[flutter_tools] also listen to web stderr stream (#53949)

packages/flutter_tools/lib/src/build_runner/resident_web_runner.dart

@@ -107,6 +107,7 @@ abstract class ResidentWebRunner extends ResidentRunner {
 
   ConnectionResult _connectionResult;
   StreamSubscription<vmservice.Event> _stdOutSub;
+  StreamSubscription<vmservice.Event> _stdErrSub;
   bool _exited = false;
   WipConnection _wipConnection;
 
@@ -143,6 +144,7 @@ abstract class ResidentWebRunner extends ResidentRunner {
       return;
     }
     await _stdOutSub?.cancel();
+    await _stdErrSub?.cancel();
     await device.device.stopApp(null);
     try {
       _generatedEntrypointDirectory?.deleteSync(recursive: true);
@@ -652,16 +654,14 @@ class _ResidentWebRunner extends ResidentWebRunner {
       _connectionResult = await webDevFS.connect(useDebugExtension);
       unawaited(_connectionResult.debugConnection.onDone.whenComplete(_cleanupAndExit));
 
-      // Cleanup old subscriptions. These will throw if there isn't anything
-      // listening, which is fine because that is what we want to ensure.
       try {
-        await _vmService.streamCancel(vmservice.EventStreams.kStdout);
+        await _vmService.streamListen(vmservice.EventStreams.kStdout);
       } on vmservice.RPCError {
         // It is safe to ignore this error because we expect an error to be
         // thrown if we're not already subscribed.
       }
       try {
-        await _vmService.streamListen(vmservice.EventStreams.kStdout);
+        await _vmService.streamListen(vmservice.EventStreams.kStderr);
       } on vmservice.RPCError {
         // It is safe to ignore this error because we expect an error to be
         // thrown if we're not already subscribed.
@@ -674,7 +674,11 @@ class _ResidentWebRunner extends ResidentWebRunner {
       }
       _stdOutSub = _vmService.onStdoutEvent.listen((vmservice.Event log) {
         final String message = utf8.decode(base64.decode(log.bytes));
-        globals.printStatus(message);
+        globals.printStatus(message, newline: false);
+      });
+      _stdErrSub = _vmService.onStderrEvent.listen((vmservice.Event log) {
+        final String message = utf8.decode(base64.decode(log.bytes));
+        globals.printStatus(message, newline: false);
       });
       unawaited(_vmService.registerService('reloadSources', 'FlutterTools'));
       _vmService.registerServiceCallback('reloadSources', (Map<String, Object> params) async {

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

@@ -116,6 +116,9 @@ void main() {
     when(mockVmService.onStdoutEvent).thenAnswer((Invocation _) {
       return const Stream<Event>.empty();
     });
+    when(mockVmService.onStderrEvent).thenAnswer((Invocation _) {
+      return const Stream<Event>.empty();
+    });
     when(mockVmService.onDebugEvent).thenAnswer((Invocation _) {
       return const Stream<Event>.empty();
     });
@@ -249,20 +252,30 @@ void main() {
     expect(await residentWebRunner.run(), 0);
   }));
 
-  test('Listens to stdout streams before running main', () => testbed.run(() async {
+  test('Listens to stdout and stderr streams before running main', () => testbed.run(() async {
     _setupMocks();
     final Completer<DebugConnectionInfo> connectionInfoCompleter = Completer<DebugConnectionInfo>();
-    final StreamController<Event> controller = StreamController<Event>.broadcast();
+    final StreamController<Event> stdoutController = StreamController<Event>.broadcast();
+    final StreamController<Event> stderrController = StreamController<Event>.broadcast();
     when(mockVmService.onStdoutEvent).thenAnswer((Invocation _) {
-      return controller.stream;
+      return stdoutController.stream;
+    });
+    when(mockVmService.onStderrEvent).thenAnswer((Invocation _) {
+      return stderrController.stream;
     });
     when(mockAppConnection.runMain()).thenAnswer((Invocation invocation) {
-      controller.add(Event.parse(<String, Object>{
+      stdoutController.add(Event.parse(<String, Object>{
         'type': 'Event',
         'kind': 'WriteEvent',
         'timestamp': 1569473488296,
         'bytes': base64.encode('THIS MESSAGE IS IMPORTANT'.codeUnits),
       }));
+       stderrController.add(Event.parse(<String, Object>{
+        'type': 'Event',
+        'kind': 'WriteEvent',
+        'timestamp': 1569473488296,
+        'bytes': base64.encode('SO IS THIS'.codeUnits),
+      }));
     });
     unawaited(residentWebRunner.run(
       connectionInfoCompleter: connectionInfoCompleter,
@@ -270,6 +283,7 @@ void main() {
     await connectionInfoCompleter.future;
 
     expect(testLogger.statusText, contains('THIS MESSAGE IS IMPORTANT'));
+    expect(testLogger.statusText, contains('SO IS THIS'));
   }));
 
   test('Does not run main with --start-paused', () => testbed.run(() async {