Properly cleans up routes (#126453)

fixes https://github.com/flutter/flutter/issues/126100

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

@@ -849,7 +849,12 @@ class HeroController extends NavigatorObserver {
     HeroFlightDirection flightType,
     bool isUserGestureTransition,
   ) {
-    if (toRoute != fromRoute && toRoute is PageRoute<dynamic> && fromRoute is PageRoute<dynamic>) {
+    if (toRoute == fromRoute ||
+        toRoute is! PageRoute<dynamic> ||
+        fromRoute is! PageRoute<dynamic>) {
+      return;
+    }
+
     final PageRoute<dynamic> from = fromRoute;
     final PageRoute<dynamic> to = toRoute;
 
@@ -880,11 +885,13 @@ class HeroController extends NavigatorObserver {
       to.offstage = to.animation!.value == 0.0;
 
       WidgetsBinding.instance.addPostFrameCallback((Duration value) {
+        if (from.navigator == null || to.navigator == null) {
+          return;
+        }
         _startHeroTransition(from, to, flightType, isUserGestureTransition);
       });
     }
   }
-  }
 
   // Find the matching pairs of heroes in from and to and either start or a new
   // hero flight, or divert an existing one.

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

@@ -2786,6 +2786,7 @@ class Navigator extends StatefulWidget {
 //                              \     |
 //                              dispose*
 //                                 |
+//                              disposing
 //                                 |
 //                              disposed
 //                                 |
@@ -2821,6 +2822,9 @@ enum _RouteLifecycle {
   removing, // we are waiting for subsequent routes to be done animating, then will switch to dispose
   // routes that are completely removed from the navigator and overlay.
   dispose, // we will dispose the route momentarily
+  disposing, // The entry is waiting for its widget subtree to be disposed
+             // first. It is stored in _entryWaitingForSubTreeDisposal while
+             // awaiting that.
   disposed, // we have disposed the route
 }
 
@@ -3047,9 +3051,26 @@ class _RouteEntry extends RouteTransitionRecord {
     currentState = _RouteLifecycle.dispose;
   }
 
-  void dispose() {
+  /// Disposes this route entry and its [route] immediately.
+  ///
+  /// This method does not wait for the widget subtree of the [route] to unmount
+  /// before disposing.
+  void forcedDispose() {
     assert(currentState.index < _RouteLifecycle.disposed.index);
     currentState = _RouteLifecycle.disposed;
+    route.dispose();
+  }
+
+  /// Disposes this route entry and its [route].
+  ///
+  /// This method waits for the widget subtree of the [route] to unmount before
+  /// disposing. If subtree is already unmounted, this method calls
+  /// [forcedDispose] immediately.
+  ///
+  /// Use [forcedDispose] if the [route] need to be disposed immediately.
+  void dispose() {
+    assert(currentState.index < _RouteLifecycle.disposing.index);
+    currentState = _RouteLifecycle.disposing;
 
     // If the overlay entries are still mounted, widgets in the route's subtree
     // may still reference resources from the route and we delay disposal of
@@ -3060,10 +3081,14 @@ class _RouteEntry extends RouteTransitionRecord {
     final Iterable<OverlayEntry> mountedEntries = route.overlayEntries.where((OverlayEntry e) => e.mounted);
 
     if (mountedEntries.isEmpty) {
-      route.dispose();
-    } else {
+      forcedDispose();
+      return;
+    }
+
     int mounted = mountedEntries.length;
     assert(mounted > 0);
+    final NavigatorState navigator = route._navigator!;
+    navigator._entryWaitingForSubTreeDisposal.add(this);
     for (final OverlayEntry entry in mountedEntries) {
       late VoidCallback listener;
       listener = () {
@@ -3073,13 +3098,28 @@ class _RouteEntry extends RouteTransitionRecord {
         entry.removeListener(listener);
         if (mounted == 0) {
           assert(route.overlayEntries.every((OverlayEntry e) => !e.mounted));
-            route.dispose();
+          // This is a listener callback of one of the overlayEntries in this
+          // route. Disposing the route also disposes its overlayEntries and
+          // violates the rule that a change notifier can't be disposed during
+          // its notifying callback.
+          //
+          // Use a microtask to ensure the overlayEntries have finished
+          // notifying their listeners before disposing.
+          return scheduleMicrotask(() {
+            if (!navigator._entryWaitingForSubTreeDisposal.remove(this)) {
+              // This route must have been destroyed as a result of navigator
+              // force dispose.
+              assert(route._navigator == null && !navigator.mounted);
+              return;
+            }
+            assert(currentState == _RouteLifecycle.disposing);
+            forcedDispose();
+          });
         }
       };
       entry.addListener(listener);
     }
   }
-  }
 
