Update typedef syntax to use Function notation and turn on lint for old notation. (#18362)

Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.

Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.

No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.

analysis_options.yaml

@@ -7,17 +7,17 @@
 # See the configuration guide for more
 # https://github.com/dart-lang/sdk/tree/master/pkg/analyzer#configuring-the-analyzer
 #
-# There are four similar analysis options files in the flutter repos:
+# There are four similar analysis options files in the flutter repo:
 #   - analysis_options.yaml (this file)
 #   - packages/flutter/lib/analysis_options_user.yaml
 #   - https://github.com/flutter/plugins/blob/master/analysis_options.yaml
 #   - https://github.com/flutter/engine/blob/master/analysis_options.yaml
 #
-# This file contains the analysis options used by Flutter tools, such as IntelliJ,
+# This file contains the analysis options used by Flutter tools, such as
-# Android Studio, and the `flutter analyze` command.
+# IntelliJ, Android Studio, and the 'flutter analyze' command.
 #
-# The flutter/plugins repo contains a copy of this file, which should be kept
+# The flutter/plugins and flutter/engine repos contain a copy of this file,
-# in sync with this file.
+# which should be kept in sync with this file.
 
 analyzer:
   language:
@@ -124,6 +124,7 @@ linter:
     - prefer_final_locals
     - prefer_foreach
     # - prefer_function_declarations_over_variables # not yet tested
+    - prefer_generic_function_type_aliases
     - prefer_initializing_formals
     # - prefer_interpolation_to_compose_strings # not yet tested
     # - prefer_iterable_whereType # https://github.com/dart-lang/sdk/issues/32463
@@ -131,6 +132,7 @@ linter:
     - prefer_is_not_empty
     - prefer_single_quotes
     - prefer_typing_uninitialized_variables
+    - public_member_api_docs
     - recursive_getters
     - slash_for_doc_comments
     - sort_constructors_first

analysis_options_repo.yaml

@@ -1,157 +0,0 @@
-# Specify analysis options.
-#
-# Until there are meta linter rules, each desired lint must be explicitly enabled.
-# See: https://github.com/dart-lang/linter/issues/288
-#
-# For a list of lints, see: http://dart-lang.github.io/linter/lints/
-# See the configuration guide for more
-# https://github.com/dart-lang/sdk/tree/master/pkg/analyzer#configuring-the-analyzer
-#
-# There are three similar analysis options files in the flutter repo:
-#   - analysis_options.yaml
-#   - analysis_options_repo.yaml (this file)
-#   - packages/flutter/lib/analysis_options_user.yaml
-#
-# This file contains the analysis options used by 'flutter analyze' when analyzing
-# the flutter repository. It is very similar to analysis_options.yaml;
-# the only difference (currently) is the public_member_api_docs option,
-# which is turned on and programmatically reduced to a single output line
-# indicating the # of violations for that rule.
-
-analyzer:
-  language:
-    enableStrictCallChecks: true
-    enableSuperMixins: true
-  strong-mode:
-    implicit-dynamic: false
-  errors:
-    # treat missing required parameters as a warning (not a hint)
-    missing_required_param: warning
-    # treat missing returns as a warning (not a hint)
-    missing_return: warning
-    # allow having TODOs in the code
-    todo: ignore
-  # `flutter analyze` (without `--watch`) just ignores directories
-  # that contain a .dartignore file, and this file does not have any
-  # effect on what files are actually analyzed.
-
-linter:
-  rules:
-    # these rules are documented on and in the same order as
-    # the Dart Lint rules page to make maintenance easier
-    # https://github.com/dart-lang/linter/blob/master/example/all.yaml
-    - always_declare_return_types
-    - always_put_control_body_on_new_line
-    # - always_put_required_named_parameters_first # we prefer having parameters in the same order as fields https://github.com/flutter/flutter/issues/10219
-    - always_require_non_null_named_parameters
-    - always_specify_types
-    - annotate_overrides
-    # - avoid_annotating_with_dynamic # conflicts with always_specify_types
-    - avoid_as
-    # - avoid_bool_literals_in_conditional_expressions # not yet tested
-    # - avoid_catches_without_on_clauses # we do this commonly
-    # - avoid_catching_errors # we do this commonly
-    - avoid_classes_with_only_static_members
-    # - avoid_double_and_int_checks # only useful when targeting JS runtime
-    - avoid_empty_else
-    # - avoid_field_initializers_in_const_classes # not yet tested
-    - avoid_function_literals_in_foreach_calls
-    - avoid_init_to_null
-    # - avoid_js_rounded_ints # only useful when targeting JS runtime
-    - avoid_null_checks_in_equality_operators
-    # - avoid_positional_boolean_parameters # not yet tested
-    # - avoid_private_typedef_functions # we prefer having typedef (discussion in https://github.com/flutter/flutter/pull/16356)
-    - avoid_relative_lib_imports
-    - avoid_renaming_method_parameters
-    - avoid_return_types_on_setters
-    # - avoid_returning_null # we do this commonly
-    # - avoid_returning_this # https://github.com/dart-lang/linter/issues/842
-    # - avoid_setters_without_getters # not yet tested
-    # - avoid_single_cascade_in_expression_statements # not yet tested
-    - avoid_slow_async_io
-    # - avoid_types_as_parameter_names # https://github.com/dart-lang/linter/pull/954/files
-    # - avoid_types_on_closure_parameters # conflicts with always_specify_types
-    # - avoid_unused_constructor_parameters # https://github.com/dart-lang/linter/pull/847
-    - await_only_futures
-    - camel_case_types
-    - cancel_subscriptions
-    # - cascade_invocations # not yet tested
-    # - close_sinks # https://github.com/flutter/flutter/issues/5789
-    # - comment_references # blocked on https://github.com/dart-lang/dartdoc/issues/1153
-    # - constant_identifier_names # https://github.com/dart-lang/linter/issues/204
-    - control_flow_in_finally
-    - directives_ordering
-    - empty_catches
-    - empty_constructor_bodies
-    - empty_statements
-    - hash_and_equals
-    - implementation_imports
-    # - invariant_booleans # https://github.com/flutter/flutter/issues/5790
-    - iterable_contains_unrelated_type
-    # - join_return_with_assignment # not yet tested
-    - library_names
-    - library_prefixes
-    - list_remove_unrelated_type
-    # - literal_only_boolean_expressions # https://github.com/flutter/flutter/issues/5791
-    - no_adjacent_strings_in_list
-    - no_duplicate_case_values
-    - non_constant_identifier_names
-    # - omit_local_variable_types # opposite of always_specify_types
-    # - one_member_abstracts # too many false positives
-    # - only_throw_errors # https://github.com/flutter/flutter/issues/5792
-    - overridden_fields
-    - package_api_docs
-    - package_names
-    - package_prefixed_library_names
-    # - parameter_assignments # we do this commonly
-    - prefer_adjacent_string_concatenation
-    - prefer_asserts_in_initializer_lists
-    - prefer_bool_in_asserts
-    - prefer_collection_literals
-    - prefer_conditional_assignment
-    - prefer_const_constructors
-    - prefer_const_constructors_in_immutables
-    - prefer_const_declarations
-    - prefer_const_literals_to_create_immutables
-    # - prefer_constructors_over_static_methods # not yet tested
-    - prefer_contains
-    - prefer_equal_for_default_values
-    # - prefer_expression_function_bodies # conflicts with https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#consider-using--for-short-functions-and-methods
-    - prefer_final_fields
-    - prefer_final_locals
-    - prefer_foreach
-    # - prefer_function_declarations_over_variables # not yet tested
-    - prefer_initializing_formals
-    # - prefer_interpolation_to_compose_strings # not yet tested
-    # - prefer_iterable_whereType # https://github.com/dart-lang/sdk/issues/32463
-    - prefer_is_empty
-    - prefer_is_not_empty
-    - prefer_single_quotes
-    - prefer_typing_uninitialized_variables
-    - public_member_api_docs # this is the only difference from analysis_options.yaml
-    - recursive_getters
-    - slash_for_doc_comments
-    - sort_constructors_first
-    - sort_unnamed_constructors_first
-    - super_goes_last
-    - test_types_in_equals
-    - throw_in_finally
-    # - type_annotate_public_apis # subset of always_specify_types
-    - type_init_formals
-    # - unawaited_futures # https://github.com/flutter/flutter/issues/5793
-    - unnecessary_brace_in_string_interps
-    - unnecessary_getters_setters
-    # - unnecessary_lambdas # https://github.com/dart-lang/linter/issues/498
-    - unnecessary_null_aware_assignments
-    - unnecessary_null_in_if_null_operators
-    - unnecessary_overrides
-    - unnecessary_parenthesis
-    # - unnecessary_statements # not yet tested
-    - unnecessary_this
-    - unrelated_type_equality_checks
-    - use_rethrow_when_possible
-    # - use_setters_to_change_properties # not yet tested
-    # - use_string_buffers # https://github.com/dart-lang/linter/pull/664
-    # - use_to_and_as_if_applicable # has false positives, so we prefer to catch this by code-review
-    - valid_regexps
-    # - void_checks # not yet tested

dev/bots/prepare_package.dart

@@ -175,7 +175,7 @@ class ProcessRunner {
   }
 }
 
-typedef Future<Uint8List> HttpReader(Uri url, {Map<String, String> headers});
+typedef HttpReader = Future<Uint8List> Function(Uri url, {Map<String, String> headers});
 
