Added --dart-flags option to flutter run (#33924)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -474,6 +474,8 @@ class AndroidDevice extends Device {
         cmd.addAll(<String>['--ez', 'start-paused', 'true']);
       if (debuggingOptions.disableServiceAuthCodes)
         cmd.addAll(<String>['--ez', 'disable-service-auth-codes', 'true']);
+      if (debuggingOptions.dartFlags.isNotEmpty)
+        cmd.addAll(<String>['--es', 'dart-flags', debuggingOptions.dartFlags]);
       if (debuggingOptions.useTestFonts)
         cmd.addAll(<String>['--ez', 'use-test-fonts', 'true']);
       if (debuggingOptions.verboseSystemLogs) {

packages/flutter_tools/lib/src/commands/run.dart

@@ -4,6 +4,8 @@
 
 import 'dart:async';
 
+import 'package:args/command_runner.dart';
+
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/time.dart';
@@ -130,6 +132,16 @@ class RunCommand extends RunCommandBase {
         defaultsTo: true,
         help: 'If necessary, build the app before running.',
       )
+      ..addOption('dart-flags',
+        hide: !verboseHelp,
+        help: 'Pass a list of comma separated flags to the Dart instance at '
+              'application startup. Flags passed through this option must be '
+              'present on the whitelist defined within the Flutter engine. If '
+              'a non-whitelisted flag is encountered, the process will be '
+              'terminated immediately.\n\n'
+              'This flag is not available on the stable channel and is only '
+              'applied in debug and profile modes. This option should only '
+              'be used for experiments and should not be used by typical users.')
       ..addOption('use-application-binary',
         hide: !verboseHelp,
         help: 'Specify a pre-built application binary to use when running.',
@@ -294,6 +306,7 @@ class RunCommand extends RunCommandBase {
         buildInfo,
         startPaused: argResults['start-paused'],
         disableServiceAuthCodes: argResults['disable-service-auth-codes'],
+        dartFlags: argResults['dart-flags'],
         useTestFonts: argResults['use-test-fonts'],
         enableSoftwareRendering: argResults['enable-software-rendering'],
         skiaDeterministicRendering: argResults['skia-deterministic-rendering'],
@@ -350,6 +363,11 @@ class RunCommand extends RunCommandBase {
       );
     }
 
+    if (argResults['dart-flags'] != null && FlutterVersion.instance.isStable) {
+      throw UsageException('--dart-flags is not available on the stable '
+                           'channel.', null);
+    }
+
     for (Device device in devices) {
       if (await device.isLocalEmulator) {
         if (await device.supportsHardwareRendering) {

packages/flutter_tools/lib/src/device.dart

@@ -377,6 +377,7 @@ class DebuggingOptions {
     this.buildInfo, {
     this.startPaused = false,
     this.disableServiceAuthCodes = false,
+    this.dartFlags = '',
     this.enableSoftwareRendering = false,
     this.skiaDeterministicRendering = false,
     this.traceSkia = false,
@@ -391,6 +392,7 @@ class DebuggingOptions {
     : debuggingEnabled = false,
       useTestFonts = false,
       startPaused = false,
+      dartFlags = '',
       disableServiceAuthCodes = false,
       enableSoftwareRendering = false,
       skiaDeterministicRendering = false,
@@ -404,6 +406,7 @@ class DebuggingOptions {
 
   final BuildInfo buildInfo;
   final bool startPaused;
+  final String dartFlags;
   final bool disableServiceAuthCodes;
   final bool enableSoftwareRendering;
   final bool skiaDeterministicRendering;

packages/flutter_tools/lib/src/ios/devices.dart

@@ -283,6 +283,11 @@ class IOSDevice extends Device {
     if (debuggingOptions.disableServiceAuthCodes)
       launchArguments.add('--disable-service-auth-codes');
 
+    if (debuggingOptions.dartFlags.isNotEmpty) {
+      final String dartFlags = debuggingOptions.dartFlags;
+      launchArguments.add('--dart-flags="$dartFlags"');
+    }
+
     if (debuggingOptions.useTestFonts)
       launchArguments.add('--use-test-fonts');
 

packages/flutter_tools/test/commands/run_test.dart

@@ -2,11 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:args/command_runner.dart';
+import 'package:flutter_tools/src/application_package.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/build_info.dart';
+import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/run.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/runner/flutter_command.dart';
+import 'package:flutter_tools/src/version.dart';
 import 'package:mockito/mockito.dart';
 
 import '../src/common.dart';
@@ -14,9 +18,20 @@ import '../src/context.dart';
 import '../src/mocks.dart';
 
 void main() {
-  final MockDeviceManager mockDeviceManager = MockDeviceManager();
-
   group('run', () {
+    MockApplicationPackageFactory mockApplicationPackageFactory;
+    MockDeviceManager mockDeviceManager;
+    MockFlutterVersion mockStableFlutterVersion;
+    MockFlutterVersion mockUnstableFlutterVersion;
+
+    setUpAll(() {
+      Cache.disableLocking();
+      mockApplicationPackageFactory = MockApplicationPackageFactory();
+      mockDeviceManager = MockDeviceManager();
+      mockStableFlutterVersion = MockFlutterVersion(isStable: true);
+      mockUnstableFlutterVersion = MockFlutterVersion(isStable: false);
+    });
+
     testUsingContext('fails when target not found', () async {
       final RunCommand command = RunCommand();
       applyMocksToCommand(command);
@@ -28,6 +43,75 @@ void main() {
       }
     });
 
