[flutter_tools] throw exception instead of string from startApp (#52365)

When attempting to start an emulator in profile mode, ensure the daemon can exit gracefully

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

@@ -459,7 +459,7 @@ class AppDomain extends Domain {
     String isolateFilter,
   }) async {
     if (await device.isLocalEmulator && !options.buildInfo.supportsEmulator) {
-      throw '${toTitleCase(options.buildInfo.friendlyModeName)} mode is not supported for emulators.';
+      throw Exception('${toTitleCase(options.buildInfo.friendlyModeName)} mode is not supported for emulators.');
     }
     // We change the current working directory for the duration of the `start` command.
     final Directory cwd = globals.fs.currentDirectory;

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

@@ -12,6 +12,7 @@ import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/base/net.dart';
@@ -114,6 +115,38 @@ void main() {
       ProcessManager: () => FakeProcessManager.any(),
     });
 
+    testUsingContext('Fails with toolExit run in profile mode on emulator with machine flag', () async {
+      globals.fs.file('pubspec.yaml').createSync();
+      globals.fs.file('.packages').writeAsStringSync('\n');
+      globals.fs.file('lib/main.dart').createSync(recursive: true);
+      final FakeDevice device = FakeDevice(isLocalEmulator: true);
+      when(deviceManager.getAllConnectedDevices()).thenAnswer((Invocation invocation) async {
+        return <Device>[device];
+      });
+      when(deviceManager.getDevices()).thenAnswer((Invocation invocation) async {
+        return <Device>[device];
+      });
+      when(deviceManager.findTargetDevices(any)).thenAnswer((Invocation invocation) async {
+        return <Device>[device];
+      });
+      when(deviceManager.hasSpecifiedAllDevices).thenReturn(false);
+      when(deviceManager.deviceDiscoverers).thenReturn(<DeviceDiscovery>[]);
+
+      final RunCommand command = RunCommand();
+      applyMocksToCommand(command);
+      await expectLater(createTestCommandRunner(command).run(<String>[
+        'run',
+        '--no-pub',
+        '--machine',
+        '--profile',
+      ]), throwsToolExit(message: 'not supported for emulators'));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => MemoryFileSystem.test(),
+      ProcessManager: () => FakeProcessManager.any(),
+      DeviceManager: () => MockDeviceManager(),
+      Stdio: () => MockStdio(),
+    });
+
     testUsingContext('Walks upward looking for a pubspec.yaml and exits if missing', () async {
       globals.fs.currentDirectory = globals.fs.directory(globals.fs.path.join('a', 'b', 'c'))
         ..createSync(recursive: true);
@@ -572,15 +605,14 @@ class TestRunCommand extends RunCommand {
   }
 }
 
-class MockStableFlutterVersion extends MockFlutterVersion {
-  @override
-  bool get isMaster => false;
-}
-
 class FakeDevice extends Fake implements Device {
+  FakeDevice({bool isLocalEmulator = false})
+   : _isLocalEmulator = isLocalEmulator;
+
   static const int kSuccess = 1;
   static const int kFailure = -1;
   TargetPlatform _targetPlatform = TargetPlatform.ios;
+  final bool _isLocalEmulator;
 
   @override
   String get id => 'fake_device';
@@ -588,7 +620,7 @@ class FakeDevice extends Fake implements Device {
   void _throwToolExit(int code) => throwToolExit(null, exitCode: code);
 
   @override
-  Future<bool> get isLocalEmulator => Future<bool>.value(false);
+  Future<bool> get isLocalEmulator => Future<bool>.value(_isLocalEmulator);
 
   @override
   bool get supportsHotReload => false;

packages/flutter_tools/test/src/common.dart

@@ -101,7 +101,7 @@ Matcher throwsToolExit({ int exitCode, Pattern message }) {
     matcher = allOf(matcher, (ToolExit e) => e.exitCode == exitCode);
   }
   if (message != null) {
-    matcher = allOf(matcher, (ToolExit e) => e.message.contains(message));
+    matcher = allOf(matcher, (ToolExit e) => e.message?.contains(message) ?? false);
   }
   return throwsA(matcher);
 }