Revert "[framework] inline AbstractNode into RenderObject" (#104257)

packages/flutter/lib/src/cupertino/dialog.dart

@@ -1566,7 +1566,9 @@ class _ActionButtonParentDataWidget
       parentData.isPressed = isPressed;
 
       // Force a repaint.
-      renderObject.parent?.markNeedsPaint();
+      final AbstractNode? targetParent = renderObject.parent;
+      if (targetParent is RenderObject)
+        targetParent.markNeedsPaint();
     }
   }
 

packages/flutter/lib/src/material/data_table.dart

@@ -4,6 +4,7 @@
 
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
@@ -1085,9 +1086,9 @@ class TableRowInkWell extends InkResponse {
   RectCallback getRectCallback(RenderBox referenceBox) {
     return () {
       RenderObject cell = referenceBox;
-      RenderObject? table = cell.parent;
+      AbstractNode? table = cell.parent;
       final Matrix4 transform = Matrix4.identity();
-      while (table != null && table is! RenderTable) {
+      while (table is RenderObject && table is! RenderTable) {
         table.applyPaintTransform(cell, transform);
         assert(table == cell.parent);
         cell = table;

packages/flutter/lib/src/material/material.dart

@@ -683,7 +683,7 @@ abstract class InkFeature {
     RenderObject node = referenceBox;
     while (node != _controller) {
       final RenderObject childNode = node;
-      node = node.parent!;
+      node = node.parent! as RenderObject;
       if (!node.paintsChild(childNode)) {
         // Some node between the reference box and this would skip painting on
         // the reference box, so bail out early and avoid unnecessary painting.

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

@@ -2145,7 +2145,7 @@ abstract class RenderBox extends RenderObject {
     assert(!_debugDoingBaseline, 'Please see the documentation for computeDistanceToActualBaseline for the required calling conventions of this method.');
     assert(!debugNeedsLayout);
     assert(() {
-      final RenderObject? parent = this.parent;
+      final RenderObject? parent = this.parent as RenderObject?;
       if (owner!.debugDoingLayout)
         return (RenderObject.debugActiveLayout == parent) && parent!.debugDoingThisLayout;
       if (owner!.debugDoingPaint)
@@ -2367,7 +2367,7 @@ abstract class RenderBox extends RenderObject {
 
   @override
   void markNeedsLayout() {
-    if (_clearCachedData() && parent != null) {
+    if (_clearCachedData() && parent is RenderObject) {
       markParentNeedsLayout();
       return;
     }

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

@@ -1039,7 +1039,7 @@ class RenderListWheelViewport
     // `child` will be the last RenderObject before the viewport when walking up from `target`.
     RenderObject child = target;
     while (child.parent != this)
-      child = child.parent!;
+      child = child.parent! as RenderObject;
 
     final ListWheelParentData parentData = child.parentData! as ListWheelParentData;
     final double targetOffset = parentData.offset.dy; // the so-called "centerPosition"

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

@@ -909,10 +909,12 @@ class PipelineOwner {
     onNeedVisualUpdate?.call();
   }
 
-  /// The unique [RenderObject] managed by this pipeline that has no parent.
+  /// The unique object managed by this pipeline that has no parent.
-  RenderObject? get rootNode => _rootNode;
+  ///
-  RenderObject? _rootNode;
+  /// This object does not have to be a [RenderObject].
-  set rootNode(RenderObject? value) {
+  AbstractNode? get rootNode => _rootNode;
+  AbstractNode? _rootNode;
+  set rootNode(AbstractNode? value) {
     if (_rootNode == value)
       return;
     _rootNode?.detach();
@@ -1320,174 +1322,13 @@ class PipelineOwner {
 /// [RenderObject.markNeedsLayout] so that if a parent has queried the intrinsic
 /// or baseline information, it gets marked dirty whenever the child's geometry
 /// changes.
-abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarget {
+abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin implements HitTestTarget {
   /// Initializes internal fields for subclasses.
   RenderObject() {
     _needsCompositing = isRepaintBoundary || alwaysNeedsCompositing;
     _wasRepaintBoundary = isRepaintBoundary;
   }
 
