Revert "Refactors global key duplication detection (#46183)" (#49847)

This reverts commit 340b193f.

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

@@ -469,7 +469,6 @@ class _CupertinoAlertRenderElement extends RenderObjectElement {
     } else if (_actionsElement == child) {
       _actionsElement = null;
     }
-    super.forgetChild(child);
   }
 
   @override

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

@@ -464,7 +464,6 @@ class _CupertinoDialogRenderElement extends RenderObjectElement {
       assert(_actionsElement == child);
       _actionsElement = null;
     }
-    super.forgetChild(child);
   }
 
   @override

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

@@ -2072,7 +2072,6 @@ class _RenderChipElement extends RenderObjectElement {
     final _ChipSlot slot = childToSlot[child];
     childToSlot.remove(child);
     slotToChild.remove(slot);
-    super.forgetChild(child);
   }
 
   void _mountChild(Widget widget, _ChipSlot slot) {

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

@@ -1511,7 +1511,6 @@ class _RenderDecorationElement extends RenderObjectElement {
     final _DecorationSlot slot = childToSlot[child];
     childToSlot.remove(child);
     slotToChild.remove(slot);
-    super.forgetChild(child);
   }
 
   void _mountChild(Widget widget, _DecorationSlot slot) {

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

@@ -992,7 +992,6 @@ class _ListTileElement extends RenderObjectElement {
     final _ListTileSlot slot = childToSlot[child];
     childToSlot.remove(child);
     slotToChild.remove(slot);
-    super.forgetChild(child);
   }
 
   void _mountChild(Widget widget, _ListTileSlot slot) {

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

@@ -1016,7 +1016,6 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
   void forgetChild(Element child) {
     assert(child == _child);
     _child = null;
-    super.forgetChild(child);
   }
 
   @override

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

@@ -132,20 +132,7 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
 
   static final Map<GlobalKey, Element> _registry = <GlobalKey, Element>{};
   static final Set<Element> _debugIllFatedElements = HashSet<Element>();
-  // This map keeps track which child reserve the global key with the parent.
-  // Parent, child -> global key.
-  // This provides us a way to remove old reservation while parent rebuilds the
-  // child in the same slot.
-  static final Map<Element, Map<Element, GlobalKey>> _debugReservations = <Element, Map<Element, GlobalKey>>{};
-
-  static void _debugRemoveReservationFor(Element parent, Element child) {
-    assert(() {
-      assert(parent != null);
-      assert(child != null);
-      _debugReservations[parent]?.remove(child);
-      return true;
-    }());
-  }
+  static final Map<GlobalKey, Element> _debugReservations = <GlobalKey, Element>{};
 
   void _register(Element element) {
     assert(() {
@@ -173,83 +160,46 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
       _registry.remove(this);
   }
 
