Assert that runApp is called in the same zone as binding.ensureInitialized (#122836)

Assert that runApp is called in the same zone as binding.ensureInitialized

dev/tracing_tests/test/common.dart

@@ -5,7 +5,9 @@
 import 'dart:developer' as developer;
 import 'dart:isolate' as isolate;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:vm_service/vm_service.dart';
 import 'package:vm_service/vm_service_io.dart';
@@ -52,3 +54,29 @@ Future<void> runFrame(VoidCallback callback) {
   callback();
   return result;
 }
+
+// This binding skips the zones tests. These tests were written before we
+// verified zones properly, and they have been legacied-in to avoid having
+// to refactor them.
+//
+// When creating new tests, avoid relying on this class.
+class ZoneIgnoringTestBinding extends WidgetsFlutterBinding {
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+  }
+
+  @override
+  bool debugCheckZone(String entryPoint) { return true; }
+
+  static ZoneIgnoringTestBinding get instance => BindingBase.checkInstance(_instance);
+  static ZoneIgnoringTestBinding? _instance;
+
+  static ZoneIgnoringTestBinding ensureInitialized() {
+    if (ZoneIgnoringTestBinding._instance == null) {
+      ZoneIgnoringTestBinding();
+    }
+    return ZoneIgnoringTestBinding.instance;
+  }
+}

dev/tracing_tests/test/image_painting_event_test.dart

@@ -13,6 +13,8 @@ import 'package:vm_service/vm_service.dart';
 import 'package:vm_service/vm_service_io.dart';
 
 void main() {
+  LiveTestWidgetsFlutterBinding.ensureInitialized();
+
   late VmService vmService;
   late LiveTestWidgetsFlutterBinding binding;
   setUpAll(() async {
@@ -27,7 +29,7 @@ void main() {
     await vmService.streamListen(EventStreams.kExtension);
 
     // Initialize bindings
-    binding = LiveTestWidgetsFlutterBinding();
+    binding = LiveTestWidgetsFlutterBinding.instance;
     binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
     binding.attachRootWidget(const SizedBox.expand());
     expect(binding.framesEnabled, true);

dev/tracing_tests/test/inflate_widget_tracing_test.dart

@@ -16,7 +16,7 @@ final Set<String> interestingLabels = <String>{
 };
 
 void main() {
-  WidgetsFlutterBinding.ensureInitialized();
+  ZoneIgnoringTestBinding.ensureInitialized();
   initTimelineTests();
   test('Children of MultiChildRenderObjectElement show up in tracing', () async {
     // We don't have expectations around the first frame because there's a race around

dev/tracing_tests/test/inflate_widget_update_test.dart

@@ -9,7 +9,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'common.dart';
 
 void main() {
-  WidgetsFlutterBinding.ensureInitialized();
+  ZoneIgnoringTestBinding.ensureInitialized();
   initTimelineTests();
   test('Widgets with updated keys produce well formed timelines', () async {
     await runFrame(() { runApp(const TestRoot()); });

dev/tracing_tests/test/timeline_test.dart

@@ -58,7 +58,7 @@ class TestRootState extends State<TestRoot> {
 }
 
 void main() {
-  WidgetsFlutterBinding.ensureInitialized();
+  ZoneIgnoringTestBinding.ensureInitialized();
   initTimelineTests();
   test('Timeline', () async {
     // We don't have expectations around the first frame because there's a race around

packages/flutter/lib/src/foundation/binding.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:convert' show json;
 import 'dart:developer' as developer;
 import 'dart:io' show exit;
@@ -265,6 +266,7 @@ abstract class BindingBase {
     assert(_debugInitializedType == null);
     assert(() {
       _debugInitializedType = runtimeType;
+      _debugBindingZone = Zone.current;
       return true;
     }());
   }
@@ -319,7 +321,7 @@ abstract class BindingBase {
           ),
           ErrorHint(
             'It is also possible that $T does not implement "initInstances()" to assign a value to "instance". See the '
-            'documentation of the BaseBinding class for more details.',
+            'documentation of the BindingBase class for more details.',
           ),
           ErrorHint(
             'The binding that was initialized was of the type "$_debugInitializedType". '
@@ -399,6 +401,95 @@ abstract class BindingBase {
     return _debugInitializedType;
   }
 
