Make Element tree root generic (#123352)

Make Element tree root generic

dev/benchmarks/microbenchmarks/lib/foundation/all_elements_bench.dart

@@ -56,19 +56,19 @@ Future<void> main() async {
 
   final Stopwatch watch = Stopwatch();
 
-  print('flutter_test allElements benchmark... (${WidgetsBinding.instance.renderViewElement})');
+  print('flutter_test allElements benchmark... (${WidgetsBinding.instance.rootElement})');
   // Make sure we get enough elements to process for consistent benchmark runs
-  int elementCount = collectAllElementsFrom(WidgetsBinding.instance.renderViewElement!, skipOffstage: false).length;
+  int elementCount = collectAllElementsFrom(WidgetsBinding.instance.rootElement!, skipOffstage: false).length;
   while (elementCount < 2458) {
     await Future<void>.delayed(Duration.zero);
-    elementCount = collectAllElementsFrom(WidgetsBinding.instance.renderViewElement!, skipOffstage: false).length;
+    elementCount = collectAllElementsFrom(WidgetsBinding.instance.rootElement!, skipOffstage: false).length;
   }
   print('element count: $elementCount');
 
   watch.start();
   for (int i = 0; i < _kNumIters; i += 1) {
     final List<Element> allElements = collectAllElementsFrom(
-      WidgetsBinding.instance.renderViewElement!,
+      WidgetsBinding.instance.rootElement!,
       skipOffstage: false,
     ).toList();
     allElements.clear();

dev/integration_tests/flutter_gallery/test/smoke_test.dart

@@ -78,7 +78,7 @@ Future<void> smokeDemo(WidgetTester tester, GalleryDemo demo) async {
 
   // Verify that the dumps are pretty.
   final String routeName = demo.routeName;
-  verifyToStringOutput('debugDumpApp', routeName, WidgetsBinding.instance.renderViewElement!.toStringDeep());
+  verifyToStringOutput('debugDumpApp', routeName, WidgetsBinding.instance.rootElement!.toStringDeep());
   verifyToStringOutput('debugDumpRenderTree', routeName, RendererBinding.instance.renderView.toStringDeep());
   verifyToStringOutput('debugDumpLayerTree', routeName, RendererBinding.instance.renderView.debugLayer?.toStringDeep() ?? '');
 

packages/flutter/lib/fix_data/fix_widgets/fix_widgets.yaml

@@ -23,6 +23,17 @@
 #     * ListWheelScrollView: fix_list_wheel_scroll_view.yaml
 version: 1
 transforms:
+  # Changes made in https://github.com/flutter/flutter/pull/123352
+  - title: "Migrate to 'rootElement'"
+    date: 2023-03-13
+    element:
+      uris: [ 'widgets.dart', 'material.dart', 'cupertino.dart' ]
+      field: 'renderViewElement'
+      inClass: 'WidgetsBinding'
+    changes:
+      - kind: 'rename'
+        newName: 'rootElement'
+
   # Changes made in https://github.com/flutter/flutter/pull/122555
   - title: "Migrate to 'decorationClipBehavior'"
     date: 2023-03-13

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

@@ -479,8 +479,8 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
   }
 
   Future<void> _forceRebuild() {
-    if (renderViewElement != null) {
-      buildOwner!.reassemble(renderViewElement!, null);
+    if (rootElement != null) {
+      buildOwner!.reassemble(rootElement!, null);
       return endOfFrame;
     }
     return Future<void>.value();
@@ -889,8 +889,8 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
     }
 
     try {
-      if (renderViewElement != null) {
-        buildOwner!.buildScope(renderViewElement!);
+      if (rootElement != null) {
+        buildOwner!.buildScope(rootElement!);
       }
       super.drawFrame();
       buildOwner!.finalizeTree();
@@ -914,12 +914,20 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
     }
   }
 
-  /// The [Element] that is at the root of the hierarchy (and which wraps the
-  /// [RenderView] object at the root of the rendering hierarchy).
+  /// The [Element] that is at the root of the element tree hierarchy.
   ///
   /// This is initialized the first time [runApp] is called.
-  Element? get renderViewElement => _renderViewElement;
-  Element? _renderViewElement;
+  Element? get rootElement => _rootElement;
+  Element? _rootElement;
+
+  /// Deprecated. Will be removed in a future version of Flutter.
+  ///
+  /// Use [rootElement] instead.
+  @Deprecated(
+    'Use rootElement instead. '
+    'This feature was deprecated after v3.9.0-16.0.pre.'
+  )
+  Element? get renderViewElement => rootElement;
 
   bool _readyToProduceFrames = false;
 