 /// Creates a pre-populated Flutter archive from a git repo.
 class ArchiveCreator {

dev/bots/test.dart

@@ -8,7 +8,7 @@ import 'dart:io';
 
 import 'package:path/path.dart' as path;
 
-typedef Future<Null> ShardRunner();
+typedef ShardRunner = Future<Null> Function();
 
 final String flutterRoot = path.dirname(path.dirname(path.dirname(path.fromUri(Platform.script))));
 final String flutter = path.join(flutterRoot, 'bin', Platform.isWindows ? 'flutter.bat' : 'flutter');

dev/bots/test/fake_process_manager.dart

@@ -150,7 +150,7 @@ class FakeProcess extends Mock implements Process {
 }
 
 /// Callback used to receive stdin input when it occurs.
-typedef void StringReceivedCallback(String received);
+typedef StringReceivedCallback = void Function(String received);
 
 /// A stream consumer class that consumes UTF8 strings as lists of ints.
 class StringStreamConsumer implements StreamConsumer<List<int>> {

dev/devicelab/lib/framework/framework.dart

@@ -20,7 +20,7 @@ const Duration _kDefaultTaskTimeout = const Duration(minutes: 15);
 
 /// Represents a unit of work performed in the CI environment that can
 /// succeed, fail and be retried independently of others.
-typedef Future<TaskResult> TaskFunction();
+typedef TaskFunction = Future<TaskResult> Function();
 
 bool _isTaskRegistered = false;
 

dev/devicelab/lib/tasks/analysis.dart

@@ -15,7 +15,7 @@ const int _kRunsPerBenchmark = 3;
 
 /// Runs a benchmark once and reports the result as a lower-is-better numeric
 /// value.
-typedef Future<double> _Benchmark();
+typedef _Benchmark = Future<double> Function();
 
 /// Path to the generated "mega gallery" app.
 Directory get _megaGalleryDirectory => dir(path.join(Directory.systemTemp.path, 'mega_gallery'));

dev/devicelab/test/adb_test.dart

@@ -112,7 +112,7 @@ CommandArgs cmd({
   );
 }
 
-typedef dynamic ExitErrorFactory();
+typedef ExitErrorFactory = dynamic Function();
 
 class CommandArgs {
   CommandArgs({ this.command, this.arguments, this.environment });

dev/integration_tests/channels/lib/src/test_step.dart

@@ -11,7 +11,7 @@ import 'pair.dart';
 
 enum TestStatus { ok, pending, failed, complete }
 
-typedef Future<TestStepResult> TestStep();
+typedef TestStep = Future<TestStepResult> Function();
 
 const String nothing = '-';
 

dev/integration_tests/platform_interaction/lib/src/test_step.dart

@@ -8,7 +8,7 @@ import 'package:flutter/material.dart';
 
 enum TestStatus { ok, pending, failed, complete }
 
-typedef Future<TestStepResult> TestStep();
+typedef TestStep = Future<TestStepResult> Function();
 
 const String nothing = '-';
 

dev/manual_tests/lib/material_arc.dart

@@ -396,7 +396,7 @@ class _RectangleDemoState extends State<_RectangleDemo> {
   }
 }
 
-typedef Widget _DemoBuilder(_ArcDemo demo);
+typedef _DemoBuilder = Widget Function(_ArcDemo demo);
 
 class _ArcDemo {
   _ArcDemo(this.title, this.builder, TickerProvider vsync)

dev/manual_tests/lib/overlay_geometry.dart

@@ -92,7 +92,7 @@ class OverlayGeometryApp extends StatefulWidget {
   OverlayGeometryAppState createState() => new OverlayGeometryAppState();
 }
 
-typedef void CardTapCallback(GlobalKey targetKey, Offset globalPosition);
+typedef CardTapCallback = void Function(GlobalKey targetKey, Offset globalPosition);
 
 class CardBuilder extends SliverChildDelegate {
   CardBuilder({ this.cardModels, this.onTapUp });

examples/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -10,8 +10,8 @@ enum _Location {
   Bermuda
 }
 
-typedef Widget DemoItemBodyBuilder<T>(DemoItem<T> item);
+typedef DemoItemBodyBuilder<T> = Widget Function(DemoItem<T> item);
-typedef String ValueToString<T>(T value);
+typedef ValueToString<T> = String Function(T value);
 
 class DualHeaderWithHint extends StatelessWidget {
   const DualHeaderWithHint({

examples/flutter_gallery/lib/demo/material/grid_list_demo.dart

@@ -10,7 +10,7 @@ enum GridDemoTileStyle {
   twoLine
 }
 
-typedef void BannerTapCallback(Photo photo);
+typedef BannerTapCallback = void Function(Photo photo);
 
 const double _kMinFlingVelocity = 800.0;
 const String _kGalleryAssetsPackage = 'flutter_gallery_assets';

examples/flutter_gallery/lib/gallery/updater.dart

@@ -8,7 +8,7 @@ import 'package:flutter/material.dart';
 
 import 'package:url_launcher/url_launcher.dart';
 
-typedef Future<String> UpdateUrlFetcher();
+typedef UpdateUrlFetcher = Future<String> Function();
 
 class Updater extends StatefulWidget {
   const Updater({ @required this.updateUrlFetcher, this.child, Key key })

examples/layers/services/isolate.dart

@@ -9,8 +9,8 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
-typedef void OnProgressListener(double completed, double total);
+typedef OnProgressListener = void Function(double completed, double total);
-typedef void OnResultListener(String result);
+typedef OnResultListener = void Function(String result);
 
 // An encapsulation of a large amount of synchronous processing.
 //

examples/layers/widgets/styled_text.dart

@@ -4,7 +4,7 @@
 
 import 'package:flutter/material.dart';
 
-typedef Widget _TextTransformer(String name, String text);
+typedef _TextTransformer = Widget Function(String name, String text);
 
 // From https://en.wikiquote.org/wiki/2001:_A_Space_Odyssey_(film)
 const String _kDialogText = '''

examples/stocks/lib/i18n/stock_messages_all.dart

@@ -12,7 +12,7 @@ import 'package:intl/src/intl_helpers.dart';
 import 'stock_messages_en.dart' as messages_en;
 import 'stock_messages_es.dart' as messages_es;
 
-typedef Future<dynamic> LibraryLoader();
+typedef LibraryLoader = Future<dynamic> Function();
 Map<String, LibraryLoader> _deferredLibraries = {
   'en': () => new Future.value(null),
   'es': () => new Future.value(null),

examples/stocks/lib/i18n/stock_messages_en.dart

@@ -12,7 +12,7 @@ final messages = new MessageLookup();
 final _keepAnalysisHappy = Intl.defaultLocale;
 
 // ignore: non_constant_identifier_names
-typedef MessageIfAbsent(String message_str, List args);
+typedef MessageIfAbsent = dynamic Function(String message_str, List args);
 
 class MessageLookup extends MessageLookupByLibrary {
   get localeName => 'en';

examples/stocks/lib/stock_home.dart

@@ -11,7 +11,7 @@ import 'stock_strings.dart';
 import 'stock_symbol_viewer.dart';
 import 'stock_types.dart';
 
-typedef void ModeUpdater(StockMode mode);
+typedef ModeUpdater = void Function(StockMode mode);
 
 enum _StockMenuItem { autorefresh, refresh, speedUp, speedDown }
 enum StockHomeTab { market, portfolio }

examples/stocks/lib/stock_row.dart

@@ -7,7 +7,7 @@ import 'package:flutter/material.dart';
 import 'stock_arrow.dart';
 import 'stock_data.dart';
 
-typedef void StockRowActionCallback(Stock stock);
+typedef StockRowActionCallback = void Function(Stock stock);
 
 class StockRow extends StatelessWidget {
   StockRow({

packages/flutter/lib/src/animation/animation.dart

@@ -22,7 +22,7 @@ enum AnimationStatus {
 }
 
 /// Signature for listeners attached using [Animation.addStatusListener].
-typedef void AnimationStatusListener(AnimationStatus status);
+typedef AnimationStatusListener = void Function(AnimationStatus status);
 
 /// An animation with a value of type `T`.
 ///

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

@@ -204,7 +204,7 @@ enum RefreshIndicatorMode {
 ///
 /// The `pulledExtent` parameter is the currently available space either from
 /// overscrolling or as held by the sliver during refresh.
-typedef Widget RefreshControlIndicatorBuilder(
+typedef RefreshControlIndicatorBuilder = Widget Function(
   BuildContext context,
   RefreshIndicatorMode refreshState,
   double pulledExtent,
@@ -216,7 +216,7 @@ typedef Widget RefreshControlIndicatorBuilder(
 /// pulled a `refreshTriggerPullDistance`. Must return a [Future]. Upon
 /// completion of the [Future], the [CupertinoRefreshControl] enters the
 /// [RefreshIndicatorMode.done] state and will start to go away.
-typedef Future<void> RefreshCallback();
+typedef RefreshCallback = Future<void> Function();
 
