|12|8|Non-nullable instance field 'encoding' must be initialized.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|1476|39|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|8384|60|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/_http/http.dart|9311|54|5|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/developer/developer.dart|332|25|23|The left operand can't be null, so the right operand is never executed.
-WARNING|STATIC_WARNING|DEAD_NULL_AWARE_EXPRESSION|lib/io/io.dart|9188|16|1|The left operand can't be null, so the right operand is never executed.

sdk_nnbd/lib/_http/http.dart

@@ -16,7 +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';
@@ -1473,7 +1474,8 @@ 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

sdk_nnbd/lib/_http/http_parser.dart

@@ -883,7 +883,9 @@ 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.

sdk_nnbd/lib/_http/websocket.dart

@@ -407,7 +407,7 @@ abstract class WebSocket
           "explicitly to WebSocket.fromUpgradedSocket.");
     }
     return new _WebSocketImpl._fromSocket(
-        socket, protocol, compression, serverSide ?? false);
+        socket, protocol, compression, serverSide);
   }
 
   /**

sdk_nnbd/lib/_internal/vm/bin/builtin.dart

@@ -33,15 +33,15 @@ void _print(arg) {
 _getPrintClosure() => _print;
 
 // The current working directory when the embedder was launched.
-Uri _workingDirectory;
+late Uri _workingDirectory;
 
 // The URI that the root script was loaded from. Remembered so that
 // package imports can be resolved relative to it. The root script is the basis
 // for the root library in the VM.
-Uri _rootScript;
+Uri? _rootScript;
 
 // packagesConfig specified for the isolate.
-Uri _packagesConfigUri;
+Uri? _packagesConfigUri;
 
 // Packages are either resolved looking up in a map or resolved from within a
 // package root.
@@ -50,11 +50,11 @@ bool get _packagesReady => (_packageMap != null) || (_packageError != null);
 // Error string set if there was an error resolving package configuration.
 // For example not finding a .packages file or packages/ directory, malformed
 // .packages file or any other related error.
-String _packageError = null;
+String? _packageError = null;
 
 // The map describing how certain package names are mapped to Uris.
-Uri _packageConfig = null;
+Uri? _packageConfig = null;
-Map<String, Uri> _packageMap = null;
+Map<String, Uri>? _packageMap = null;
 
 // Special handling for Windows paths so that they are compatible with URI
 // handling.
@@ -128,11 +128,12 @@ Uri _resolvePackageUri(Uri uri) {
     _log('Resolving package with uri path: ${uri.path}');
   }
   var resolvedUri;
-  if (_packageError != null) {
+  final error = _packageError;
+  if (error != null) {
     if (_traceLoading) {
-      _log("Resolving package with pending resolution error: $_packageError");
+      _log("Resolving package with pending resolution error: $error");
     }
-    throw _packageError;
+    throw error;
   } else {
     if (packageNameEnd < 0) {
       // Package URIs must have a path after the package name, even if it's
@@ -141,7 +142,7 @@ Uri _resolvePackageUri(Uri uri) {
           "'package:${uri.path}/', not 'package:${uri.path}'";
     }
     var packageName = uri.path.substring(0, packageNameEnd);
-    var mapping = _packageMap[packageName];
+    final mapping = _packageMap![packageName];
     if (_traceLoading) {
       _log("Mapped '$packageName' package to '$mapping'");
     }
@@ -162,14 +163,14 @@ Uri _resolvePackageUri(Uri uri) {
   return resolvedUri;
 }
 
-void _requestPackagesMap(Uri packageConfig) {
+void _requestPackagesMap(Uri? packageConfig) {
   var msg = null;
   if (packageConfig != null) {
     // Explicitly specified .packages path.
     msg = _handlePackagesRequest(_traceLoading, -2, packageConfig);
   } else {
     // Search for .packages starting at the root script.
-    msg = _handlePackagesRequest(_traceLoading, -1, _rootScript);
+    msg = _handlePackagesRequest(_traceLoading, -1, _rootScript!);
   }
   if (_traceLoading) {
     _log("Requested packages map for '$_rootScript'.");
@@ -186,10 +187,11 @@ void _requestPackagesMap(Uri packageConfig) {
     assert(msg.length >= 2);
     assert(msg[1] == null);
     _packageConfig = Uri.parse(msg[0]);
-    _packageMap = new Map<String, Uri>();
+    final pmap = new Map<String, Uri>();
+    _packageMap = pmap;
     for (var i = 2; i < msg.length; i += 2) {
       // TODO(iposva): Complain about duplicate entries.
-      _packageMap[msg[i]] = Uri.parse(msg[i + 1]);
+      pmap[msg[i]] = Uri.parse(msg[i + 1]);
     }
     if (_traceLoading) {
       _log("Setup package map: $_packageMap");
@@ -591,9 +593,6 @@ String _setPackagesMap(String packagesParam) {
   if (_traceLoading) {
     _log("Resolving packages map: $packagesParam");
   }
-  if (_workingDirectory == null) {
-    throw 'No current working directory set.';
-  }
   var packagesName = _sanitizeWindowsPath(packagesParam);
   var packagesUri = Uri.parse(packagesName);
   if (packagesUri.scheme == '') {
@@ -616,9 +615,6 @@ String _resolveScriptUri(String scriptName) {
   if (_traceLoading) {
     _log("Resolving script: $scriptName");
   }
-  if (_workingDirectory == null) {
-    throw 'No current working directory set.';
-  }
   scriptName = _sanitizeWindowsPath(scriptName);
 
