[flutter_tool] Fix DesktopLogReader to capture all output (#88116)

packages/flutter_tools/lib/src/desktop_device.dart

@@ -308,9 +308,25 @@ class DesktopLogReader extends DeviceLogReader {
 
   /// Begin listening to the stdout and stderr streams of the provided [process].
   void initializeProcess(Process process) {
-    process.stdout.listen(_inputController.add);
-    process.stderr.listen(_inputController.add);
-    process.exitCode.whenComplete(_inputController.close);
+    final StreamSubscription<List<int>> stdoutSub = process.stdout.listen(
+      _inputController.add,
+    );
+    final StreamSubscription<List<int>> stderrSub = process.stderr.listen(
+      _inputController.add,
+    );
+    process.exitCode.whenComplete(() async {
+      // Wait for output to be fully processed.
+      await Future.wait<void>(<Future<void>>[
+        stdoutSub.asFuture<void>(),
+        stderrSub.asFuture<void>(),
+      ]);
+      // The streams as futures have already completed, so waiting for the
+      // potentially async stream cancellation to complete likely has no
+      // benefit.
+      unawaited(stdoutSub.cancel());
+      unawaited(stderrSub.cancel());
+      await _inputController.close();
+    });
   }
 
   @override

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

@@ -258,7 +258,7 @@ void main() {
       FakeCommand(
         command: const <String>['debug', 'arg1', 'arg2'],
         stdout: 'Observatory listening on http://127.0.0.1/0\n',
-        completer: completer
+        completer: completer,
       ),
     ]);
     final FakeDesktopDevice device = setUpDesktopDevice(processManager: processManager);
@@ -268,12 +268,49 @@ void main() {
       prebuiltApplication: true,
       debuggingOptions: DebuggingOptions.enabled(
         BuildInfo.debug,
-        dartEntrypointArgs: <String>['arg1', 'arg2']
+        dartEntrypointArgs: <String>['arg1', 'arg2'],
       ),
     );
 
     expect(result.started, true);
   });
+
+  testWithoutContext('Device logger captues all output', () async {
+    final Completer<void> exitCompleter = Completer<void>();
+    final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
+      FakeCommand(
+        command: const <String>['debug', 'arg1', 'arg2'],
+        exitCode: -1,
+        stderr: 'Oops\n',
+        completer: exitCompleter,
+        outputFollowsExit: true,
+      ),
+    ]);
+    final FakeDesktopDevice device = setUpDesktopDevice(
+      processManager: processManager,
+    );
+    final Completer<void> testCompleter = Completer<void>();
+    final List<String> logOutput = <String>[];
+    device.getLogReader().logLines.listen((String line) {
+      logOutput.add(line);
+    }, onDone: () {
+      expect(logOutput, contains('Oops'));
+      testCompleter.complete();
+    });
+    unawaited(Future<void>(() {
+      exitCompleter.complete();
+    }));
+    final FakeApplicationPackage package = FakeApplicationPackage();
+    await device.startApp(
+      package,
+      prebuiltApplication: true,
+      debuggingOptions: DebuggingOptions.enabled(
+        BuildInfo.debug,
+        dartEntrypointArgs: <String>['arg1', 'arg2'],
+      ),
+    );
+    await testCompleter.future;
+  });
 }
 
 FakeDesktopDevice setUpDesktopDevice({

packages/flutter_tools/test/general.shard/macos/macos_device_test.dart

@@ -62,8 +62,8 @@ void main() {
       processManager: FakeProcessManager.list(<FakeCommand>[
         FakeCommand(
           command: const <String>['release/executable'],
-          stdout: 'Hello World',
-          stderr: 'Goodnight, Moon',
+          stdout: 'Hello World\n',
+          stderr: 'Goodnight, Moon\n',
           completer: completer,
         )
       ]),
@@ -82,7 +82,7 @@ void main() {
 
     final DeviceLogReader logReader = device.getLogReader(app: package);
 
-    expect(logReader.logLines, emits('Hello WorldGoodnight, Moon'));
+    expect(logReader.logLines, emitsInAnyOrder(<String>['Hello World', 'Goodnight, Moon']));
     completer.complete();
   });
 

packages/flutter_tools/test/src/fake_process_manager.dart

@@ -32,6 +32,7 @@ class FakeCommand {
     this.completer,
     this.stdin,
     this.exception,
+    this.outputFollowsExit = false,
   }) : assert(command != null),
        assert(duration != null),
        assert(exitCode != null);
@@ -99,6 +100,10 @@ class FakeCommand {
   /// If provided, this exception will be thrown when the fake command is run.
   final Object? exception;
 
+  /// Indicates that output will only be emitted after the `exitCode` [Future]
+  /// on [io.Process] completes.
+  final bool outputFollowsExit;
+
   void _matches(
     List<String> command,
     String? workingDirectory,
@@ -127,19 +132,35 @@ class _FakeProcess implements io.Process {
     IOSink? stdin,
     this._stdout,
     this._completer,
+    bool outputFollowsExit,
   ) : exitCode = Future<void>.delayed(duration).then((void value) {
         if (_completer != null) {
           return _completer.future.then((void _) => _exitCode);
         }
         return _exitCode;
       }),
-      stdin = stdin ?? IOSink(StreamController<List<int>>().sink),
-      stderr = _stderr == null
-        ? const Stream<List<int>>.empty()
-        : Stream<List<int>>.value(utf8.encode(_stderr)),
-      stdout = _stdout == null
-        ? const Stream<List<int>>.empty()
-        : Stream<List<int>>.value(utf8.encode(_stdout));
+      stdin = stdin ?? IOSink(StreamController<List<int>>().sink)
+  {
+    if (_stderr == null) {
+      stderr = const Stream<List<int>>.empty();
+    } else if (outputFollowsExit) {
+      stderr = Stream<List<int>>.fromFuture(exitCode.then((_) {
+        return Future<List<int>>(() => utf8.encode(_stderr));
+      }));
+    } else {
+      stderr = Stream<List<int>>.value(utf8.encode(_stderr));
+    }
+
+    if (_stdout == null) {
+      stdout = const Stream<List<int>>.empty();
+    } else if (outputFollowsExit) {
+      stdout = Stream<List<int>>.fromFuture(exitCode.then((_) {
+        return Future<List<int>>(() => utf8.encode(_stdout));
+      }));
+    } else {
+      stdout = Stream<List<int>>.value(utf8.encode(_stdout));
+    }
+  }
 
   final int _exitCode;
   final Completer<void>? _completer;
@@ -153,13 +174,13 @@ class _FakeProcess implements io.Process {
   final String _stderr;
 
   @override
-  final Stream<List<int>> stderr;
+  late final Stream<List<int>> stderr;
 
   @override
   final IOSink stdin;
 
   @override
-  final Stream<List<int>> stdout;
+  late final Stream<List<int>> stdout;
 
   final String _stdout;
 
@@ -250,6 +271,7 @@ abstract class FakeProcessManager implements ProcessManager {
       fakeCommand.stdin,
       fakeCommand.stdout,
       fakeCommand.completer,
+      fakeCommand.outputFollowsExit,
     );
   }
 
@@ -350,6 +372,7 @@ class _FakeAnyProcessManager extends FakeProcessManager {
       exitCode: 0,
       stdout: '',
       stderr: '',
+      outputFollowsExit: false,
     );
   }