enable lint prefer_generic_function_type_aliases (#21680)

diff --git a/packages/flutter_tools/lib/src/base/context.dart b/packages/flutter_tools/lib/src/base/context.dart
index 2f8fca1..df3de18 100644
--- a/packages/flutter_tools/lib/src/base/context.dart
+++ b/packages/flutter_tools/lib/src/base/context.dart

@@ -11,7 +11,7 @@
 ///
 /// Generators are allowed to return `null`, in which case the context will
 /// store the `null` value as the value for that type.
-typedef dynamic Generator();
+typedef Generator = dynamic Function();
 
 /// An exception thrown by [AppContext] when you try to get a [Type] value from
 /// the context, and the instantiation of the value results in a dependency

diff --git a/packages/flutter_tools/lib/src/base/fingerprint.dart b/packages/flutter_tools/lib/src/base/fingerprint.dart
index 4d33ba4..fed1cbf 100644
--- a/packages/flutter_tools/lib/src/base/fingerprint.dart
+++ b/packages/flutter_tools/lib/src/base/fingerprint.dart

@@ -13,7 +13,7 @@
 import '../version.dart';
 import 'file_system.dart';
 
-typedef bool FingerprintPathFilter(String path);
+typedef FingerprintPathFilter = bool Function(String path);
 
 /// A tool that can be used to compute, compare, and write [Fingerprint]s for a
 /// set of input files and associated build settings.

diff --git a/packages/flutter_tools/lib/src/base/io.dart b/packages/flutter_tools/lib/src/base/io.dart
index 4beb040..b26e20e 100644
--- a/packages/flutter_tools/lib/src/base/io.dart
+++ b/packages/flutter_tools/lib/src/base/io.dart

@@ -77,7 +77,7 @@
         WebSocketTransformer;
 
 /// Exits the process with the given [exitCode].
-typedef void ExitFunction(int exitCode);
+typedef ExitFunction = void Function(int exitCode);
 
 const ExitFunction _defaultExitFunction = io.exit;
 

diff --git a/packages/flutter_tools/lib/src/base/logger.dart b/packages/flutter_tools/lib/src/base/logger.dart
index d71d974..a9d09d4 100644
--- a/packages/flutter_tools/lib/src/base/logger.dart
+++ b/packages/flutter_tools/lib/src/base/logger.dart

@@ -13,7 +13,7 @@
 
 const int kDefaultStatusPadding = 59;
 
-typedef void VoidCallback();
+typedef VoidCallback = void Function();
 
 abstract class Logger {
   bool get isVerbose => false;

diff --git a/packages/flutter_tools/lib/src/base/net.dart b/packages/flutter_tools/lib/src/base/net.dart
index 1f761f3..94c724e 100644
--- a/packages/flutter_tools/lib/src/base/net.dart
+++ b/packages/flutter_tools/lib/src/base/net.dart

@@ -11,7 +11,7 @@
 
 const int kNetworkProblemExitCode = 50;
 
-typedef HttpClient HttpClientFactory();
+typedef HttpClientFactory = HttpClient Function();
 
 /// Download a file from the given URL and return the bytes.
 Future<List<int>> fetchUrl(Uri url) async {

diff --git a/packages/flutter_tools/lib/src/base/process.dart b/packages/flutter_tools/lib/src/base/process.dart
index 09c146c..caf6349 100644
--- a/packages/flutter_tools/lib/src/base/process.dart
+++ b/packages/flutter_tools/lib/src/base/process.dart

@@ -11,10 +11,10 @@
 import 'process_manager.dart';
 import 'utils.dart';
 
-typedef String StringConverter(String string);
+typedef StringConverter = String Function(String string);
 
 /// A function that will be run before the VM exits.
-typedef Future<dynamic> ShutdownHook();
+typedef ShutdownHook = Future<dynamic> Function();
 
 // TODO(ianh): We have way too many ways to run subprocesses in this project.
 // Convert most of these into one or more lightweight wrappers around the

diff --git a/packages/flutter_tools/lib/src/base/utils.dart b/packages/flutter_tools/lib/src/base/utils.dart
index 8b22e86..102a0ec 100644
--- a/packages/flutter_tools/lib/src/base/utils.dart
+++ b/packages/flutter_tools/lib/src/base/utils.dart

@@ -251,7 +251,7 @@
 
 Clock get clock => context[Clock];
 
-typedef Future<Null> AsyncCallback();
+typedef AsyncCallback = Future<Null> Function();
 
 /// A [Timer] inspired class that:
 ///   - has a different initial value for the first callback delay

diff --git a/packages/flutter_tools/lib/src/commands/daemon.dart b/packages/flutter_tools/lib/src/commands/daemon.dart
index 2a91d94..81337c9 100644
--- a/packages/flutter_tools/lib/src/commands/daemon.dart
+++ b/packages/flutter_tools/lib/src/commands/daemon.dart