   var scriptUri = Uri.parse(scriptName);
@@ -657,7 +653,7 @@ Future<Uri> _getPackageConfigFuture() {
   return Future.value(_packageConfig);
 }
 
-Future<Uri> _resolvePackageUriFuture(Uri packageUri) {
+Future<Uri?> _resolvePackageUriFuture(Uri packageUri) {
   if (_traceLoading) {
     _log("Request for package Uri resolution from user code: $packageUri");
   }
@@ -671,7 +667,7 @@ Future<Uri> _resolvePackageUriFuture(Uri packageUri) {
   if (!_packagesReady) {
     _requestPackagesMap(_packagesConfigUri);
   }
-  Uri resolvedUri;
+  Uri? resolvedUri;
   try {
     resolvedUri = _resolvePackageUri(packageUri);
   } catch (e, s) {

sdk_nnbd/lib/_internal/vm/bin/vmservice_io.dart

@@ -45,7 +45,7 @@ Future<Server>? serverFuture;
 Server _lazyServerBoot() {
   var localServer = server;
   if (localServer != null) {
-    return server;
+    return localServer;
   }
   // Lazily create service.
   final service = VMService();

sdk_nnbd/lib/_internal/vm/bin/vmservice_server.dart

@@ -383,11 +383,11 @@ class Server {
     client.onRequest(message); // exception free, no need to try catch
   }
 
-  Future<void> _dumpServiceInfoToFile() async {
+  Future<void> _dumpServiceInfoToFile(String serviceInfoFilenameLocal) async {
     final serviceInfo = <String, dynamic>{
       'uri': serverAddress.toString(),
     };
-    final file = File.fromUri(Uri.parse(_serviceInfoFilename));
+    final file = File.fromUri(Uri.parse(serviceInfoFilenameLocal));
     return file.writeAsString(json.encode(serviceInfo));
   }
 
@@ -456,7 +456,7 @@ class Server {
     final serviceInfoFilenameLocal = _serviceInfoFilename;
     if (serviceInfoFilenameLocal != null &&
         serviceInfoFilenameLocal.isNotEmpty) {
-      await _dumpServiceInfoToFile();
+      await _dumpServiceInfoToFile(serviceInfoFilenameLocal);
     }
     // Server is up and running.
     _notifyServerState(serverAddress.toString());

sdk_nnbd/lib/_internal/vm/lib/developer.dart

@@ -18,20 +18,20 @@ import "dart:isolate" show SendPort;
 // part "timeline.dart"
 
 @patch
-bool debugger({bool when: true, String message}) native "Developer_debugger";
+bool debugger({bool when: true, String? message}) native "Developer_debugger";
 
 @patch
 Object inspect(Object object) native "Developer_inspect";
 
 @patch
 void log(String message,
-    {DateTime time,
+    {DateTime? time,
-    int sequenceNumber,
+    int? sequenceNumber,
     int level: 0,
     String name: '',
-    Zone zone,
+    Zone? zone,
-    Object error,
+    Object? error,
-    StackTrace stackTrace}) {
+    StackTrace? stackTrace}) {
   if (message is! String) {
     throw new ArgumentError.value(message, "message", "Must be a String");
   }
@@ -51,7 +51,7 @@ void log(String message,
 int _nextSequenceNumber = 0;
 
 _log(String message, int timestamp, int sequenceNumber, int level, String name,
-    Zone zone, Object error, StackTrace stackTrace) native "Developer_log";
+    Zone? zone, Object? error, StackTrace? stackTrace) native "Developer_log";
 