-  /// 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 the given [child] to be greater than this node's own
-  /// [depth].
-  ///
-  /// Only call this method from overrides of [redepthChildren].
-  @protected
-  void redepthChild(RenderObject child) {
-    assert(child.owner == owner);
-    if (child._depth <= _depth) {
-      child._depth = _depth + 1;
-      child.redepthChildren();
-    }
-  }
-
-  /// Adjust the [depth] of this node's children, if any.
-  ///
-  /// Override this method in subclasses with child nodes to call [redepthChild]
-  /// for each child. Do not call this method directly.
-  void redepthChildren() { }
-
-  /// The owner for this node (null if unattached).
-  ///
-  /// The entire subtree that this node belongs to will have the same owner.
-  PipelineOwner? get owner => _owner;
-  PipelineOwner? _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(PipelineOwner owner) {
-    assert(!_debugDisposed);
-    assert(owner != null);
-    assert(_owner == null);
-    _owner = owner;
-
-    // If the node was dirtied in some way while unattached, make sure to add
-    // it to the appropriate dirty list now that an owner is available
-    if (_needsLayout && _relayoutBoundary != null) {
-      // Don't enter this block if we've never laid out at all;
-      // scheduleInitialLayout() will handle it
-      _needsLayout = false;
-      markNeedsLayout();
-    }
-    if (_needsCompositingBitsUpdate) {
-      _needsCompositingBitsUpdate = false;
-      markNeedsCompositingBitsUpdate();
-    }
-    if (_needsPaint && _layerHandle.layer != null) {
-      // Don't enter this block if we've never painted at all;
-      // scheduleInitialPaint() will handle it
-      _needsPaint = false;
-      markNeedsPaint();
-    }
-    if (_needsSemanticsUpdate && _semanticsConfiguration.isSemanticBoundary) {
-      // Don't enter this block if we've never updated semantics at all;
-      // scheduleInitialSemantics() will handle it
-      _needsSemanticsUpdate = false;
-      markNeedsSemanticsUpdate();
-    }
-  }
-
-  /// 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 parent of this node in the tree.
-  RenderObject? get parent => _parent;
-  RenderObject? _parent;
-
-  /// Called by subclasses when they decide a render object is a child.
-  ///
-  /// Only for use by subclasses when changing their child lists. Calling this
-  /// in other cases will lead to an inconsistent tree and probably cause crashes.
-  @protected
-  @mustCallSuper
-  void adoptChild(RenderObject child) {
-    assert(_debugCanPerformMutations);
-    assert(child != null);
-
-    setupParentData(child);
-    markNeedsLayout();
-    markNeedsCompositingBitsUpdate();
-    markNeedsSemanticsUpdate();
-
-    assert(child != null);
-    assert(child._parent == null);
-    assert(() {
-      RenderObject 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);
-  }
-
-  /// Called by subclasses when they decide a render object is no longer a child.
-  ///
-  /// Only for use by subclasses when changing their child lists. Calling this
-  /// in other cases will lead to an inconsistent tree and probably cause crashes.
-  @protected
-  @mustCallSuper
-  void dropChild(RenderObject child) {
-    assert(_debugCanPerformMutations);
-    assert(child != null);
-    assert(child.parentData != null);
-
-    child._cleanRelayoutBoundary();
-    child.parentData!.detach();
-    child.parentData = null;
-
-    assert(child != null);
-    assert(child._parent == this);
-    assert(child.attached == attached);
-    child._parent = null;
-    if (attached)
-      child.detach();
-
-    markNeedsLayout();
-    markNeedsCompositingBitsUpdate();
-    markNeedsSemanticsUpdate();
-  }
-
   /// Cause the entire subtree rooted at the given [RenderObject] to be marked
   /// dirty for layout, paint, etc, so that the effects of a hot reload can be
   /// seen, or so that the effect of changing a global debug flag (such as
@@ -1588,6 +1429,39 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
       child.parentData = ParentData();
   }
 
