enable prefer_function_declarations_over_variables lint (#77398)

analysis_options.yaml

@@ -159,7 +159,7 @@ linter:
     - prefer_final_locals
     - prefer_for_elements_to_map_fromIterable
     - prefer_foreach
-    # - prefer_function_declarations_over_variables # not yet tested
+    - prefer_function_declarations_over_variables
     - prefer_generic_function_type_aliases
     - prefer_if_elements_to_conditional_expressions
     - prefer_if_null_operators

dev/benchmarks/macrobenchmarks/test/frame_policy.dart

@@ -5,7 +5,6 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/gestures.dart';
-import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:integration_test/integration_test.dart';
 
@@ -21,9 +20,9 @@ void main() {
       await tester.pumpAndSettle();
       final Offset location = tester.getCenter(find.byType(ListView));
       int frameCount = 0;
-      final FrameCallback frameCounter = (Duration elapsed) {
+      void frameCounter(Duration elapsed) {
         frameCount += 1;
-      };
+      }
       tester.binding.addPersistentFrameCallback(frameCounter);
 
       const int timeInSecond = 1;

dev/devicelab/bin/tasks/module_host_with_custom_build_test.dart

@@ -77,7 +77,7 @@ Future<void> main() async {
         Directory(path.join(hostAppDir.path, 'gradle', 'wrapper')),
       );
 
-      final Function clean = () async {
+      Future<void> clean() async {
         section('Clean');
         await inDirectory(hostAppDir, () async {
           await exec(gradlewExecutable,
@@ -87,7 +87,7 @@ Future<void> main() async {
             },
           );
         });
-      };
+      }
 
       if (!Platform.isWindows) {
         section('Make $gradlewExecutable executable');

dev/devicelab/test/adb_test.dart

@@ -179,7 +179,6 @@ class FakeDevice extends AndroidDevice {
   FakeDevice({String deviceId}) : super(deviceId: deviceId);
 
   static String output = '';
-  static ExitErrorFactory exitErrorFactory = () => null;
 
   static List<CommandArgs> commandLog = <CommandArgs>[];
 
@@ -222,8 +221,5 @@ class FakeDevice extends AndroidDevice {
       arguments: arguments,
       environment: environment,
     ));
-    final dynamic exitError = exitErrorFactory();
-    if (exitError != null)
-      throw exitError;
   }
 }

dev/tools/localization/gen_cupertino_localizations.dart

@@ -4,7 +4,7 @@
 
 import 'localizations_utils.dart';
 
-HeaderGenerator generateCupertinoHeader = (String regenerateInstructions) {
+String generateCupertinoHeader(String regenerateInstructions) {
   return '''
 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
@@ -27,11 +27,11 @@ import '../cupertino_localizations.dart';
 // These classes are constructed by the [getCupertinoTranslation] method at the
 // bottom of this file, and used by the [_GlobalCupertinoLocalizationsDelegate.load]
 // method defined in `flutter_localizations/lib/src/cupertino_localizations.dart`.''';
-};
+}
 
 /// Returns the source of the constructor for a GlobalCupertinoLocalizations
 /// subclass.
-ConstructorGenerator generateCupertinoConstructor = (LocaleInfo locale) {
+String generateCupertinoConstructor(LocaleInfo locale) {
   final String localeName = locale.originalString;
   return '''
   /// Create an instance of the translation bundle for ${describeLocale(localeName)}.
@@ -58,7 +58,7 @@ ConstructorGenerator generateCupertinoConstructor = (LocaleInfo locale) {
     singleDigitSecondFormat: singleDigitSecondFormat,
     decimalFormat: decimalFormat,
   );''';
-};
+}
 
 const String cupertinoFactoryName = 'getCupertinoTranslation';
 

dev/tools/localization/gen_material_localizations.dart

@@ -4,7 +4,7 @@
 
 import 'localizations_utils.dart';
 
-HeaderGenerator generateMaterialHeader = (String regenerateInstructions) {
+String generateMaterialHeader(String regenerateInstructions) {
   return '''
 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
@@ -27,11 +27,11 @@ import '../material_localizations.dart';
 // These classes are constructed by the [getMaterialTranslation] method at the
 // bottom of this file, and used by the [_MaterialLocalizationsDelegate.load]
 // method defined in `flutter_localizations/lib/src/material_localizations.dart`.''';
-};
+}
 
 /// Returns the source of the constructor for a GlobalMaterialLocalizations
 /// subclass.
-ConstructorGenerator generateMaterialConstructor = (LocaleInfo locale) {
+String generateMaterialConstructor(LocaleInfo locale) {
   final String localeName = locale.originalString;
   return '''
   /// Create an instance of the translation bundle for ${describeLocale(localeName)}.
@@ -60,7 +60,7 @@ ConstructorGenerator generateMaterialConstructor = (LocaleInfo locale) {
     decimalFormat: decimalFormat,
     twoDigitZeroPaddedFormat: twoDigitZeroPaddedFormat,
   );''';
-};
+}
 
 const String materialFactoryName = 'getMaterialTranslation';
 

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -2223,7 +2223,7 @@ class _NavigationBarComponentsTransition {
 
 /// Navigation bars' hero rect tween that will move between the static bars
 /// but keep a constant size that's the bigger of both navigation bars.
-CreateRectTween _linearTranslateWithLargestRectSizeTween = (Rect? begin, Rect? end) {
+RectTween _linearTranslateWithLargestRectSizeTween(Rect? begin, Rect? end) {
   final Size largestSize = Size(
     math.max(begin!.size.width, end!.size.width),
     math.max(begin.size.height, end.size.height),
@@ -2232,9 +2232,9 @@ CreateRectTween _linearTranslateWithLargestRectSizeTween = (Rect? begin, Rect? e
     begin: begin.topLeft & largestSize,
     end: end.topLeft & largestSize,
   );
-};
+}
 
-final HeroPlaceholderBuilder _navBarHeroLaunchPadBuilder = (
+Widget _navBarHeroLaunchPadBuilder(
   BuildContext context,
   Size heroSize,
   Widget child,
@@ -2258,10 +2258,10 @@ final HeroPlaceholderBuilder _navBarHeroLaunchPadBuilder = (
     visible: false,
     child: child,
   );
-};
+}
 
 /// Navigation bars' hero flight shuttle builder.
-final HeroFlightShuttleBuilder _navBarHeroFlightShuttleBuilder = (
+Widget _navBarHeroFlightShuttleBuilder(
   BuildContext flightContext,
   Animation<double> animation,
   HeroFlightDirection flightDirection,
@@ -2310,4 +2310,4 @@ final HeroFlightShuttleBuilder _navBarHeroFlightShuttleBuilder = (
         topNavBar: fromNavBar,
       );
   }
-};
+}

packages/flutter/lib/src/foundation/assertions.dart

@@ -876,7 +876,9 @@ class FlutterError extends Error with DiagnosticableTreeMixin implements Asserti
   ///
   /// Do not call [onError] directly, instead, call [reportError], which
   /// forwards to [onError] if it is not null.
-  static FlutterExceptionHandler? onError = (FlutterErrorDetails details) => presentError(details);
+  static FlutterExceptionHandler? onError = _defaultErrorHandler;
+
+  static void _defaultErrorHandler(FlutterErrorDetails details) => presentError(details);
 
   /// Called by the Flutter framework before attempting to parse a [StackTrace].
   ///
@@ -901,7 +903,9 @@ class FlutterError extends Error with DiagnosticableTreeMixin implements Asserti
   ///   return stack;
   /// };
   /// ```
-  static StackTraceDemangler demangleStackTrace = (StackTrace stackTrace) => stackTrace;
+  static StackTraceDemangler demangleStackTrace = _defaultStackTraceDemangler;
+
+  static StackTrace _defaultStackTraceDemangler(StackTrace stackTrace) => stackTrace;
 
   /// Called whenever the Flutter framework wants to present an error to the
   /// users.

packages/flutter/lib/src/material/animated_icons/animated_icons.dart

@@ -99,7 +99,7 @@ class AnimatedIcon extends StatelessWidget {
   /// horizontally (e.g back arrow will point right).
   final TextDirection? textDirection;
 