 /// A sliver widget implementing the iOS-style pull to refresh content control.
 ///

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

@@ -6,11 +6,11 @@ import 'basic_types.dart';
 import 'print.dart';
 
 /// Signature for [FlutterError.onError] handler.
-typedef void FlutterExceptionHandler(FlutterErrorDetails details);
+typedef FlutterExceptionHandler = void Function(FlutterErrorDetails details);
 
 /// Signature for [FlutterErrorDetails.informationCollector] callback
 /// and other callbacks that collect information into a string buffer.
-typedef void InformationCollector(StringBuffer information);
+typedef InformationCollector = void Function(StringBuffer information);
 
 /// Class for information provided to [FlutterExceptionHandler] callbacks.
 ///

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

@@ -12,7 +12,7 @@ export 'dart:ui' show VoidCallback;
 /// Signature for callbacks that report that an underlying value has changed.
 ///
 /// See also [ValueSetter].
-typedef void ValueChanged<T>(T value);
+typedef ValueChanged<T> = void Function(T value);
 
 /// Signature for callbacks that report that a value has been set.
 ///
@@ -26,7 +26,7 @@ typedef void ValueChanged<T>(T value);
 ///
 ///  * [ValueGetter], the getter equivalent of this signature.
 ///  * [AsyncValueSetter], an asynchronous version of this signature.
-typedef void ValueSetter<T>(T value);
+typedef ValueSetter<T> = void Function(T value);
 
 /// Signature for callbacks that are to report a value on demand.
 ///
@@ -34,10 +34,10 @@ typedef void ValueSetter<T>(T value);
 ///
 ///  * [ValueSetter], the setter equivalent of this signature.
 ///  * [AsyncValueGetter], an asynchronous version of this signature.
-typedef T ValueGetter<T>();
+typedef ValueGetter<T> = T Function();
 
 /// Signature for callbacks that filter an iterable.
-typedef Iterable<T> IterableFilter<T>(Iterable<T> input);
+typedef IterableFilter<T> = Iterable<T> Function(Iterable<T> input);
 
 /// Signature of callbacks that have no arguments and return no data, but that
 /// return a [Future] to indicate when their work is complete.
@@ -47,7 +47,7 @@ typedef Iterable<T> IterableFilter<T>(Iterable<T> input);
 ///  * [VoidCallback], a synchronous version of this signature.
 ///  * [AsyncValueGetter], a signature for asynchronous getters.
 ///  * [AsyncValueSetter], a signature for asynchronous setters.
-typedef Future<Null> AsyncCallback();
+typedef AsyncCallback = Future<Null> Function();
 
 /// Signature for callbacks that report that a value has been set and return a
 /// [Future] that completes when the value has been saved.
@@ -56,7 +56,7 @@ typedef Future<Null> AsyncCallback();
 ///
 ///  * [ValueSetter], a synchronous version of this signature.
 ///  * [AsyncValueGetter], the getter equivalent of this signature.
-typedef Future<Null> AsyncValueSetter<T>(T value);
+typedef AsyncValueSetter<T> = Future<Null> Function(T value);
 
 /// Signature for callbacks that are to asynchronously report a value on demand.
 ///
@@ -64,7 +64,7 @@ typedef Future<Null> AsyncValueSetter<T>(T value);
 ///
 ///  * [ValueGetter], a synchronous version of this signature.
 ///  * [AsyncValueSetter], the setter equivalent of this signature.
-typedef Future<T> AsyncValueGetter<T>();
+typedef AsyncValueGetter<T> = Future<T> Function();
 
 
 // BITFIELD

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

@@ -22,7 +22,7 @@ import 'print.dart';
 /// "type" key will be set to the string `_extensionType` to indicate
 /// that this is a return value from a service extension, and the
 /// "method" key will be set to the full name of the method.
-typedef Future<Map<String, dynamic>> ServiceExtensionCallback(Map<String, String> parameters);
+typedef ServiceExtensionCallback = Future<Map<String, dynamic>> Function(Map<String, String> parameters);
 
 /// Base class for mixins that provide singleton services (also known as
 /// "bindings").

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

@@ -1661,7 +1661,7 @@ class ObjectFlagProperty<T> extends DiagnosticsProperty<T> {
 /// May throw exception if accessing the property would throw an exception
 /// and callers must handle that case gracefully. For example, accessing a
 /// property may trigger an assert that layout constraints were violated.
-typedef T ComputePropertyValueCallback<T>();
+typedef ComputePropertyValueCallback<T> = T Function();
 
 /// Property with a [value] of type [T].
 ///

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

@@ -18,7 +18,7 @@ import 'profile.dart';
 /// of classes, not closures or instance methods of objects.
 ///
 /// {@macro flutter.foundation.compute.limitations}
-typedef R ComputeCallback<Q, R>(Q message);
+typedef ComputeCallback<Q, R> = R Function(Q message);
 
 /// Spawn an isolate, run `callback` on that isolate, passing it `message`, and
 /// (eventually) return the value returned by `callback`.

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

@@ -5,7 +5,7 @@
 import 'dart:async';
 
 /// Signature for callbacks passed to [LicenseRegistry.addLicense].
-typedef Stream<LicenseEntry> LicenseEntryCollector();
+typedef LicenseEntryCollector = Stream<LicenseEntry> Function();
 
 /// A string that represents one paragraph in a [LicenseEntry].
 ///

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

@@ -6,7 +6,7 @@ import 'dart:async';
 import 'dart:collection';
 
 /// Signature for [debugPrint] implementations.
-typedef void DebugPrintCallback(String message, { int wrapWidth });
+typedef DebugPrintCallback = void Function(String message, { int wrapWidth });
 
 /// Prints a message to the console, which you can access using the "flutter"
 /// tool's "logs" command ("flutter logs").

packages/flutter/lib/src/gestures/drag_details.dart

@@ -38,7 +38,7 @@ class DragDownDetails {
 /// The `details` object provides the position of the touch.
 ///
 /// See [DragGestureRecognizer.onDown].
-typedef void GestureDragDownCallback(DragDownDetails details);
+typedef GestureDragDownCallback = void Function(DragDownDetails details);
 
 /// Details object for callbacks that use [GestureDragStartCallback].
 ///
@@ -80,7 +80,7 @@ class DragStartDetails {
 /// touched the surface.
 ///
 /// See [DragGestureRecognizer.onStart].
-typedef void GestureDragStartCallback(DragStartDetails details);
+typedef GestureDragStartCallback = void Function(DragStartDetails details);
 
 /// Details object for callbacks that use [GestureDragUpdateCallback].
 ///
@@ -150,7 +150,7 @@ class DragUpdateDetails {
 /// has travelled since the last update.
 ///
 /// See [DragGestureRecognizer.onUpdate].
-typedef void GestureDragUpdateCallback(DragUpdateDetails details);
+typedef GestureDragUpdateCallback = void Function(DragUpdateDetails details);
 
 /// Details object for callbacks that use [GestureDragEndCallback].
 ///

packages/flutter/lib/src/gestures/long_press.dart

@@ -9,7 +9,7 @@ import 'recognizer.dart';
 
 /// Signature for when a pointer has remained in contact with the screen at the
 /// same location for a long period of time.
-typedef void GestureLongPressCallback();
+typedef GestureLongPressCallback = void Function();
 
 /// Recognizes when the user has pressed down at the same location for a long
 /// period of time.

packages/flutter/lib/src/gestures/monodrag.dart

@@ -22,13 +22,13 @@ enum _DragState {
 /// the screen is available in the `details`.
 ///
 /// See [DragGestureRecognizer.onEnd].
-typedef void GestureDragEndCallback(DragEndDetails details);
+typedef GestureDragEndCallback = void Function(DragEndDetails details);
 
 /// Signature for when the pointer that previously triggered a
 /// [GestureDragDownCallback] did not complete.
 ///
 /// See [DragGestureRecognizer.onCancel].
-typedef void GestureDragCancelCallback();
+typedef GestureDragCancelCallback = void Function();
 
 /// Recognizes movement.
 ///

packages/flutter/lib/src/gestures/multidrag.dart

@@ -17,7 +17,7 @@ import 'recognizer.dart';
 import 'velocity_tracker.dart';
 
 /// Signature for when [MultiDragGestureRecognizer] recognizes the start of a drag gesture.
-typedef Drag GestureMultiDragStartCallback(Offset position);
+typedef GestureMultiDragStartCallback = Drag Function(Offset position);
 
 /// Per-pointer state for a [MultiDragGestureRecognizer].
 ///

packages/flutter/lib/src/gestures/multitap.dart

@@ -15,22 +15,22 @@ import 'tap.dart';
 
