Allow writing startup_info.json to somewhere other than the build dir (#79338)

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

@@ -39,7 +39,10 @@ abstract class RunCommandBase extends FlutterCommand with DeviceBasedDevelopment
     argParser
       ..addFlag('trace-startup',
         negatable: false,
-        help: 'Trace application startup, then exit, saving the trace to a file.',
+        help: 'Trace application startup, then exit, saving the trace to a file. '
+              'By default, this will be saved in the "build" directory. If the '
+              'FLUTTER_TEST_OUTPUTS_DIR environment variable is set, the file '
+              'will be written there instead.',
       )
       ..addFlag('verbose-system-logs',
         negatable: false,

packages/flutter_tools/lib/src/run_cold.dart

@@ -18,6 +18,7 @@ import 'resident_runner.dart';
 import 'tracing.dart';
 import 'vmservice.dart';
 
+const String kFlutterTestOutputsDirEnvName = 'FLUTTER_TEST_OUTPUTS_DIR';
 class ColdRunner extends ResidentRunner {
   ColdRunner(
     List<FlutterDevice> devices, {
@@ -118,11 +119,12 @@ class ColdRunner extends ResidentRunner {
       final FlutterDevice device = flutterDevices.first;
       if (device.vmService != null) {
         globals.printStatus('Tracing startup on ${device.device.name}.');
+        final String outputPath = globals.platform.environment[kFlutterTestOutputsDirEnvName] ?? getBuildDirectory();
         await downloadStartupTrace(
           device.vmService,
           awaitFirstFrame: awaitFirstFrameWhenTracing,
           logger: globals.logger,
-          output: globals.fs.directory(getBuildDirectory()),
+          output: globals.fs.directory(outputPath),
         );
       }
       appFinished();

packages/flutter_tools/lib/src/tracing.dart

@@ -92,7 +92,7 @@ class Tracing {
 }
 
 /// Download the startup trace information from the given observatory client and
-/// store it to build/start_up_info.json.
+/// store it to `$output/start_up_info.json`.
 Future<void> downloadStartupTrace(FlutterVmService vmService, {
   bool awaitFirstFrame = true,
   @required Logger logger,

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

@@ -7,14 +7,17 @@
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
+import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/compile.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/resident_runner.dart';
 import 'package:flutter_tools/src/run_cold.dart';
+import 'package:flutter_tools/src/tracing.dart';
 import 'package:flutter_tools/src/vmservice.dart';
 import 'package:meta/meta.dart';
 import 'package:mockito/mockito.dart';
+import 'package:vm_service/vm_service.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
@@ -50,7 +53,6 @@ void main() {
   group('cleanupAtFinish()', () {
     MockFlutterDevice mockFlutterDeviceFactory(Device device) {
       final MockFlutterDevice mockFlutterDevice = MockFlutterDevice();
-      when(mockFlutterDevice.stopEchoingDeviceLog()).thenAnswer((Invocation invocation) => Future<void>.value(null));
       when(mockFlutterDevice.device).thenReturn(device);
       return mockFlutterDevice;
     }
@@ -69,13 +71,20 @@ void main() {
       ).cleanupAtFinish();
 
       verify(mockDevice1.dispose());
-      verify(mockFlutterDevice1.stopEchoingDeviceLog());
+      expect(mockFlutterDevice1.stopEchoingDeviceLogCount, 1);
       verify(mockDevice2.dispose());
-      verify(mockFlutterDevice2.stopEchoingDeviceLog());
+      expect(mockFlutterDevice2.stopEchoingDeviceLogCount, 1);
     });
   });
 