@@ -951,7 +959,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
     });
   }
 
-  /// Takes a widget and attaches it to the [renderViewElement], creating it if
+  /// Takes a widget and attaches it to the [rootElement], creating it if
   /// necessary.
   ///
   /// This is called by [runApp] to configure the widget tree.
@@ -961,23 +969,23 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
   ///  * [RenderObjectToWidgetAdapter.attachToRenderTree], which inflates a
   ///    widget and attaches it to the render tree.
   void attachRootWidget(Widget rootWidget) {
-    final bool isBootstrapFrame = renderViewElement == null;
+    final bool isBootstrapFrame = rootElement == null;
     _readyToProduceFrames = true;
-    _renderViewElement = RenderObjectToWidgetAdapter<RenderBox>(
+    _rootElement = RenderObjectToWidgetAdapter<RenderBox>(
       container: renderView,
       debugShortDescription: '[root]',
       child: rootWidget,
-    ).attachToRenderTree(buildOwner!, renderViewElement as RenderObjectToWidgetElement<RenderBox>?);
+    ).attachToRenderTree(buildOwner!, rootElement as RenderObjectToWidgetElement<RenderBox>?);
     if (isBootstrapFrame) {
       SchedulerBinding.instance.ensureVisualUpdate();
     }
   }
 
-  /// Whether the [renderViewElement] has been initialized.
+  /// Whether the [rootElement] has been initialized.
   ///
   /// This will be false until [runApp] is called (or [WidgetTester.pumpWidget]
   /// is called in the context of a [TestWidgetsFlutterBinding]).
-  bool get isRootWidgetAttached => _renderViewElement != null;
+  bool get isRootWidgetAttached => _rootElement != null;
 
   @override
   Future<void> performReassemble() {
@@ -986,8 +994,8 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
       return true;
     }());
 
-    if (renderViewElement != null) {
-      buildOwner!.reassemble(renderViewElement!, BindingBase.debugReassembleConfig);
+    if (rootElement != null) {
+      buildOwner!.reassemble(rootElement!, BindingBase.debugReassembleConfig);
     }
     return super.performReassemble();
   }
@@ -1069,8 +1077,8 @@ String _debugDumpAppString() {
   const String mode = kDebugMode ? 'DEBUG MODE' : kReleaseMode ? 'RELEASE MODE' : 'PROFILE MODE';
   final StringBuffer buffer = StringBuffer();
   buffer.writeln('${WidgetsBinding.instance.runtimeType} - $mode');
-  if (WidgetsBinding.instance.renderViewElement != null) {
-    buffer.writeln(WidgetsBinding.instance.renderViewElement!.toStringDeep());
+  if (WidgetsBinding.instance.rootElement != null) {
+    buffer.writeln(WidgetsBinding.instance.rootElement!.toStringDeep());
   } else {
     buffer.writeln('<no tree currently mounted>');
   }
@@ -1148,7 +1156,7 @@ class RenderObjectToWidgetAdapter<T extends RenderObject> extends RenderObjectWi
   String toStringShort() => debugShortDescription ?? super.toStringShort();
 }
 
-/// A [RootRenderObjectElement] that is hosted by a [RenderObject].
+/// The root of the element tree that is hosted by a [RenderObject].
 ///
 /// This element class is the instantiation of a [RenderObjectToWidgetAdapter]
 /// widget. It can be used only as the root of an [Element] tree (it cannot be
@@ -1158,7 +1166,7 @@ class RenderObjectToWidgetAdapter<T extends RenderObject> extends RenderObjectWi
 /// whose container is the [RenderView] that connects to the Flutter engine. In
 /// this usage, it is normally instantiated by the bootstrapping logic in the
 /// [WidgetsFlutterBinding] singleton created by [runApp].
-class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObjectElement {
+class RenderObjectToWidgetElement<T extends RenderObject> extends RenderObjectElement with RootElementMixin {
   /// Creates an element that is hosted by a [RenderObject].
   ///
   /// The [RenderObject] created by this element is not automatically set as a