-  void _debugReserveFor(Element parent, Element child) {
+  void _debugReserveFor(Element parent) {
     assert(() {
       assert(parent != null);
-      assert(child != null);
-      _debugReservations[parent] ??= <Element, GlobalKey>{};
-      _debugReservations[parent][child] = this;
+      if (_debugReservations.containsKey(this) && _debugReservations[this] != parent) {
+        // Reserving a new parent while the old parent is not attached is ok.
+        // This can happen when a renderObject detaches and re-attaches to rendering
+        // tree multiple times.
+        if (_debugReservations[this].renderObject?.attached == false) {
+          _debugReservations[this] = parent;
           return true;
-    }());
         }
-
-  static void _debugVerifyGlobalKeyReservation() {
-    assert(() {
-      final Map<GlobalKey, Element> keyToParent = <GlobalKey, Element>{};
-      _debugReservations.forEach((Element parent, Map<Element, GlobalKey> chidToKey) {
-        // We ignore parent that are detached.
-        if (parent.renderObject?.attached == false)
-          return;
-        chidToKey.forEach((Element child, GlobalKey key) {
-          // If parent = null, the node is deactivated by its parent and is
-          // not re-attached to other part of the tree. We should ignore this
-          // node.
-          if (child._parent == null)
-            return;
-          // It is possible the same key registers to the same parent twice
-          // with different children. That is illegal, but it is not in the
-          // scope of this check. Such error will be detected in
-          // _debugVerifyIllFatedPopulation or
-          // _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans.
-          if (keyToParent.containsKey(key) && keyToParent[key] != parent) {
-            // We have duplication reservations for the same global key.
-            final Element older = keyToParent[key];
-            final Element newer = parent;
-            FlutterError error;
-            if (older.toString() != newer.toString()) {
-              error = FlutterError.fromParts(<DiagnosticsNode>[
+        // It's possible for an element to get built multiple times in one
+        // frame, in which case it'll reserve the same child's key multiple
+        // times. We catch multiple children of one widget having the same key
+        // by verifying that an element never steals elements from itself, so we
+        // don't care to verify that here as well.
+        final String older = _debugReservations[this].toString();
+        final String newer = parent.toString();
+        if (older != newer) {
+          throw FlutterError.fromParts(<DiagnosticsNode>[
             ErrorSummary('Multiple widgets used the same GlobalKey.'),
             ErrorDescription(
-                  'The key $key was used by multiple widgets. The parents of those widgets were:\n'
-                    '- ${older.toString()}\n'
-                    '- ${newer.toString()}\n'
+              'The key $this was used by multiple widgets. The parents of those widgets were:\n'
+              '- $older\n'
+              '- $newer\n'
               'A GlobalKey can only be specified on one widget at a time in the widget tree.'
             ),
           ]);
-            } else {
-              error = FlutterError.fromParts(<DiagnosticsNode>[
+        }
+        throw FlutterError.fromParts(<DiagnosticsNode>[
           ErrorSummary('Multiple widgets used the same GlobalKey.'),
           ErrorDescription(
-                  'The key $key was used by multiple widgets. The parents of those widgets were '
+            'The key $this was used by multiple widgets. The parents of those widgets were '
             'different widgets that both had the following description:\n'
-                    '  ${parent.toString()}\n'
+            '  $parent\n'
             'A GlobalKey can only be specified on one widget at a time in the widget tree.'
           ),
         ]);
       }
-            // Fix the tree by removing the duplicated child from one of its
-            // parents to resolve the duplicated key issue. This allows us to
-            // tear down the tree during testing without producing additional
-            // misleading exceptions.
-            if (child._parent != older) {
-              older.visitChildren((Element currentChild) {
-                if (currentChild == child)
-                  older.forgetChild(child);
-              });
-            }
-            if (child._parent != newer) {
-              newer.visitChildren((Element currentChild) {
-                if (currentChild == child)
-                  newer.forgetChild(child);
-              });
-            }
-            throw error;
-          } else {
-            keyToParent[key] = parent;
-          }
-        });
-      });
-      _debugReservations.clear();
+      _debugReservations[this] = parent;
       return true;
     }());
   }
@@ -265,13 +215,13 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
           final GlobalKey key = element.widget.key as GlobalKey;
           assert(_registry.containsKey(key));
           duplicates ??= <GlobalKey, Set<Element>>{};
-          // Uses ordered set to produce consistent error message.
-          final Set<Element> elements = duplicates.putIfAbsent(key, () => LinkedHashSet<Element>());
+          final Set<Element> elements = duplicates.putIfAbsent(key, () => HashSet<Element>());
           elements.add(element);
           elements.add(_registry[key]);
         }
       }
       _debugIllFatedElements.clear();
+      _debugReservations.clear();
       if (duplicates != null) {
         final List<DiagnosticsNode> information = <DiagnosticsNode>[];
         information.add(ErrorSummary('Multiple widgets used the same GlobalKey.'));
@@ -2689,7 +2639,6 @@ class BuildOwner {
       });
       assert(() {
         try {
-          GlobalKey._debugVerifyGlobalKeyReservation();
           GlobalKey._debugVerifyIllFatedPopulation();
           if (_debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans != null &&
               _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans.isNotEmpty) {
@@ -3144,12 +3093,18 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   /// |  **child != null**  |  Old child is removed, returns null. | Old child updated if possible, returns child or new [Element]. |
   @protected
   Element updateChild(Element child, Widget newWidget, dynamic newSlot) {
+    assert(() {
+      final Key key = newWidget?.key;
+      if (key is GlobalKey) {
+        key._debugReserveFor(this);
+      }
+      return true;
+    }());
     if (newWidget == null) {
       if (child != null)
         deactivateChild(child);
       return null;
     }
-    Element newChild;
     if (child != null) {
       bool hasSameSuperclass = true;
       // When the type of a widget is changed between Stateful and Stateless via
@@ -3173,11 +3128,13 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
         hasSameSuperclass = oldElementClass == newWidgetClass;
         return true;
       }());
-      if (child.widget == newWidget && hasSameSuperclass) {
+      if (hasSameSuperclass) {
+        if (child.widget == newWidget) {
           if (child.slot != newSlot)
             updateSlotForChild(child, newSlot);
-        newChild = child;
-      } else if (Widget.canUpdate(child.widget, newWidget) && hasSameSuperclass) {
+          return child;
+        }
+        if (Widget.canUpdate(child.widget, newWidget)) {
           if (child.slot != newSlot)
             updateSlotForChild(child, newSlot);
           child.update(newWidget);
@@ -3186,27 +3143,13 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
             child.owner._debugElementWasRebuilt(child);
             return true;
           }());
-        newChild = child;
-      } else {
-        deactivateChild(child);
-        assert(child._parent == null);
-        newChild = inflateWidget(newWidget, newSlot);
+          return child;
         }
-    } else {
-      newChild = inflateWidget(newWidget, newSlot);
       }
-
-    assert(() {
-      if (child != null)
-        _debugRemoveGlobalKeyReservation(child);
-      final Key key = newWidget?.key;
-      if (key is GlobalKey) {
-        key._debugReserveFor(this, newChild);
+      deactivateChild(child);
+      assert(child._parent == null);
     }
-      return true;
-    }());
-
-    return newChild;
+    return inflateWidget(newWidget, newSlot);
   }
 
