Catch StateError and output more useful error message when DDS fails to start (#72736)

packages/flutter_tools/lib/src/base/dds.dart

@@ -11,6 +11,14 @@ import 'common.dart';
 import 'io.dart' as io;
 import 'logger.dart';
 
+@visibleForTesting
+Future<dds.DartDevelopmentService> Function(
+  Uri,
+  {bool enableAuthCodes,
+  bool ipv6,
+  Uri serviceUri,
+}) ddsLauncherCallback = dds.DartDevelopmentService.startDartDevelopmentService;
+
 /// Helper class to launch a [dds.DartDevelopmentService]. Allows for us to
 /// mock out this functionality for testing purposes.
 class DartDevelopmentService {
@@ -44,7 +52,7 @@ class DartDevelopmentService {
       'connecting to VM service at $observatoryUri.',
     );
     try {
-      _ddsInstance = await dds.DartDevelopmentService.startDartDevelopmentService(
+      _ddsInstance = await ddsLauncherCallback(
           observatoryUri,
           serviceUri: ddsUri,
           enableAuthCodes: !disableServiceAuthCodes,
@@ -59,9 +67,21 @@ class DartDevelopmentService {
     } on dds.DartDevelopmentServiceException catch (e) {
       logger.printTrace('Warning: Failed to start DDS: ${e.message}');
       if (e.errorCode == dds.DartDevelopmentServiceException.existingDdsInstanceError) {
-        _existingDdsUri = Uri.parse(
-          e.message.split(' ').firstWhere((String e) => e.startsWith('http'))
-        );
+        try {
+          _existingDdsUri = Uri.parse(
+            e.message.split(' ').firstWhere((String e) => e.startsWith('http'))
+          );
+        } on StateError {
+          logger.printError(
+            'DDS has failed to start and there is not an existing DDS instance '
+            'available to connect to. Please comment on '
+            'https://github.com/flutter/flutter/issues/72385 with output from '
+            '"flutter doctor -v" and the following error message:\n\n ${e.message}.'
+          );
+          // Wrap the DDS error message in a StateError so it can be collected
+          // by the crash handler.
+          throw StateError(e.message);
+        }
       }
       if (!_completer.isCompleted) {
         _completer.complete();

packages/flutter_tools/lib/src/resident_runner.dart

@@ -236,10 +236,10 @@ class FlutterDevice {
       bool existingDds = false;
       vm_service.VmService service;
       if (!disableDds) {
-        void handleError(Exception e) {
+        void handleError(Exception e, StackTrace st) {
           globals.printTrace('Fail to connect to service protocol: $observatoryUri: $e');
           if (!completer.isCompleted) {
-            completer.completeError('failed to connect to $observatoryUri');
+            completer.completeError('failed to connect to $observatoryUri', st);
           }
         }
         // This first try block is meant to catch errors that occur during DDS startup
@@ -252,16 +252,16 @@ class FlutterDevice {
             ipv6,
             disableServiceAuthCodes,
           );
-        } on dds.DartDevelopmentServiceException catch (e) {
+        } on dds.DartDevelopmentServiceException catch (e, st) {
           if (!allowExistingDdsInstance ||
               (e.errorCode != dds.DartDevelopmentServiceException.existingDdsInstanceError)) {
-            handleError(e);
+            handleError(e, st);
             return;
           } else {
             existingDds = true;
           }
-        } on Exception catch (e) {
-          handleError(e);
+        } on Exception catch (e, st) {
+          handleError(e, st);
           return;
         }
       }

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -2683,6 +2683,7 @@ void main() {
     when(mockDevice.getLogReader(app: anyNamed('app'))).thenReturn(mockLogReader);
     when(mockDevice.dds).thenReturn(mockDds);
     when(mockDds.startDartDevelopmentService(any, any, any, any)).thenThrow(FakeDartDevelopmentServiceException());
+    when(mockDds.uri).thenReturn(Uri.parse('http://localhost:1234'));
     when(mockDds.done).thenAnswer((_) => noopCompleter.future);
 
     final TestFlutterDevice flutterDevice = TestFlutterDevice(
@@ -2703,6 +2704,36 @@ void main() {
     }) async => mockVMService,
   }));
 
+  testUsingContext('Failed DDS start outputs error message', () => testbed.run(() async {
+    // See https://github.com/flutter/flutter/issues/72385 for context.
+    fakeVmServiceHost = FakeVmServiceHost(requests: <VmServiceExpectation>[]);
+    final MockDevice mockDevice = MockDevice();
+    when(mockDevice.dds).thenReturn(DartDevelopmentService(logger: testLogger));
+    ddsLauncherCallback = (Uri uri, {bool enableAuthCodes, bool ipv6, Uri serviceUri}) {
+      throw FakeDartDevelopmentServiceException(message: 'No URI');
+    };
+    final TestFlutterDevice flutterDevice = TestFlutterDevice(
+      mockDevice,
+      observatoryUris: Stream<Uri>.value(testUri),
+    );
+    bool caught = false;
+    final Completer<void>done = Completer<void>();
+    runZonedGuarded(() {
+      flutterDevice.connect(allowExistingDdsInstance: true).then((_) => done.complete());
+    }, (Object e, StackTrace st) {
+      expect(e is StateError, true);
+      expect((e as StateError).message, contains('No URI'));
+      expect(testLogger.errorText, contains(
+        'DDS has failed to start and there is not an existing DDS instance',
+      ));
+      done.complete();
+      caught = true;
+    });
+    await done.future;
+    if (!caught) {
+      fail('Expected a StateError to be thrown.');
+    }
+  }));
 
   testUsingContext('nextPlatform moves through expected platforms', () {
     expect(nextPlatform('android', TestFeatureFlags()), 'iOS');
@@ -2726,11 +2757,14 @@ class MockProcessManager extends Mock implements ProcessManager {}
 class MockResidentCompiler extends Mock implements ResidentCompiler {}
 
 class FakeDartDevelopmentServiceException implements dds.DartDevelopmentServiceException {
+  FakeDartDevelopmentServiceException({this.message = defaultMessage});
+
   @override
   final int errorCode = dds.DartDevelopmentServiceException.existingDdsInstanceError;
 
   @override
-  final String message = 'A DDS instance is already connected at http://localhost:8181';
+  final String message;
+  static const String defaultMessage = 'A DDS instance is already connected at http://localhost:8181';
 }
 
 class TestFlutterDevice extends FlutterDevice {