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

@@ -2499,7 +2499,7 @@ abstract class BuildContext {
 /// Additional build owners can be built to manage off-screen widget trees.
 ///
 /// To assign a build owner to a tree, use the
-/// [RootRenderObjectElement.assignOwner] method on the root element of the
+/// [RootElementMixin.assignOwner] method on the root element of the
 /// widget tree.
 ///
 /// {@tool dartpad}
@@ -6323,14 +6323,29 @@ abstract class RenderObjectElement extends Element {
   }
 }
 
-/// The element at the root of the tree.
+/// Deprecated. Unused in the framework and will be removed in a future version
+/// of Flutter.
 ///
-/// Only root elements may have their owner set explicitly. All other
-/// elements inherit their owner from their parent.
-abstract class RootRenderObjectElement extends RenderObjectElement {
+/// Classes that extend this class can extend [RenderObjectElement] and mixin
+/// [RootElementMixin] instead.
+@Deprecated(
+  'Use RootElementMixin instead. '
+  'This feature was deprecated after v3.9.0-16.0.pre.'
+)
+abstract class RootRenderObjectElement extends RenderObjectElement with RootElementMixin {
   /// Initializes fields for subclasses.
+  @Deprecated(
+    'Use RootElementMixin instead. '
+    'This feature was deprecated after v3.9.0-16.0.pre.'
+  )
   RootRenderObjectElement(super.widget);
+}
 
+/// Mixin for the element at the root of the tree.
+///
+/// Only root elements may have their owner set explicitly. All other
+/// elements inherit their owner from their parent.
+mixin RootElementMixin on Element {
   /// Set the owner of the element. The owner will be propagated to all the
   /// descendants of this element.
   ///

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

@@ -914,8 +914,8 @@ mixin WidgetInspectorService {
   @protected
   Future<void> forceRebuild() {
     final WidgetsBinding binding = WidgetsBinding.instance;
-    if (binding.renderViewElement != null) {
-      binding.buildOwner!.reassemble(binding.renderViewElement!, null);
+    if (binding.rootElement != null) {
+      binding.buildOwner!.reassemble(binding.rootElement!, null);
       return binding.endOfFrame;
     }
     return Future<void>.value();
@@ -1832,7 +1832,7 @@ mixin WidgetInspectorService {
   }
 
   Map<String, Object?>? _getRootWidget(String groupName) {
-    return _nodeToJson(WidgetsBinding.instance.renderViewElement?.toDiagnosticsNode(), InspectorSerializationDelegate(groupName: groupName, service: this));
+    return _nodeToJson(WidgetsBinding.instance.rootElement?.toDiagnosticsNode(), InspectorSerializationDelegate(groupName: groupName, service: this));
   }
 
   /// Returns a JSON representation of the [DiagnosticsNode] for the root
@@ -1846,7 +1846,7 @@ mixin WidgetInspectorService {
     Map<String, Object>? Function(DiagnosticsNode, InspectorSerializationDelegate)? addAdditionalPropertiesCallback,
   }) {
     return _nodeToJson(
-      WidgetsBinding.instance.renderViewElement?.toDiagnosticsNode(),
+      WidgetsBinding.instance.rootElement?.toDiagnosticsNode(),
       InspectorSerializationDelegate(
         groupName: groupName,
         subtreeDepth: 1000000,

packages/flutter/test/widgets/fast_reassemble_test.dart

@@ -17,34 +17,34 @@ void main() {
     expect(Fizz.count, 0);
 
     DebugReassembleConfig config = DebugReassembleConfig(widgetName: 'Bar');
-    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.renderViewElement!, config);
+    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.rootElement!, config);
 
     expect(Foo.count, 0);
     expect(Bar.count, 1);
     expect(Fizz.count, 1);
 
     config = DebugReassembleConfig(widgetName: 'Fizz');
-    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.renderViewElement!, config);
+    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.rootElement!, config);
 
     expect(Foo.count, 0);
     expect(Bar.count, 1);
     expect(Fizz.count, 2);
 
     config = DebugReassembleConfig(widgetName: 'NoMatch');
-    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.renderViewElement!, config);
+    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.rootElement!, config);
 
     expect(Foo.count, 0);
     expect(Bar.count, 1);
     expect(Fizz.count, 2);
 
     config = DebugReassembleConfig();
-    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.renderViewElement!, config);
+    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.rootElement!, config);
 
     expect(Foo.count, 1);
     expect(Bar.count, 2);
     expect(Fizz.count, 3);
 