 /// Signature for callback when the user has tapped the screen at the same
 /// location twice in quick succession.
-typedef void GestureDoubleTapCallback();
+typedef GestureDoubleTapCallback = void Function();
 
 /// Signature used by [MultiTapGestureRecognizer] for when a pointer that might
 /// cause a tap has contacted the screen at a particular location.
-typedef void GestureMultiTapDownCallback(int pointer, TapDownDetails details);
+typedef GestureMultiTapDownCallback = void Function(int pointer, TapDownDetails details);
 
 /// Signature used by [MultiTapGestureRecognizer] for when a pointer that will
 /// trigger a tap has stopped contacting the screen at a particular location.
-typedef void GestureMultiTapUpCallback(int pointer, TapUpDetails details);
+typedef GestureMultiTapUpCallback = void Function(int pointer, TapUpDetails details);
 
 /// Signature used by [MultiTapGestureRecognizer] for when a tap has occurred.
-typedef void GestureMultiTapCallback(int pointer);
+typedef GestureMultiTapCallback = void Function(int pointer);
 
 /// Signature for when the pointer that previously triggered a
 /// [GestureMultiTapDownCallback] will not end up causing a tap.
-typedef void GestureMultiTapCancelCallback(int pointer);
+typedef GestureMultiTapCancelCallback = void Function(int pointer);
 
 /// TapTracker helps track individual tap sequences as part of a
 /// larger gesture.

packages/flutter/lib/src/gestures/pointer_router.dart

@@ -9,7 +9,7 @@ import 'package:flutter/foundation.dart';
 import 'events.dart';
 
 /// A callback that receives a [PointerEvent]
-typedef void PointerRoute(PointerEvent event);
+typedef PointerRoute = void Function(PointerEvent event);
 
 /// A routing table for [PointerEvent] events.
 class PointerRouter {

packages/flutter/lib/src/gestures/recognizer.dart

@@ -22,7 +22,7 @@ export 'pointer_router.dart' show PointerRouter;
 /// [GestureRecognizer.invokeCallback]. This allows the
 /// [GestureRecognizer.invokeCallback] mechanism to be generically used with
 /// anonymous functions that return objects of particular types.
-typedef T RecognizerCallback<T>();
+typedef RecognizerCallback<T> = T Function();
 
 /// The base class that all gesture recognizers inherit from.
 ///

packages/flutter/lib/src/gestures/scale.dart

@@ -84,14 +84,14 @@ class ScaleEndDetails {
 
 /// Signature for when the pointers in contact with the screen have established
 /// a focal point and initial scale of 1.0.
-typedef void GestureScaleStartCallback(ScaleStartDetails details);
+typedef GestureScaleStartCallback = void Function(ScaleStartDetails details);
 
 /// Signature for when the pointers in contact with the screen have indicated a
 /// new focal point and/or scale.
-typedef void GestureScaleUpdateCallback(ScaleUpdateDetails details);
+typedef GestureScaleUpdateCallback = void Function(ScaleUpdateDetails details);
 
 /// Signature for when the pointers are no longer in contact with the screen.
-typedef void GestureScaleEndCallback(ScaleEndDetails details);
+typedef GestureScaleEndCallback = void Function(ScaleEndDetails details);
 
 bool _isFlingGesture(Velocity velocity) {
   assert(velocity != null);

packages/flutter/lib/src/gestures/tap.dart

@@ -26,7 +26,7 @@ class TapDownDetails {
 ///
 /// The position at which the pointer contacted the screen is available in the
 /// `details`.
-typedef void GestureTapDownCallback(TapDownDetails details);
+typedef GestureTapDownCallback = void Function(TapDownDetails details);
 
 /// Details for [GestureTapUpCallback], such as position.
 class TapUpDetails {
@@ -45,14 +45,14 @@ class TapUpDetails {
 ///
 /// The position at which the pointer stopped contacting the screen is available
 /// in the `details`.
-typedef void GestureTapUpCallback(TapUpDetails details);
+typedef GestureTapUpCallback = void Function(TapUpDetails details);
 
 /// Signature for when a tap has occurred.
-typedef void GestureTapCallback();
+typedef GestureTapCallback = void Function();
 
 /// Signature for when the pointer that previously triggered a
 /// [GestureTapDownCallback] will not end up causing a tap.
-typedef void GestureTapCancelCallback();
+typedef GestureTapCancelCallback = void Function();
 
 /// Recognizes taps.
 ///

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

@@ -125,7 +125,7 @@ class AnimatedIcon extends StatelessWidget {
   }
 }
 
-typedef ui.Path _UiPathFactory();
+typedef _UiPathFactory = ui.Path Function();
 
 class _AnimatedIconPainter extends CustomPainter {
   _AnimatedIconPainter({
@@ -296,4 +296,4 @@ T _interpolate<T>(List<T> values, double progress, _Interpolator<T> interpolator
   return interpolator(values[lowIdx], values[highIdx], t);
 }
 
-typedef T _Interpolator<T>(T a, T b, double progress);
+typedef _Interpolator<T> = T Function(T a, T b, double progress);

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

@@ -193,7 +193,7 @@ const List<_Diagonal> _allDiagonals = const <_Diagonal>[
   const _Diagonal(_CornerId.bottomLeft, _CornerId.topRight),
 ];
 
-typedef dynamic _KeyFunc<T>(T input);
+typedef _KeyFunc<T> = dynamic Function(T input);
 
 // Select the element for which the key function returns the maximum value.
 T _maxBy<T>(Iterable<T> input, _KeyFunc<T> keyFunc) {

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

@@ -21,7 +21,7 @@ import 'theme_data.dart';
 import 'tooltip.dart';
 
 /// Signature for [DataColumn.onSort] callback.
-typedef void DataColumnSortCallback(int columnIndex, bool ascending);
+typedef DataColumnSortCallback = void Function(int columnIndex, bool ascending);
 
 /// Column configuration for a [DataTable].
 ///

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

@@ -1008,7 +1008,7 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
 /// Signature for predicating dates for enabled date selections.
 ///
 /// See [showDatePicker].
-typedef bool SelectableDayPredicate(DateTime day);
+typedef SelectableDayPredicate = bool Function(DateTime day);
 
 /// Shows a dialog containing a material design date picker.
 ///

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

@@ -43,11 +43,11 @@ class _SaltedKey<S, V> extends LocalKey {
 ///
 /// The position of the panel within an [ExpansionPanelList] is given by
 /// [panelIndex].
-typedef void ExpansionPanelCallback(int panelIndex, bool isExpanded);
+typedef ExpansionPanelCallback = void Function(int panelIndex, bool isExpanded);
 
 /// Signature for the callback that's called when the header of the
 /// [ExpansionPanel] needs to rebuild.
-typedef Widget ExpansionPanelHeaderBuilder(BuildContext context, bool isExpanded);
+typedef ExpansionPanelHeaderBuilder = Widget Function(BuildContext context, bool isExpanded);
 
 /// A material expansion panel. It has a header and a body and can be either
 /// expanded or collapsed. The body of the panel is only visible when it is

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

@@ -12,7 +12,7 @@ import 'theme.dart';
 /// Signature for the callback used by ink effects to obtain the rectangle for the effect.
 ///
 /// Used by [InkHighlight] and [InkSplash], for example.
-typedef Rect RectCallback();
+typedef RectCallback = Rect Function();
 
 /// The various kinds of material in material design. Used to
 /// configure the default behavior of [Material] widgets.

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

@@ -739,19 +739,19 @@ Future<T> showMenu<T>({
 /// dismissed.
 ///
 /// Used by [PopupMenuButton.onSelected].
-typedef void PopupMenuItemSelected<T>(T value);
+typedef PopupMenuItemSelected<T> = void Function(T value);
 
 /// Signature for the callback invoked when a [PopupMenuButton] is dismissed
 /// without selecting an item.
 ///
 /// Used by [PopupMenuButton.onCanceled].
-typedef void PopupMenuCanceled();
+typedef PopupMenuCanceled = void Function();
 
 /// Signature used by [PopupMenuButton] to lazily construct the items shown when
 /// the button is pressed.
 ///
 /// Used by [PopupMenuButton.itemBuilder].
-typedef List<PopupMenuEntry<T>> PopupMenuItemBuilder<T>(BuildContext context);
+typedef PopupMenuItemBuilder<T> = List<PopupMenuEntry<T>> Function(BuildContext context);
 
 /// Displays a menu when pressed and calls [onSelected] when the menu is dismissed
 /// because an item was selected. The value passed to [onSelected] is the value of

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

@@ -32,7 +32,7 @@ const Duration _kIndicatorScaleDuration = const Duration(milliseconds: 200);
 /// finished.
 ///
 /// Used by [RefreshIndicator.onRefresh].
-typedef Future<Null> RefreshCallback();
+typedef RefreshCallback = Future<Null> Function();
 
 // The state machine moves through these modes only when the scrollable
 // identified by scrollableKey has been scrolled to its min or max limit.