@@ -73,9 +73,9 @@
   }
 }
 
-typedef void DispatchCommand(Map<String, dynamic> command);
+typedef DispatchCommand = void Function(Map<String, dynamic> command);
 
-typedef Future<dynamic> CommandHandler(Map<String, dynamic> args);
+typedef CommandHandler = Future<dynamic> Function(Map<String, dynamic> args);
 
 class Daemon {
   Daemon(
@@ -305,7 +305,7 @@
   }
 }
 
-typedef Future<void> _RunOrAttach({
+typedef _RunOrAttach = Future<void> Function({
   Completer<DebugConnectionInfo> connectionInfoCompleter,
   Completer<void> appStartedCompleter
 });
@@ -553,7 +553,7 @@
   }
 }
 
-typedef void _DeviceEventHandler(Device device);
+typedef _DeviceEventHandler = void Function(Device device);
 
 /// This domain lets callers list and monitor connected devices.
 ///

diff --git a/packages/flutter_tools/lib/src/commands/drive.dart b/packages/flutter_tools/lib/src/commands/drive.dart
index 61f8d11..419371a 100644
--- a/packages/flutter_tools/lib/src/commands/drive.dart
+++ b/packages/flutter_tools/lib/src/commands/drive.dart

@@ -179,7 +179,7 @@
 }
 
 /// Finds a device to test on. May launch a simulator, if necessary.
-typedef Future<Device> TargetDeviceFinder();
+typedef TargetDeviceFinder = Future<Device> Function();
 TargetDeviceFinder targetDeviceFinder = findTargetDevice;
 void restoreTargetDeviceFinder() {
   targetDeviceFinder = findTargetDevice;
@@ -213,7 +213,7 @@
 }
 
 /// Starts the application on the device given command configuration.
-typedef Future<LaunchResult> AppStarter(DriveCommand command);
+typedef AppStarter = Future<LaunchResult> Function(DriveCommand command);
 
 AppStarter appStarter = _startApp; // (mutable for testing)
 void restoreAppStarter() {
@@ -272,7 +272,7 @@
 }
 
 /// Runs driver tests.
-typedef Future<Null> TestRunner(List<String> testArgs, String observatoryUri);
+typedef TestRunner = Future<Null> Function(List<String> testArgs, String observatoryUri);
 TestRunner testRunner = _runTests;
 void restoreTestRunner() {
   testRunner = _runTests;
@@ -299,7 +299,7 @@
 
 
 /// Stops the application.
-typedef Future<bool> AppStopper(DriveCommand command);
+typedef AppStopper = Future<bool> Function(DriveCommand command);
 AppStopper appStopper = _stopApp;
 void restoreAppStopper() {
   appStopper = _stopApp;

diff --git a/packages/flutter_tools/lib/src/compile.dart b/packages/flutter_tools/lib/src/compile.dart
index ff1f3e7..a98644c 100644
--- a/packages/flutter_tools/lib/src/compile.dart
+++ b/packages/flutter_tools/lib/src/compile.dart

@@ -17,7 +17,7 @@
 
 KernelCompiler get kernelCompiler => context[KernelCompiler];
 
-typedef void CompilerMessageConsumer(String message);
+typedef CompilerMessageConsumer = void Function(String message);
 
 class CompilerOutput {
   final String outputFilename;

diff --git a/packages/flutter_tools/lib/src/dart/pub.dart b/packages/flutter_tools/lib/src/dart/pub.dart
index 816c775..b4b6e6b 100644
--- a/packages/flutter_tools/lib/src/dart/pub.dart
+++ b/packages/flutter_tools/lib/src/dart/pub.dart

@@ -123,7 +123,7 @@
     throwToolExit('$directory: pub did not update .packages file (pubspec.yaml file has a newer timestamp)');
 }
 
-typedef String MessageFilter(String message);
+typedef MessageFilter = String Function(String message);
 
 /// Runs pub in 'batch' mode, forwarding complete lines written by pub to its
 /// stdout/stderr streams to the corresponding stream of this process, optionally

diff --git a/packages/flutter_tools/lib/src/test/flutter_platform.dart b/packages/flutter_tools/lib/src/test/flutter_platform.dart
index 7e171d5..695b235 100644
--- a/packages/flutter_tools/lib/src/test/flutter_platform.dart
+++ b/packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -189,7 +189,7 @@
 
 enum _InitialResult { crashed, timedOut, connected }
 enum _TestResult { crashed, harnessBailed, testBailed }
-typedef Future<Null> _Finalizer();
+typedef _Finalizer = Future<Null> Function();
 
 class _CompilationRequest {
   String path;