-  static final _UiPathFactory _pathFactory = () => ui.Path();
+  static ui.Path _pathFactory() => ui.Path();
 
   @override
   Widget build(BuildContext context) {

packages/flutter/lib/src/material/range_slider.dart

@@ -524,7 +524,7 @@ class _RangeSliderState extends State<RangeSlider> with TickerProviderStateMixin
   // immediately selected while the drag displacement is zero. If the first
   // non-zero displacement is negative, then the left thumb is selected, and if its
   // positive, then the right thumb is selected.
-  static final RangeThumbSelector _defaultRangeThumbSelector = (
+  Thumb? _defaultRangeThumbSelector(
     TextDirection textDirection,
     RangeValues values,
     double tapValue,
@@ -566,9 +566,7 @@ class _RangeSliderState extends State<RangeSlider> with TickerProviderStateMixin
         return Thumb.end;
     }
     return null;
-  };
+  }
-
-
 
   @override
   Widget build(BuildContext context) {

packages/flutter/lib/src/painting/image_provider.dart

@@ -758,14 +758,14 @@ class ResizeImage extends ImageProvider<_SizeAwareCacheKey> {
 
   @override
   ImageStreamCompleter load(_SizeAwareCacheKey key, DecoderCallback decode) {
-    final DecoderCallback decodeResize = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
+    Future<ui.Codec> decodeResize(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
       assert(
         cacheWidth == null && cacheHeight == null && allowUpscaling == null,
         'ResizeImage cannot be composed with another ImageProvider that applies '
         'cacheWidth, cacheHeight, or allowUpscaling.'
       );
       return decode(bytes, cacheWidth: width, cacheHeight: height, allowUpscaling: this.allowUpscaling);
-    };
+    }
     final ImageStreamCompleter completer = imageProvider.load(key.providerCacheKey, decodeResize);
     if (!kReleaseMode) {
       completer.debugLabel = '${completer.debugLabel} - Resized(${key.width}×${key.height})';

packages/flutter/lib/src/rendering/list_wheel_viewport.dart

@@ -945,18 +945,18 @@ class RenderListWheelViewport
     Offset offsetToCenter,
   ) {
     // Paint child cylindrically, without [overAndUnderCenterOpacity].
-    final PaintingContextCallback painter = (PaintingContext context, Offset offset) {
+    void painter(PaintingContext context, Offset offset) {
       context.paintChild(
         child,
         // Paint everything in the center (e.g. angle = 0), then transform.
         offset + offsetToCenter,
       );
-    };
+    }
 
     // Paint child cylindrically, with [overAndUnderCenterOpacity].
-    final PaintingContextCallback opacityPainter = (PaintingContext context, Offset offset) {
+    void opacityPainter(PaintingContext context, Offset offset) {
       context.pushOpacity(offset, (overAndUnderCenterOpacity * 255).round(), painter);
-    };
+    }
 
     context.pushTransform(
       needsCompositing,

packages/flutter/lib/src/widgets/heroes.dart

@@ -1031,7 +1031,7 @@ class HeroController extends NavigatorObserver {
     _flights.remove(flight.manifest.tag);
   }
 
-  static final HeroFlightShuttleBuilder _defaultHeroFlightShuttleBuilder = (
+  Widget _defaultHeroFlightShuttleBuilder(
     BuildContext flightContext,
     Animation<double> animation,
     HeroFlightDirection flightDirection,
@@ -1040,7 +1040,7 @@ class HeroController extends NavigatorObserver {
   ) {
     final Hero toHero = toHeroContext.widget as Hero;
     return toHero.child;
-  };
+  }
 }
 
 /// Enables or disables [Hero]es in the widget subtree.

packages/flutter/lib/src/widgets/navigator.dart

@@ -3171,9 +3171,9 @@ class _RouteEntry extends RouteTransitionRecord {
     );
   }
 
-  static final _RouteEntryPredicate isPresentPredicate = (_RouteEntry entry) => entry.isPresent;
+  static bool isPresentPredicate(_RouteEntry entry) => entry.isPresent;
-  static final _RouteEntryPredicate suitableForTransitionAnimationPredicate = (_RouteEntry entry) => entry.suitableForTransitionAnimation;
+  static bool suitableForTransitionAnimationPredicate(_RouteEntry entry) => entry.suitableForTransitionAnimation;
-  static final _RouteEntryPredicate willBePresentPredicate = (_RouteEntry entry) => entry.willBePresent;
+  static bool willBePresentPredicate(_RouteEntry entry) => entry.willBePresent;
 
   static _RouteEntryPredicate isRoutePredicate(Route<dynamic> route) {
     return (_RouteEntry entry) => entry.route == route;

packages/flutter/lib/src/widgets/restoration.dart

@@ -849,11 +849,11 @@ mixin RestorationMixin<S extends StatefulWidget> on State<S> {
 
     if (!property.isRegistered) {
       property._register(restorationId, this);
-      final VoidCallback listener = () {
+      void listener() {
         if (bucket == null)
           return;
         _updateProperty(property);
-      };
+      }
       property.addListener(listener);
       _properties[property] = listener;
     }

packages/flutter/test/animation/iteration_patterns_test.dart

@@ -18,15 +18,15 @@ void main() {
     );
     final List<String> log = <String>[];
 
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
-    final VoidCallback listener3 = () { log.add('listener3'); };
+    void listener3() { log.add('listener3'); }
-    final VoidCallback listener4 = () { log.add('listener4'); };
+    void listener4() { log.add('listener4'); }
-    final VoidCallback listener2 = () {
+    void listener2() {
       log.add('listener2');
       controller.removeListener(listener1);
       controller.removeListener(listener3);
       controller.addListener(listener4);
-    };
+    }
 
     controller.addListener(listener1);
     controller.addListener(listener2);
@@ -51,15 +51,15 @@ void main() {
     );
     final List<String> log = <String>[];
 
-    final AnimationStatusListener listener1 = (AnimationStatus status) { log.add('listener1'); };
+    void listener1(AnimationStatus status) { log.add('listener1'); }
-    final AnimationStatusListener listener3 = (AnimationStatus status) { log.add('listener3'); };
+    void listener3(AnimationStatus status) { log.add('listener3'); }
-    final AnimationStatusListener listener4 = (AnimationStatus status) { log.add('listener4'); };
+    void listener4(AnimationStatus status) { log.add('listener4'); }
-    final AnimationStatusListener listener2 = (AnimationStatus status) {
+    void listener2(AnimationStatus status) {
       log.add('listener2');
       controller.removeStatusListener(listener1);
       controller.removeStatusListener(listener3);
       controller.addStatusListener(listener4);
-    };
+    }
 
     controller.addStatusListener(listener1);
     controller.addStatusListener(listener2);
@@ -86,12 +86,12 @@ void main() {
     );
     final List<String> log = <String>[];
 
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
-    final VoidCallback badListener = () {
+    void badListener() {
       log.add('badListener');
       throw ArgumentError();
-    };
+    }
-    final VoidCallback listener2 = () { log.add('listener2'); };
+    void listener2() { log.add('listener2'); }
 
     controller.addListener(listener1);
     controller.addListener(badListener);
@@ -109,12 +109,12 @@ void main() {
     );
     final List<String> log = <String>[];
 