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

@@ -43,7 +43,7 @@ const FloatingActionButtonAnimator _kDefaultFloatingActionButtonAnimator = Float
 /// not end with a [Path.close]. The returned [Path] is built under the
 /// assumption it will be added to an existing path that is at the `start`
 /// coordinates using [Path.addPath].
-typedef Path ComputeNotch(Rect host, Rect guest, Offset start, Offset end);
+typedef ComputeNotch = Path Function(Rect host, Rect guest, Offset start, Offset end);
 
 enum _ScaffoldSlot {
   body,

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

@@ -26,7 +26,7 @@ import 'theme.dart';
 /// See also:
 ///
 ///   * [Slider.semanticFormatterCallback], which shows an example use case.
-typedef String SemanticFormatterCallback(double value);
+typedef SemanticFormatterCallback = String Function(double value);
 
 /// A Material Design slider.
 ///

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

@@ -174,7 +174,7 @@ class _TabStyle extends AnimatedWidget {
   }
 }
 
-typedef void _LayoutCallback(List<double> xOffsets, TextDirection textDirection, double width);
+typedef _LayoutCallback = void Function(List<double> xOffsets, TextDirection textDirection, double width);
 
 class _TabLabelBarRenderer extends RenderFlex {
   _TabLabelBarRenderer({

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

@@ -66,7 +66,7 @@ class ImageInfo {
 /// frame is requested if the call was asynchronous (after the current frame)
 /// and no rendering frame is requested if the call was synchronous (within the
 /// same stack frame as the call to [ImageStream.addListener]).
-typedef void ImageListener(ImageInfo image, bool synchronousCall);
+typedef ImageListener = void Function(ImageInfo image, bool synchronousCall);
 
 /// A handle to an image resource.
 ///

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

@@ -22,7 +22,7 @@ import 'proxy_box.dart';
 /// The returned list must not be mutated after this function completes. To
 /// change the semantic information, the function must return a new list
 /// instead.
-typedef List<CustomPainterSemantics> SemanticsBuilderCallback(Size size);
+typedef SemanticsBuilderCallback = List<CustomPainterSemantics> Function(Size size);
 
 /// The interface used by [CustomPaint] (in the widgets library) and
 /// [RenderCustomPaint] (in the rendering library).

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

@@ -22,7 +22,7 @@ const double _kCaretWidth = 1.0; // pixels
 /// (including the cursor location).
 ///
 /// Used by [RenderEditable.onSelectionChanged].
-typedef void SelectionChangedHandler(TextSelection selection, RenderEditable renderObject, SelectionChangedCause cause);
+typedef SelectionChangedHandler = void Function(TextSelection selection, RenderEditable renderObject, SelectionChangedCause cause);
 
 /// Indicates what triggered the change in selected text (including changes to
 /// the cursor location).
@@ -46,7 +46,7 @@ enum SelectionChangedCause {
 /// Signature for the callback that reports when the caret location changes.
 ///
 /// Used by [RenderEditable.onCaretChanged].
-typedef void CaretChangedHandler(Rect caretRect);
+typedef CaretChangedHandler = void Function(Rect caretRect);
 
 /// Represents the coordinates of the point in a selection, and the text
 /// direction at that point, relative to top left of the [RenderEditable] that

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

@@ -212,7 +212,7 @@ bool _startIsTopLeft(Axis direction, TextDirection textDirection, VerticalDirect
   return null;
 }
 
-typedef double _ChildSizingFunction(RenderBox child, double extent);
+typedef _ChildSizingFunction = double Function(RenderBox child, double extent);
 
 /// Displays its children in a one-dimensional array.
 ///

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

@@ -10,7 +10,7 @@ import 'object.dart';
 /// Parent data for use with [RenderListBody].
 class ListBodyParentData extends ContainerBoxParentData<RenderBox> { }
 
-typedef double _ChildSizingFunction(RenderBox child);
+typedef _ChildSizingFunction = double Function(RenderBox child);
 
 /// Displays its children sequentially along a given axis, forcing them to the
 /// dimensions of the parent in the other axis.

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

@@ -13,7 +13,7 @@ import 'object.dart';
 import 'viewport.dart';
 import 'viewport_offset.dart';
 
-typedef double _ChildSizingFunction(RenderBox child);
+typedef _ChildSizingFunction = double Function(RenderBox child);
 
 /// [ParentData] for use with [RenderListWheelViewport].
 class ListWheelParentData extends ContainerBoxParentData<RenderBox> { }

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

@@ -42,7 +42,7 @@ class ParentData {
 /// of the [PaintingContext.canvas] to the coordinate system of the callee.
 ///
 /// Used by many of the methods of [PaintingContext].
-typedef void PaintingContextCallback(PaintingContext context, Offset offset);
+typedef PaintingContextCallback = void Function(PaintingContext context, Offset offset);
 
 /// A place to paint.
 ///
@@ -531,12 +531,12 @@ abstract class Constraints {
 /// Signature for a function that is called for each [RenderObject].
 ///
 /// Used by [RenderObject.visitChildren] and [RenderObject.visitChildrenForSemantics].
-typedef void RenderObjectVisitor(RenderObject child);
+typedef RenderObjectVisitor = void Function(RenderObject child);
 
 /// Signature for a function that is called during layout.
 ///
 /// Used by [RenderObject.invokeLayoutCallback].
-typedef void LayoutCallback<T extends Constraints>(T constraints);
+typedef LayoutCallback<T extends Constraints> = void Function(T constraints);
 
 /// A reference to the semantics tree.
 ///

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

@@ -876,7 +876,7 @@ class RenderAnimatedOpacity extends RenderProxyBox {
 /// Signature for a function that creates a [Shader] for a given [Rect].
 ///
 /// Used by [RenderShaderMask] and the [ShaderMask] widget.
-typedef Shader ShaderCallback(Rect bounds);
+typedef ShaderCallback = Shader Function(Rect bounds);
 
 /// Applies a mask generated by a [Shader] to its child.
 ///
@@ -2390,22 +2390,22 @@ class RenderFractionalTranslation extends RenderProxyBox {
 /// Signature for listening to [PointerDownEvent] events.
 ///
 /// Used by [Listener] and [RenderPointerListener].
-typedef void PointerDownEventListener(PointerDownEvent event);
+typedef PointerDownEventListener = void Function(PointerDownEvent event);
 
 /// Signature for listening to [PointerMoveEvent] events.
 ///
 /// Used by [Listener] and [RenderPointerListener].
-typedef void PointerMoveEventListener(PointerMoveEvent event);
+typedef PointerMoveEventListener = void Function(PointerMoveEvent event);
 
 /// Signature for listening to [PointerUpEvent] events.
 ///
 /// Used by [Listener] and [RenderPointerListener].
-typedef void PointerUpEventListener(PointerUpEvent event);
+typedef PointerUpEventListener = void Function(PointerUpEvent event);
 
 /// Signature for listening to [PointerCancelEvent] events.
 ///
 /// Used by [Listener] and [RenderPointerListener].
-typedef void PointerCancelEventListener(PointerCancelEvent event);
+typedef PointerCancelEventListener = void Function(PointerCancelEvent event);
 
 /// Calls callbacks in response to pointer events.
 ///

packages/flutter/lib/src/scheduler/binding.dart

@@ -39,13 +39,13 @@ set timeDilation(double value) {
 /// scheduler's epoch. Use timeStamp to determine how far to advance animation
 /// timelines so that all the animations in the system are synchronized to a
 /// common time base.
-typedef void FrameCallback(Duration timeStamp);
+typedef FrameCallback = void Function(Duration timeStamp);
 
 /// Signature for [Scheduler.scheduleTask] callbacks.
 ///
 /// The type argument `T` is the task's return value. Consider [void] if the
 /// task does not return a value.
-typedef T TaskCallback<T>();
+typedef TaskCallback<T> = T Function();
 
 /// Signature for the [SchedulerBinding.schedulingStrategy] callback. Called
 /// whenever the system needs to decide whether a task at a given
@@ -55,7 +55,7 @@ typedef T TaskCallback<T>();
 /// at this time, false otherwise.
 ///
 /// See also [defaultSchedulingStrategy].
-typedef bool SchedulingStrategy({ int priority, SchedulerBinding scheduler });
+typedef SchedulingStrategy = bool Function({ int priority, SchedulerBinding scheduler });
 
 class _TaskEntry<T> {
   _TaskEntry(this.task, this.priority, this.debugLabel, this.flow) {

packages/flutter/lib/src/scheduler/ticker.dart

@@ -12,7 +12,7 @@ import 'binding.dart';
 ///
 /// The argument is the time that the object had spent enabled so far
 /// at the time of the callback being called.
-typedef void TickerCallback(Duration elapsed);
+typedef TickerCallback = void Function(Duration elapsed);
 
 /// An interface implemented by classes that can vend [Ticker] objects.
 ///

packages/flutter/lib/src/semantics/semantics.dart

@@ -23,19 +23,19 @@ export 'semantics_event.dart';
 /// Return false to stop visiting nodes.
 ///
 /// Used by [SemanticsNode.visitChildren].
-typedef bool SemanticsNodeVisitor(SemanticsNode node);
+typedef SemanticsNodeVisitor = bool Function(SemanticsNode node);
 
