Introduce the PipelineOwner tree (#122231)

Introduce the PipelineOwner tree

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

@@ -30,7 +30,6 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
     super.initInstances();
     _instance = this;
     _pipelineOwner = PipelineOwner(
-      onNeedVisualUpdate: ensureVisualUpdate,
       onSemanticsOwnerCreated: _handleSemanticsOwnerCreated,
       onSemanticsUpdate: _handleSemanticsUpdate,
       onSemanticsOwnerDisposed: _handleSemanticsOwnerDisposed,
@@ -45,8 +44,7 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
     if (kIsWeb) {
       addPostFrameCallback(_handleWebFirstFrame);
     }
-    addSemanticsEnabledListener(_handleSemanticsEnabledChanged);
-    _handleSemanticsEnabledChanged();
+    _pipelineOwner.attach(_manifold);
   }
 
   /// The current [RendererBinding], if one has been created.
@@ -201,6 +199,8 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
     }
   }
 
+  late final PipelineManifold _manifold = _BindingPipelineManifold(this);
+
   /// Creates a [RenderView] object to be the root of the
   /// [RenderObject] rendering tree, and initializes it so that it
   /// will be rendered when the next frame is requested.
@@ -330,17 +330,6 @@ mixin RendererBinding on BindingBase, ServicesBinding, SchedulerBinding, Gesture
     super.dispatchEvent(event, hitTestResult);
   }
 
-  SemanticsHandle? _semanticsHandle;
-
-  void _handleSemanticsEnabledChanged() {
-    if (semanticsEnabled) {
-      _semanticsHandle ??= _pipelineOwner.ensureSemantics();
-    } else {
-      _semanticsHandle?.dispose();
-      _semanticsHandle = null;
-    }
-  }
-
   @override
   void performSemanticsAction(SemanticsActionEvent action) {
     _pipelineOwner.semanticsOwner?.performAction(action.nodeId, action.type, action.arguments);
@@ -621,3 +610,26 @@ class RenderingFlutterBinding extends BindingBase with GestureBinding, Scheduler
     return RendererBinding.instance;
   }
 }
+
+/// A [PipelineManifold] implementation that is backed by the [RendererBinding].
+class _BindingPipelineManifold extends ChangeNotifier implements PipelineManifold {
+  _BindingPipelineManifold(this._binding) {
+    _binding.addSemanticsEnabledListener(notifyListeners);
+  }
+
+  final RendererBinding _binding;
+
+  @override
+  void requestVisualUpdate() {
+    _binding.ensureVisualUpdate();
+  }
+
+  @override
+  bool get semanticsEnabled => _binding.semanticsEnabled;
+
+  @override
+  void dispose() {
+    _binding.removeSemanticsEnabledListener(notifyListeners);
+    super.dispose();
+  }
+}

packages/flutter/test/rendering/binding_pipeline_manifold_init_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 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('Initializing the RendererBinding does not crash when semantics is enabled', () {
+    try {
+      MyRenderingFlutterBinding();
+    } catch (e) {
+      fail('Initializing the RenderingBinding threw an unexpected error:\n$e');
+    }
+    expect(RendererBinding.instance, isA<MyRenderingFlutterBinding>());
+    expect(SemanticsBinding.instance.semanticsEnabled, isTrue);
+  });
+}
+
+// Binding that pretends the platform had semantics enabled before the binding
+// is initialized.
+class MyRenderingFlutterBinding extends RenderingFlutterBinding {
+  @override
+  bool get semanticsEnabled => true;
+}

packages/flutter/test/rendering/binding_pipeline_manifold_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 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'rendering_tester.dart';
+
+void main() {
+  MyTestRenderingFlutterBinding.ensureInitialized();
+
+  tearDown(() {
+    final List<PipelineOwner> children = <PipelineOwner>[];
+    RendererBinding.instance.pipelineOwner.visitChildren((PipelineOwner child) {
+      children.add(child);
+    });
+    children.forEach(RendererBinding.instance.pipelineOwner.dropChild);
+  });
+
+  test("BindingPipelineManifold notifies binding if render object managed by binding's PipelineOwner tree needs visual update", () {
+    final PipelineOwner child = PipelineOwner();
+    RendererBinding.instance.pipelineOwner.adoptChild(child);
+
+    final RenderObject renderObject = TestRenderObject();
+    child.rootNode = renderObject;
+    renderObject.scheduleInitialLayout();
+    RendererBinding.instance.pipelineOwner.flushLayout();
+
+    MyTestRenderingFlutterBinding.instance.ensureVisualUpdateCount = 0;
+    renderObject.markNeedsLayout();
+    expect(MyTestRenderingFlutterBinding.instance.ensureVisualUpdateCount, 1);
+  });
+
+  test('Turning global semantics on/off creates semantics owners in PipelineOwner tree', () {
+    final PipelineOwner child = PipelineOwner(
+      onSemanticsUpdate: (_) { },
+    );
+    RendererBinding.instance.pipelineOwner.adoptChild(child);
+
+    expect(child.semanticsOwner, isNull);
+    expect(RendererBinding.instance.pipelineOwner.semanticsOwner, isNull);
+
+    final SemanticsHandle handle = SemanticsBinding.instance.ensureSemantics();
+
+    expect(child.semanticsOwner, isNotNull);
+    expect(RendererBinding.instance.pipelineOwner.semanticsOwner, isNotNull);
+
+    handle.dispose();
+
+    expect(child.semanticsOwner, isNull);
+    expect(RendererBinding.instance.pipelineOwner.semanticsOwner, isNull);
+  });
+}
+
+class MyTestRenderingFlutterBinding extends TestRenderingFlutterBinding {
+  static MyTestRenderingFlutterBinding get instance => BindingBase.checkInstance(_instance);
+  static MyTestRenderingFlutterBinding? _instance;
+
+  static MyTestRenderingFlutterBinding ensureInitialized() {
+    if (_instance != null) {
+      return _instance!;
+    }
+    return MyTestRenderingFlutterBinding();
+  }
+
+  @override
+  void initInstances() {
+    super.initInstances();
+    _instance = this;
+  }
+
+  int ensureVisualUpdateCount = 0;
+
+  @override
+  void ensureVisualUpdate() {
+    super.ensureVisualUpdate();
+    ensureVisualUpdateCount++;
+  }
+}
+
+class TestRenderObject extends RenderObject {
+  @override
+  void debugAssertDoesMeetConstraints() { }
+
+  @override
+  Rect get paintBounds => Rect.zero;
+
+  @override
+  void performLayout() { }
+
+  @override
+  void performResize() { }
+
+  @override
+  Rect get semanticBounds => Rect.zero;
+}

packages/flutter_test/lib/src/widget_tester.dart

@@ -1045,7 +1045,7 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
   void _verifySemanticsHandlesWereDisposed() {
     assert(_lastRecordedSemanticsHandles != null);
     // TODO(goderbauer): Fix known leak in web engine when running integration tests and remove this "correction", https://github.com/flutter/flutter/issues/121640.
-    final int knownWebEngineLeakForLiveTestsCorrection = kIsWeb && binding is LiveTestWidgetsFlutterBinding ? 2 : 0;
+    final int knownWebEngineLeakForLiveTestsCorrection = kIsWeb && binding is LiveTestWidgetsFlutterBinding ? 1 : 0;
 
     if (_currentSemanticsHandles - knownWebEngineLeakForLiveTestsCorrection > _lastRecordedSemanticsHandles!) {
       throw FlutterError.fromParts(<DiagnosticsNode>[