Inline AbstractNode into SemanticsNode and Layer (#128467)

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

@@ -136,7 +136,7 @@ const String _flutterRenderingLibrary = 'package:flutter/rendering.dart';
 ///
 ///  * [RenderView.compositeFrame], which implements this recomposition protocol
 ///    for painting [RenderObject] trees on the display.
-abstract class Layer extends AbstractNode with DiagnosticableTreeMixin {
+abstract class Layer with DiagnosticableTreeMixin {
   /// Creates an instance of Layer.
   Layer() {
     if (kFlutterMemoryAllocationsEnabled) {
@@ -344,8 +344,8 @@ abstract class Layer extends AbstractNode with DiagnosticableTreeMixin {
   ///
   /// Only subclasses of [ContainerLayer] can have children in the layer tree.
   /// All other layer classes are used for leaves in the layer tree.
-  @override
-  ContainerLayer? get parent => super.parent as ContainerLayer?;
+  ContainerLayer? get parent => _parent;
+  ContainerLayer? _parent;
 
   // Whether this layer has any changes since its last call to [addToScene].
   //
@@ -495,6 +495,71 @@ abstract class Layer extends AbstractNode with DiagnosticableTreeMixin {
     _needsAddToScene = _needsAddToScene || alwaysNeedsAddToScene;
   }
 
+  /// The owner for this node (null if unattached).
+  ///
+  /// The entire subtree that this node belongs to will have the same owner.
+  Object? get owner => _owner;
+  Object? _owner;
+
+  /// Whether this node is in a tree whose root is attached to something.
+  ///
+  /// This becomes true during the call to [attach].
+  ///
+  /// This becomes false during the call to [detach].
+  bool get attached => _owner != null;
+
+  /// Mark this node as attached to the given owner.
+  ///
+  /// Typically called only from the [parent]'s [attach] method, and by the
+  /// [owner] to mark the root of a tree as attached.
+  ///
+  /// Subclasses with children should override this method to first call their
+  /// inherited [attach] method, and then [attach] all their children to the
+  /// same [owner].
+  ///
+  /// Implementations of this method should start with a call to the inherited
+  /// method, as in `super.attach(owner)`.
+  @mustCallSuper
+  void attach(covariant Object owner) {
+    assert(_owner == null);
+    _owner = owner;
+  }
+
+  /// Mark this node as detached.
+  ///
+  /// Typically called only from the [parent]'s [detach], and by the [owner] to
+  /// mark the root of a tree as detached.
+  ///
+  /// Subclasses with children should override this method to first call their
+  /// inherited [detach] method, and then [detach] all their children.
+  ///
+  /// Implementations of this method should end with a call to the inherited
+  /// method, as in `super.detach()`.
+  @mustCallSuper
+  void detach() {
+    assert(_owner != null);
+    _owner = null;
+    assert(parent == null || attached == parent!.attached);
+  }
+
+  /// The depth of this node in the tree.
+  ///
+  /// The depth of nodes in a tree monotonically increases as you traverse down
+  /// the tree.
+  int get depth => _depth;
+  int _depth = 0;
+
+  /// Adjust the [depth] of this node's children, if any.
+  ///
+  /// Override this method in subclasses with child nodes to call
+  /// [ContainerLayer.redepthChild] for each child. Do not call this method
+  /// directly.
+  @protected
+  void redepthChildren() {
+    // ContainerLayer provides an implementation since its the only one that
+    // can actually have children.
+  }
+
   /// This layer's next sibling in the parent layer's child list.
   Layer? get nextSibling => _nextSibling;
   Layer? _nextSibling;
@@ -503,30 +568,6 @@ abstract class Layer extends AbstractNode with DiagnosticableTreeMixin {
   Layer? get previousSibling => _previousSibling;
   Layer? _previousSibling;
 