   /// Add this element to the tree in the given slot of the given parent.
@@ -3244,9 +3187,6 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     }());
   }
 
-  void _debugRemoveGlobalKeyReservation(Element child) {
-    GlobalKey._debugRemoveReservationFor(this, child);
-  }
   /// Change the widget used to configure this element.
   ///
   /// The framework calls this function when the parent wishes to use a
@@ -3265,16 +3205,6 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
         && depth != null
         && _active
         && Widget.canUpdate(widget, newWidget));
-    // This Element was told to update and we can now release all the global key
-    // reservations of forgotten children. We cannot do this earlier because the
-    // forgotten children still represent global key duplications if the element
-    // never updates (the forgotten children are not removed from the tree
-    // until the call to update happens)
-    assert(() {
-      _debugForgottenChildrenWithGlobalKey.forEach(_debugRemoveGlobalKeyReservation);
-      _debugForgottenChildrenWithGlobalKey.clear();
-      return true;
-    }());
     _widget = newWidget;
   }
 
@@ -3471,10 +3401,6 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     }());
   }
 
-  // The children that have been forgotten by forgetChild. This will be used in
-  // [update] to remove the global key reservations of forgotten children.
-  final Set<Element> _debugForgottenChildrenWithGlobalKey = HashSet<Element>();
-
   /// Remove the given child from the element's child list, in preparation for
   /// the child being reused elsewhere in the element tree.
   ///
@@ -3483,23 +3409,12 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   ///
   /// The element will still have a valid parent when this is called. After this
   /// is called, [deactivateChild] is called to sever the link to this object.
-  ///
-  /// The [update] is responsible for updating or creating the new child that
-  /// will replace this [child].
   @protected
-  @mustCallSuper
   void forgetChild(Element child) {
-    // This method is called on the old parent when the given child (with a
-    // global key) is given a new parent. We cannot remove the global key
-    // reservation directly in this method because the forgotten child is not
-    // removed from the tree until this Element is updated in [update]. If
-    // [update] is never called, the forgotten child still represents a global
-    // key duplication that we need to catch.
-    assert(() {
-      if (child.widget.key is GlobalKey)
-        _debugForgottenChildrenWithGlobalKey.add(child);
-      return true;
-    }());
+    // TODO(chunhtai): Creates empty body for subclass to call super. This will
+    // enable us to fix internal tests pro-actively for upcoming breaking
+    // change.
+    // https://github.com/flutter/flutter/issues/43780.
   }
 
   void _activateWithParent(Element parent, dynamic newSlot) {
@@ -4529,7 +4444,6 @@ abstract class ComponentElement extends Element {
   void forgetChild(Element child) {
     assert(child == _child);
     _child = null;
-    super.forgetChild(child);
   }
 }
 