   bool get willBePresent {
     return currentState.index <= _RouteLifecycle.idle.index &&
@@ -3257,6 +3297,15 @@ class _NavigatorReplaceObservation extends _NavigatorObservation {
 class NavigatorState extends State<Navigator> with TickerProviderStateMixin, RestorationMixin {
   late GlobalKey<OverlayState> _overlayKey;
   List<_RouteEntry> _history = <_RouteEntry>[];
+  /// A set for entries that are waiting to dispose until their subtrees are
+  /// disposed.
+  ///
+  /// These entries are not considered to be in the _history and will usually
+  /// remove themselves from this set once they can dispose.
+  ///
+  /// The navigator keep track of these entries so that, in case the navigator
+  /// itself is disposed, it can dispose these entries immediately.
+  final Set<_RouteEntry> _entryWaitingForSubTreeDisposal = <_RouteEntry>{};
   final _HistoryProperty _serializableHistory = _HistoryProperty();
   final Queue<_NavigatorObservation> _observedRouteAdditions = Queue<_NavigatorObservation>();
   final Queue<_NavigatorObservation> _observedRouteDeletions = Queue<_NavigatorObservation>();
@@ -3338,9 +3387,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
     registerForRestoration(_serializableHistory, 'history');
 
     // Delete everything in the old history and clear the overlay.
-    while (_history.isNotEmpty) {
-      _history.removeLast().dispose();
-    }
+    _forcedDisposeAllRouteEntries();
     assert(_history.isEmpty);
     _overlayKey = GlobalKey<OverlayState>();
 
@@ -3423,6 +3470,28 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
     }
   }
 
+  /// Dispose all lingering router entries immediately.
+  void _forcedDisposeAllRouteEntries() {
+    _entryWaitingForSubTreeDisposal.removeWhere((_RouteEntry entry) {
+      entry.forcedDispose();
+      return true;
+    });
+    while (_history.isNotEmpty) {
+      _disposeRouteEntry(_history.removeLast(), graceful: false);
+    }
+  }
+
+  static void _disposeRouteEntry(_RouteEntry entry, {required bool graceful}) {
+    for (final OverlayEntry overlayEntry in entry.route.overlayEntries) {
+      overlayEntry.remove();
+    }
+    if (graceful) {
+      entry.dispose();
+    } else {
+      entry.forcedDispose();
+    }
+  }
+
   void _updateHeroController(HeroController? newHeroController) {
     if (_heroControllerFromScope != newHeroController) {
       if (newHeroController != null) {
@@ -3595,9 +3664,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
     }());
     _updateHeroController(null);
     focusNode.dispose();
-    for (final _RouteEntry entry in _history) {
-      entry.dispose();
-    }
+    _forcedDisposeAllRouteEntries();
     _rawNextPagelessRestorationScopeId.dispose();
     _serializableHistory.dispose();
     userGestureInProgressNotifier.dispose();
@@ -4022,6 +4089,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
           // Delay disposal until didChangeNext/didChangePrevious have been sent.
           toBeDisposed.add(_history.removeAt(index));
           entry = next;
+        case _RouteLifecycle.disposing:
         case _RouteLifecycle.disposed:
         case _RouteLifecycle.staging:
           assert(false);
@@ -4051,10 +4119,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
     // Lastly, removes the overlay entries of all marked entries and disposes
     // them.
     for (final _RouteEntry entry in toBeDisposed) {
-      for (final OverlayEntry overlayEntry in entry.route.overlayEntries) {
-        overlayEntry.remove();
-      }
-      entry.dispose();
+      _disposeRouteEntry(entry, graceful: true);
     }
     if (rearrangeOverlay) {
       overlay?.rearrange(_allRouteOverlayEntries);