 /// Signature for [SemanticsAction]s that move the cursor.
 ///
 /// If `extendSelection` is set to true the cursor movement should extend the
 /// current selection or (if nothing is currently selected) start a selection.
-typedef void MoveCursorHandler(bool extendSelection);
+typedef MoveCursorHandler = void Function(bool extendSelection);
 
 /// Signature for the [SemanticsAction.setSelection] handlers to change the
 /// text selection (or re-position the cursor) to `selection`.
-typedef void SetSelectionHandler(TextSelection selection);
+typedef SetSelectionHandler = void Function(TextSelection selection);
 
-typedef void _SemanticsActionHandler(dynamic args);
+typedef _SemanticsActionHandler = void Function(dynamic args);
 
 /// A tag for a [SemanticsNode].
 ///

packages/flutter/lib/src/services/platform_messages.dart

@@ -10,7 +10,7 @@ import 'package:flutter/foundation.dart';
 
 import 'platform_channel.dart';
 
-typedef Future<ByteData> _MessageHandler(ByteData message);
+typedef _MessageHandler = Future<ByteData> Function(ByteData message);
 
 /// Sends binary messages to and receives binary messages from platform plugins.
 ///

packages/flutter/lib/src/services/text_formatter.dart

@@ -53,7 +53,7 @@ abstract class TextInputFormatter {
 
 /// Function signature expected for creating custom [TextInputFormatter]
 /// shorthands via [TextInputFormatter.withFunction];
-typedef TextEditingValue TextInputFormatFunction(
+typedef TextInputFormatFunction = TextEditingValue Function(
     TextEditingValue oldValue,
     TextEditingValue newValue,
 );

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

@@ -57,7 +57,7 @@ enum CrossFadeState {
 ///   );
 /// }
 /// ```
-typedef Widget AnimatedCrossFadeBuilder(Widget topChild, Key topChildKey, Widget bottomChild, Key bottomChildKey);
+typedef AnimatedCrossFadeBuilder = Widget Function(Widget topChild, Key topChildKey, Widget bottomChild, Key bottomChildKey);
 
 /// A widget that cross-fades between two given children and animates itself
 /// between their sizes.

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

@@ -14,10 +14,10 @@ import 'scroll_view.dart';
 import 'ticker_provider.dart';
 
 /// Signature for the builder callback used by [AnimatedList].
-typedef Widget AnimatedListItemBuilder(BuildContext context, int index, Animation<double> animation);
+typedef AnimatedListItemBuilder = Widget Function(BuildContext context, int index, Animation<double> animation);
 
 /// Signature for the builder callback used by [AnimatedListState.removeItem].
-typedef Widget AnimatedListRemovedItemBuilder(BuildContext context, Animation<double> animation);
+typedef AnimatedListRemovedItemBuilder = Widget Function(BuildContext context, Animation<double> animation);
 
 // The default insert/remove animation duration.
 const Duration _kDuration = const Duration(milliseconds: 300);

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

@@ -43,7 +43,7 @@ class _AnimatedSwitcherChildEntry {
 ///
 /// The function should return a widget which wraps the given `child`. It may
 /// also use the `animation` to inform its transition. It must not return null.
-typedef Widget AnimatedSwitcherTransitionBuilder(Widget child, Animation<double> animation);
+typedef AnimatedSwitcherTransitionBuilder = Widget Function(Widget child, Animation<double> animation);
 
 /// Signature for builders used to generate custom layouts for
 /// [AnimatedSwitcher].
@@ -55,7 +55,7 @@ typedef Widget AnimatedSwitcherTransitionBuilder(Widget child, Animation<double>
 /// The `previousChildren` list is an unmodifiable list, sorted with the oldest
 /// at the beginning and the newest at the end. It does not include the
 /// `currentChild`.
-typedef Widget AnimatedSwitcherLayoutBuilder(Widget currentChild, List<Widget> previousChildren);
+typedef AnimatedSwitcherLayoutBuilder = Widget Function(Widget currentChild, List<Widget> previousChildren);
 
 /// A widget that by default does a [FadeTransition] between a new widget and
 /// the widget previously set on the [AnimatedSwitcher] as a child.

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

@@ -31,7 +31,7 @@ export 'dart:ui' show Locale;
 /// The `locale` is the device's locale when the app started, or the device
 /// locale the user selected after the app was started. The `supportedLocales`
 /// parameter is just the value of [WidgetsApp.supportedLocales].
-typedef Locale LocaleResolutionCallback(Locale locale, Iterable<Locale> supportedLocales);
+typedef LocaleResolutionCallback = Locale Function(Locale locale, Iterable<Locale> supportedLocales);
 
 /// The signature of [WidgetsApp.onGenerateTitle].
 ///
@@ -41,7 +41,7 @@ typedef Locale LocaleResolutionCallback(Locale locale, Iterable<Locale> supporte
 /// localized title.
 ///
 /// This function must not return null.
-typedef String GenerateAppTitle(BuildContext context);
+typedef GenerateAppTitle = String Function(BuildContext context);
 
 /// A convenience class that wraps a number of widgets that are commonly
 /// required for an application.

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

@@ -288,7 +288,7 @@ class AsyncSnapshot<T> {
 /// itself based on a snapshot from interacting with a [Stream].
 /// * [FutureBuilder], which delegates to an [AsyncWidgetBuilder] to build
 /// itself based on a snapshot from interacting with a [Future].
-typedef Widget AsyncWidgetBuilder<T>(BuildContext context, AsyncSnapshot<T> snapshot);
+typedef AsyncWidgetBuilder<T> = Widget Function(BuildContext context, AsyncSnapshot<T> snapshot);
 
 /// Widget that builds itself based on the latest snapshot of interaction with
 /// a [Stream].

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

@@ -5402,7 +5402,7 @@ class Builder extends StatelessWidget {
 /// Signature for the builder callback used by [StatefulBuilder].
 ///
 /// Call [setState] to schedule the [StatefulBuilder] to rebuild.
-typedef Widget StatefulWidgetBuilder(BuildContext context, StateSetter setState);
+typedef StatefulWidgetBuilder = Widget Function(BuildContext context, StateSetter setState);
 
 /// A platonic widget that both has state and calls a closure to obtain its child widget.
 ///

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

@@ -20,7 +20,7 @@ const double _kDismissThreshold = 0.4;
 /// the given `direction`.
 ///
 /// Used by [Dismissible.onDismissed].
-typedef void DismissDirectionCallback(DismissDirection direction);
+typedef DismissDirectionCallback = void Function(DismissDirection direction);
 
 /// The direction in which a [Dismissible] can be dismissed.
 enum DismissDirection {

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

@@ -14,12 +14,12 @@ import 'overlay.dart';
 /// Signature for determining whether the given data will be accepted by a [DragTarget].
 ///
 /// Used by [DragTarget.onWillAccept].
-typedef bool DragTargetWillAccept<T>(T data);
+typedef DragTargetWillAccept<T> = bool Function(T data);
 
 /// Signature for causing a [DragTarget] to accept the given data.
 ///
 /// Used by [DragTarget.onAccept].
-typedef void DragTargetAccept<T>(T data);
+typedef DragTargetAccept<T> = void Function(T data);
 
 /// Signature for building children of a [DragTarget].
 ///
@@ -29,17 +29,17 @@ typedef void DragTargetAccept<T>(T data);
 /// this [DragTarget] and that will not be accepted by the [DragTarget].
 ///
 /// Used by [DragTarget.builder].
-typedef Widget DragTargetBuilder<T>(BuildContext context, List<T> candidateData, List<dynamic> rejectedData);
+typedef DragTargetBuilder<T> = Widget Function(BuildContext context, List<T> candidateData, List<dynamic> rejectedData);
 
 /// Signature for when a [Draggable] is dropped without being accepted by a [DragTarget].
 ///
 /// Used by [Draggable.onDraggableCanceled].
-typedef void DraggableCanceledCallback(Velocity velocity, Offset offset);
+typedef DraggableCanceledCallback = void Function(Velocity velocity, Offset offset);
 
 /// Signature for when a [Draggable] leaves a [DragTarget].
 ///
 /// Used by [DragTarget.onLeave].
-typedef void DragTargetLeave<T>(T data);
+typedef DragTargetLeave<T> = void Function(T data);
 
 /// Where the [Draggable] should be anchored during a drag.
 enum DragAnchor {
@@ -481,7 +481,7 @@ class _DragTargetState<T> extends State<DragTarget<T>> {
 }
 
 enum _DragEndKind { dropped, canceled }
-typedef void _OnDragEnd(Velocity velocity, Offset offset, bool wasAccepted);
+typedef _OnDragEnd = void Function(Velocity velocity, Offset offset, bool wasAccepted);
 
 // The lifetime of this object is a little dubious right now. Specifically, it
 // lives as long as the pointer is down. Arguably it should self-immolate if the