+  /// Called by subclasses when they decide a render object is a child.
+  ///
+  /// Only for use by subclasses when changing their child lists. Calling this
+  /// in other cases will lead to an inconsistent tree and probably cause crashes.
+  @override
+  void adoptChild(RenderObject child) {
+    assert(_debugCanPerformMutations);
+    assert(child != null);
+    setupParentData(child);
+    markNeedsLayout();
+    markNeedsCompositingBitsUpdate();
+    markNeedsSemanticsUpdate();
+    super.adoptChild(child);
+  }
+
+  /// Called by subclasses when they decide a render object is no longer a child.
+  ///
+  /// Only for use by subclasses when changing their child lists. Calling this
+  /// in other cases will lead to an inconsistent tree and probably cause crashes.
+  @override
+  void dropChild(RenderObject child) {
+    assert(_debugCanPerformMutations);
+    assert(child != null);
+    assert(child.parentData != null);
+    child._cleanRelayoutBoundary();
+    child.parentData!.detach();
+    child.parentData = null;
+    super.dropChild(child);
+    markNeedsLayout();
+    markNeedsCompositingBitsUpdate();
+    markNeedsSemanticsUpdate();
+  }
+
   /// Calls visitor for each immediate child of this render object.
   ///
   /// Override in subclasses with children and call the visitor for each child.
@@ -1687,17 +1561,50 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
           result = false;
           break;
         }
-        if (node.parent == null) {
+        if (node.parent is! RenderObject) {
           result = true;
           break;
         }
-        node = node.parent!;
+        node = node.parent! as RenderObject;
       }
       return true;
     }());
     return result;
   }
 
+  @override
+  PipelineOwner? get owner => super.owner as PipelineOwner?;
+
+  @override
+  void attach(PipelineOwner owner) {
+    assert(!_debugDisposed);
+    super.attach(owner);
+    // If the node was dirtied in some way while unattached, make sure to add
+    // it to the appropriate dirty list now that an owner is available
+    if (_needsLayout && _relayoutBoundary != null) {
+      // Don't enter this block if we've never laid out at all;
+      // scheduleInitialLayout() will handle it
+      _needsLayout = false;
+      markNeedsLayout();
+    }
+    if (_needsCompositingBitsUpdate) {
+      _needsCompositingBitsUpdate = false;
+      markNeedsCompositingBitsUpdate();
+    }
+    if (_needsPaint && _layerHandle.layer != null) {
+      // Don't enter this block if we've never painted at all;
+      // scheduleInitialPaint() will handle it
+      _needsPaint = false;
+      markNeedsPaint();
+    }
+    if (_needsSemanticsUpdate && _semanticsConfiguration.isSemanticBoundary) {
+      // Don't enter this block if we've never updated semantics at all;
+      // scheduleInitialSemantics() will handle it
+      _needsSemanticsUpdate = false;
+      markNeedsSemanticsUpdate();
+    }
+  }
+
   /// Whether this render object's layout information is dirty.
   ///
   /// This is only set in debug mode. In general, render objects should not need
@@ -1759,7 +1666,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     while (node != _relayoutBoundary) {
       assert(node._relayoutBoundary == _relayoutBoundary);
       assert(node.parent != null);
-      node = node.parent!;
+      node = node.parent! as RenderObject;
       if ((!node._needsLayout) && (!node._debugDoingThisLayout))
         return false;
     }
@@ -1850,7 +1757,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
   void markParentNeedsLayout() {
     _needsLayout = true;
     assert(this.parent != null);
-    final RenderObject parent = this.parent!;
+    final RenderObject parent = this.parent! as RenderObject;
     if (!_doingThisLayoutWithCallback) {
       parent.markNeedsLayout();
     } else {
@@ -1882,7 +1789,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     if (_relayoutBoundary == this) {
       return;
     }
-    final RenderObject? parentRelayoutBoundary = parent?._relayoutBoundary;
+    final RenderObject? parentRelayoutBoundary = (parent as RenderObject?)?._relayoutBoundary;
     assert(parentRelayoutBoundary != null);
     if (parentRelayoutBoundary != _relayoutBoundary) {
       _relayoutBoundary = parentRelayoutBoundary;
@@ -1908,7 +1815,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
   void scheduleInitialLayout() {
     assert(!_debugDisposed);
     assert(attached);
-    assert(parent == null);
+    assert(parent is! RenderObject);
     assert(!owner!._debugDoingLayout);
     assert(_relayoutBoundary == null);
     _relayoutBoundary = this;
@@ -2022,8 +1929,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     ));
     assert(!_debugDoingThisResize);
     assert(!_debugDoingThisLayout);
-    final bool isRelayoutBoundary = !parentUsesSize || sizedByParent || constraints.isTight || parent == null;
+    final bool isRelayoutBoundary = !parentUsesSize || sizedByParent || constraints.isTight || parent is! RenderObject;
-    final RenderObject relayoutBoundary = isRelayoutBoundary ? this : parent!._relayoutBoundary!;
+    final RenderObject relayoutBoundary = isRelayoutBoundary ? this : (parent! as RenderObject)._relayoutBoundary!;
     assert(() {
       _debugCanParentUseSize = parentUsesSize;
       return true;
@@ -2393,8 +2300,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     if (_needsCompositingBitsUpdate)
       return;
     _needsCompositingBitsUpdate = true;
-    if (parent != null) {
+    if (parent is RenderObject) {
-      final RenderObject parent = this.parent!;
+      final RenderObject parent = this.parent! as RenderObject;
       if (parent._needsCompositingBitsUpdate)
         return;
 