+    testUsingContext('dart-flags option is not available on stable channel', () async {
+      when(mockDeviceManager.getDevices()).thenAnswer((Invocation invocation) {
+        return Stream<Device>.fromIterable(<Device>[
+          FakeDevice(),
+        ]);
+      });
+
+      final RunCommand command = TestRunCommand();
+      final List<String> args = <String> [
+                                  'run',
+                                  '--dart-flags', '"--observe"',
+                                  '--no-hot',
+                                ];
+
+      // Stable branch.
+      try {
+        await createTestCommandRunner(command).run(args);
+        fail('Expect exception');
+      // ignore: unused_catch_clause
+      } on UsageException catch(e) {
+        // Not available while on stable branch.
+      }
+    }, overrides: <Type, Generator>{
+      DeviceManager: () => mockDeviceManager,
+      FlutterVersion: () => mockStableFlutterVersion,
+    });
+
+    testUsingContext('dart-flags option is only populated for debug and profile modes', () async {
+      when(mockDeviceManager.getDevices()).thenAnswer((Invocation invocation) {
+        return Stream<Device>.fromIterable(<Device>[
+          FakeDevice(),
+        ]);
+      });
+      final RunCommand command = TestRunCommand();
+      final List<String> args = <String> [
+                                  'run',
+                                  '--dart-flags', '"--observe"',
+                                  '--no-hot',
+                                ];
+
+      // Debug mode
+      try {
+        await createTestCommandRunner(command).run(args);
+        fail('Expect exception');
+      } on ToolExit catch (e) {
+        expect(e.exitCode ?? 1, 1);
+      }
+
+      // Profile mode
+      try {
+        await createTestCommandRunner(command).run(<String>[...args, '--profile']);
+        fail('Expect exception');
+      } on ToolExit catch (e) {
+        expect(e.exitCode ?? 1, 1);
+      }
+
+      // Release mode
+      try {
+        await createTestCommandRunner(command).run(<String>[...args, '--release']);
+        fail('Expect exception');
+      } on ToolExit catch (e) {
+        expect(e.exitCode ?? 1, 1);
+      }
+    }, overrides: <Type, Generator>{
+      ApplicationPackageFactory: () => mockApplicationPackageFactory,
+      DeviceManager: () => mockDeviceManager,
+      FlutterVersion: () => mockUnstableFlutterVersion,
+    });
+
     testUsingContext('should only request artifacts corresponding to connected devices', () async {
       when(mockDeviceManager.getDevices()).thenAnswer((Invocation invocation) {
         return Stream<Device>.fromIterable(<Device>[
@@ -89,3 +173,65 @@ class MockDevice extends Mock implements Device {
   @override
   Future<TargetPlatform> get targetPlatform async => _targetPlatform;
 }
+
+class TestRunCommand extends RunCommand {
+  @override
+  // ignore: must_call_super
+  Future<void> validateCommand() async {
+    devices = await deviceManager.getDevices().toList();
+  }
+}
+
+class MockStableFlutterVersion extends MockFlutterVersion {
+  @override
+  bool get isStable => true;
+}
+
+class FakeDevice extends Fake implements Device {
+  final TargetPlatform _targetPlatform = TargetPlatform.ios;
+
+  void _throwToolExit(int code) => throwToolExit(null, exitCode: code);
+
+  @override
+  Future<bool> get isLocalEmulator => Future<bool>.value(false);
+
+  @override
+  bool get supportsHotReload => false;
+
+  @override
+  DeviceLogReader getLogReader({ ApplicationPackage app }) {
+    return MockDeviceLogReader();
+  }
+
+  @override
+  String get name => 'FakeDevice';
+
+  @override
+  Future<TargetPlatform> get targetPlatform async => _targetPlatform;
+
+  @override
+  Future<LaunchResult> startApp(
+    ApplicationPackage package, {
+    String mainPath,
+    String route,
+    DebuggingOptions debuggingOptions,
+    Map<String, dynamic> platformArgs,
+    bool prebuiltApplication = false,
+    bool usesTerminalUi = true,
+    bool ipv6 = false,
+  }) async {
+    final String dartFlags = debuggingOptions.dartFlags;
+    if (debuggingOptions.buildInfo.isRelease) {
+      if (dartFlags.isNotEmpty) {
+        _throwToolExit(-1);
+      }
+      _throwToolExit(1);
+    } else {
+      if (dartFlags.isEmpty) {
+        _throwToolExit(-1);
+      }
+      _throwToolExit(1);
+    }
+    return null;
+  }
+}

packages/flutter_tools/test/src/context.dart

@@ -332,8 +332,12 @@ class MockXcodeProjectInterpreter implements XcodeProjectInterpreter {
 }
 
 class MockFlutterVersion extends Mock implements FlutterVersion {
+  MockFlutterVersion({bool isStable = false}) : _isStable = isStable;
+
+  final bool _isStable;
+
   @override
-  bool get isStable => false;
+  bool get isStable => _isStable;
 }
 
 class MockClock extends Mock implements SystemClock {}

packages/flutter_tools/test/src/mocks.dart

@@ -37,6 +37,18 @@ class MockApplicationPackageStore extends ApplicationPackageStore {
   );
 }
 
+class MockApplicationPackageFactory extends Mock implements ApplicationPackageFactory {
+  final MockApplicationPackageStore _store = MockApplicationPackageStore();
+
+  @override
+  Future<ApplicationPackage> getPackageForPlatform(
+    TargetPlatform platform, {
+    File applicationBinary,
+  }) async {
+    return _store.getPackageForPlatform(platform);
+  }
+}
+
 /// An SDK installation with several SDK levels (19, 22, 23).
 class MockAndroidSdk extends Mock implements AndroidSdk {
   static Directory createSdkDirectory({