enable lint prefer_generic_function_type_aliases (flutter#21680)

Author: a14n

analysis_options.yaml

@@ -128,7 +128,7 @@ linter:
     - prefer_final_locals
     - prefer_foreach
     # - prefer_function_declarations_over_variables # not yet tested
-    # - prefer_generic_function_type_aliases # not yet tested
+    - prefer_generic_function_type_aliases
     - prefer_initializing_formals
     # - prefer_interpolation_to_compose_strings # not yet tested
     - prefer_is_empty

dev/bots/analyze.dart

@@ -11,7 +11,7 @@ import 'package:meta/meta.dart';
 
 import 'run_command.dart';
 
-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/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

@@ -9,7 +9,7 @@ import 'package:path/path.dart' as path;
 
 import 'run_command.dart';
 
-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

@@ -151,7 +151,7 @@ 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 = 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/test/adb_test.dart

@@ -122,7 +122,7 @@ 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)