+  Zone? _debugBindingZone;
+
+  /// Whether [debugCheckZone] should throw (true) or just report the error (false).
+  ///
+  /// Setting this to true makes it easier to catch cases where the zones are
+  /// misconfigured, by allowing debuggers to stop at the point of error.
+  ///
+  /// Currently this defaults to false, to avoid suddenly breaking applications
+  /// that are affected by this check but appear to be working today. Applications
+  /// are encouraged to resolve any issues that cause the [debugCheckZone] message
+  /// to appear, as even if they appear to be working today, they are likely to be
+  /// hiding hard-to-find bugs, and are more brittle (likely to collect bugs in
+  /// the future).
+  ///
+  /// To silence the message displayed by [debugCheckZone], ensure that the same
+  /// zone is used when calling `ensureInitialized()` as when calling the framework
+  /// in any other context (e.g. via [runApp]).
+  static bool debugZoneErrorsAreFatal = false;
+
+  /// Checks that the current [Zone] is the same as that which was used
+  /// to initialize the binding.
+  ///
+  /// If the current zone ([Zone.current]) is not the zone that was active when
+  /// the binding was initialized, then this method generates a [FlutterError]
+  /// exception with detailed information. The exception is either thrown
+  /// directly, or reported via [FlutterError.reportError], depending on the
+  /// value of [BindingBase.debugZoneErrorsAreFatal].
+  ///
+  /// To silence the message displayed by [debugCheckZone], ensure that the same
+  /// zone is used when calling `ensureInitialized()` as when calling the
+  /// framework in any other context (e.g. via [runApp]). For example, consider
+  /// keeping a reference to the zone used to initialize the binding, and using
+  /// [Zone.run] to use it again when calling into the framework.
+  ///
+  /// ## Usage
+  ///
+  /// The binding is considered initialized once [BindingBase.initInstances] has
+  /// run; if this is called before then, it will throw an [AssertionError].
+  ///
+  /// The `entryPoint` parameter is the name of the API that is checking the
+  /// zones are consistent, for example, `'runApp'`.
+  ///
+  /// This function always returns true (if it does not throw). It is expected
+  /// to be invoked via the binding instance, e.g.:
+  ///
+  /// ```dart
+  /// void startup() {
+  ///   WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
+  ///   assert(binding.debugCheckZone('startup'));
+  ///   // ...
+  /// }
+  /// ```
+  ///
+  /// If the binding expects to be used with multiple zones, it should override
+  /// this method to return true always without throwing. (For example, the
+  /// bindings used with [flutter_test] do this as they make heavy use of zones
+  /// to drive the framework with an artificial clock and to catch errors and
+  /// report them as test failures.)
+  bool debugCheckZone(String entryPoint) {
+    assert(() {
+      assert(_debugBindingZone != null, 'debugCheckZone can only be used after the binding is fully initialized.');
+      if (Zone.current != _debugBindingZone) {
+        final Error message = FlutterError(
+          'Zone mismatch.\n'
+          'The Flutter bindings were initialized in a different zone than is now being used. '
+          'This will likely cause confusion and bugs as any zone-specific configuration will '
+          'inconsistently use the configuration of the original binding initialization zone '
+          'or this zone based on hard-to-predict factors such as which zone was active when '
+          'a particular callback was set.\n'
+          'It is important to use the same zone when calling `ensureInitialized` on the binding '
+          'as when calling `$entryPoint` later.\n'
+          'To make this ${ debugZoneErrorsAreFatal ? 'error non-fatal' : 'warning fatal' }, '
+          'set BindingBase.debugZoneErrorsAreFatal to ${!debugZoneErrorsAreFatal} before the '
+          'bindings are initialized (i.e. as the first statement in `void main() { }`).',
+        );
+        if (debugZoneErrorsAreFatal) {
+          throw message;
+        }
+        FlutterError.reportError(FlutterErrorDetails(
+          exception: message,
+          stack: StackTrace.current,
+          context: ErrorDescription('during $entryPoint'),
+        ));
+      }
+      return true;
+    }());
+    return true;
+  }
+
   /// Called when the binding is initialized, to register service
   /// extensions.
   ///