-    final AnimationStatusListener listener1 = (AnimationStatus status) { log.add('listener1'); };
+    void listener1(AnimationStatus status) { log.add('listener1'); }
-    final AnimationStatusListener badListener = (AnimationStatus status) {
+    void badListener(AnimationStatus status) {
       log.add('badListener');
       throw ArgumentError();
-    };
+    }
-    final AnimationStatusListener listener2 = (AnimationStatus status) { log.add('listener2'); };
+    void listener2(AnimationStatus status) { log.add('listener2'); }
 
     controller.addStatusListener(listener1);
     controller.addStatusListener(badListener);

packages/flutter/test/animation/listener_helpers_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter/widgets.dart';
 void main() {
   test('AnimationLocalStatusListenersMixin with AnimationLazyListenerMixin - removing unregistered listener is no-op', () {
     final _TestAnimationLocalStatusListeners uut = _TestAnimationLocalStatusListeners();
-    final AnimationStatusListener fakeListener = (AnimationStatus status) { };
+    void fakeListener(AnimationStatus status) { }
     uut.removeStatusListener(fakeListener);
     expect(uut.callsToStart, 0);
     expect(uut.callsToStop, 0);
@@ -16,7 +16,7 @@ void main() {
 
   test('AnimationLocalListenersMixin with AnimationLazyListenerMixin - removing unregistered listener is no-op', () {
     final _TestAnimationLocalListeners uut = _TestAnimationLocalListeners();
-    final VoidCallback fakeListener = () { };
+    void fakeListener() { }
     uut.removeListener(fakeListener);
     expect(uut.callsToStart, 0);
     expect(uut.callsToStop, 0);

packages/flutter/test/cupertino/colors_test.dart

@@ -496,7 +496,7 @@ void main() {
     setUp(() { color = null; });
 
     testWidgets('dynamic color works in cupertino override theme', (WidgetTester tester) async {
-      final CupertinoDynamicColor Function() typedColor = () => color! as CupertinoDynamicColor;
+      CupertinoDynamicColor typedColor() => color! as CupertinoDynamicColor;
 
       await tester.pumpWidget(
         MaterialApp(

packages/flutter/test/cupertino/refresh_test.dart

@@ -31,7 +31,7 @@ void main() {
     );
   }
 
-  final VoidCallback uiTestGroup = () {
+  void uiTestGroup() {
     testWidgets("doesn't invoke anything without user interaction", (WidgetTester tester) async {
       await tester.pumpWidget(
         Directionality(
@@ -956,9 +956,9 @@ void main() {
         initialFirstCellY + 50
       );
     }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS,  TargetPlatform.macOS }));
-  };
+  }
 
-  final VoidCallback stateMachineTestGroup = () {
+  void stateMachineTestGroup() {
     testWidgets('starts in inactive state', (WidgetTester tester) async {
       await tester.pumpWidget(
         Directionality(
@@ -1345,7 +1345,7 @@ void main() {
       );
       expect(tester.widget<CupertinoActivityIndicator>(find.byType(CupertinoActivityIndicator)).progress, 100.0 / 100.0);
     });
-  };
+  }
 
   group('UI tests long list', uiTestGroup);
 

packages/flutter/test/cupertino/text_form_field_row_test.dart

@@ -93,7 +93,7 @@ void main() {
 
   testWidgets('Passes onEditingComplete to underlying CupertinoTextField',
       (WidgetTester tester) async {
-    final VoidCallback onEditingComplete = () {};
+    void onEditingComplete() {}
 
     await tester.pumpWidget(
       CupertinoApp(

packages/flutter/test/cupertino/theme_test.dart

@@ -217,7 +217,7 @@ void main() {
     }
   }
 
-  final VoidCallback dynamicColorsTestGroup = () {
+  void dynamicColorsTestGroup() {
     testWidgets('CupertinoTheme.of resolves colors', (WidgetTester tester) async {
       final CupertinoThemeData data = CupertinoThemeData(brightness: currentBrightness, primaryColor: CupertinoColors.systemRed);
       final CupertinoThemeData theme = await testTheme(tester, data);
@@ -249,7 +249,7 @@ void main() {
       colorMatches(theme.textTheme.pickerTextStyle.color, CupertinoColors.label);
       colorMatches(theme.textTheme.dateTimePickerTextStyle.color, CupertinoColors.label);
     });
-  };
+  }
 
   currentBrightness = Brightness.light;
   group('light colors', dynamicColorsTestGroup);

packages/flutter/test/foundation/change_notifier_test.dart

@@ -34,13 +34,13 @@ class B extends A with ChangeNotifier {
 void main() {
   testWidgets('ChangeNotifier', (WidgetTester tester) async {
     final List<String> log = <String>[];
-    final VoidCallback listener = () { log.add('listener'); };
+    void listener() { log.add('listener'); }
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
-    final VoidCallback listener2 = () { log.add('listener2'); };
+    void listener2() { log.add('listener2'); }
-    final VoidCallback badListener = () {
+    void badListener() {
       log.add('badListener');
       throw ArgumentError();
-    };
+    }
 
     final TestNotifier test = TestNotifier();
 
@@ -111,15 +111,15 @@ void main() {
     final TestNotifier test = TestNotifier();
     final List<String> log = <String>[];
 
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
-    final VoidCallback listener3 = () { log.add('listener3'); };
+    void listener3() { log.add('listener3'); }
-    final VoidCallback listener4 = () { log.add('listener4'); };
+    void listener4() { log.add('listener4'); }
-    final VoidCallback listener2 = () {
+    void listener2() {
       log.add('listener2');
       test.removeListener(listener1);
       test.removeListener(listener3);
       test.addListener(listener4);
-    };
+    }
 
     test.addListener(listener1);
     test.addListener(listener2);
@@ -141,8 +141,8 @@ void main() {
     final TestNotifier source = TestNotifier();
     final List<String> log = <String>[];
 
-    final VoidCallback listener3 = () { log.add('listener3'); };
+    void listener3() { log.add('listener3'); }
-    final VoidCallback listener2 = () { log.add('listener2'); };
+    void listener2() { log.add('listener2'); }
     void listener1() {
       log.add('listener1');
       source.addListener(listener2);
@@ -167,7 +167,7 @@ void main() {
       log.add('selfRemovingListener');
       source.removeListener(selfRemovingListener);
     }
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
 
     source.addListener(listener1);
     source.addListener(selfRemovingListener);
@@ -205,8 +205,8 @@ void main() {
     final List<String> log = <String>[];
 
     final Listenable merged = Listenable.merge(<Listenable>[source1, source2]);
-    final VoidCallback listener1 = () { log.add('listener1'); };
+    void listener1() { log.add('listener1'); }
-    final VoidCallback listener2 = () { log.add('listener2'); };
+    void listener2() { log.add('listener2'); }
 
     merged.addListener(listener1);
     source1.notify();
@@ -237,7 +237,7 @@ void main() {
     final List<String> log = <String>[];
 
     final Listenable merged = Listenable.merge(<Listenable?>[null, source1, null, source2, null]);
-    final VoidCallback listener = () { log.add('listener'); };
+    void listener() { log.add('listener'); }
 
     merged.addListener(listener);
     source1.notify();
@@ -252,7 +252,7 @@ void main() {
     final List<String> log = <String>[];
 
     final Listenable merged = Listenable.merge(<Listenable>[source1, source2]);
-    final VoidCallback listener = () { log.add('listener'); };
+    void listener() { log.add('listener'); }
 
     merged.addListener(listener);
     source1.notify();
@@ -279,7 +279,7 @@ void main() {
     final ValueNotifier<double> notifier = ValueNotifier<double>(2.0);
 
     final List<double> log = <double>[];
-    final VoidCallback listener = () { log.add(notifier.value); };
+    void listener() { log.add(notifier.value); }
 
     notifier.addListener(listener);
     notifier.value = 3.0;
@@ -325,7 +325,7 @@ void main() {
 
     final TestNotifier source1 = TestNotifier();
     final TestNotifier source2 = TestNotifier();
-    final VoidCallback fakeListener = () { };
+    void fakeListener() { }
 
     final Listenable listenableUnderTest = Listenable.merge(<Listenable>[source1, source2]);
     expect(source1.isListenedTo, isFalse);

packages/flutter/test/foundation/diagnostics_test.dart

@@ -1197,7 +1197,7 @@ void main() {
   });
 
   test('callback property test', () {
-    final Function onClick = () { };
+    void onClick() { }
     final ObjectFlagProperty<Function> present = ObjectFlagProperty<Function>(
       'onClick',
       onClick,
@@ -1631,7 +1631,7 @@ void main() {
   });
 
   test('has property test', () {
-    final Function onClick = () { };
+    void onClick() { }
     final ObjectFlagProperty<Function> has = ObjectFlagProperty<Function>.has(
       'onClick',
       onClick,
@@ -1656,8 +1656,8 @@ void main() {
   test('iterable flags property test', () {
     // Normal property
     {
-      final Function onClick = () { };
+      void onClick() { }
-      final Function onMove = () { };
+      void onMove() { }
       final Map<String, Function> value = <String, Function>{
         'click': onClick,
         'move': onMove,
@@ -1675,8 +1675,8 @@ void main() {
 