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

@@ -24,7 +24,7 @@ export 'package:flutter/rendering.dart' show SelectionChangedCause;
 
 /// Signature for the callback that reports when the user changes the selection
 /// (including the cursor location).
-typedef void SelectionChangedCallback(TextSelection selection, SelectionChangedCause cause);
+typedef SelectionChangedCallback = void Function(TextSelection selection, SelectionChangedCause cause);
 
 const Duration _kCursorBlinkHalfPeriod = const Duration(milliseconds: 500);
 

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

@@ -311,7 +311,7 @@ enum FadeInImagePhase {
   completed,
 }
 
-typedef void _ImageProviderResolverListener();
+typedef _ImageProviderResolverListener = void Function();
 
 class _ImageProviderResolver {
   _ImageProviderResolver({

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

@@ -183,17 +183,17 @@ class _FormScope extends InheritedWidget {
 /// Signature for validating a form field.
 ///
 /// Used by [FormField.validator].
-typedef String FormFieldValidator<T>(T value);
+typedef FormFieldValidator<T> = String Function(T value);
 
 /// Signature for being notified when a form field changes value.
 ///
 /// Used by [FormField.onSaved].
-typedef void FormFieldSetter<T>(T newValue);
+typedef FormFieldSetter<T> = void Function(T newValue);
 
 /// Signature for building the widget representing the form field.
 ///
 /// Used by [FormField.builder].
-typedef Widget FormFieldBuilder<T>(FormFieldState<T> field);
+typedef FormFieldBuilder<T> = Widget Function(FormFieldState<T> field);
 
 /// A single form field.
 ///

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

@@ -829,7 +829,7 @@ enum _StateLifecycle {
 }
 
 /// The signature of [State.setState] functions.
-typedef void StateSetter(VoidCallback fn);
+typedef StateSetter = void Function(VoidCallback fn);
 
 /// The logic and internal state for a [StatefulWidget].
 ///
@@ -1751,7 +1751,7 @@ class _InactiveElements {
 ///
 /// It is safe to call `element.visitChildElements` reentrantly within
 /// this callback.
-typedef void ElementVisitor(Element element);
+typedef ElementVisitor = void Function(Element element);
 
 /// A handle to the location of a widget in the widget tree.
 ///
@@ -3518,7 +3518,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
 ///  * [FlutterError.reportError], which is typically called with the same
 ///    [FlutterErrorDetails] object immediately prior to [ErrorWidget.builder]
 ///    being called.
-typedef Widget ErrorWidgetBuilder(FlutterErrorDetails details);
+typedef ErrorWidgetBuilder = Widget Function(FlutterErrorDetails details);
 
 /// A widget that renders an exception's message.
 ///
@@ -3581,13 +3581,13 @@ class ErrorWidget extends LeafRenderObjectWidget {
 /// or [State.build].
 ///
 /// Used by [Builder.builder], [OverlayEntry.builder], etc.
-typedef Widget WidgetBuilder(BuildContext context);
+typedef WidgetBuilder = Widget Function(BuildContext context);
 
 /// Signature for a function that creates a widget for a given index, e.g., in a
 /// list.
 ///
 /// Used by [ListView.builder] and other APIs that use lazily-generated widgets.
-typedef Widget IndexedWidgetBuilder(BuildContext context, int index);
+typedef IndexedWidgetBuilder = Widget Function(BuildContext context, int index);
 
 /// A builder that builds a widget given a child.
 ///
@@ -3595,7 +3595,7 @@ typedef Widget IndexedWidgetBuilder(BuildContext context, int index);
 ///
 /// Used by [AnimatedBuilder.builder], as well as [WidgetsApp.builder] and
 /// [MaterialApp.builder].
-typedef Widget TransitionBuilder(BuildContext context, Widget child);
+typedef TransitionBuilder = Widget Function(BuildContext context, Widget child);
 
 /// An [Element] that composes other [Element]s.
 ///

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

@@ -61,10 +61,10 @@ abstract class GestureRecognizerFactory<T extends GestureRecognizer> {
 }
 
 /// Signature for closures that implement [GestureRecognizerFactory.constructor].
-typedef T GestureRecognizerFactoryConstructor<T extends GestureRecognizer>();
+typedef GestureRecognizerFactoryConstructor<T extends GestureRecognizer> = T Function();
 
 /// Signature for closures that implement [GestureRecognizerFactory.initializer].
-typedef void GestureRecognizerFactoryInitializer<T extends GestureRecognizer>(T instance);
+typedef GestureRecognizerFactoryInitializer<T extends GestureRecognizer> = void Function(T instance);
 
 /// Factory for creating gesture recognizers that delegates to callbacks.
 ///

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

@@ -18,9 +18,9 @@ import 'transitions.dart';
 /// This is typically used with a [HeroController] to provide an animation for
 /// [Hero] positions that looks nicer than a linear movement. For example, see
 /// [MaterialRectArcTween].
-typedef Tween<Rect> CreateRectTween(Rect begin, Rect end);
+typedef CreateRectTween = Tween<Rect> Function(Rect begin, Rect end);
 
-typedef void _OnFlightEnded(_HeroFlight flight);
+typedef _OnFlightEnded = void Function(_HeroFlight flight);
 
 enum _HeroFlightType {
   push, // Fly the "to" hero and animate with the "to" route.

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

@@ -223,10 +223,10 @@ abstract class ImplicitlyAnimatedWidget extends StatefulWidget {
 ///
 /// This is the type of one of the arguments of [TweenVisitor], the signature
 /// used by [AnimatedWidgetBaseState.forEachTween].
-typedef Tween<T> TweenConstructor<T>(T targetValue);
+typedef TweenConstructor<T> = Tween<T> Function(T targetValue);
 
 /// Signature for callbacks passed to [AnimatedWidgetBaseState.forEachTween].
-typedef Tween<T> TweenVisitor<T>(Tween<T> tween, T targetValue, TweenConstructor<T> constructor);
+typedef TweenVisitor<T> = Tween<T> Function(Tween<T> tween, T targetValue, TweenConstructor<T> constructor);
 
 /// A base class for widgets with implicit animations.
 ///

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

@@ -9,7 +9,7 @@ import 'debug.dart';
 import 'framework.dart';
 
 /// The signature of the [LayoutBuilder] builder function.
-typedef Widget LayoutWidgetBuilder(BuildContext context, BoxConstraints constraints);
+typedef LayoutWidgetBuilder = Widget Function(BuildContext context, BoxConstraints constraints);
 
 /// Builds a widget tree that can depend on the parent widget's size.
 ///

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

@@ -23,16 +23,16 @@ import 'ticker_provider.dart';
 /// Creates a route for the given route settings.
 ///
 /// Used by [Navigator.onGenerateRoute] and [Navigator.onUnknownRoute].
-typedef Route<dynamic> RouteFactory(RouteSettings settings);
+typedef RouteFactory = Route<dynamic> Function(RouteSettings settings);
 
 /// Signature for the [Navigator.popUntil] predicate argument.
-typedef bool RoutePredicate(Route<dynamic> route);
+typedef RoutePredicate = bool Function(Route<dynamic> route);
 
 /// Signature for a callback that verifies that it's OK to call [Navigator.pop].
 ///
 /// Used by [Form.onWillPop], [ModalRoute.addScopedWillPopCallback],
 /// [ModalRoute.removeScopedWillPopCallback], and [WillPopScope].
-typedef Future<bool> WillPopCallback();
+typedef WillPopCallback = Future<bool> Function();
 
 /// Indicates whether the current route should be popped.
 ///

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

@@ -34,7 +34,7 @@ import 'viewport.dart';
 /// [SliverAppBar.forceElevated] property to ensure that the app bar shows a
 /// shadow, since it would otherwise not necessarily be aware that it had
 /// content ostensibly below it.
-typedef List<Widget> NestedScrollViewHeaderSliversBuilder(BuildContext context, bool innerBoxIsScrolled);
+typedef NestedScrollViewHeaderSliversBuilder = List<Widget> Function(BuildContext context, bool innerBoxIsScrolled);
 
 /// A scrolling view inside of which can be nested other scrolling views, with
 /// their scroll positions being intrinsically linked.
@@ -454,7 +454,7 @@ class _NestedScrollMetrics extends FixedScrollMetrics {
   final double correctionOffset;
 }
 
-typedef ScrollActivity _NestedScrollActivityGetter(_NestedScrollPosition position);
+typedef _NestedScrollActivityGetter = ScrollActivity Function(_NestedScrollPosition position);
 
 class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldController {
   _NestedScrollCoordinator(this._state, this._parent, this._onHasScrolledBodyChanged) {

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

@@ -10,7 +10,7 @@ import 'framework.dart';
 /// notification to continue to be dispatched to further ancestors.
 ///
 /// Used by [NotificationListener.onNotification].
-typedef bool NotificationListenerCallback<T extends Notification>(T notification);
+typedef NotificationListenerCallback<T extends Notification> = bool Function(T notification);
 
 /// A notification that can bubble up the widget tree.
 ///

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

@@ -10,7 +10,7 @@ import 'media_query.dart';
 /// Signature for a function that builds a widget given an [Orientation].
 ///
 /// Used by [OrientationBuilder.builder].
-typedef Widget OrientationWidgetBuilder(BuildContext context, Orientation orientation);
+typedef OrientationWidgetBuilder = Widget Function(BuildContext context, Orientation orientation);
 
 /// Builds a widget tree that can depend on the parent widget's orientation
 /// (distinct from the device orientation).