-  @override
-  void dropChild(Layer child) {
-    assert(!_debugMutationsLocked);
-    if (!alwaysNeedsAddToScene) {
-      markNeedsAddToScene();
-    }
-    if (child._compositionCallbackCount != 0) {
-      _updateSubtreeCompositionObserverCount(-child._compositionCallbackCount);
-    }
-    super.dropChild(child);
-  }
-
-  @override
-  void adoptChild(Layer child) {
-    assert(!_debugMutationsLocked);
-    if (!alwaysNeedsAddToScene) {
-      markNeedsAddToScene();
-    }
-    if (child._compositionCallbackCount != 0) {
-      _updateSubtreeCompositionObserverCount(child._compositionCallbackCount);
-    }
-    super.adoptChild(child);
-  }
-
   /// Removes this layer from its parent layer's child list.
   ///
   /// This has no effect if the layer's parent is already null.
@@ -1198,7 +1239,7 @@ class ContainerLayer extends Layer {
       assert(node != child); // indicates we are about to create a cycle
       return true;
     }());
-    adoptChild(child);
+    _adoptChild(child);
     child._previousSibling = lastChild;
     if (lastChild != null) {
       lastChild!._nextSibling = child;
@@ -1209,6 +1250,52 @@ class ContainerLayer extends Layer {
     assert(child.attached == attached);
   }
 
+  void _adoptChild(Layer child) {
+    assert(!_debugMutationsLocked);
+    if (!alwaysNeedsAddToScene) {
+      markNeedsAddToScene();
+    }
+    if (child._compositionCallbackCount != 0) {
+      _updateSubtreeCompositionObserverCount(child._compositionCallbackCount);
+    }
+    assert(child._parent == null);
+    assert(() {
+      Layer node = this;
+      while (node.parent != null) {
+        node = node.parent!;
+      }
+      assert(node != child); // indicates we are about to create a cycle
+      return true;
+    }());
+    child._parent = this;
+    if (attached) {
+      child.attach(_owner!);
+    }
+    redepthChild(child);
+  }
+
+  @override
+  void redepthChildren() {
+    Layer? child = firstChild;
+    while (child != null) {
+      redepthChild(child);
+      child = child.nextSibling;
+    }
+  }
+
+  /// Adjust the [depth] of the given [child] to be greater than this node's own
+  /// [depth].
+  ///
+  /// Only call this method from overrides of [redepthChildren].
+  @protected
+  void redepthChild(Layer child) {
+    assert(child.owner == owner);
+    if (child._depth <= _depth) {
+      child._depth = _depth + 1;
+      child.redepthChildren();
+    }
+  }
+
   // Implementation of [Layer.remove].
   void _removeChild(Layer child) {
     assert(child.parent == this);
@@ -1235,11 +1322,27 @@ class ContainerLayer extends Layer {
     assert(lastChild == null || _debugUltimatePreviousSiblingOf(lastChild!, equals: firstChild));
     child._previousSibling = null;
     child._nextSibling = null;
-    dropChild(child);
+    _dropChild(child);
     child._parentHandle.layer = null;
     assert(!child.attached);
   }
 
+  void _dropChild(Layer child) {
+    assert(!_debugMutationsLocked);
+    if (!alwaysNeedsAddToScene) {
+      markNeedsAddToScene();
+    }
+    if (child._compositionCallbackCount != 0) {
+      _updateSubtreeCompositionObserverCount(-child._compositionCallbackCount);
+    }
+    assert(child._parent == this);
+    assert(child.attached == attached);
+    child._parent = null;
+    if (attached) {
+      child.detach();
+    }
+  }
+
   /// Removes all of this layer's children from its child list.
   void removeAllChildren() {
     assert(!_debugMutationsLocked);
@@ -1249,7 +1352,7 @@ class ContainerLayer extends Layer {
       child._previousSibling = null;
       child._nextSibling = null;
       assert(child.attached == attached);
-      dropChild(child);
+      _dropChild(child);
       child._parentHandle.layer = null;
       child = next;
     }

packages/flutter/lib/src/semantics/semantics.dart

@@ -1646,7 +1646,7 @@ void debugResetSemanticsIdCounter() {
 /// (i.e., during [PipelineOwner.flushSemantics]), which happens after
 /// compositing. The semantics tree is then uploaded into the engine for use
 /// by assistive technology.
-class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
+class SemanticsNode with DiagnosticableTreeMixin {
   /// Creates a semantic node.
   ///
   /// Each semantic node has a unique identifier that is assigned when the node
@@ -1923,7 +1923,7 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
           if (child.parent == this) {
             // we might have already had our child stolen from us by
             // another node that is deeper in the tree.
-            dropChild(child);
+            _dropChild(child);
           }
           sawChange = true;
         }
@@ -1937,10 +1937,10 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
           // ancestors. In that case, we drop the child eagerly here.
           // TODO(ianh): Find a way to assert that the same node didn't
           // actually appear in the tree in two places.
-          child.parent?.dropChild(child);
+          child.parent?._dropChild(child);
         }
         assert(!child.attached);
-        adoptChild(child);
+        _adoptChild(child);
         sawChange = true;
       }
     }
@@ -1998,22 +1998,73 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
     return true;
   }
 