@@ -2535,8 +2442,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
         owner!._nodesNeedingPaint.add(this);
         owner!.requestVisualUpdate();
       }
-    } else if (parent != null) {
+    } else if (parent is RenderObject) {
-      final RenderObject parent = this.parent!;
+      final RenderObject parent = this.parent! as RenderObject;
       parent.markNeedsPaint();
       assert(parent == this.parent);
     } else {
@@ -2604,8 +2511,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     assert(_needsPaint || _needsCompositedLayerUpdate);
     assert(_layerHandle.layer != null);
     assert(!_layerHandle.layer!.attached);
-    RenderObject? node = parent;
+    AbstractNode? node = parent;
-    while (node != null) {
+    while (node is RenderObject) {
       if (node.isRepaintBoundary) {
         if (node._layerHandle.layer == null)
           break; // looks like the subtree here has never been painted. let it handle itself.
@@ -2626,7 +2533,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
   void scheduleInitialPaint(ContainerLayer rootLayer) {
     assert(rootLayer.attached);
     assert(attached);
-    assert(parent == null);
+    assert(parent is! RenderObject);
     assert(!owner!._debugDoingPaint);
     assert(isRepaintBoundary);
     assert(_layerHandle.layer == null);
@@ -2644,7 +2551,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     assert(!_debugDisposed);
     assert(rootLayer.attached);
     assert(attached);
-    assert(parent == null);
+    assert(parent is! RenderObject);
     assert(!owner!._debugDoingPaint);
     assert(isRepaintBoundary);
     assert(_layerHandle.layer != null); // use scheduleInitialPaint the first time
@@ -2695,8 +2602,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     }
     assert(() {
       if (_needsCompositingBitsUpdate) {
-        if (parent != null) {
+        if (parent is RenderObject) {
-          final RenderObject parent = this.parent!;
+          final RenderObject parent = this.parent! as RenderObject;
           bool visitedByParent = false;
           parent.visitChildren((RenderObject child) {
             if (child == this) {
@@ -2854,12 +2761,12 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     final bool ancestorSpecified = ancestor != null;
     assert(attached);
     if (ancestor == null) {
-      final RenderObject? rootNode = owner!.rootNode;
+      final AbstractNode? rootNode = owner!.rootNode;
-      if (rootNode != null)
+      if (rootNode is RenderObject)
         ancestor = rootNode;
     }
     final List<RenderObject> renderers = <RenderObject>[];
-    for (RenderObject renderer = this; renderer != ancestor; renderer = renderer.parent!) {
+    for (RenderObject renderer = this; renderer != ancestor; renderer = renderer.parent! as RenderObject) {
       renderers.add(renderer);
       assert(renderer.parent != null); // Failed to find ancestor in parent chain.
     }
@@ -2927,7 +2834,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
   void scheduleInitialSemantics() {
     assert(!_debugDisposed);
     assert(attached);
-    assert(parent == null);
+    assert(parent is! RenderObject);
     assert(!owner!._debugDoingSemantics);
     assert(_semantics == null);
     assert(_needsSemanticsUpdate);
@@ -2989,7 +2896,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     if (_semantics != null && !_semantics!.isMergedIntoParent) {
       _semantics!.sendEvent(semanticsEvent);
     } else if (parent != null) {
-      final RenderObject renderParent = parent!;
+      final RenderObject renderParent = parent! as RenderObject;
       renderParent.sendSemanticsEvent(semanticsEvent);
     }
   }
@@ -3065,12 +2972,12 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     bool isEffectiveSemanticsBoundary = _semanticsConfiguration.isSemanticBoundary && wasSemanticsBoundary;
     RenderObject node = this;
 