     // Reversed-order property
     {
-      final Function onClick = () { };
+      void onClick() { }
-      final Function onMove = () { };
+      void onMove() { }
       final Map<String, Function> value = <String, Function>{
         'move': onMove,
         'click': onClick,
@@ -1692,7 +1692,7 @@ void main() {
 
     // Partially empty property
     {
-      final Function onClick = () { };
+      void onClick() { }
       final Map<String, Function?> value = <String, Function?>{
         'move': null,
         'click': onClick,

packages/flutter/test/material/dropdown_form_field_test.dart

@@ -11,7 +11,7 @@ import 'package:flutter/material.dart';
 import '../rendering/mock_canvas.dart';
 
 const List<String> menuItems = <String>['one', 'two', 'three', 'four'];
-final ValueChanged<String?> onChanged = (_) { };
+void onChanged<T>(T _) { }
 final Type dropdownButtonType = DropdownButton<String>(
   onChanged: (_) { },
   items: const <DropdownMenuItem<String>>[],

packages/flutter/test/material/dropdown_test.dart

@@ -14,7 +14,7 @@ import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 const List<String> menuItems = <String>['one', 'two', 'three', 'four'];
-final ValueChanged<String?> onChanged = (_) { };
+void onChanged<T>(T _) { }
 
 final Type dropdownButtonType = DropdownButton<String>(
   onChanged: (_) { },

packages/flutter/test/material/feedback_test.dart

@@ -70,9 +70,9 @@ void main () {
       final SemanticsTester semanticsTester = SemanticsTester(tester);
 
       int callbackCount = 0;
-      final VoidCallback callback = () {
+      void callback() {
         callbackCount++;
-      };
+      }
 
       await tester.pumpWidget(TestWidget(
         tapHandler: (BuildContext context) {
@@ -132,9 +132,9 @@ void main () {
     testWidgets('forLongPress Wrapper', (WidgetTester tester) async {
       final SemanticsTester semanticsTester = SemanticsTester(tester);
       int callbackCount = 0;
-      final VoidCallback callback = () {
+      void callback() {
         callbackCount++;
-      };
+      }
 
       await tester.pumpWidget(TestWidget(
         longPressHandler: (BuildContext context) {

packages/flutter/test/material/input_decorator_test.dart

@@ -965,7 +965,7 @@ void main() {
     final Key buildCounterKey = UniqueKey();
     const String counterText = 'I show instead of count';
     final Widget counter = Text('hello', key: counterKey);
-    final InputCounterWidgetBuilder buildCounter = (
+    Widget buildCounter(
       BuildContext context, {
       required int currentLength,
       required int? maxLength,
@@ -975,7 +975,7 @@ void main() {
         '${currentLength.toString()} of ${maxLength.toString()}',
         key: buildCounterKey,
       );
-    };
+    }
 
     await tester.pumpWidget(buildFrame(
       counterText: counterText,

packages/flutter/test/material/popup_menu_test.dart

@@ -466,12 +466,12 @@ void main() {
         child: Text('XXX'),
       ),
     );
-    final WidgetPredicate popupMenu = (Widget widget) {
+    bool popupMenu(Widget widget) {
       final String widgetType = widget.runtimeType.toString();
       // TODO(mraleph): Remove the old case below.
       return widgetType == '_PopupMenu<int?>' // normal case
           || widgetType == '_PopupMenu'; // for old versions of Dart that don't reify method type arguments
-    };
+    }
 
     Future<void> openMenu(TextDirection textDirection, Alignment alignment) async {
       return TestAsyncUtils.guard<void>(() async {

packages/flutter/test/material/range_slider_test.dart

@@ -1347,9 +1347,9 @@ void main() {
       int? divisions,
       bool enabled = true,
     }) {
-      final ValueChanged<RangeValues> onChanged = (RangeValues newValues) {
+      void onChanged(RangeValues newValues) {
         values = newValues;
-      };
+      }
       return MaterialApp(
         home: Scaffold(
           // The builder is used to pass the context from the MaterialApp widget

packages/flutter/test/material/stepper_test.dart

@@ -380,30 +380,29 @@ void main() {
       canceledPressed = true;
     }
 
-    final ControlsWidgetBuilder builder =
+    Widget builder(BuildContext context, { VoidCallback? onStepContinue, VoidCallback? onStepCancel }) {
-      (BuildContext context, { VoidCallback? onStepContinue, VoidCallback? onStepCancel }) {
+      return Container(
-        return Container(
+        margin: const EdgeInsets.only(top: 16.0),
-          margin: const EdgeInsets.only(top: 16.0),
+        child: ConstrainedBox(
-          child: ConstrainedBox(
+          constraints: const BoxConstraints.tightFor(height: 48.0),
-            constraints: const BoxConstraints.tightFor(height: 48.0),
+          child: Row(
-            child: Row(
+            children: <Widget>[
-              children: <Widget>[
+              TextButton(
-                TextButton(
+                onPressed: onStepContinue,
-                  onPressed: onStepContinue,
+                child: const Text('Let us continue!'),
-                  child: const Text('Let us continue!'),
+              ),
+              Container(
+                margin: const EdgeInsetsDirectional.only(start: 8.0),
+                child: TextButton(
+                  onPressed: onStepCancel,
+                  child: const Text('Cancel This!'),
                 ),
-                Container(
+              ),
-                  margin: const EdgeInsetsDirectional.only(start: 8.0),
+            ],
-                  child: TextButton(
-                    onPressed: onStepCancel,
-                    child: const Text('Cancel This!'),
-                  ),
-                ),
-              ],
-            ),
           ),
-        );
+        ),
-      };
+      );
+    }
 
     await tester.pumpWidget(
       MaterialApp(

packages/flutter/test/material/text_field_test.dart

@@ -252,7 +252,7 @@ void main() {
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.macOS, TargetPlatform.windows, TargetPlatform.linux }), skip: kIsWeb);
 
   testWidgets('TextField passes onEditingComplete to EditableText', (WidgetTester tester) async {
-    final VoidCallback onEditingComplete = () { };
+    void onEditingComplete() { }
 
     await tester.pumpWidget(
       MaterialApp(
@@ -489,10 +489,10 @@ void main() {
   testWidgets('TextInputFormatter gets correct selection value', (WidgetTester tester) async {
     late TextEditingValue actualOldValue;
     late TextEditingValue actualNewValue;
-    final FormatEditUpdateCallback callBack = (TextEditingValue oldValue, TextEditingValue newValue) {
+    void callBack(TextEditingValue oldValue, TextEditingValue newValue) {
       actualOldValue = oldValue;
       actualNewValue = newValue;
-    };
+    }
     final FocusNode focusNode = FocusNode();
     final TextEditingController controller = TextEditingController(text: '123');
     await tester.pumpWidget(

packages/flutter/test/material/text_form_field_test.dart

@@ -201,7 +201,7 @@ void main() {
   });
 
   testWidgets('Passes onEditingComplete to underlying TextField', (WidgetTester tester) async {
-    final VoidCallback onEditingComplete = () { };
+    void onEditingComplete() { }
 
     await tester.pumpWidget(
       MaterialApp(

packages/flutter/test/painting/image_cache_test.dart

@@ -136,9 +136,9 @@ void main() {
   });
 
   test('Returns null if an error is caught resolving an image', () {
-    final DecoderCallback _basicDecoder = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
+    Future<ui.Codec> _basicDecoder(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
       return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling ?? false);
-    };
+    }
     final ErrorImageProvider errorImage = ErrorImageProvider();
     expect(() => imageCache!.putIfAbsent(errorImage, () => errorImage.load(errorImage, _basicDecoder)), throwsA(isA<Error>()));
     bool caughtError = false;

packages/flutter/test/painting/image_provider_and_image_cache_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:typed_data';
+import 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
@@ -16,9 +17,9 @@ import 'mocks_for_image_cache.dart';
 void main() {
   TestRenderingFlutterBinding();
 