 @patch
 void _postEvent(String eventKind, String eventData)

sdk_nnbd/lib/_internal/vm/lib/ffi_patch.dart

@@ -29,7 +29,7 @@ int sizeOf<T extends NativeType>() {
   // This is not super fast, but it is faster than a runtime entry.
   // Hot loops with elementAt().load() do not use this sizeOf, elementAt is
   // optimized per NativeType statically to prevent use of sizeOf at runtime.
-  final int knownSize = _knownSizes[T];
+  final int? knownSize = _knownSizes[T];
   if (knownSize != null) return knownSize;
   if (T == IntPtr) return _intPtrSize;
   if (T == Pointer) return _intPtrSize;
@@ -84,7 +84,7 @@ class Pointer<T extends NativeType> {
   @patch
   static Pointer<NativeFunction<T>> fromFunction<T extends Function>(
       @DartRepresentationOf("T") Function f,
-      [Object exceptionalReturn]) {
+      [Object? exceptionalReturn]) {
     throw UnsupportedError(
         "Pointer.fromFunction cannot be called dynamically.");
   }

sdk_nnbd/lib/_internal/vm/lib/isolate_patch.dart

@@ -333,7 +333,7 @@ class Isolate {
   }
 
   @patch
-  static Future<Uri> resolvePackageUri(Uri packageUri) {
+  static Future<Uri?> resolvePackageUri(Uri packageUri) {
     var hook = VMLibraryHooks.resolvePackageUriFuture;
     if (hook == null) {
       throw new UnsupportedError("Isolate.resolvePackageUri");

sdk_nnbd/lib/_internal/vm/lib/mirrors_impl.dart

@@ -424,7 +424,7 @@ class _ClassMirror extends _ObjectMirror implements ClassMirror, _TypeMirror {
     return _qualifiedName = _computeQualifiedName(owner, simpleName);
   }
 
-  DeclarationMirror get owner {
+  DeclarationMirror? get owner {
     var o = _owner;
     if (o != null) return o;
 
@@ -927,7 +927,7 @@ class _TypedefMirror extends _DeclarationMirror
   bool get isTopLevel => true;
 
   DeclarationMirror? _owner;
-  DeclarationMirror get owner {
+  DeclarationMirror? get owner {
     var o = _owner;
     if (o != null) return o;
     var uri = _ClassMirror._libraryUri(_reflectee);

sdk_nnbd/lib/_internal/vm/lib/typed_data_patch.dart

@@ -378,10 +378,11 @@ mixin _IntListMixin implements List<int> {
   }
 
   void fillRange(int start, int end, [int? fillValue]) {
-    if (fillValue == null && start < end) {
+    RangeError.checkValidRange(start, end, this.length);
+    if (start == end) return;
+    if (fillValue == null) {
       throw ArgumentError.notNull("fillValue");
     }
-    RangeError.checkValidRange(start, end, this.length);
     for (var i = start; i < end; ++i) {
       this[i] = fillValue;
     }
@@ -736,10 +737,11 @@ mixin _DoubleListMixin implements List<double> {
 
   void fillRange(int start, int end, [double? fillValue]) {
     // TODO(eernst): Could use zero as default and not throw; issue .
-    if (fillValue == null && start < end) {
+    RangeError.checkValidRange(start, end, this.length);
+    if (start == end) return;
+    if (fillValue == null) {
       throw ArgumentError.notNull("fillValue");
     }
-    RangeError.checkValidRange(start, end, this.length);
     for (var i = start; i < end; ++i) {
       this[i] = fillValue;
     }
@@ -1174,10 +1176,11 @@ abstract class _Float32x4ListMixin implements List<Float32x4> {
   }
 
   void fillRange(int start, int end, [Float32x4? fillValue]) {
-    if (fillValue == null && start < end) {
+    RangeError.checkValidRange(start, end, this.length);
+    if (start == end) return;
+    if (fillValue == null) {
       throw ArgumentError.notNull("fillValue");
     }
-    RangeError.checkValidRange(start, end, this.length);
     for (var i = start; i < end; ++i) {
       this[i] = fillValue;
     }
@@ -1532,10 +1535,11 @@ abstract class _Int32x4ListMixin implements List<Int32x4> {
   }
 
   void fillRange(int start, int end, [Int32x4? fillValue]) {
-    if (fillValue == null && start < end) {
+    RangeError.checkValidRange(start, end, this.length);
+    if (start == end) return;
+    if (fillValue == null) {
       throw ArgumentError.notNull("fillValue");
     }
-    RangeError.checkValidRange(start, end, this.length);
     for (var i = start; i < end; ++i) {
       this[i] = fillValue;
     }
@@ -1891,10 +1895,11 @@ abstract class _Float64x2ListMixin implements List<Float64x2> {
   }
 