-    while (!isEffectiveSemanticsBoundary && node.parent != null) {
+    while (!isEffectiveSemanticsBoundary && node.parent is RenderObject) {
       if (node != this && node._needsSemanticsUpdate)
         break;
       node._needsSemanticsUpdate = true;
 
-      node = node.parent!;
+      node = node.parent! as RenderObject;
       isEffectiveSemanticsBoundary = node._semanticsConfiguration.isSemanticBoundary;
       if (isEffectiveSemanticsBoundary && node._semantics == null) {
         // We have reached a semantics boundary that doesn't own a semantics node.
@@ -3092,7 +2999,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     if (!node._needsSemanticsUpdate) {
       node._needsSemanticsUpdate = true;
       if (owner != null) {
-        assert(node._semanticsConfiguration.isSemanticBoundary || node.parent == null);
+        assert(node._semanticsConfiguration.isSemanticBoundary || node.parent is! RenderObject);
         owner!._nodesNeedingSemantics.add(node);
         owner!.requestVisualUpdate();
       }
@@ -3101,7 +3008,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
 
   /// Updates the semantic information of the render object.
   void _updateSemantics() {
-    assert(_semanticsConfiguration.isSemanticBoundary || parent == null);
+    assert(_semanticsConfiguration.isSemanticBoundary || parent is! RenderObject);
     if (_needsLayout) {
       // There's not enough information in this subtree to compute semantics.
       // The subtree is probably being kept alive by a viewport but not laid out.
@@ -3155,7 +3062,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
         fragments.add(fragment);
         fragment.addAncestor(this);
         fragment.addTags(config.tagsForChildren);
-        if (config.explicitChildNodes || parent == null) {
+        if (config.explicitChildNodes || parent is! RenderObject) {
           fragment.markAsExplicit();
           continue;
         }
@@ -3180,7 +3087,7 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     _needsSemanticsUpdate = false;
 
     _SemanticsFragment result;
-    if (parent == null) {
+    if (parent is! RenderObject) {
       assert(!config.hasBeenAnnotated);
       assert(!mergeIntoParent);
       result = _RootSemanticsFragment(
@@ -3283,9 +3190,9 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
       }
       if (_relayoutBoundary != null && _relayoutBoundary != this) {
         int count = 1;
-        RenderObject? target = parent ;
+        RenderObject? target = parent as RenderObject?;
         while (target != null && target != _relayoutBoundary) {
-          target = target.parent;
+          target = target.parent as RenderObject?;
           count += 1;
         }
         header += ' relayoutBoundary=up$count';
@@ -3404,8 +3311,8 @@ abstract class RenderObject with DiagnosticableTreeMixin implements HitTestTarge
     Duration duration = Duration.zero,
     Curve curve = Curves.ease,
   }) {
-    if (parent != null) {
+    if (parent is RenderObject) {
-      final RenderObject renderParent = parent!;
+      final RenderObject renderParent = parent! as RenderObject;
       renderParent.showOnScreen(
         descendant: descendant ?? this,
         rect: rect,
@@ -4329,12 +4236,12 @@ class _SemanticsGeometry {
     assert(transform != null);
     assert(clipRectTransform != null);
     assert(clipRectTransform.isIdentity());
-    RenderObject intermediateParent = child.parent!;
+    RenderObject intermediateParent = child.parent! as RenderObject;
     assert(intermediateParent != null);
     while (intermediateParent != ancestor) {
       intermediateParent.applyPaintTransform(child, transform);
-      intermediateParent = intermediateParent.parent!;
+      intermediateParent = intermediateParent.parent! as RenderObject;
-      child = child.parent!;
+      child = child.parent! as RenderObject;
       assert(intermediateParent != null);
     }
     ancestor.applyPaintTransform(child, transform);

