Detach debugger when VM connection fails on iOS (#68046)

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

@@ -468,10 +468,12 @@ class IOSDevice extends Device {
         packageName: FlutterProject.current().manifest.appName,
       );
       if (localUri == null) {
+        iosDeployDebugger?.detach();
         return LaunchResult.failed();
       }
       return LaunchResult.succeeded(observatoryUri: localUri);
     } on ProcessException catch (e) {
+      iosDeployDebugger?.detach();
       _logger.printError(e.message);
       return LaunchResult.failed();
     } finally {

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

@@ -25,6 +25,9 @@ const String noProvisioningProfileErrorTwo = 'Error 0xe8000067';
 const String deviceLockedError = 'e80000e2';
 const String unknownAppLaunchError = 'Error 0xe8000022';
 
+// Another debugger instance is already attached?
+const String processLaunchFailedError = 'error: process launch failed';
+
 class IOSDeploy {
   IOSDeploy({
     @required Artifacts artifacts,
@@ -412,6 +415,13 @@ Error launching app. Try launching from within Xcode via:
     open ios/Runner.xcworkspace
 
 Your Xcode version may be too old for your iOS version.
+═══════════════════════════════════════════════════════════════════════════════════''',
+        emphasis: true);
+  } else if (stdout.contains(processLaunchFailedError)) {
+    logger.printError('''
+═══════════════════════════════════════════════════════════════════════════════════
+Could not attach the debugger.
+Try uninstalling the app from your device and retrying.
 ═══════════════════════════════════════════════════════════════════════════════════''',
         emphasis: true);
   }

packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart

@@ -210,6 +210,21 @@ void main () {
         await iosDeployDebugger.launchAndAttach();
         expect(logger.errorText, contains('Try launching from within Xcode'));
       });
+
+      testWithoutContext('cannot attach', () async {
+        final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
+          const FakeCommand(
+            command: <String>['ios-deploy'],
+            stdout: 'error: process launch failed: timed out waiting for app to launch',
+          ),
+        ]);
+        final IOSDeployDebugger iosDeployDebugger = IOSDeployDebugger.test(
+          processManager: processManager,
+          logger: logger,
+        );
+        await iosDeployDebugger.launchAndAttach();
+        expect(logger.errorText, contains('Could not attach the debugger'));
+      });
     });
 
     testWithoutContext('detach', () async {

packages/flutter_tools/test/general.shard/ios/ios_device_start_prebuilt_test.dart

@@ -411,6 +411,62 @@ void main() {
   }, overrides: <Type, Generator>{
     Usage: () => MockUsage(),
   });
+
+  // Still uses context for analytics.
+  testUsingContext(
+      'IOSDevice.startApp detaches lldb when VM service connection fails',
+      () async {
+    final FileSystem fileSystem = MemoryFileSystem.test();
+
+    final MockIOSDeploy mockIOSDeploy = MockIOSDeploy();
+    final MockIOSDeployDebugger mockIOSDeployDebugger = MockIOSDeployDebugger();
+    when(mockIOSDeploy.prepareDebuggerForLaunch(
+            deviceId: anyNamed('deviceId'),
+            bundlePath: anyNamed('bundlePath'),
+            launchArguments: anyNamed('launchArguments'),
+            interfaceType: anyNamed('interfaceType')))
+        .thenReturn(mockIOSDeployDebugger);
+    when(mockIOSDeploy.installApp(
+            deviceId: anyNamed('deviceId'),
+            bundlePath: anyNamed('bundlePath'),
+            launchArguments: anyNamed('launchArguments'),
+            interfaceType: anyNamed('interfaceType')))
+        .thenAnswer((_) async => 0);
+
+    when(mockIOSDeployDebugger.launchAndAttach()).thenAnswer((_) async => true);
+
+    final IOSDevice device = setUpIOSDevice(
+      fileSystem: fileSystem,
+      iosDeploy: mockIOSDeploy,
+      vmServiceConnector: (String string, {Log log}) async {
+        throw const io.SocketException(
+          'OS Error: Connection refused, errno = 61, address = localhost, port '
+          '= 58943',
+        );
+      },
+    );
+    final IOSApp iosApp = PrebuiltIOSApp(
+      projectBundleId: 'app',
+      bundleName: 'Runner',
+      bundleDir: fileSystem.currentDirectory,
+    );
+    device.portForwarder = const NoOpDevicePortForwarder();
+    device.setLogReader(iosApp, FakeDeviceLogReader());
+
+    final LaunchResult launchResult = await device.startApp(
+      iosApp,
+      prebuiltApplication: true,
+      debuggingOptions: DebuggingOptions.enabled(BuildInfo.debug),
+      platformArgs: <String, dynamic>{},
+      fallbackPollingDelay: Duration.zero,
+      fallbackThrottleTimeout: const Duration(milliseconds: 10),
+    );
+
+    expect(launchResult.started, false);
+    verify(mockIOSDeployDebugger.detach()).called(1);
+  }, overrides: <Type, Generator>{
+    Usage: () => MockUsage(),
+  });
 }
 
 IOSDevice setUpIOSDevice({
@@ -419,6 +475,7 @@ IOSDevice setUpIOSDevice({
   Logger logger,
   ProcessManager processManager,
   VmServiceConnector vmServiceConnector,
+  IOSDeploy iosDeploy,
 }) {
   final Artifacts artifacts = Artifacts.test();
   final FakePlatform macPlatform = FakePlatform(
@@ -441,7 +498,8 @@ IOSDevice setUpIOSDevice({
     platform: macPlatform,
     iProxy: IProxy.test(logger: logger, processManager: processManager ?? FakeProcessManager.any()),
     logger: logger ?? BufferLogger.test(),
-    iosDeploy: IOSDeploy(
+    iosDeploy: iosDeploy ??
+        IOSDeploy(
           logger: logger ?? BufferLogger.test(),
           platform: macPlatform,
           processManager: processManager ?? FakeProcessManager.any(),
@@ -465,3 +523,5 @@ class MockDeviceLogReader extends Mock implements DeviceLogReader  {}
 class MockUsage extends Mock implements Usage {}
 class MockVmService extends Mock implements VmService {}
 class MockDartDevelopmentService extends Mock implements DartDevelopmentService {}
+class MockIOSDeployDebugger extends Mock implements IOSDeployDebugger {}
+class MockIOSDeploy extends Mock implements IOSDeploy {}