Delinting future awaits round 3 (#10791)

* round 3

* partially address comments

* merge

* review notes

* review

* review

* review

packages/flutter_tools/bin/fuchsia_builder.dart

@@ -42,7 +42,7 @@ const List<String> _kRequiredOptions = const <String>[
 Future<Null> main(List<String> args) async {
   final AppContext executableContext = new AppContext();
   executableContext.setVariable(Logger, new StdoutLogger());
-  executableContext.runInZone(() {
+  await executableContext.runInZone(() {
     // Initialize the context with some defaults.
     context.putIfAbsent(Platform, () => const LocalPlatform());
     context.putIfAbsent(FileSystem, () => const LocalFileSystem());

packages/flutter_tools/bin/fuchsia_tester.dart

@@ -38,7 +38,7 @@ const List<String> _kRequiredOptions = const <String>[
 Future<Null> main(List<String> args) async {
   final AppContext executableContext = new AppContext();
   executableContext.setVariable(Logger, new StdoutLogger());
-  executableContext.runInZone(() {
+  await executableContext.runInZone(() {
     // Initialize the context with some defaults.
     context.putIfAbsent(Platform, () => const LocalPlatform());
     context.putIfAbsent(FileSystem, () => const LocalFileSystem());

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

@@ -73,7 +73,7 @@ class LogsCommand extends FlutterCommand {
 
     // Wait for the log reader to be finished.
     final int result = await exitCompleter.future;
-    subscription.cancel();
+    await subscription.cancel();
     if (result != 0)
       throwToolExit('Error listening to $logReader logs.');
   }

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

@@ -340,7 +340,8 @@ class RunCommand extends RunCommandBase {
     //
     // Do not add more operations to the future.
     final Completer<Null> appStartedTimeRecorder = new Completer<Null>.sync();
-    appStartedTimeRecorder.future.then(
+    // This callback can't throw.
+    appStartedTimeRecorder.future.then( // ignore: unawaited_futures
       (_) { appStartedTime = clock.now(); }
     );
 

packages/flutter_tools/lib/src/devfs.dart

@@ -286,7 +286,8 @@ class _DevFSHttpWriter {
     } catch (e) {
       if (retry < kMaxRetries) {
         printTrace('Retrying writing "$deviceUri" to DevFS due to error: $e');
-        _scheduleWrite(deviceUri, content, retry + 1);
+        // Synchronization is handled by the _completer below.
+        _scheduleWrite(deviceUri, content, retry + 1); // ignore: unawaited_futures
         return;
       } else {
         printError('Error writing "$deviceUri" to DevFS: $e');

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

@@ -142,11 +142,12 @@ Future<String> getCodeSigningIdentityDevelopmentTeam({BuildableIOSApp iosApp, bo
       ..close();
 
   final String opensslOutput = await UTF8.decodeStream(opensslProcess.stdout);
-  opensslProcess.stderr.drain<String>();
+  // Fire and forget discard of the stderr stream so we don't hold onto resources.
+  // Don't care about the result.
+  opensslProcess.stderr.drain<String>(); // ignore: unawaited_futures
 
-  if (await opensslProcess.exitCode != 0) {
+  if (await opensslProcess.exitCode != 0)
     return null;
-  }
 
   return _certificateOrganizationalUnitExtractionPattern
       .firstMatch(opensslOutput)

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

@@ -237,7 +237,7 @@ class IOSSimulator extends Device {
   Future<bool> installApp(ApplicationPackage app) async {
     try {
       final IOSApp iosApp = app;
-      SimControl.instance.install(id, iosApp.simulatorBundlePath);
+      await SimControl.instance.install(id, iosApp.simulatorBundlePath);
       return true;
     } catch (e) {
       return false;
@@ -382,7 +382,7 @@ class IOSSimulator extends Device {
       printError('Error waiting for a debug connection: $error');
       return new LaunchResult.failed();
     } finally {
-      observatoryDiscovery.cancel();
+      await observatoryDiscovery.cancel();
     }
   }
 
@@ -556,7 +556,9 @@ class _IOSSimulatorLogReader extends DeviceLogReader {
       _systemProcess.stderr.transform(UTF8.decoder).transform(const LineSplitter()).listen(_onSystemLine);
     }
 
-    _deviceProcess.exitCode.whenComplete(() {
+    // We don't want to wait for the process or its callback. Best effort
+    // cleanup in the callback.
+    _deviceProcess.exitCode.whenComplete(() { // ignore: unawaited_futures
       if (_linesController.hasListener)
         _linesController.close();
     });

packages/flutter_tools/lib/src/resident_runner.dart

@@ -99,8 +99,10 @@ class FlutterDevice {
     if (flutterViews == null || flutterViews.isEmpty)
       return;
     for (FlutterView view in flutterViews) {
-      if (view != null && view.uiIsolate != null)
-        view.uiIsolate.flutterExit();
+      if (view != null && view.uiIsolate != null) {
+        // Manage waits specifically below.
+        view.uiIsolate.flutterExit(); // ignore: unawaited_futures
+      }
     }
     await new Future<Null>.delayed(const Duration(milliseconds: 100));
   }
@@ -563,8 +565,9 @@ abstract class ResidentRunner {
   }
 