@@ -5683,7 +5597,6 @@ class LeafRenderObjectElement extends RenderObjectElement {
   @override
   void forgetChild(Element child) {
     assert(false);
-    super.forgetChild(child);
   }
 
   @override
@@ -5733,7 +5646,6 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
   void forgetChild(Element child) {
     assert(child == _child);
     _child = null;
-    super.forgetChild(child);
   }
 
   @override
@@ -5840,7 +5752,6 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
     assert(_children.contains(child));
     assert(!_forgottenChildren.contains(child));
     _forgottenChildren.add(child);
-    super.forgetChild(child);
   }
 
   @override

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

@@ -60,7 +60,6 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
   void forgetChild(Element child) {
     assert(child == _child);
     _child = null;
-    super.forgetChild(child);
   }
 
   @override

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

@@ -924,7 +924,6 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
   @override
   void forgetChild(Element child) {
     _childElements.remove(child.slot);
-    super.forgetChild(child);
   }
 
 }

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

@@ -1160,7 +1160,6 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
     assert(child.slot != null);
     assert(_childElements.containsKey(child.slot));
     _childElements.remove(child.slot);
-    super.forgetChild(child);
   }
 
   @override

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

@@ -230,7 +230,6 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
   void forgetChild(Element child) {
     assert(child == this.child);
     this.child = null;
-    super.forgetChild(child);
   }
 
   @override

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

@@ -344,7 +344,6 @@ class _TableElement extends RenderObjectElement {
   @override
   bool forgetChild(Element child) {
     _forgottenChildren.add(child);
-    super.forgetChild(child);
     return true;
   }
 }

packages/flutter/test/foundation/diagnostics_json_test.dart

@@ -221,6 +221,11 @@ void main() {
 class _TestElement extends Element {
   _TestElement() : super(const Placeholder());
 
+  @override
+  void forgetChild(Element child) {
+    // Intentionally left empty.
+  }
+
   @override
   void performRebuild() {
     // Intentionally left empty.

packages/flutter/test/widgets/framework_test.dart

@@ -6,8 +6,6 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
-typedef ElementRebuildCallback = void Function(StatefulElement element);
-
 class TestState extends State<StatefulWidget> {
   @override
   Widget build(BuildContext context) => null;
@@ -63,358 +61,6 @@ void main() {
     expect(keyA, isNot(equals(keyB)));
   });
 