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

@@ -43,7 +43,7 @@ abstract class RenderAbstractViewport extends RenderObject {
     while (object != null) {
       if (object is RenderAbstractViewport)
         return object;
-      object = object.parent;
+      object = object.parent as RenderObject?;
     }
     return null;
   }
@@ -764,7 +764,7 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
     RenderBox? pivot;
     bool onlySlivers = target is RenderSliver; // ... between viewport and `target` (`target` included).
     while (child.parent != this) {
-      final RenderObject parent = child.parent!;
+      final RenderObject parent = child.parent! as RenderObject;
       assert(parent != null, '$target must be a descendant of $this');
       if (child is RenderBox) {
         pivot = child;
@@ -1214,7 +1214,7 @@ abstract class RenderViewportBase<ParentDataClass extends ContainerParentDataMix
     } else {
       // `descendant` is between leading and trailing edge and hence already
       //  fully shown on screen. No action necessary.
-      final Matrix4 transform = descendant.getTransformTo(viewport.parent);
+      final Matrix4 transform = descendant.getTransformTo(viewport.parent! as RenderObject);
       return MatrixUtils.transformRect(transform, rect ?? descendant.paintBounds);
     }
 

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

@@ -2169,8 +2169,8 @@ class LayoutId extends ParentDataWidget<MultiChildLayoutParentData> {
     final MultiChildLayoutParentData parentData = renderObject.parentData! as MultiChildLayoutParentData;
     if (parentData.id != id) {
       parentData.id = id;
-      final RenderObject? targetParent = renderObject.parent;
+      final AbstractNode? targetParent = renderObject.parent;
-      if (targetParent != null)
+      if (targetParent is RenderObject)
         targetParent.markNeedsLayout();
     }
   }
@@ -4132,8 +4132,8 @@ class Positioned extends ParentDataWidget<StackParentData> {
     }
 
     if (needsLayout) {
-      final RenderObject? targetParent = renderObject.parent;
+      final AbstractNode? targetParent = renderObject.parent;
-      if (targetParent != null)
+      if (targetParent is RenderObject)
         targetParent.markNeedsLayout();
     }
   }
@@ -4992,8 +4992,8 @@ class Flexible extends ParentDataWidget<FlexParentData> {
     }
 
     if (needsLayout) {
-      final RenderObject? targetParent = renderObject.parent;
+      final AbstractNode? targetParent = renderObject.parent;
-      if (targetParent != null)
+      if (targetParent is RenderObject)
         targetParent.markNeedsLayout();
     }
   }

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

@@ -1747,8 +1747,8 @@ class KeepAlive extends ParentDataWidget<KeepAliveParentDataMixin> {
     final KeepAliveParentDataMixin parentData = renderObject.parentData! as KeepAliveParentDataMixin;
     if (parentData.keepAlive != keepAlive) {
       parentData.keepAlive = keepAlive;
-      final RenderObject? targetParent = renderObject.parent;
+      final AbstractNode? targetParent = renderObject.parent;
-      if (targetParent != null && !keepAlive)
+      if (targetParent is RenderObject && !keepAlive)
         targetParent.markNeedsLayout(); // No need to redo layout if it became true.
     }
   }

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

@@ -433,8 +433,8 @@ class TableCell extends ParentDataWidget<TableCellParentData> {
     final TableCellParentData parentData = renderObject.parentData! as TableCellParentData;
     if (parentData.verticalAlignment != verticalAlignment) {
       parentData.verticalAlignment = verticalAlignment;
-      final RenderObject? targetParent = renderObject.parent;
+      final AbstractNode? targetParent = renderObject.parent;
-      if (targetParent != null)
+      if (targetParent is RenderObject)
         targetParent.markNeedsLayout();
     }
   }

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

@@ -552,7 +552,7 @@ class _ScreenshotPaintingContext extends PaintingContext {
   }) {
     RenderObject repaintBoundary = renderObject;
     while (repaintBoundary != null && !repaintBoundary.isRepaintBoundary) {
-      repaintBoundary = repaintBoundary.parent!;
+      repaintBoundary = repaintBoundary.parent! as RenderObject;
     }
     assert(repaintBoundary != null);
     final _ScreenshotData data = _ScreenshotData(target: renderObject);
@@ -1510,7 +1510,7 @@ mixin WidgetInspectorService {
     final List<RenderObject> chain = <RenderObject>[];
     while (renderObject != null) {
       chain.add(renderObject);
-      renderObject = renderObject.parent;
+      renderObject = renderObject.parent as RenderObject?;
     }
     return _followDiagnosticableChain(chain.reversed.toList());
   }
@@ -2565,7 +2565,7 @@ class _RenderInspectorOverlay extends RenderBox {
     context.addLayer(_InspectorOverlayLayer(
       overlayRect: Rect.fromLTWH(offset.dx, offset.dy, size.width, size.height),
       selection: selection,
-      rootRenderObject: parent != null ? parent! : null,
+      rootRenderObject: parent is RenderObject ? parent! as RenderObject : null,
     ));
   }
 }
@@ -2841,14 +2841,14 @@ class _InspectorOverlayLayer extends Layer {
   /// overlays in the same app (i.e. an storyboard), a selected or candidate
   /// render object may not belong to this tree.
   bool _isInInspectorRenderObjectTree(RenderObject child) {
-    RenderObject? current = child.parent;
+    RenderObject? current = child.parent as RenderObject?;
     while (current != null) {
       // We found the widget inspector render object.
       if (current is RenderStack
           && current.lastChild is _RenderInspectorOverlay) {
         return rootRenderObject == current;
       }
-      current = current.parent;
+      current = current.parent as RenderObject?;
     }
     return false;
   }