-  final DecoderCallback _basicDecoder = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
+  Future<ui.Codec> _basicDecoder(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
     return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling ?? false);
-  };
+  }
 
   FlutterExceptionHandler? oldError;
   setUp(() {

packages/flutter/test/painting/image_provider_network_image_test.dart

@@ -18,9 +18,9 @@ import '../rendering/rendering_tester.dart';
 void main() {
   TestRenderingFlutterBinding();
 
-  final DecoderCallback _basicDecoder = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
+  Future<Codec>  _basicDecoder(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool? allowUpscaling}) {
     return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling ?? false);
-  };
+  }
 
   late _FakeHttpClient httpClient;
 

packages/flutter/test/painting/image_provider_resize_image_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:typed_data';
+import 'dart:ui' as ui;
 
 import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -98,12 +99,12 @@ void main() {
     final MemoryImage memoryImage = MemoryImage(bytes);
     final ResizeImage resizeImage = ResizeImage(memoryImage, width: 123, height: 321);
 
-    final DecoderCallback decode = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
+    Future<ui.Codec> decode(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
       expect(cacheWidth, 123);
       expect(cacheHeight, 321);
       expect(allowUpscaling, false);
       return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
-    };
+    }
 
     resizeImage.load(await resizeImage.obtainKey(ImageConfiguration.empty), decode);
   });

packages/flutter/test/painting/image_stream_test.dart

@@ -105,7 +105,7 @@ void main() {
     await tester.idle();
     expect(mockCodec.numFramesAsked, 0);
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
     await tester.idle();
     expect(mockCodec.numFramesAsked, 1);
@@ -120,7 +120,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
     await tester.idle();
     expect(mockCodec.numFramesAsked, 0);
@@ -143,7 +143,7 @@ void main() {
     await tester.idle();
     expect(mockCodec.numFramesAsked, 0);
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     final ImageStreamListener streamListener = ImageStreamListener(listener);
     imageStream.addListener(streamListener);
     await tester.idle();
@@ -291,7 +291,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
     codecCompleter.complete(mockCodec);
     // MultiFrameImageStreamCompleter only sets an error handler for the next
@@ -467,7 +467,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
     final ImageStreamCompleterHandle handle = imageStream.keepAlive();
 
@@ -508,13 +508,13 @@ void main() {
     );
 
     final List<ImageInfo> emittedImages1 = <ImageInfo>[];
-    final ImageListener listener1 = (ImageInfo image, bool synchronousCall) {
+    void listener1(ImageInfo image, bool synchronousCall) {
       emittedImages1.add(image);
-    };
+    }
     final List<ImageInfo> emittedImages2 = <ImageInfo>[];
-    final ImageListener listener2 = (ImageInfo image, bool synchronousCall) {
+    void listener2(ImageInfo image, bool synchronousCall) {
       emittedImages2.add(image);
-    };
+    }
     imageStream.addListener(ImageStreamListener(listener1));
     imageStream.addListener(ImageStreamListener(listener2));
 
@@ -554,7 +554,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
 
     codecCompleter.complete(mockCodec);
@@ -587,7 +587,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
 
     codecCompleter.complete(mockCodec);
@@ -623,9 +623,9 @@ void main() {
     );
 
     dynamic capturedException;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
-    };
+    }
 
     streamUnderTest.addListener(ImageStreamListener(
       (ImageInfo image, bool synchronousCall) { },
@@ -658,7 +658,7 @@ void main() {
       scale: 1.0,
     );
 
-    final ImageListener listener = (ImageInfo image, bool synchronousCall) { };
+    void listener(ImageInfo image, bool synchronousCall) { }
     imageStream.addListener(ImageStreamListener(listener));
 
     codecCompleter.complete(mockCodec);
@@ -723,9 +723,9 @@ void main() {
     );
 
     int onImageCount = 0;
-    final ImageListener activeListener = (ImageInfo image, bool synchronousCall) {
+    void activeListener(ImageInfo image, bool synchronousCall) {
       onImageCount += 1;
-    };
+    }
     bool lastListenerDropped = false;
     imageStream.addOnLastListenerRemovedCallback(() {
       lastListenerDropped = true;

packages/flutter/test/rendering/proxy_getters_and_setters_test.dart

@@ -51,16 +51,16 @@ void main() {
   });
 
   test('RenderShaderMask getters and setters', () {
-    final ShaderCallback callback1 = (Rect bounds) {
+    Shader callback1(Rect bounds) {
       assert(false); // The test should not call this.
       const LinearGradient gradient = LinearGradient(colors: <Color>[Colors.red]);
       return gradient.createShader(Rect.zero);
-    };
+    }
-    final ShaderCallback callback2 = (Rect bounds) {
+    Shader callback2(Rect bounds) {
       assert(false); // The test should not call this.
       const LinearGradient gradient = LinearGradient(colors: <Color>[Colors.blue]);
       return gradient.createShader(Rect.zero);
-    };
+    }
     final RenderShaderMask box = RenderShaderMask(shaderCallback: callback1);
     expect(box.shaderCallback, equals(callback1));
     box.shaderCallback = callback2;

packages/flutter/test/rendering/stack_test.dart

@@ -106,9 +106,9 @@ void main() {
       );
 
       final List<RenderObject> visitedChildren = <RenderObject>[];
-      final RenderObjectVisitor visitor = (RenderObject child) {
+      void visitor(RenderObject child) {
         visitedChildren.add(child);
-      };
+      }
 
       stack.visitChildrenForSemantics(visitor);
 

packages/flutter/test/semantics/semantics_test.dart

@@ -616,18 +616,18 @@ void main() {
     config.isFocused = true;
     config.isTextField = true;
 
-    final VoidCallback onShowOnScreen = () { };
+    void onShowOnScreen() { }
-    final VoidCallback onScrollDown = () { };
+    void onScrollDown() { }
-    final VoidCallback onScrollUp = () { };
+    void onScrollUp() { }
-    final VoidCallback onScrollLeft = () { };
+    void onScrollLeft() { }
-    final VoidCallback onScrollRight = () { };
+    void onScrollRight() { }
-    final VoidCallback onLongPress = () { };
+    void onLongPress() { }
-    final VoidCallback onDecrease = () { };
+    void onDecrease() { }
-    final VoidCallback onIncrease = () { };
+    void onIncrease() { }
-    final MoveCursorHandler onMoveCursorForwardByCharacter = (bool _) { };
+    void onMoveCursorForwardByCharacter(bool _) { }
-    final MoveCursorHandler onMoveCursorBackwardByCharacter = (bool _) { };
+    void onMoveCursorBackwardByCharacter(bool _) { }
-    final VoidCallback onTap = () { };
+    void onTap() { }
-    final VoidCallback onCustomAction = () { };
+    void onCustomAction() { }
 
     config.onShowOnScreen = onShowOnScreen;
     config.onScrollDown = onScrollDown;

packages/flutter/test/services/channel_buffers_test.dart

@@ -30,9 +30,9 @@ void main() {
     final TestChannelBuffersFlutterBinding binding = TestChannelBuffersFlutterBinding();
     expect(binding.defaultBinaryMessenger, isNotNull);
     bool didCallCallback = false;
-    final ui.PlatformMessageResponseCallback callback = (ByteData? responseData) {
+    void callback(ByteData? responseData) {
       didCallCallback = true;
-    };
+    }
     const String payload = 'bar';
     final ByteData data = _makeByteData(payload);
     ui.channelBuffers.push(channel, data, callback);

packages/flutter/test/services/platform_views_test.dart

@@ -148,7 +148,7 @@ void main() {
     test('OnPlatformViewCreated callback', () async {
       viewsController.registerViewType('webview');
       final List<int> createdViews = <int>[];
-      final PlatformViewCreatedCallback callback = (int id) { createdViews.add(id); };
+      void callback(int id) { createdViews.add(id); }
 
       final AndroidViewController controller1 = PlatformViewsService.initAndroidView(
         id: 0,

packages/flutter/test/widgets/animated_list_test.dart

@@ -8,14 +8,14 @@ import 'package:flutter/widgets.dart';
 