-  testWidgets('GlobalKey correct case 1 - can move global key from container widget to layoutbuilder', (WidgetTester tester) async {
-    final Key key = GlobalKey(debugLabel: 'correct');
-    await tester.pumpWidget(Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        Container(
-          key: const ValueKey<int>(1),
-          child: SizedBox(key: key),
-        ),
-        LayoutBuilder(
-          key: const ValueKey<int>(2),
-          builder: (BuildContext context, BoxConstraints constraints) {
-            return const Placeholder();
-          },
-        ),
-      ],
-    ));
-
-    await tester.pumpWidget(Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        Container(
-          key: const ValueKey<int>(1),
-          child: const Placeholder(),
-        ),
-        LayoutBuilder(
-          key: const ValueKey<int>(2),
-          builder: (BuildContext context, BoxConstraints constraints) {
-            return SizedBox(key: key);
-          },
-        ),
-      ],
-    ));
-  });
-
-  testWidgets('GlobalKey correct case 2 - can move global key from layoutbuilder to container widget', (WidgetTester tester) async {
-    final Key key = GlobalKey(debugLabel: 'correct');
-    await tester.pumpWidget(Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        Container(
-          key: const ValueKey<int>(1),
-          child: const Placeholder(),
-        ),
-        LayoutBuilder(
-          key: const ValueKey<int>(2),
-          builder: (BuildContext context, BoxConstraints constraints) {
-            return SizedBox(key: key);
-          },
-        ),
-      ],
-    ));
-    await tester.pumpWidget(Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        Container(
-          key: const ValueKey<int>(1),
-          child: SizedBox(key: key),
-        ),
-        LayoutBuilder(
-          key: const ValueKey<int>(2),
-          builder: (BuildContext context, BoxConstraints constraints) {
-            return const Placeholder();
-          },
-        ),
-      ],
-    ));
-  });
-
-  testWidgets('GlobalKey correct case 3 - can deal with early rebuild in layoutbuilder - move backward', (WidgetTester tester) async {
-    const Key key1 = GlobalObjectKey('Text1');
-    const Key key2 = GlobalObjectKey('Text2');
-    Key rebuiltKeyOfSecondChildBeforeLayout;
-    Key rebuiltKeyOfFirstChildAfterLayout;
-    Key rebuiltKeyOfSecondChildAfterLayout;
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildBeforeLayout =
-                    statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    // Result will be written during first build and need to clear it to remove
-    // noise.
-    rebuiltKeyOfSecondChildBeforeLayout = null;
-
-    final _StatefulState state = tester.firstState(find.byType(_Stateful).at(1));
-    state.rebuild();
-    // Reorders the items
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfFirstChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfFirstChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-    expect(rebuiltKeyOfFirstChildAfterLayout, key2);
-    expect(rebuiltKeyOfSecondChildAfterLayout, key1);
-  });
-
-  testWidgets('GlobalKey correct case 4 - can deal with early rebuild in layoutbuilder - move forward', (WidgetTester tester) async {
-    const Key key1 = GlobalObjectKey('Text1');
-    const Key key2 = GlobalObjectKey('Text2');
-    const Key key3 = GlobalObjectKey('Text3');
-    Key rebuiltKeyOfSecondChildBeforeLayout;
-    Key rebuiltKeyOfSecondChildAfterLayout;
-    Key rebuiltKeyOfThirdChildAfterLayout;
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildBeforeLayout = statefulWidget.child.key;
-                },
-              ),
-              const _Stateful(
-                child: Text(
-                  'Text3',
-                  textDirection: TextDirection.ltr,
-                  key: key3,
-                ),
-              ),
-            ],
-          );
-        },
-      )
-    );
-    // Result will be written during first build and need to clear it to remove
-    // noise.
-    rebuiltKeyOfSecondChildBeforeLayout = null;
-
-    final _StatefulState state = tester.firstState(find.byType(_Stateful).at(1));
-    state.rebuild();
-    // Reorders the items
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text3',
-                  textDirection: TextDirection.ltr,
-                  key: key3,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfThirdChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfThirdChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-    expect(rebuiltKeyOfSecondChildAfterLayout, key3);
-    expect(rebuiltKeyOfThirdChildAfterLayout, key2);
-  });
-
-  testWidgets('GlobalKey correct case 5 - can deal with early rebuild in layoutbuilder - only one global key', (WidgetTester tester) async {
-    const Key key1 = GlobalObjectKey('Text1');
-    Key rebuiltKeyOfSecondChildBeforeLayout;
-    Key rebuiltKeyOfThirdChildAfterLayout;
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildBeforeLayout = statefulWidget.child.key;
-                },
-              ),
-              const _Stateful(
-                child: Text(
-                  'Text3',
-                  textDirection: TextDirection.ltr,
-                ),
-              ),
-            ],
-          );
-        },
-      )
-    );
-    // Result will be written during first build and need to clear it to remove
-    // noise.
-    rebuiltKeyOfSecondChildBeforeLayout = null;
-
-    final _StatefulState state = tester.firstState(find.byType(_Stateful).at(1));
-    state.rebuild();
-    // Reorders the items
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text3',
-                  textDirection: TextDirection.ltr,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key1);
-                },
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key1);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfThirdChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfThirdChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    expect(rebuiltKeyOfSecondChildBeforeLayout, key1);
-    expect(rebuiltKeyOfThirdChildAfterLayout, key1);
-  });
-
   testWidgets('GlobalKey duplication 1 - double appearance', (WidgetTester tester) async {