   Future<Null> stopEchoingDeviceLog() async {
-    for (FlutterDevice device in flutterDevices)
-      device.stopEchoingDeviceLog();
+    await Future.wait(
+      flutterDevices.map((FlutterDevice device) => device.stopEchoingDeviceLog())
+    );
   }
 
   /// If the [reloadSources] parameter is not null the 'reloadSources' service
@@ -591,7 +594,10 @@ abstract class ResidentRunner {
     // Listen for service protocol connection to close.
     for (FlutterDevice device in flutterDevices) {
       for (VMService service in device.vmServices) {
-        service.done.then<Null>(
+        // This hooks up callbacks for when the connection stops in the future.
+        // We don't want to wait for them. We don't handle errors in those callbacks'
+        // futures either because they just print to logger and is not critical.
+        service.done.then<Null>( // ignore: unawaited_futures
           _serviceProtocolDone,
           onError: _serviceProtocolError
         ).whenComplete(_serviceDisconnected);

packages/flutter_tools/lib/src/test/coverage_collector.dart

@@ -42,7 +42,10 @@ class CoverageCollector extends TestWatcher {
 
     final int pid = process.pid;
     int exitCode;
-    process.exitCode.then<Null>((int code) {
+    // Synchronization is enforced by the API contract. Error handling
+    // synchronization is done in the code below where `exitCode` is checked.
+    // Callback cannot throw.
+    process.exitCode.then<Null>((int code) { // ignore: unawaited_futures
       exitCode = code;
     });
     if (exitCode != null)

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -153,7 +153,8 @@ class _FlutterPlatform extends PlatformPlugin {
     bool subprocessActive = false;
     bool controllerSinkClosed = false;
     try {
-      controller.sink.done.whenComplete(() { controllerSinkClosed = true; });
+      // Callback can't throw since it's just setting a variable.
+      controller.sink.done.whenComplete(() { controllerSinkClosed = true; }); // ignore: unawaited_futures
 
       // Prepare our WebSocket server to talk to the engine subproces.
       final HttpServer server = await HttpServer.bind(host, 0);
@@ -272,7 +273,8 @@ class _FlutterPlatform extends PlatformPlugin {
           subprocessActive = false;
           final String message = _getErrorMessage(_getExitCodeMessage(exitCode, 'before connecting to test harness'), testPath, shellPath);
           controller.sink.addError(message);
-          controller.sink.close();
+          // Awaited for with 'sink.done' below.
+          controller.sink.close(); // ignore: unawaited_futures
           printTrace('test $ourTestCount: waiting for controller sink to close');
           await controller.sink.done;
           break;
@@ -280,7 +282,8 @@ class _FlutterPlatform extends PlatformPlugin {
           printTrace('test $ourTestCount: timed out waiting for process with pid ${process.pid} to connect to test harness');
           final String message = _getErrorMessage('Test never connected to test harness.', testPath, shellPath);
           controller.sink.addError(message);
-          controller.sink.close();
+          // Awaited for with 'sink.done' below.
+          controller.sink.close(); // ignore: unawaited_futures
           printTrace('test $ourTestCount: waiting for controller sink to close');
           await controller.sink.done;
           break;
@@ -332,8 +335,10 @@ class _FlutterPlatform extends PlatformPlugin {
             testDone.future.then<_TestResult>((Null _) { return _TestResult.testBailed; }),
           ]);
 
-          harnessToTest.cancel();
-          testToHarness.cancel();
+          await Future.wait(<Future<Null>>[
+            harnessToTest.cancel(),
+            testToHarness.cancel(),
+          ]);
 
           switch (testResult) {
             case _TestResult.crashed:
@@ -342,7 +347,8 @@ class _FlutterPlatform extends PlatformPlugin {
               subprocessActive = false;
               final String message = _getErrorMessage(_getExitCodeMessage(exitCode, 'before test harness closed its WebSocket'), testPath, shellPath);
               controller.sink.addError(message);
-              controller.sink.close();
+              // Awaited for with 'sink.done' below.
+              controller.sink.close(); // ignore: unawaited_futures
               printTrace('test $ourTestCount: waiting for controller sink to close');
               await controller.sink.done;
               break;
@@ -384,7 +390,8 @@ class _FlutterPlatform extends PlatformPlugin {
         }
       }
       if (!controllerSinkClosed) {
-        controller.sink.close();
+        // Waiting below with await.
+        controller.sink.close(); // ignore: unawaited_futures
         printTrace('test $ourTestCount: waiting for controller sink to close');
         await controller.sink.done;
       }