packages/flutter/lib/src/widgets/binding.dart

@@ -1031,6 +1031,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
 ///    ensure the widget, element, and render trees are all built.
 void runApp(Widget app) {
   final WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
+  assert(binding.debugCheckZone('runApp'));
   binding
     ..scheduleAttachRootWidget(binding.wrapWithDefaultView(app))
     ..scheduleWarmUpFrame();

packages/flutter/test/foundation/binding_2_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+class TestBinding extends BindingBase { }
+
+void main() {
+  test('BindingBase.debugCheckZone', () async {
+    final BindingBase binding = TestBinding();
+    binding.debugCheckZone('test1');
+    BindingBase.debugZoneErrorsAreFatal = true;
+    Zone.current.fork().run(() {
+      try {
+        binding.debugCheckZone('test2');
+        fail('expected an exception');
+      } catch (error) {
+        expect(error, isA<FlutterError>());
+        expect(error.toString(),
+          'Zone mismatch.\n'
+          'The Flutter bindings were initialized in a different zone than is now being used. '
+          'This will likely cause confusion and bugs as any zone-specific configuration will '
+          'inconsistently use the configuration of the original binding initialization zone '
+          'or this zone based on hard-to-predict factors such as which zone was active when '
+          'a particular callback was set.\n'
+          'It is important to use the same zone when calling `ensureInitialized` on the '
+          'binding as when calling `test2` later.\n'
+          'To make this error non-fatal, set BindingBase.debugZoneErrorsAreFatal to false '
+          'before the bindings are initialized (i.e. as the first statement in `void main() { }`).',
+        );
+      }
+    });
+    BindingBase.debugZoneErrorsAreFatal = false;
+    Zone.current.fork().run(() {
+      bool sawError = false;
+      final FlutterExceptionHandler? lastHandler = FlutterError.onError;
+      FlutterError.onError = (FlutterErrorDetails details) {
+        final Object error = details.exception;
+        expect(error, isA<FlutterError>());
+        expect(error.toString(),
+          'Zone mismatch.\n'
+          'The Flutter bindings were initialized in a different zone than is now being used. '
+          'This will likely cause confusion and bugs as any zone-specific configuration will '
+          'inconsistently use the configuration of the original binding initialization zone '
+          'or this zone based on hard-to-predict factors such as which zone was active when '
+          'a particular callback was set.\n'
+          'It is important to use the same zone when calling `ensureInitialized` on the '
+          'binding as when calling `test3` later.\n'
+          'To make this warning fatal, set BindingBase.debugZoneErrorsAreFatal to true '
+          'before the bindings are initialized (i.e. as the first statement in `void main() { }`).',
+        );
+        sawError = true;
+      };
+      binding.debugCheckZone('test3');
+      expect(sawError, isTrue);
+      FlutterError.onError = lastHandler;
+    });
+  });
+}

packages/flutter/test/foundation/binding_test.dart

@@ -27,7 +27,6 @@ class FooLibraryBinding extends BindingBase with FooBinding {
   }
 }
 
-
 void main() {
   test('BindingBase.debugBindingType', () async {
     expect(BindingBase.debugBindingType(), isNull);

packages/flutter/test/painting/binding_test.dart

@@ -47,6 +47,9 @@ class TestBindingBase implements BindingBase {
   @override
   void initInstances() {}
 
+  @override
+  bool debugCheckZone(String entryPoint) { return true; }
+
   @override
   void initServiceExtensions() {}
 

packages/flutter/test/widgets/run_app_async_test.dart

@@ -3,12 +3,39 @@
 // found in the LICENSE file.
 