     final Key key = GlobalKey(debugLabel: 'problematic');
     await tester.pumpWidget(Stack(
@@ -855,173 +501,7 @@ void main() {
       ],
     ));
     FlutterError.onError = oldHandler;
-    expect(count, 1);
-  });
-
-  testWidgets('GlobalKey duplication 18 - subtree build duplicate key with same type', (WidgetTester tester) async {
-    final Key key = GlobalKey(debugLabel: 'problematic');
-    final Stack stack = Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        const SwapKeyWidget(childKey: ValueKey<int>(0)),
-        Container(key: const ValueKey<int>(1)),
-        Container(key: key),
-      ],
-    );
-    await tester.pumpWidget(stack);
-    final SwapKeyWidgetState state = tester.state(find.byType(SwapKeyWidget));
-    state.swapKey(key);
-    await tester.pump();
-    final dynamic exception = tester.takeException();
-    expect(exception, isFlutterError);
-    expect(
-      exception.toString(),
-      equalsIgnoringHashCodes(
-        'Duplicate GlobalKey detected in widget tree.\n'
-        'The following GlobalKey was specified multiple times in the widget tree. This will lead '
-        'to parts of the widget tree being truncated unexpectedly, because the second time a key is seen, the '
-        'previous instance is moved to the new location. The key was:\n'
-        '- [GlobalKey#00000 problematic]\n'
-        'This was determined by noticing that after the widget with the above global key was '
-        'moved out of its previous parent, that previous parent never updated during this frame, meaning that '
-        'it either did not update at all or updated before the widget was moved, in either case implying that '
-        'it still thinks that it should have a child with that global key.\n'
-        'The specific parent that did not update after having one or more children forcibly '
-        'removed due to GlobalKey reparenting is:\n'
-        '- Stack(alignment: AlignmentDirectional.topStart, textDirection: ltr, fit: loose, '
-        'overflow: clip, renderObject: RenderStack#00000)\n'
-        'A GlobalKey can only be specified on one widget at a time in the widget tree.'
-      ),
-    );
-  });
-
-  testWidgets('GlobalKey duplication 19 - subtree build duplicate key with different types', (WidgetTester tester) async {
-    final Key key = GlobalKey(debugLabel: 'problematic');
-    final Stack stack = Stack(
-      textDirection: TextDirection.ltr,
-      children: <Widget>[
-        const SwapKeyWidget(childKey: ValueKey<int>(0)),
-        Container(key: const ValueKey<int>(1)),
-        Container(child: SizedBox(key: key)),
-      ],
-    );
-    await tester.pumpWidget(stack);
-    final SwapKeyWidgetState state = tester.state(find.byType(SwapKeyWidget));
-    state.swapKey(key);
-    await tester.pump();
-    final dynamic exception = tester.takeException();
-    expect(exception, isFlutterError);
-    expect(
-      exception.toString(),
-      equalsIgnoringHashCodes(
-        'Multiple widgets used the same GlobalKey.\n'
-        'The key [GlobalKey#95367 problematic] was used by 2 widgets:\n'
-        '  SizedBox-[GlobalKey#00000 problematic]\n'
-        '  Container-[GlobalKey#00000 problematic]\n'
-        'A GlobalKey can only be specified on one widget at a time in the widget tree.'
-      ),
-    );
-  });
-
-  testWidgets('GlobalKey duplication 20 - real duplication with early rebuild in layoutbuilder will throw', (WidgetTester tester) async {
-    const Key key1 = GlobalObjectKey('Text1');
-    const Key key2 = GlobalObjectKey('Text2');
-    Key rebuiltKeyOfSecondChildBeforeLayout;
-    Key rebuiltKeyOfFirstChildAfterLayout;
-    Key rebuiltKeyOfSecondChildAfterLayout;
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              const _Stateful(
-                child: Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key1,
-                ),
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildBeforeLayout = statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    // Result will be written during first build and need to clear it to remove
-    // noise.
-    rebuiltKeyOfSecondChildBeforeLayout = null;
-
-    final _StatefulState state = tester.firstState(find.byType(_Stateful).at(1));
-    state.rebuild();
-
-    await tester.pumpWidget(
-      LayoutBuilder(
-        builder: (BuildContext context, BoxConstraints constraints) {
-          return Column(
-            children: <Widget>[
-              _Stateful(
-                child: const Text(
-                  'Text2',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfFirstChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfFirstChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-              _Stateful(
-                child: const Text(
-                  'Text1',
-                  textDirection: TextDirection.ltr,
-                  key: key2,
-                ),
-                onElementRebuild: (StatefulElement element) {
-                  // Verifies the early rebuild happens before layout.
-                  expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-                  // We don't want noise to override the result;
-                  expect(rebuiltKeyOfSecondChildAfterLayout, isNull);
-                  final _Stateful statefulWidget = element.widget as _Stateful;
-                  rebuiltKeyOfSecondChildAfterLayout = statefulWidget.child.key;
-                },
-              ),
-            ],
-          );
-        },
-      )
-    );
-    expect(rebuiltKeyOfSecondChildBeforeLayout, key2);
-    expect(rebuiltKeyOfFirstChildAfterLayout, key2);
-    expect(rebuiltKeyOfSecondChildAfterLayout, key2);
-    final dynamic exception = tester.takeException();
-    expect(exception, isFlutterError);
-    expect(
-      exception.toString(),
-      equalsIgnoringHashCodes(
-        'Multiple widgets used the same GlobalKey.\n'
-        'The key [GlobalObjectKey String#00000] was used by multiple widgets. The '
-        'parents of those widgets were:\n'
-        '- _Stateful(state: _StatefulState#00000)\n'
-        '- _Stateful(state: _StatefulState#00000)\n'
-        'A GlobalKey can only be specified on one widget at a time in the widget tree.'
-      ),
-    );
+    expect(count, 2);
   });
 