-    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.renderViewElement!, null);
+    WidgetsBinding.instance.buildOwner!.reassemble(WidgetsBinding.instance.rootElement!, null);
 
     expect(Foo.count, 2);
     expect(Bar.count, 3);

packages/flutter/test/widgets/memory_allocations_test.dart

@@ -58,7 +58,7 @@ class _TestLeafRenderObjectWidget extends LeafRenderObjectWidget {
   }
 }
 
-class _TestElement extends RootRenderObjectElement{
+class _TestElement extends RenderObjectElement with RootElementMixin {
   _TestElement(): super(_TestLeafRenderObjectWidget());
 
   void makeInactive() {

packages/flutter/test/widgets/run_app_async_test.dart

@@ -50,9 +50,9 @@ void main() {
         ),
       );
       // Rendering tree is not built synchronously.
-      expect(WidgetsBinding.instance.renderViewElement, isNull);
+      expect(WidgetsBinding.instance.rootElement, isNull);
       fakeAsync.flushTimers();
-      expect(WidgetsBinding.instance.renderViewElement, isNotNull);
+      expect(WidgetsBinding.instance.rootElement, isNotNull);
     });
   });
 }

packages/flutter/test/widgets/widget_inspector_test.dart

@@ -873,7 +873,7 @@ class _TestWidgetInspectorService extends TestWidgetInspectorService {
       final List<Object?> chainElements = jsonList! as List<Object?>;
       final List<Element> expectedChain = elementB.debugGetDiagnosticChain().reversed.toList();
       // Sanity check that the chain goes back to the root.
-      expect(expectedChain.first, tester.binding.renderViewElement);
+      expect(expectedChain.first, tester.binding.rootElement);
 
       expect(chainElements.length, equals(expectedChain.length));
       for (int i = 0; i < expectedChain.length; i += 1) {
@@ -2081,7 +2081,7 @@ class _TestWidgetInspectorService extends TestWidgetInspectorService {
       final List<Object?> chainElements = jsonList! as List<Object?>;
       final List<Element> expectedChain = elementB.debugGetDiagnosticChain().reversed.toList();
       // Sanity check that the chain goes back to the root.
-      expect(expectedChain.first, tester.binding.renderViewElement);
+      expect(expectedChain.first, tester.binding.rootElement);
 
       expect(chainElements.length, equals(expectedChain.length));
       for (int i = 0; i < expectedChain.length; i += 1) {
@@ -2327,7 +2327,7 @@ class _TestWidgetInspectorService extends TestWidgetInspectorService {
       // directories so we get an empty tree other than the root that is always
       // included.
       final Object? rootWidget = service.toObject(rootJson['valueId']! as String);
-      expect(rootWidget, equals(WidgetsBinding.instance.renderViewElement));
+      expect(rootWidget, equals(WidgetsBinding.instance.rootElement));
       List<Object?> childrenJson = rootJson['children']! as List<Object?>;
       // There are no summary tree children.
       expect(childrenJson.length, equals(0));

packages/flutter/test/widgets/widget_inspector_test_utils.dart

@@ -106,8 +106,8 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
     rebuildCount++;
     final WidgetsBinding binding = WidgetsBinding.instance;
 
-    if (binding.renderViewElement != null) {
-      binding.buildOwner!.reassemble(binding.renderViewElement!, null);
+    if (binding.rootElement != null) {
+      binding.buildOwner!.reassemble(binding.rootElement!, null);
     }
   }
 

packages/flutter/test_fixes/widgets/widgets.dart

@@ -12,6 +12,9 @@ void main() {
   Object object;
   TickerProvider vsync;
 
+  // Changes made in https://github.com/flutter/flutter/pull/123352
+  WidgetsBinding.instance.renderViewElement;
+
   // Changes made in https://github.com/flutter/flutter/pull/119647
   MediaQueryData.fromWindow(View.of(context));
 

packages/flutter/test_fixes/widgets/widgets.dart.expect

@@ -12,6 +12,9 @@ void main() {
   Object object;
   TickerProvider vsync;
 