packages/flutter/test/material/tooltip_test.dart

@@ -1941,5 +1941,5 @@ Future<void> testGestureTap(WidgetTester tester, Finder tooltip) async {
 SemanticsNode findDebugSemantics(RenderObject object) {
   if (object.debugSemantics != null)
     return object.debugSemantics!;
-  return findDebugSemantics(object.parent!);
+  return findDebugSemantics(object.parent! as RenderObject);
 }

packages/flutter/test/material/tooltip_theme_test.dart

@@ -1357,5 +1357,5 @@ void main() {
 SemanticsNode findDebugSemantics(RenderObject object) {
   if (object.debugSemantics != null)
     return object.debugSemantics!;
-  return findDebugSemantics(object.parent!);
+  return findDebugSemantics(object.parent! as RenderObject);
 }

packages/flutter/test/rendering/cached_intrinsics_test.dart

@@ -118,7 +118,7 @@ void main() {
     expect(parentData!.offset.dy, -(viewHeight / 2.0));
     expect(test.calls, 2); // The layout constraints change will clear the cached data.
 
-    final RenderObject parent = test.parent!;
+    final RenderObject parent = test.parent! as RenderObject;
     expect(parent.debugNeedsLayout, false);
 
     // Do not forget notify parent dirty after the cached data be cleared by `layout()`

packages/flutter/test/rendering/editable_test.dart

@@ -935,7 +935,7 @@ void main() {
       editable.painter = null;
       editable.paintCount = 0;
 
-      final RenderObject? parent = editable.parent;
+      final AbstractNode? parent = editable.parent;
       if (parent is RenderConstrainedBox)
         parent.child = null;
     });

packages/flutter/test/rendering/non_render_object_root_test.dart

@@ -0,0 +1,61 @@
+// 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';
+
+class RealRoot extends AbstractNode {
+  RealRoot(this.child) {
+    adoptChild(child);
+  }
+
+  final RenderObject child;
+
+  @override
+  void redepthChildren() {
+    redepthChild(child);
+  }
+
+  @override
+  void attach(Object owner) {
+    super.attach(owner);
+    child.attach(owner as PipelineOwner);
+  }
+
+  @override
+  void detach() {
+    super.detach();
+    child.detach();
+  }
+
+  @override
+  PipelineOwner? get owner => super.owner as PipelineOwner?;
+
+  void layout() {
+    child.layout(BoxConstraints.tight(const Size(500.0, 500.0)));
+  }
+}
+
+void main() {
+  TestRenderingFlutterBinding.ensureInitialized();
+
+  test('non-RenderObject roots', () {
+    RenderPositionedBox child;
+    final RealRoot root = RealRoot(
+      child = RenderPositionedBox(
+        child: RenderSizedBox(const Size(100.0, 100.0)),
+      ),
+    );
+    root.attach(PipelineOwner());
+
+    child.scheduleInitialLayout();
+    root.layout();
+
+    child.markNeedsLayout();
+    root.layout();
+  });
+}

packages/flutter/test/rendering/proxy_box_test.dart

@@ -689,9 +689,9 @@ void main() {
 
   test('Offstage implements paintsChild correctly', () {
     final RenderBox box = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
-    final RenderProxyBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
+    final RenderBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
     final RenderOffstage offstage = RenderOffstage(offstage: false, child: box);
-    parent.child  = offstage;
+    parent.adoptChild(offstage);
 
     expect(offstage.paintsChild(box), true);
 