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index a99c278..599940d 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart

@@ -22,7 +22,7 @@
 import 'vmservice_record_replay.dart';
 
 /// A function that opens a two-way communication channel to the specified [uri].
-typedef Future<StreamChannel<String>> _OpenChannel(Uri uri);
+typedef _OpenChannel = Future<StreamChannel<String>> Function(Uri uri);
 
 _OpenChannel _openChannel = _defaultOpenChannel;
 
@@ -37,13 +37,13 @@
 /// hot mode.
 ///
 /// See: https://github.com/dart-lang/sdk/issues/30023
-typedef Future<Null> ReloadSources(
+typedef ReloadSources = Future<Null> Function(
   String isolateId, {
   bool force,
   bool pause,
 });
 
-typedef Future<String> CompileExpression(
+typedef CompileExpression = Future<String> Function(
   String isolateId,
   String expression,
   List<String> definitions,

diff --git a/packages/flutter_tools/test/base/flags_test.dart b/packages/flutter_tools/test/base/flags_test.dart
index 8f65690..99122de 100644
--- a/packages/flutter_tools/test/base/flags_test.dart
+++ b/packages/flutter_tools/test/base/flags_test.dart

@@ -11,7 +11,7 @@
 import '../src/common.dart';
 import '../src/context.dart';
 
-typedef FutureOr<Null> _TestMethod();
+typedef _TestMethod = FutureOr<Null> Function();
 
 void main() {
   Cache.disableLocking();

diff --git a/packages/flutter_tools/test/dart/pub_get_test.dart b/packages/flutter_tools/test/dart/pub_get_test.dart
index 373ef17..16e23f3 100644
--- a/packages/flutter_tools/test/dart/pub_get_test.dart
+++ b/packages/flutter_tools/test/dart/pub_get_test.dart

@@ -146,7 +146,7 @@
   });
 }
 
-typedef void StartCallback(List<dynamic> command);
+typedef StartCallback = void Function(List<dynamic> command);
 
 class MockProcessManager implements ProcessManager {
   MockProcessManager(this.fakeExitCode);

diff --git a/packages/flutter_tools/test/ios/cocoapods_test.dart b/packages/flutter_tools/test/ios/cocoapods_test.dart
index a39c8d2..435bb96 100644
--- a/packages/flutter_tools/test/ios/cocoapods_test.dart
+++ b/packages/flutter_tools/test/ios/cocoapods_test.dart

@@ -18,7 +18,7 @@
 import '../src/common.dart';
 import '../src/context.dart';
 
-typedef Future<ProcessResult> InvokeProcess();
+typedef InvokeProcess = Future<ProcessResult> Function();
 
 void main() {
   FileSystem fs;

diff --git a/packages/flutter_tools/test/runner/flutter_command_test.dart b/packages/flutter_tools/test/runner/flutter_command_test.dart
index 29ab6df..2e78161 100644
--- a/packages/flutter_tools/test/runner/flutter_command_test.dart
+++ b/packages/flutter_tools/test/runner/flutter_command_test.dart

@@ -161,7 +161,7 @@
 
 }
 
-typedef Future<FlutterCommandResult> CommandFunction();
+typedef CommandFunction = Future<FlutterCommandResult> Function();
 
 class DummyFlutterCommand extends FlutterCommand {
 

diff --git a/packages/flutter_tools/test/src/context.dart b/packages/flutter_tools/test/src/context.dart
index 0885212..743b623 100644
--- a/packages/flutter_tools/test/src/context.dart
+++ b/packages/flutter_tools/test/src/context.dart

@@ -34,7 +34,7 @@
 MockDeviceManager get testDeviceManager => context[DeviceManager];
 MockDoctor get testDoctor => context[Doctor];
 
-typedef void ContextInitializer(AppContext testContext);
+typedef ContextInitializer = void Function(AppContext testContext);
 
 @isTest
 void testUsingContext(String description, dynamic testMethod(), {

diff --git a/packages/flutter_tools/test/src/mocks.dart b/packages/flutter_tools/test/src/mocks.dart
index 1aab448..408d111 100644
--- a/packages/flutter_tools/test/src/mocks.dart
+++ b/packages/flutter_tools/test/src/mocks.dart

@@ -109,7 +109,7 @@
 }
 
 /// A strategy for creating Process objects from a list of commands.
-typedef Process ProcessFactory(List<String> command);
+typedef ProcessFactory = Process Function(List<String> command);
 
 /// A ProcessManager that starts Processes by delegating to a ProcessFactory.
 class MockProcessManager implements ProcessManager {