   group('cold run', () {
+    MemoryFileSystem memoryFileSystem;
+    FakePlatform fakePlatform;
+    setUp(() {
+      memoryFileSystem = MemoryFileSystem();
+      fakePlatform = FakePlatform(environment: <String, String>{});
+    });
+
     testUsingContext('calls runCold on attached device', () async {
       final MockDevice mockDevice = MockDevice();
       final MockFlutterDevice mockFlutterDevice = MockFlutterDevice();
@@ -101,10 +110,78 @@ void main() {
           route: anyNamed('route'),
       ));
     });
+
+    testUsingContext('with traceStartup, no env variable', () async {
+      final MockDevice mockDevice = MockDevice();
+      final MockFlutterDevice mockFlutterDevice = MockFlutterDevice();
+      when(mockFlutterDevice.device).thenReturn(mockDevice);
+      when(mockFlutterDevice.runCold(
+          coldRunner: anyNamed('coldRunner'),
+          route: anyNamed('route')
+      )).thenAnswer((Invocation invocation) => Future<int>.value(0));
+      final List<FlutterDevice> devices = <FlutterDevice>[mockFlutterDevice];
+      final File applicationBinary = MemoryFileSystem.test().file('binary');
+      final int result = await ColdRunner(
+        devices,
+        applicationBinary: applicationBinary,
+        debuggingOptions: DebuggingOptions.disabled(BuildInfo.debug),
+        target: 'main.dart',
+        traceStartup: true,
+      ).run(
+        enableDevTools: false,
+      );
+
+      expect(result, 0);
+      expect(memoryFileSystem.directory(getBuildDirectory()).childFile('start_up_info.json').existsSync(), true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => memoryFileSystem,
+      ProcessManager: () => FakeProcessManager.any(),
+      Platform: () => fakePlatform,
+    });
+
+    testUsingContext('with traceStartup, env variable', () async {
+      fakePlatform.environment[kFlutterTestOutputsDirEnvName] = 'test_output_dir';
+
+      final MockDevice mockDevice = MockDevice();
+      final MockFlutterDevice mockFlutterDevice = MockFlutterDevice();
+      when(mockFlutterDevice.device).thenReturn(mockDevice);
+      when(mockFlutterDevice.runCold(
+          coldRunner: anyNamed('coldRunner'),
+          route: anyNamed('route')
+      )).thenAnswer((Invocation invocation) => Future<int>.value(0));
+      final List<FlutterDevice> devices = <FlutterDevice>[mockFlutterDevice];
+      final File applicationBinary = MemoryFileSystem.test().file('binary');
+      final int result = await ColdRunner(
+        devices,
+        applicationBinary: applicationBinary,
+        debuggingOptions: DebuggingOptions.disabled(BuildInfo.debug),
+        target: 'main.dart',
+        traceStartup: true,
+      ).run(
+        enableDevTools: false,
+      );
+
+      expect(result, 0);
+      expect(memoryFileSystem.directory('test_output_dir').childFile('start_up_info.json').existsSync(), true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => memoryFileSystem,
+      ProcessManager: () => FakeProcessManager.any(),
+      Platform: () => fakePlatform,
+    });
   });
 }
 
-class MockFlutterDevice extends Mock implements FlutterDevice {}
+class MockFlutterDevice extends Mock implements FlutterDevice {
+  int stopEchoingDeviceLogCount = 0;
+
+  @override
+  Future<void> stopEchoingDeviceLog() async {
+    stopEchoingDeviceLogCount += 1;
+  }
+
+  @override
+  FlutterVmService get vmService => FakeFlutterVmService();
+}
 class MockDevice extends Mock implements Device {
   MockDevice() {
     when(isSupported()).thenReturn(true);
@@ -141,3 +218,51 @@ class TestFlutterDevice extends FlutterDevice {
 }
 
 class FakeResidentCompiler extends Fake implements ResidentCompiler {}
+
+class FakeFlutterVmService extends Fake implements FlutterVmService {
+  @override
+  VmService get service => FakeVmService();
+
+  @override
+  Future<List<FlutterView>> getFlutterViews({bool returnEarly = false, Duration delay = const Duration(milliseconds: 50)}) async {
+    return <FlutterView>[];
+  }
+
+  @override
+  Future<bool> flutterAlreadyPaintedFirstUsefulFrame({String isolateId}) async => true;
+
+  @override
+  Future<Response> getTimeline() async {
+    return Response.parse(<String, dynamic>{
+      'traceEvents': <dynamic>[
+        <String, dynamic>{
+          'name': kFlutterEngineMainEnterEventName,
+          'ts': 123,
+        },
+        <String, dynamic>{
+          'name': kFirstFrameBuiltEventName,
+          'ts': 124,
+        },
+        <String, dynamic>{
+          'name': kFirstFrameRasterizedEventName,
+          'ts': 124,
+        },
+      ],
+    });
+  }
+
+  @override
+  Future<void> setTimelineFlags(List<String> recordedStreams) async {}
+}
+
+class FakeVmService extends Fake implements VmService {
+  @override
+  Future<Success> streamListen(String streamId) async => Success();
+
+  @override
+  Stream<Event> get onExtensionEvent {
+    return Stream<Event>.fromIterable(<Event>[
+      Event(kind: 'Extension', extensionKind: 'Flutter.FirstFrame', timestamp: 1),
+    ]);
+  }
+}