 void main() {
   testWidgets('AnimatedList', (WidgetTester tester) async {
-    final AnimatedListItemBuilder builder = (BuildContext context, int index, Animation<double> animation) {
+    Widget builder(BuildContext context, int index, Animation<double> animation) {
       return SizedBox(
         height: 100.0,
         child: Center(
           child: Text('item $index'),
         ),
       );
-    };
+    }
     final GlobalKey<AnimatedListState> listKey = GlobalKey<AnimatedListState>();
 
     await tester.pumpWidget(

packages/flutter/test/widgets/app_navigator_key_test.dart

@@ -5,7 +5,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 
-final RouteFactory generateRoute = (RouteSettings settings) => PageRouteBuilder<void>(
+Route<void> generateRoute(RouteSettings settings) => PageRouteBuilder<void>(
   settings: settings,
   pageBuilder: (BuildContext context, Animation<double> animation1, Animation<double> animation2) {
     return const Placeholder();

packages/flutter/test/widgets/autocomplete_test.dart

@@ -212,7 +212,7 @@ void main() {
     late Iterable<User> lastOptions;
     late AutocompleteOnSelected<User> lastOnSelected;
     late User lastUserSelected;
-    late final AutocompleteOptionToString<User> displayStringForOption = (User option) => option.name;
+    String displayStringForOption(User option) => option.name;
     late FocusNode focusNode;
     late TextEditingController textEditingController;
 

packages/flutter/test/widgets/fade_in_image_test.dart

@@ -320,13 +320,13 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
+        Future<ui.Codec> decode(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
           expect(cacheWidth, 20);
           expect(cacheHeight, 30);
           expect(allowUpscaling, false);
           called = true;
           return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
-        };
+        }
         final ImageProvider resizeImage = image.placeholder;
         expect(image.placeholder, isA<ResizeImage>());
         expect(called, false);
@@ -343,13 +343,13 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
+        Future<ui.Codec> decode(Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
           expect(cacheWidth, null);
           expect(cacheHeight, null);
           expect(allowUpscaling, false);
           called = true;
           return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
-        };
+        }
         // image.placeholder should be an instance of MemoryImage instead of ResizeImage
         final ImageProvider memoryImage = image.placeholder;
         expect(image.placeholder, isA<MemoryImage>());

packages/flutter/test/widgets/gesture_detector_semantics_test.dart

@@ -117,7 +117,7 @@ void main() {
 
     final Set<String> logs = <String>{};
     final GlobalKey<RawGestureDetectorState> detectorKey = GlobalKey();
-    final VoidCallback performLayout = () {
+    void performLayout() {
       detectorKey.currentState!.replaceGestureRecognizers(<Type, GestureRecognizerFactory>{
         TapGestureRecognizer: GestureRecognizerFactoryWithHandlers<TapGestureRecognizer>(
           () => TapGestureRecognizer(),
@@ -126,7 +126,7 @@ void main() {
           },
         ),
       });
-    };
+    }
 
     bool hasLayoutPerformer = false;
     late VoidCallback introduceLayoutPerformer;

packages/flutter/test/widgets/gesture_detector_test.dart

@@ -252,7 +252,7 @@ void main() {
     }, variant: buttonVariant);
 
     testWidgets('cache render object', (WidgetTester tester) async {
-      final GestureTapCallback inputCallback = () { };
+      void inputCallback() { }
 
       await tester.pumpWidget(
         Center(

packages/flutter/test/widgets/heroes_test.dart

@@ -2244,7 +2244,7 @@ Future<void> main() async {
 
   testWidgets('On an iOS back swipe and snap, only a single flight should take place', (WidgetTester tester) async {
     int shuttlesBuilt = 0;
-    final HeroFlightShuttleBuilder shuttleBuilder = (
+    Widget shuttleBuilder(
       BuildContext flightContext,
       Animation<double> animation,
       HeroFlightDirection flightDirection,
@@ -2253,7 +2253,7 @@ Future<void> main() async {
     ) {
       shuttlesBuilt += 1;
       return const Text("I'm flying in a jetplane");
-    };
+    }
 
     final GlobalKey<NavigatorState> navigatorKey = GlobalKey();
     await tester.pumpWidget(

packages/flutter/test/widgets/image_test.dart

@@ -477,13 +477,13 @@ void main() {
     dynamic capturedException;
     StackTrace? capturedStackTrace;
     ImageInfo? capturedImage;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
       capturedStackTrace = stackTrace;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -519,13 +519,13 @@ void main() {
     dynamic reportedException;
     StackTrace? reportedStackTrace;
     ImageInfo? capturedImage;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
       capturedStackTrace = stackTrace;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
     FlutterError.onError = (FlutterErrorDetails flutterError) {
       reportedException = flutterError.exception;
       reportedStackTrace = flutterError.stack;
@@ -568,13 +568,13 @@ void main() {
     dynamic capturedException;
     StackTrace? capturedStackTrace;
     ImageInfo? capturedImage;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
       capturedStackTrace = stackTrace;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -611,14 +611,14 @@ void main() {
     StackTrace? capturedStackTrace;
     ImageInfo? capturedImage;
     int errorListenerCalled = 0;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
       capturedStackTrace = stackTrace;
       errorListenerCalled++;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -656,14 +656,14 @@ void main() {
     dynamic reportedException;
     StackTrace? reportedStackTrace;
     ImageInfo? capturedImage;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       errorListenerCalled = true;
       reportedException = exception;
       reportedStackTrace = stackTrace;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -698,12 +698,12 @@ void main() {
   testWidgets('Removing listener removes one listener and error listener', (WidgetTester tester) async {
     int errorListenerCalled = 0;
     ImageInfo? capturedImage;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       errorListenerCalled++;
-    };
+    }
-    final ImageListener listener = (ImageInfo info, bool synchronous) {
+    void listener(ImageInfo info, bool synchronous) {
       capturedImage = info;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -805,10 +805,10 @@ void main() {
   testWidgets('Precache completes with onError on error', (WidgetTester tester) async {
     dynamic capturedException;
     StackTrace? capturedStackTrace;
-    final ImageErrorListener errorListener = (dynamic exception, StackTrace? stackTrace) {
+    void errorListener(dynamic exception, StackTrace? stackTrace) {
       capturedException = exception;
       capturedStackTrace = stackTrace;
-    };
+    }
 
     final Exception testException = Exception('cannot resolve host');
     final StackTrace testStack = StackTrace.current;
@@ -1419,8 +1419,8 @@ void main() {
       ),
     ));
 
-    final bool Function(_TestImageProvider) loadCalled = (_TestImageProvider provider) => provider.loadCalled;
+    bool loadCalled(_TestImageProvider provider) => provider.loadCalled;
-    final bool Function(_TestImageProvider) loadNotCalled = (_TestImageProvider provider) => !provider.loadCalled;
+    bool loadNotCalled(_TestImageProvider provider) => !provider.loadCalled;
 
     expect(find.bySemanticsLabel('5'), findsOneWidget);
     expect(imageProviders.length, 12);

packages/flutter/test/widgets/list_view_builder_test.dart

@@ -68,7 +68,7 @@ void main() {
     // so if our widget is 200 pixels tall, it should fit exactly 3 times.
     // but if we are offset by 300 pixels, there will be 4, numbered 1-4.
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return SizedBox(
         key: ValueKey<int>(index),
@@ -76,7 +76,7 @@ void main() {
         height: 400.0, // should be overridden by itemExtent
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     Widget buildWidget() {
       return Directionality(
@@ -141,7 +141,7 @@ void main() {
     // so if our widget is 200 pixels wide, it should fit exactly 4 times.
     // but if we are offset by 300 pixels, there will be 5, numbered 1-5.
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return SizedBox(
         key: ValueKey<int>(index),
@@ -149,7 +149,7 @@ void main() {
         height: 500.0, // this should be ignored
         child: Text('$index'),
       );
-    };
+    }
 