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

@@ -84,6 +84,9 @@ abstract class OverlayRoute<T> extends Route<T> {
 
   @override
   void dispose() {
+    for (final OverlayEntry entry in _overlayEntries) {
+      entry.dispose();
+    }
     _overlayEntries.clear();
     super.dispose();
   }
@@ -704,7 +707,9 @@ mixin LocalHistoryRoute<T> on Route<T> {
         // elements during finalizeTree. The state is locked at this moment, and
         // we can only notify state has changed in the next frame.
         SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
+          if (isActive) {
             changedInternalState();
+          }
         });
       } else {
         changedInternalState();

packages/flutter/test/material/about_test.dart

@@ -427,7 +427,7 @@ void main() {
     final FakeLicenseEntry licenseEntry = FakeLicenseEntry();
     licenseCompleter.complete(licenseEntry);
     expect(licenseEntry.packagesCalled, false);
-  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String, int?>{'ValueNotifier<_OverlayEntryWidgetState?>': null})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
+  });
 
   testWidgetsWithLeakTracking('LicensePage returns late if unmounted', (WidgetTester tester) async {
     final Completer<LicenseEntry> licenseCompleter = Completer<LicenseEntry>();
@@ -452,7 +452,7 @@ void main() {
 
     await tester.pumpAndSettle();
     expect(licenseEntry.packagesCalled, true);
-  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String, int?>{'ValueNotifier<_OverlayEntryWidgetState?>': null})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
+  });
 
   testWidgetsWithLeakTracking('LicensePage logic defaults to executable name for app name', (WidgetTester tester) async {
     await tester.pumpWidget(
@@ -1128,7 +1128,7 @@ void main() {
 
     // Configure to show the default layout.
     await tester.binding.setSurfaceSize(defaultSize);
-  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String, int?>{'ValueNotifier<_OverlayEntryWidgetState?>': null})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
+  });
 
   testWidgetsWithLeakTracking('LicensePage master view layout position - rtl', (WidgetTester tester) async {
     const TextDirection textDirection = TextDirection.rtl;
@@ -1191,7 +1191,7 @@ void main() {
 
     // Configure to show the default layout.
     await tester.binding.setSurfaceSize(defaultSize);
-  }, leakTrackingConfig: const LeakTrackingTestConfig(notDisposedAllowList: <String, int?>{'ValueNotifier<_OverlayEntryWidgetState?>': null})); // TODO(goderbauer): Fix leak, https://github.com/flutter/flutter/issues/126100.
+  });
 
   testWidgetsWithLeakTracking('License page title in lateral UI does not use AppBarTheme.foregroundColor', (WidgetTester tester) async {
     // This is a regression test for https://github.com/flutter/flutter/issues/108991

packages/flutter/test/widgets/navigator_test.dart

@@ -4171,7 +4171,7 @@ class RouteAnnouncementSpy extends Route<void> {
   final AnnouncementCallBack? onDidPopNext;
 
   @override
-  List<OverlayEntry> get overlayEntries => <OverlayEntry>[
+  final List<OverlayEntry> overlayEntries = <OverlayEntry>[
     OverlayEntry(
       builder: (BuildContext context) => const Placeholder(),
     ),

packages/flutter/test/widgets/routes_test.dart

@@ -401,7 +401,7 @@ void main() {
       ],
     );
     await tester.pumpWidget(Container());
-    expect(results, equals(<String>['A: dispose', 'b: dispose']));
+    expect(results, equals(<String>['b: dispose', 'A: dispose']));
     expect(routes.isEmpty, isTrue);
     results.clear();
   });