-  // AbstractNode OVERRIDES
+  /// The owner for this node (null if unattached).
+  ///
+  /// The entire subtree that this node belongs to will have the same owner.
+  SemanticsOwner? get owner => _owner;
+  SemanticsOwner? _owner;
 
-  @override
-  SemanticsOwner? get owner => super.owner as SemanticsOwner?;
+  /// Whether this node is in a tree whose root is attached to something.
+  ///
+  /// This becomes true during the call to [attach].
+  ///
+  /// This becomes false during the call to [detach].
+  bool get attached => _owner != null;
 
-  @override
-  SemanticsNode? get parent => super.parent as SemanticsNode?;
+  /// The parent of this node in the tree.
+  SemanticsNode? get parent => _parent;
+  SemanticsNode? _parent;
 
-  @override
-  void redepthChildren() {
-    _children?.forEach(redepthChild);
+  /// The depth of this node in the tree.
+  ///
+  /// The depth of nodes in a tree monotonically increases as you traverse down
+  /// the tree.
+  int get depth => _depth;
+  int _depth = 0;
+
+  void _redepthChild(SemanticsNode child) {
+    assert(child.owner == owner);
+    if (child._depth <= _depth) {
+      child._depth = _depth + 1;
+      child._redepthChildren();
+    }
   }
 
-  @override
+  void _redepthChildren() {
+    _children?.forEach(_redepthChild);
+  }
+
+  void _adoptChild(SemanticsNode child) {
+    assert(child._parent == null);
+    assert(() {
+      SemanticsNode node = this;
+      while (node.parent != null) {
+        node = node.parent!;
+      }
+      assert(node != child); // indicates we are about to create a cycle
+      return true;
+    }());
+    child._parent = this;
+    if (attached) {
+      child.attach(_owner!);
+    }
+    _redepthChild(child);
+  }
+
+  void _dropChild(SemanticsNode child) {
+    assert(child._parent == this);
+    assert(child.attached == attached);
+    child._parent = null;
+    if (attached) {
+      child.detach();
+    }
+  }
+
+  /// Mark this node as attached to the given owner.
+  @visibleForTesting
   void attach(SemanticsOwner owner) {
-    super.attach(owner);
+    assert(_owner == null);
+    _owner = owner;
     while (owner._nodes.containsKey(id)) {
       // Ids may repeat if the Flutter has generated > 2^16 ids. We need to keep
       // regenerating the id until we found an id that is not used.
@@ -2032,14 +2083,16 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
     }
   }
 
-  @override
+  /// Mark this node as detached.
+  @visibleForTesting
   void detach() {
+    assert(_owner != null);
     assert(owner!._nodes.containsKey(id));
     assert(!owner!._detachedNodes.contains(this));
     owner!._nodes.remove(id);
     owner!._detachedNodes.add(this);
-    super.detach();
-    assert(owner == null);
+    _owner = null;
+    assert(parent == null || attached == parent!.attached);
     if (_children != null) {
       for (final SemanticsNode child in _children!) {
         // The list of children may be stale and may contain nodes that have

packages/flutter/test/rendering/layers_test.dart

@@ -899,8 +899,7 @@ void main() {
       expect(() => layer.markNeedsAddToScene(), throwsAssertionError);
       expect(() => layer.debugMarkClean(), throwsAssertionError);
       expect(() => layer.updateSubtreeNeedsAddToScene(), throwsAssertionError);
-      expect(() => layer.dropChild(ContainerLayer()), throwsAssertionError);
-      expect(() => layer.adoptChild(ContainerLayer()), throwsAssertionError);
+      expect(() => layer.remove(), throwsAssertionError);
       expect(() => (layer as ContainerLayer).append(ContainerLayer()), throwsAssertionError);
       expect(() => layer.engineLayer = null, throwsAssertionError);
       compositedB1 = true;