 import 'package:fake_async/fake_async.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+// This test is very fragile and bypasses some zone-related checks.
+// It is written this way to verify some invariants that would otherwise
+// be difficult to check.
+// Do not use this test as a guide for writing good Flutter code.
+
+class TestBinding extends WidgetsFlutterBinding {
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+  }
+
+  @override
+  bool debugCheckZone(String entryPoint) { return true; }
+
+  static TestBinding get instance => BindingBase.checkInstance(_instance);
+  static TestBinding? _instance;
+
+  static TestBinding ensureInitialized() {
+    if (TestBinding._instance == null) {
+      TestBinding();
+    }
+    return TestBinding.instance;
+  }
+}
+
 void main() {
   setUp(() {
-    WidgetsFlutterBinding.ensureInitialized();
+    TestBinding.ensureInitialized();
     WidgetsBinding.instance.resetEpoch();
   });
 

packages/flutter_driver/lib/src/extension/extension.dart

@@ -39,6 +39,11 @@ class _DriverBinding extends BindingBase with SchedulerBinding, ServicesBinding,
   final List<FinderExtension>? finders;
   final List<CommandExtension>? commands;
 
+  // Because you can't really control which zone a driver test uses,
+  // we override the test for zones here.
+  @override
+  bool debugCheckZone(String entryPoint) { return true; }
+
   @override
   void initServiceExtensions() {
     super.initServiceExtensions();

packages/flutter_test/lib/src/binding.dart

@@ -369,6 +369,13 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     // doesn't get generated for tests.
   }
 
+  @override
+  bool debugCheckZone(String entryPoint) {
+    // We skip all the zone checks in tests because the test framework makes heavy use
+    // of zones and so the zones never quite match the way the framework expects.
+    return true;
+  }
+
   /// Whether there is currently a test executing.
   bool get inTest;
 
@@ -815,9 +822,9 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
     };
     FlutterError.demangleStackTrace = (StackTrace stack) {
       // package:stack_trace uses ZoneSpecification.errorCallback to add useful
-      // information to stack traces, in this case the Trace and Chain classes
-      // can be present. Because these StackTrace implementations do not follow
-      // the format the framework expects, we covert them to a vm trace here.
+      // information to stack traces, meaning Trace and Chain classes can be
+      // present. Because these StackTrace implementations do not follow the
+      // format the framework expects, we convert them to a vm trace here.
       if (stack is stack_trace.Trace) {
         return stack.vmTrace;
       }

packages/flutter_test/test/live_widget_controller_test.dart

@@ -2,11 +2,38 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+// This test is very fragile and bypasses some zone-related checks.
+// It is written this way to verify some invariants that would otherwise
+// be difficult to check.
+// Do not use this test as a guide for writing good Flutter code.
+
+class TestBinding extends WidgetsFlutterBinding {
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+  }
+
+  @override
+  bool debugCheckZone(String entryPoint) { return true; }
+
+  static TestBinding get instance => BindingBase.checkInstance(_instance);
+  static TestBinding? _instance;
+
+  static TestBinding ensureInitialized() {
+    if (TestBinding._instance == null) {
+      TestBinding();
+    }
+    return TestBinding.instance;
+  }
+}
+
 class CountButton extends StatefulWidget {
   const CountButton({super.key});
 
@@ -65,6 +92,8 @@ class _AnimateSampleState extends State<AnimateSample>
 }
 
 void main() {
+  TestBinding.ensureInitialized();
+
   test('Test pump on LiveWidgetController', () async {
     runApp(const MaterialApp(home: Center(child: CountButton())));
 
@@ -109,7 +138,7 @@ void main() {
     final List<PointerEventRecord> records = <PointerEventRecord>[
       PointerEventRecord(Duration.zero, <PointerEvent>[
         // Typically PointerAddedEvent is not used in testers, but for records
-        // captured on a device it is usually what start a gesture.
+        // captured on a device it is usually what starts a gesture.
         PointerAddedEvent(
           position: location,
         ),