@@ -702,9 +702,9 @@ void main() {
 
   test('Opacity implements paintsChild correctly', () {
     final RenderBox box = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
-    final RenderProxyBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
+    final RenderBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
     final RenderOpacity opacity = RenderOpacity(child: box);
-    parent.child = opacity;
+    parent.adoptChild(opacity);
 
     expect(opacity.paintsChild(box), true);
 
@@ -714,11 +714,11 @@ void main() {
   });
 
   test('AnimatedOpacity sets paint matrix to zero when alpha == 0', () {
-    final RenderProxyBox box = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
+    final RenderBox box = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
-    final RenderProxyBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
+    final RenderBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
     final AnimationController opacityAnimation = AnimationController(value: 1, vsync: FakeTickerProvider());
     final RenderAnimatedOpacity opacity = RenderAnimatedOpacity(opacity: opacityAnimation, child: box);
-    parent.child = opacity;
+    parent.adoptChild(opacity);
 
     // Make it listen to the animation.
     opacity.attach(PipelineOwner());
@@ -732,10 +732,10 @@ void main() {
 
   test('AnimatedOpacity sets paint matrix to zero when alpha == 0 (sliver)', () {
     final RenderSliver sliver = RenderSliverToBoxAdapter(child: RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20)));
-    final RenderSliverPadding parent = RenderSliverPadding(padding: const EdgeInsets.all(4));
+    final RenderBox parent = RenderConstrainedBox(additionalConstraints: const BoxConstraints.tightFor(width: 20));
     final AnimationController opacityAnimation = AnimationController(value: 1, vsync: FakeTickerProvider());
     final RenderSliverAnimatedOpacity opacity = RenderSliverAnimatedOpacity(opacity: opacityAnimation, sliver: sliver);
-    parent.child = opacity;
+    parent.adoptChild(opacity);
 
     // Make it listen to the animation.
     opacity.attach(PipelineOwner());

packages/flutter/test/widgets/heroes_test.dart

@@ -2924,8 +2924,8 @@ Future<void> main() async {
     final ScrollController controller = ScrollController();
 
     RenderAnimatedOpacity? findRenderAnimatedOpacity() {
-      RenderObject? parent = tester.renderObject(find.byType(Placeholder));
+      AbstractNode? parent = tester.renderObject(find.byType(Placeholder));
-      while (parent != null && parent is! RenderAnimatedOpacity) {
+      while (parent is RenderObject && parent is! RenderAnimatedOpacity) {
         parent = parent.parent;
       }
       return parent is RenderAnimatedOpacity ? parent : null;

packages/flutter_driver/lib/src/common/handler_factory.dart

@@ -308,7 +308,7 @@ mixin CommandHandlerFactory {
     SemanticsNode? node;
     while (renderObject != null && node == null) {
       node = renderObject.debugSemantics;
-      renderObject = renderObject.parent;
+      renderObject = renderObject.parent as RenderObject?;
     }
     if (node == null)
       throw StateError('No semantics data found');

packages/flutter_test/lib/src/_matchers_io.dart

@@ -23,7 +23,7 @@ Future<ui.Image> captureImage(Element element) {
   assert(element.renderObject != null);
   RenderObject renderObject = element.renderObject!;
   while (!renderObject.isRepaintBoundary) {
-    renderObject = renderObject.parent!;
+    renderObject = renderObject.parent! as RenderObject;
   }
   assert(!renderObject.debugNeedsPaint);
   final OffsetLayer layer = renderObject.debugLayer! as OffsetLayer;

packages/flutter_test/lib/src/_matchers_web.dart

@@ -82,7 +82,7 @@ RenderObject _findRepaintBoundary(Element element) {
   assert(element.renderObject != null);
   RenderObject renderObject = element.renderObject!;
   while (!renderObject.isRepaintBoundary) {
-    renderObject = renderObject.parent!;
+    renderObject = renderObject.parent! as RenderObject;
   }
   return renderObject;
 }

packages/flutter_test/lib/src/controller.dart

@@ -1168,7 +1168,7 @@ abstract class WidgetController {
     RenderObject? renderObject = element.findRenderObject();
     SemanticsNode? result = renderObject?.debugSemantics;
     while (renderObject != null && (result == null || result.isMergedIntoParent)) {
-      renderObject = renderObject.parent;
+      renderObject = renderObject.parent as RenderObject?;
       result = renderObject?.debugSemantics;
     }
     if (result == null)