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

@@ -48,13 +48,13 @@ abstract class PageRoute<T> extends ModalRoute<T> {
 /// primary contents.
 ///
 /// See [ModalRoute.buildPage] for complete definition of the parameters.
-typedef Widget RoutePageBuilder(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation);
+typedef RoutePageBuilder = Widget Function(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation);
 
 /// Signature for the [PageRouteBuilder] function that builds the route's
 /// transitions.
 ///
 /// See [ModalRoute.buildTransitions] for complete definition of the parameters.
-typedef Widget RouteTransitionsBuilder(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child);
+typedef RouteTransitionsBuilder = Widget Function(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child);
 
 Widget _defaultTransitionsBuilder(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child) {
   return child;

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

@@ -284,7 +284,7 @@ class UserScrollNotification extends ScrollNotification {
 
 /// A predicate for [ScrollNotification], used to customize widgets that
 /// listen to notifications from their children.
-typedef bool ScrollNotificationPredicate(ScrollNotification notification);
+typedef ScrollNotificationPredicate = bool Function(ScrollNotification notification);
 
 /// A [ScrollNotificationPredicate] that checks whether
 /// `notification.depth == 0`, which means that the notification did not bubble

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

@@ -25,7 +25,7 @@ export 'package:flutter/physics.dart' show Tolerance;
 
 /// Signature used by [Scrollable] to build the viewport through which the
 /// scrollable content is displayed.
-typedef Widget ViewportBuilder(BuildContext context, ViewportOffset position);
+typedef ViewportBuilder = Widget Function(BuildContext context, ViewportOffset position);
 
 /// A widget that scrolls.
 ///

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

@@ -58,7 +58,7 @@ enum _TextSelectionHandlePosition { start, end }
 /// of the [RenderBox] given by the [TextSelectionOverlay.renderObject].
 ///
 /// Used by [TextSelectionOverlay.onSelectionOverlayChanged].
-typedef void TextSelectionOverlayChanged(TextEditingValue value, Rect caretRect);
+typedef TextSelectionOverlayChanged = void Function(TextEditingValue value, Rect caretRect);
 
 /// An interface for manipulating the selection, to be used by the implementor
 /// of the toolbar widget.

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

@@ -24,9 +24,9 @@ import 'icon_data.dart';
 
 /// Signature for the builder callback used by
 /// [WidgetInspector.selectButtonBuilder].
-typedef Widget InspectorSelectButtonBuilder(BuildContext context, VoidCallback onPressed);
+typedef InspectorSelectButtonBuilder = Widget Function(BuildContext context, VoidCallback onPressed);
 
-typedef void _RegisterServiceExtensionCallback({
+typedef _RegisterServiceExtensionCallback = void Function({
   @required String name,
   @required ServiceExtensionCallback callback
 });
@@ -93,7 +93,7 @@ List<_DiagnosticsPathNode> _followDiagnosticableChain(List<Diagnosticable> chain
 
 /// Signature for the selection change callback used by
 /// [WidgetInspectorService.selectionChangedCallback].
-typedef void InspectorSelectionChangedCallback();
+typedef InspectorSelectionChangedCallback = void Function();
 
 /// Structure to help reference count Dart objects referenced by a GUI tool
 /// using [WidgetInspectorService].

packages/flutter/test/gestures/arena_test.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/gestures.dart';
 import 'package:test/test.dart';
 
-typedef void GestureArenaCallback(Object key);
+typedef GestureArenaCallback = void Function(Object key);
 
 const int primaryKey = 4;
 

packages/flutter/test/gestures/gesture_binding_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:test/test.dart';
 
-typedef void HandleEventCallback(PointerEvent event);
+typedef HandleEventCallback = void Function(PointerEvent event);
 
 class TestGestureFlutterBinding extends BindingBase with GestureBinding {
   HandleEventCallback callback;

packages/flutter/test/gestures/gesture_tester.dart

@@ -31,7 +31,7 @@ class GestureTester {
   }
 }
 
-typedef void GestureTest(GestureTester tester);
+typedef GestureTest = void Function(GestureTester tester);
 
 @isTest
 void testGesture(String description, GestureTest callback) {

packages/flutter/test/gestures/locking_test.dart

@@ -9,7 +9,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:test/test.dart';
 
-typedef void HandleEventCallback(PointerEvent event);
+typedef HandleEventCallback = void Function(PointerEvent event);
 
 class TestGestureFlutterBinding extends BindingBase with GestureBinding {
   HandleEventCallback callback;

packages/flutter/test/material/feedback_test.dart

@@ -224,4 +224,4 @@ class TestWidget extends StatelessWidget {
   }
 }
 
-typedef VoidCallback HandlerCreator(BuildContext context);
+typedef HandlerCreator = VoidCallback Function(BuildContext context);

packages/flutter/test/material/tabs_test.dart

@@ -69,7 +69,7 @@ Widget buildFrame({
   );
 }
 
-typedef Widget TabControllerFrameBuilder(BuildContext context, TabController controller);
+typedef TabControllerFrameBuilder = Widget Function(BuildContext context, TabController controller);
 
 class TabControllerFrame extends StatefulWidget {
   const TabControllerFrame({ this.length, this.initialIndex = 0, this.builder });

packages/flutter/test/rendering/mock_canvas.dart

@@ -59,13 +59,13 @@ Matcher get paintsAssertion => new _TestRecordingCanvasPaintsAssertionMatcher();
 /// ```dart
 /// if (methodName == #drawCircle) { ... }
 /// ```
-typedef bool PaintPatternPredicate(Symbol methodName, List<dynamic> arguments);
+typedef PaintPatternPredicate = bool Function(Symbol methodName, List<dynamic> arguments);
 
 /// The signature of [RenderObject.paint] functions.
-typedef void _ContextPainterFunction(PaintingContext context, Offset offset);
+typedef _ContextPainterFunction = void Function(PaintingContext context, Offset offset);
 
 /// The signature of functions that paint directly on a canvas.
-typedef void _CanvasPainterFunction(Canvas canvas);
+typedef _CanvasPainterFunction = void Function(Canvas canvas);
 
 /// Builder interface for patterns used to match display lists (canvas calls).
 ///

packages/flutter/test/widgets/dismissible_test.dart

@@ -61,7 +61,7 @@ Widget buildTest({ double startToEndThreshold, TextDirection textDirection = Tex
   );
 }
 
-typedef Future<Null> DismissMethod(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection });
+typedef DismissMethod = Future<Null> Function(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection });
 
 Future<Null> dismissElement(WidgetTester tester, Finder finder, { @required AxisDirection gestureDirection }) async {
   Offset downLocation;

packages/flutter/test/widgets/dispose_ancestor_lookup_test.dart

@@ -5,7 +5,7 @@
 import 'package:flutter_test/flutter_test.dart' hide TypeMatcher;
 import 'package:flutter/widgets.dart';
 
-typedef void TestCallback(BuildContext context);
+typedef TestCallback = void Function(BuildContext context);
 
 class TestWidget extends StatefulWidget {
   const TestWidget(this.callback);

packages/flutter/test/widgets/navigator_test.dart

@@ -42,7 +42,7 @@ class SecondWidgetState extends State<SecondWidget> {
   }
 }
 
-typedef void ExceptionCallback(dynamic exception);
+typedef ExceptionCallback = void Function(dynamic exception);
 
 class ThirdWidget extends StatelessWidget {
   const ThirdWidget({ this.targetKey, this.onException });
@@ -89,7 +89,7 @@ class OnTapPage extends StatelessWidget {
   }
 }
 
-typedef void OnObservation(Route<dynamic> route, Route<dynamic> previousRoute);
+typedef OnObservation = void Function(Route<dynamic> route, Route<dynamic> previousRoute);
 
 class TestObserver extends NavigatorObserver {
   OnObservation onPushed;

packages/flutter/test/widgets/semantics_traversal_test.dart

@@ -14,7 +14,7 @@ import 'package:flutter_test/flutter_test.dart';
 
 import 'semantics_tester.dart';
 
-typedef Future<Null> TraversalTestFunction(TraversalTester tester);
+typedef TraversalTestFunction = Future<Null> Function(TraversalTester tester);
 const Size tenByTen = const Size(10.0, 10.0);
 
 void main() {

packages/flutter/test/widgets/shape_decoration_test.dart

@@ -105,7 +105,7 @@ Future<Null> main() async {
   });
 }
 
-typedef void Logger(String caller);
+typedef Logger = void Function(String caller);
 
 class TestBorder extends ShapeBorder {
   const TestBorder(this.onLog) : assert(onLog != null);