     Widget buildWidget() {
       return Directionality(
@@ -215,10 +215,10 @@ void main() {
     // items are 300 tall. Scrolling should cause two or three items
     // to be built.
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return Text('$index', key: ValueKey<int>(index), textDirection: TextDirection.ltr);
-    };
+    }
 
     final Widget testWidget = Directionality(
       textDirection: TextDirection.ltr,

packages/flutter/test/widgets/list_view_viewporting_test.dart

@@ -68,7 +68,7 @@ void main() {
     // so if our widget is 200 pixels tall, it should fit exactly 3 times.
     // but if we are offset by 300 pixels, there will be 4, numbered 1-4.
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return SizedBox(
         key: ValueKey<int>(index),
@@ -76,7 +76,7 @@ void main() {
         height: 200.0,
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     Widget builder() {
       return Directionality(
@@ -131,7 +131,7 @@ void main() {
     // so if our widget is 200 pixels wide, it should fit exactly 4 times.
     // but if we are offset by 300 pixels, there will be 5, numbered 1-5.
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return SizedBox(
         key: ValueKey<int>(index),
@@ -139,7 +139,7 @@ void main() {
         width: 200.0,
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     Widget builder() {
       return Directionality(
@@ -182,7 +182,7 @@ void main() {
     final List<int> callbackTracker = <int>[];
     final List<String?> text = <String?>[];
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       callbackTracker.add(index);
       return SizedBox(
         key: ValueKey<int>(index),
@@ -190,7 +190,7 @@ void main() {
         height: 220.0,
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     void collectText(Widget widget) {
       if (widget is Text)
@@ -233,7 +233,7 @@ void main() {
     late StateSetter setState;
     ThemeData themeData = ThemeData.light();
 
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       return Container(
         key: ValueKey<int>(index),
         width: 500.0, // this should be ignored
@@ -241,7 +241,7 @@ void main() {
         color: Theme.of(context).primaryColor,
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     final Widget viewport = ListView.builder(
       itemBuilder: itemBuilder,
@@ -273,7 +273,7 @@ void main() {
   });
 
   testWidgets('ListView padding', (WidgetTester tester) async {
-    final IndexedWidgetBuilder itemBuilder = (BuildContext context, int index) {
+    Widget itemBuilder(BuildContext context, int index) {
       return Container(
         key: ValueKey<int>(index),
         width: 500.0, // this should be ignored
@@ -281,7 +281,7 @@ void main() {
         color: Colors.green[500],
         child: Text('$index', textDirection: TextDirection.ltr),
       );
-    };
+    }
 
     await tester.pumpWidget(
       Directionality(

packages/flutter/test/widgets/list_wheel_scroll_view_test.dart

@@ -880,7 +880,7 @@ void main() {
   group('scroll notifications', () {
     testWidgets('no onSelectedItemChanged callback on first build', (WidgetTester tester) async {
       bool itemChangeCalled = false;
-      final ValueChanged<int> onItemChange = (_) { itemChangeCalled = true; };
+      void onItemChange(int _) { itemChangeCalled = true; }
 
       await tester.pumpWidget(
         Directionality(

packages/flutter/test/widgets/mouse_region_test.dart

@@ -1424,8 +1424,8 @@ void main() {
     await gesture.addPointer(location: const Offset(5, 5));
     addTearDown(gesture.removePointer);
 
-    final PointerHoverEventListener onHover = (_) {};
+    void onHover(PointerHoverEvent _) {}
-    final VoidCallback onPaintChild = () { logs.add('paint'); };
+    void onPaintChild() { logs.add('paint'); }
 
     await tester.pumpWidget(_Scaffold(
       topLeft: SizedBox(
@@ -1471,7 +1471,7 @@ void main() {
     await gesture.addPointer(location: const Offset(100, 100));
     addTearDown(gesture.removePointer);
 
-    final VoidCallback onPaintChild = () { logPaints.add('paint'); };
+    void onPaintChild() { logPaints.add('paint'); }
 
     await tester.pumpWidget(_Scaffold(
       topLeft: SizedBox(
@@ -1521,7 +1521,7 @@ void main() {
     await gesture.addPointer(location: const Offset(100, 100));
     addTearDown(gesture.removePointer);
 
-    final VoidCallback onPaintChild = () { logPaints.add('paint'); };
+    void onPaintChild() { logPaints.add('paint'); }
 
     await tester.pumpWidget(_Scaffold(
       topLeft: SizedBox(

packages/flutter/test/widgets/platform_view_test.dart

@@ -870,10 +870,10 @@ void main() {
       viewsController.registerViewType('webview');
 
       int factoryInvocationCount = 0;
-      final ValueGetter<EagerGestureRecognizer> constructRecognizer = () {
+      EagerGestureRecognizer constructRecognizer() {
         factoryInvocationCount += 1;
         return EagerGestureRecognizer();
-      };
+      }
 
       await tester.pumpWidget(
         AndroidView(
@@ -1919,10 +1919,10 @@ void main() {
       viewsController.registerViewType('webview');
 
       int factoryInvocationCount = 0;
-      final ValueGetter<EagerGestureRecognizer> constructRecognizer = () {
+      EagerGestureRecognizer constructRecognizer() {
         factoryInvocationCount += 1;
         return EagerGestureRecognizer();
-      };
+      }
 
       await tester.pumpWidget(
         UiKitView(
@@ -2194,10 +2194,10 @@ void main() {
     testWidgets('PlatformViewRenderBox reconstructed with same gestureRecognizers', (WidgetTester tester) async {
 
       int factoryInvocationCount = 0;
-      final ValueGetter<EagerGestureRecognizer> constructRecognizer = () {
+      EagerGestureRecognizer constructRecognizer() {
         ++ factoryInvocationCount;
         return EagerGestureRecognizer();
-      };
+      }
 
       final PlatformViewSurface platformViewSurface = PlatformViewSurface(
               controller: controller,
@@ -2218,10 +2218,10 @@ void main() {
     testWidgets('PlatformViewSurface rebuilt with same gestureRecognizers', (WidgetTester tester) async {
 
       int factoryInvocationCount = 0;
-      final ValueGetter<EagerGestureRecognizer> constructRecognizer = () {
+      EagerGestureRecognizer constructRecognizer() {
         ++ factoryInvocationCount;
         return EagerGestureRecognizer();
-      };
+      }
 
       await tester.pumpWidget(
         PlatformViewSurface(

packages/flutter_driver/lib/src/common/error.dart

@@ -50,10 +50,12 @@ typedef DriverLogCallback = void Function(String source, String message);
 /// messages from the driver subsystem.
 ///
 /// The default implementation prints `"$source: $message"` to stderr.
-DriverLogCallback driverLog = (String source, String message) {
+DriverLogCallback driverLog = _defaultDriverLogger;
+
+void _defaultDriverLogger(String source, String message) {
   try {
     stderr.writeln('$source: $message');
   } on FileSystemException {
     // May encounter IO error: https://github.com/flutter/flutter/issues/69314
   }
-};
+}

packages/flutter_driver/test/src/real_tests/extension_test.dart

@@ -1035,7 +1035,7 @@ void main() {
 
   group('extension commands', () {
     int invokes = 0;
-    final VoidCallback stubCallback = () => invokes++;
+    void stubCallback() => invokes++;
 
     final Widget debugTree = Directionality(
       textDirection: TextDirection.ltr,

packages/flutter_test/lib/src/frame_timing_summarizer.dart

@@ -35,8 +35,7 @@ class FrameTimingSummarizer {
     );
     final List<Duration> vsyncOverheadSorted =
         List<Duration>.from(vsyncOverhead)..sort();
-    final Duration Function(Duration, Duration) add =
+    Duration add(Duration a, Duration b) => a + b;
-        (Duration a, Duration b) => a + b;
     return FrameTimingSummarizer._(
       frameBuildTime: frameBuildTime,
       frameRasterizerTime: frameRasterizerTime,

packages/flutter_tools/lib/src/isolated/devfs_web.dart

@@ -241,8 +241,7 @@ class WebAssetServer implements AssetReader {
     // load the through the isolate APIs.
     final Directory directory =
         await _loadDwdsDirectory(globals.fs, globals.logger);
-    final shelf.Middleware middleware =
+    shelf.Handler middleware(FutureOr<shelf.Response> Function(shelf.Request) innerHandler) {
-        (FutureOr<shelf.Response> Function(shelf.Request) innerHandler) {
       return (shelf.Request request) async {
         if (request.url.path.endsWith('dwds/src/injected/client.js')) {
           final Uri uri = directory.uri.resolve('src/injected/client.js');
@@ -254,7 +253,7 @@ class WebAssetServer implements AssetReader {
         }
         return innerHandler(request);
       };
-    };
+    }
 