+  // Changes made in https://github.com/flutter/flutter/pull/123352
+  WidgetsBinding.instance.rootElement;
+
   // Changes made in https://github.com/flutter/flutter/pull/119647
   MediaQueryData.fromView(View.of(context));
 

packages/flutter/test_release/widgets/memory_allocations_test.dart

@@ -55,7 +55,7 @@ class _TestRenderObject extends RenderObject {
   Rect get semanticBounds => throw UnimplementedError();
 }
 
-class _TestElement extends RootRenderObjectElement{
+class _TestElement extends RenderObjectElement with RootElementMixin {
   _TestElement(): super(_TestLeafRenderObjectWidget());
 
   void makeInactive() {

packages/flutter_test/lib/src/_matchers_web.dart

@@ -57,7 +57,7 @@ class MatchesGoldenFile extends AsyncMatcher {
     final RenderObject renderObject = _findRepaintBoundary(element);
     final Size size = renderObject.paintBounds.size;
     final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.instance;
-    final Element e = binding.renderViewElement!;
+    final Element e = binding.rootElement!;
     final ui.FlutterView view = binding.platformDispatcher.implicitView!;
 
     // Unlike `flutter_tester`, we don't have the ability to render an element

packages/flutter_test/lib/src/binding.dart

@@ -908,7 +908,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
       // directly called again.
       DiagnosticsNode treeDump;
       try {
-        treeDump = renderViewElement?.toDiagnosticsNode() ?? DiagnosticsNode.message('<no tree>');
+        treeDump = rootElement?.toDiagnosticsNode() ?? DiagnosticsNode.message('<no tree>');
         // We try to stringify the tree dump here (though we immediately discard the result) because
         // we want to make sure that if it can't be serialised, we replace it with a message that
         // says the tree could not be serialised. Otherwise, the real exception might get obscured
@@ -1372,7 +1372,7 @@ class AutomatedTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
     assert(inTest);
     try {
       debugBuildingDirtyElements = true;
-      buildOwner!.buildScope(renderViewElement!);
+      buildOwner!.buildScope(rootElement!);
       if (_phase != EnginePhase.build) {
         pipelineOwner.flushLayout();
         if (_phase != EnginePhase.layout) {

packages/flutter_test/lib/src/controller.dart

@@ -379,7 +379,7 @@ abstract class WidgetController {
   /// using [Iterator.moveNext].
   Iterable<Element> get allElements {
     TestAsyncUtils.guardSync();
-    return collectAllElementsFrom(binding.renderViewElement!, skipOffstage: false);
+    return collectAllElementsFrom(binding.rootElement!, skipOffstage: false);
   }
 
   /// The matching element in the widget tree.

packages/flutter_test/lib/src/finders.dart

@@ -493,7 +493,7 @@ abstract class Finder {
   @protected
   Iterable<Element> get allCandidates {
     return collectAllElementsFrom(
-      WidgetsBinding.instance.renderViewElement!,
+      WidgetsBinding.instance.rootElement!,
       skipOffstage: skipOffstage,
     );
   }

packages/flutter_test/lib/src/widget_tester.dart

@@ -750,7 +750,7 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
       'your widget tree in a RootRestorationScope?',
     );
     return TestAsyncUtils.guard<void>(() async {
-      final Widget widget = ((binding.renderViewElement! as RenderObjectToWidgetElement<RenderObject>).widget as RenderObjectToWidgetAdapter<RenderObject>).child!;
+      final Widget widget = ((binding.rootElement! as RenderObjectToWidgetElement<RenderObject>).widget as RenderObjectToWidgetAdapter<RenderObject>).child!;
       final TestRestorationData restorationData = binding.restorationManager.restorationData;
       runApp(Container(key: UniqueKey()));
       await pump();
@@ -863,7 +863,7 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
         .whereType<RenderObject>()
         .first;
       final Element? innerTargetElement = _lastWhereOrNull(
-        collectAllElementsFrom(binding.renderViewElement!, skipOffstage: true),
+        collectAllElementsFrom(binding.rootElement!, skipOffstage: true),
         (Element element) => element.renderObject == innerTarget,
       );
       if (innerTargetElement == null) {