From a63ee24b17580e8236ea84085cf39db9851c32b0 Mon Sep 17 00:00:00 2001
From: LongCatIsLooong <31859944+LongCatIsLooong@users.noreply.github.com>
Date: Fri, 25 Mar 2022 16:20:14 -0700
Subject: [PATCH] Reland "Avoid calling `performLayout` when only the relayout
 boundary is different" (#100581)

---
 .../flutter/lib/src/rendering/object.dart     | 44 ++++++++++---
 .../rendering/relayout_boundary_test.dart     | 61 +++++++++++++++++++
 2 files changed, 96 insertions(+), 9 deletions(-)
 create mode 100644 packages/flutter/test/rendering/relayout_boundary_test.dart

diff --git a/packages/flutter/lib/src/rendering/object.dart b/packages/flutter/lib/src/rendering/object.dart
index 0f7ef628f7..3c176c5793 100644
--- a/packages/flutter/lib/src/rendering/object.dart
+++ b/packages/flutter/lib/src/rendering/object.dart
@@ -1629,7 +1629,16 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
       assert(_debugSubtreeRelayoutRootAlreadyMarkedNeedsLayout());
       return;
     }
-    assert(_relayoutBoundary != null);
+    if (_relayoutBoundary == null) {
+      _needsLayout = true;
+      if (parent != null) {
+        // _relayoutBoundary is cleaned by an ancestor in RenderObject.layout.
+        // Conservatively mark everything dirty until it reaches the closest
+        // known relayout boundary.
+        markParentNeedsLayout();
+      }
+      return;
+    }
     if (_relayoutBoundary != this) {
       markParentNeedsLayout();
     } else {
@@ -1683,16 +1692,31 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
   void _cleanRelayoutBoundary() {
     if (_relayoutBoundary != this) {
       _relayoutBoundary = null;
-      _needsLayout = true;
       visitChildren(_cleanChildRelayoutBoundary);
     }
   }
 
+  void _propagateRelayoutBoundary() {
+    if (_relayoutBoundary == this) {
+      return;
+    }
+    final RenderObject? parentRelayoutBoundary = (parent as RenderObject?)?._relayoutBoundary;
+    assert(parentRelayoutBoundary != null);
+    if (parentRelayoutBoundary != _relayoutBoundary) {
+      _relayoutBoundary = parentRelayoutBoundary;
+      visitChildren(_propagateRelayoutBoundaryToChild);
+    }
+  }
+
   // Reduces closure allocation for visitChildren use cases.
   static void _cleanChildRelayoutBoundary(RenderObject child) {
     child._cleanRelayoutBoundary();
   }
 
+  static void _propagateRelayoutBoundaryToChild(RenderObject child) {
+    child._propagateRelayoutBoundary();
+  }
+
   /// Bootstrap the rendering pipeline by scheduling the very first layout.
   ///
   /// Requires this render object to be attached and that this render object
@@ -1814,17 +1838,14 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
     ));
     assert(!_debugDoingThisResize);
     assert(!_debugDoingThisLayout);
-    RenderObject? relayoutBoundary;
-    if (!parentUsesSize || sizedByParent || constraints.isTight || parent is! RenderObject) {
-      relayoutBoundary = this;
-    } else {
-      relayoutBoundary = (parent! as RenderObject)._relayoutBoundary;
-    }
+    final bool isRelayoutBoundary = !parentUsesSize || sizedByParent || constraints.isTight || parent is! RenderObject;
+    final RenderObject relayoutBoundary = isRelayoutBoundary ? this : (parent! as RenderObject)._relayoutBoundary!;
     assert(() {
       _debugCanParentUseSize = parentUsesSize;
       return true;
     }());
-    if (!_needsLayout && constraints == _constraints && relayoutBoundary == _relayoutBoundary) {
+
+    if (!_needsLayout && constraints == _constraints) {
       assert(() {
         // in case parentUsesSize changed since the last invocation, set size
         // to itself, so it has the right internal debug values.
@@ -1839,6 +1860,11 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
         return true;
       }());
 
+      if (relayoutBoundary != _relayoutBoundary) {
+        _relayoutBoundary = relayoutBoundary;
+        visitChildren(_propagateRelayoutBoundaryToChild);
+      }
+
       if (!kReleaseMode && debugProfileLayoutsEnabled)
         Timeline.finishSync();
       return;
diff --git a/packages/flutter/test/rendering/relayout_boundary_test.dart b/packages/flutter/test/rendering/relayout_boundary_test.dart
new file mode 100644
index 0000000000..1823f1ad69
--- /dev/null
+++ b/packages/flutter/test/rendering/relayout_boundary_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/rendering.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('relayout boundary change does not trigger relayout', (WidgetTester tester) async {
+    final RenderLayoutCount renderLayoutCount = RenderLayoutCount();
+    final Widget layoutCounter = Center(
+      key: GlobalKey(),
+      child: WidgetToRenderBoxAdapter(renderBox: renderLayoutCount),
+    );
+
+    await tester.pumpWidget(
+      Center(
+        child: SizedBox(
+          width: 100,
+          height: 100,
+          child: Center(
+            child: SizedBox(
+              width: 100,
+              height: 100,
+              child: Center(
+                child: layoutCounter,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(renderLayoutCount.layoutCount, 1);
+
+    await tester.pumpWidget(
+      Center(
+        child: SizedBox(
+          width: 100,
+          height: 100,
+          child: layoutCounter,
+        ),
+      ),
+    );
+
+    expect(renderLayoutCount.layoutCount, 1);
+  });
+}
+
+// This class is needed because LayoutBuilder's RenderObject does not always
+// call the builder method in its PerformLayout method.
+class RenderLayoutCount extends RenderBox {
+  int layoutCount = 0;
+
+  @override
+  void performLayout() {
+    layoutCount += 1;
+    size = constraints.biggest;
+  }
+}