     logging.Logger.root.onRecord.listen((logging.LogRecord event) {
       globals.printTrace('${event.loggerName}: ${event.message}');

packages/flutter_tools/lib/src/localizations/gen_l10n.dart

@@ -420,13 +420,13 @@ String _generateLookupBody(
   bool useDeferredLoading,
   String fileName,
 ) {
-  final String Function(LocaleInfo) generateSwitchClauseTemplate = (LocaleInfo locale) {
+  String generateSwitchClauseTemplate(LocaleInfo locale) {
     return (useDeferredLoading ?
       switchClauseDeferredLoadingTemplate : switchClauseTemplate)
       .replaceAll('@(localeClass)', '$className${locale.camelCase()}')
       .replaceAll('@(appClass)', className)
       .replaceAll('@(library)', '${fileName}_${locale.languageCode}');
-  };
+  }
   return lookupBodyTemplate
     .replaceAll('@(lookupAllCodesSpecified)', _generateLookupByAllCodes(
       allBundles,

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -14,7 +14,6 @@ import '../application_package.dart';
 import '../base/common.dart';
 import '../base/context.dart';
 import '../base/io.dart' as io;
-import '../base/signals.dart';
 import '../base/terminal.dart';
 import '../base/user_messages.dart';
 import '../base/utils.dart';
@@ -1068,7 +1067,7 @@ abstract class FlutterCommand extends Command<void> {
   }
 
   void _registerSignalHandlers(String commandPath, DateTime startTime) {
-    final SignalHandler handler = (io.ProcessSignal s) {
+    void handler(io.ProcessSignal s) {
       globals.cache.releaseLock();
       _sendPostUsage(
         commandPath,
@@ -1076,7 +1075,7 @@ abstract class FlutterCommand extends Command<void> {
         startTime,
         globals.systemClock.now(),
       );
-    };
+    }
     globals.signals.addHandler(io.ProcessSignal.SIGTERM, handler);
     globals.signals.addHandler(io.ProcessSignal.SIGINT, handler);
   }

packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart

@@ -37,7 +37,7 @@ import '../../src/context.dart';
 import '../../src/fakes.dart';
 import '../../src/testbed.dart';
 
-final Generator _kNoColorOutputPlatform = () => FakePlatform(
+FakePlatform _kNoColorOutputPlatform() => FakePlatform(
   localeName: 'en_US.UTF-8',
   environment: <String, String>{},
   stdoutSupportsAnsi: false,

packages/flutter_tools/test/commands.shard/permeable/create_test.dart

@@ -40,7 +40,7 @@ const String frameworkRevision = '12345678';
 const String frameworkChannel = 'omega';
 const String _kDisabledPlatformRequestedMessage = 'currently not supported on your local environment.';
 // TODO(fujino): replace FakePlatform.fromPlatform() with FakePlatform()
-final Generator _kNoColorTerminalPlatform = () => FakePlatform.fromPlatform(const LocalPlatform())..stdoutSupportsAnsi = false;
+FakePlatform _kNoColorTerminalPlatform() => FakePlatform.fromPlatform(const LocalPlatform())..stdoutSupportsAnsi = false;
 final Map<Type, Generator> noColorTerminalOverride = <Type, Generator>{
   Platform: _kNoColorTerminalPlatform,
 };

packages/flutter_tools/test/general.shard/application_package_test.dart

@@ -25,7 +25,7 @@ import '../src/common.dart';
 import '../src/context.dart';
 import '../src/fakes.dart';
 
-final Generator _kNoColorTerminalPlatform = () => FakePlatform(stdoutSupportsAnsi: false);
+FakePlatform _kNoColorTerminalPlatform() => FakePlatform(stdoutSupportsAnsi: false);
 final Map<Type, Generator> noColorTerminalOverride = <Type, Generator>{
   Platform: _kNoColorTerminalPlatform,
 };

packages/flutter_tools/test/general.shard/ios/mac_test.dart

@@ -22,7 +22,7 @@ import '../../src/common.dart';
 import '../../src/context.dart';
 import '../../src/fakes.dart';
 
-final Generator _kNoColorTerminalPlatform = () => FakePlatform(stdoutSupportsAnsi: false);
+FakePlatform _kNoColorTerminalPlatform() => FakePlatform(stdoutSupportsAnsi: false);
 final Map<Type, Generator> noColorTerminalOverride = <Type, Generator>{
   Platform: _kNoColorTerminalPlatform,
 };

packages/flutter_tools/test/general.shard/macos/application_package_test.dart

@@ -198,8 +198,7 @@ void main() {
 
 class MockOperatingSystemUtils extends Mock implements OperatingSystemUtils {}
 
-final Generator _kNoColorTerminalPlatform =
+FakePlatform _kNoColorTerminalPlatform() => FakePlatform(stdoutSupportsAnsi: false);
-    () => FakePlatform(stdoutSupportsAnsi: false);
 final Map<Type, Generator> noColorTerminalOverride = <Type, Generator>{
   Platform: _kNoColorTerminalPlatform,
 };

packages/flutter_tools/test/general.shard/version_test.dart

@@ -797,7 +797,7 @@ void fakeData(
     throw StateError('Unexpected call to Cache.setStampFor(${invocation.positionalArguments}, ${invocation.namedArguments})');
   });
 
-  final Answering<ProcessResult> syncAnswer = (Invocation invocation) {
+  ProcessResult syncAnswer(Invocation invocation) {
     bool argsAre(String a1, [ String a2, String a3, String a4, String a5, String a6, String a7, String a8, String a9 ]) {
       const ListEquality<String> equality = ListEquality<String>();
       final List<String> args = invocation.positionalArguments.single as List<String>;
@@ -828,7 +828,7 @@ void fakeData(
     }
 
     throw StateError('Unexpected call to ProcessManager.run(${invocation.positionalArguments}, ${invocation.namedArguments})');
-  };
+  }
 
   when(pm.runSync(any, workingDirectory: anyNamed('workingDirectory'))).thenAnswer(syncAnswer);
   when(pm.run(any, workingDirectory: anyNamed('workingDirectory'))).thenAnswer((Invocation invocation) async {

packages/flutter_tools/test/src/mocks.dart

@@ -87,11 +87,13 @@ typedef _ProcessFactory = Process Function(List<String> command);
 
 /// A ProcessManager that starts Processes by delegating to a ProcessFactory.
 class MockProcessManager extends Mock implements ProcessManager {
-  _ProcessFactory processFactory = (List<String> commands) => FakeProcess();
+  _ProcessFactory processFactory = _defaulProcessFactory;
   bool canRunSucceeds = true;
   bool runSucceeds = true;
   List<String> commands;
 
+  static Process _defaulProcessFactory(List<String> commands) => FakeProcess();
+
   @override
   bool canRun(dynamic command, { String workingDirectory }) => canRunSucceeds;
 

packages/flutter_web_plugins/test/navigation/url_strategy_test.dart

@@ -143,7 +143,7 @@ class TestPlatformLocation extends PlatformLocation {
   String hash = '';
 
   @override
-  Object? Function() state = () => null;
+  Object? get state => null;
 
   /// Mocks the base href of the document.
   String baseHref = '';

packages/fuchsia_remote_debug_protocol/lib/src/common/logging.dart

@@ -50,12 +50,12 @@ typedef LoggingFunction = void Function(LogMessage log);
 ///   '[${log.levelName}]::${log.tag}--${log.time}: ${log.message}'
 ///
 /// Exits with status code 1 if the `log` is [LoggingLevel.severe].
-LoggingFunction defaultLoggingFunction = (LogMessage log) {
+void defaultLoggingFunction(LogMessage log) {
   print('[${log.levelName}]::${log.tag}--${log.time}: ${log.message}');
   if (log.level == LoggingLevel.severe) {
     exit(1);
   }
-};
+}
 
 /// Represents a logging message created by the logger.
 ///