   void fillRange(int start, int end, [Float64x2? fillValue]) {
-    if (fillValue == null && start < end) {
+    RangeError.checkValidRange(start, end, this.length);
+    if (start == end) return;
+    if (fillValue == null) {
       throw ArgumentError.notNull("fillValue");
     }
-    RangeError.checkValidRange(start, end, this.length);
     for (var i = start; i < end; ++i) {
       this[i] = fillValue;
     }

sdk_nnbd/lib/_internal/vm/lib/wasm_patch.dart

@@ -105,11 +105,12 @@ class _NativeWasmImports extends NativeFieldWrapperClass1
 }
 
 class _NativeWasmMemory extends NativeFieldWrapperClass1 implements WasmMemory {
-  int _pages;
+  late int _pages;
-  Uint8List _buffer;
+  late Uint8List _buffer;
 
-  _NativeWasmMemory(int initialPages, int? maxPages) : _pages = initialPages {
+  _NativeWasmMemory(int initialPages, int? maxPages) {
     _buffer = _init(initialPages, maxPages);
+    _pages = initialPages;
   }
 
   _NativeWasmMemory.fromInstance(_NativeWasmInstance inst) {

sdk_nnbd/lib/cli/wait_for.dart

@@ -57,10 +57,11 @@ void Function(int)? _waitForEventClosure;
 
 class _WaitForUtils {
   static void waitForEvent({Duration? timeout}) {
-    if (_waitForEventClosure == null) {
+    final closure = _waitForEventClosure;
+    if (closure == null) {
       throw new UnsupportedError("waitFor is not supported by this embedder");
     }
-    _waitForEventClosure(timeout == null ? 0 : max(1, timeout.inMilliseconds));
+    closure(timeout == null ? 0 : max(1, timeout.inMilliseconds));
   }
 }
 
@@ -145,7 +146,7 @@ T waitFor<T>(Future<T> future, {Duration? timeout}) {
   Timer.run(() {}); // Ensure that previous calls to waitFor are woken up.
 
   if (error != null) {
-    throw new AsyncError(error, stacktrace);
+    throw new AsyncError(error!, stacktrace);
   }
 
   return result;

sdk_nnbd/lib/developer/profiler.dart

@@ -63,7 +63,7 @@ class Gauge extends Metric {
   }
 
   Gauge(String name, String description, this.min, this.max)
-      : _value = min ?? double.negativeInfinity,
+      : _value = min,
         super(name, description) {
     // TODO: When NNBD is complete, delete the following two lines.
     ArgumentError.checkNotNull(min, 'min');

sdk_nnbd/lib/ffi/ffi.dart

@@ -54,7 +54,7 @@ class Pointer<T extends NativeType> extends NativeType {
   /// [dynamic].
   external static Pointer<NativeFunction<T>> fromFunction<T extends Function>(
       @DartRepresentationOf("T") Function f,
-      [Object exceptionalReturn]);
+      [Object? exceptionalReturn]);
 
   /// Access to the raw pointer value.
   /// On 32-bit systems, the upper 32-bits of the result are 0.

sdk_nnbd/lib/internal/internal.dart

@@ -229,6 +229,24 @@ class NotNullableError<T> extends Error implements TypeError {
       "Null is not a valid value for the parameter '$_name' of type '$T'";
 }
 
+/// A function that returns the value or default value (if invoked with `null`
+/// value) for non-nullable function parameters in Null safety enabled code.
+///
+/// Because Dart does not have full null safety
+/// until all legacy code has been removed from a program,
+/// a non-nullable parameter can still end up with a `null` value.
+/// This function can be used to get a default value for a parameter
+/// when a `null` value is passed in for a non-nullable parameter.
+///
+/// TODO(40810) - Remove uses of this function when Dart has full null safety.
+T valueOfNonNullableParamWithDefault<T extends Object>(T value, T defaultVal) {
+  if ((value as dynamic) == null) {
+    return defaultVal;
+  } else {
+    return value;
+  }
+}
+
 /**
  * HTTP status codes.  Exported in dart:io and dart:html.
  */

sdk_nnbd/lib/io/secure_socket.dart

@@ -709,7 +709,6 @@ class _RawSecureSocket extends Stream<RawSocketEvent>
       return 0;
     }
     if (_status != connectedStatus) return 0;
-    offset ??= 0;
     bytes ??= data.length - offset;
 
     int written =