   testWidgets('GlobalKey - dettach and re-attach child to different parents', (WidgetTester tester) async {
@@ -1278,6 +758,9 @@ class NullChildElement extends Element {
       visitor(null);
   }
 
+  @override
+  void forgetChild(Element child) { }
+
   @override
   void performRebuild() { }
 }
@@ -1289,6 +772,9 @@ class DirtyElementWithCustomBuildOwner extends Element {
 
   final BuildOwner _owner;
 
+  @override
+  void forgetChild(Element child) {}
+
   @override
   void performRebuild() {}
 
@@ -1337,66 +823,3 @@ class DependentState extends State<DependentStatefulWidget> {
     deactivatedCount += 1;
   }
 }
-
-class SwapKeyWidget extends StatefulWidget {
-  const SwapKeyWidget({this.childKey}): super();
-
-  final Key childKey;
-  @override
-  SwapKeyWidgetState createState() => SwapKeyWidgetState();
-}
-
-class SwapKeyWidgetState extends State<SwapKeyWidget> {
-  Key key;
-
-  @override
-  void initState() {
-    super.initState();
-    key = widget.childKey;
-  }
-
-  void swapKey(Key newKey) {
-    setState(() {
-      key = newKey;
-    });
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return Container(key: key);
-  }
-}
-
-class _Stateful extends StatefulWidget {
-  const _Stateful({Key key, this.child, this.onElementRebuild}) : super(key: key);
-  final Text child;
-  final ElementRebuildCallback onElementRebuild;
-  @override
-  State<StatefulWidget> createState() => _StatefulState();
-
-  @override
-  StatefulElement createElement() => StatefulElementSpy(this);
-}
-
-class _StatefulState extends State<_Stateful> {
-  void rebuild() => setState(() {});
-
-  @override
-  Widget build(BuildContext context) {
-    return widget.child;
-  }
-}
-
-class StatefulElementSpy extends StatefulElement {
-  StatefulElementSpy(StatefulWidget widget) : super(widget);
-
-  _Stateful get _statefulWidget => widget as _Stateful;
-
-  @override
-  void rebuild() {
-    if (_statefulWidget.onElementRebuild != null) {
-      _statefulWidget.onElementRebuild(this);
-    }
-    super.rebuild();
-  }
-}