Add a hook for scroll position to notify scrolling context when dimen… (#87076)

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

@@ -525,7 +525,6 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
       _gestureDetectorKey.currentState!.replaceSemanticsActions(actions);
   }
 
-
   // GESTURE RECOGNITION AND POINTER IGNORING
 
   final GlobalKey<RawGestureDetectorState> _gestureDetectorKey = GlobalKey<RawGestureDetectorState>();
@@ -719,6 +718,15 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
     }
   }
 
+  bool _handleScrollMetricsNotification(ScrollMetricsNotification notification) {
+    if (notification.depth == 0) {
+      final RenderObject? scrollSemanticsRenderObject = _scrollSemanticsKey.currentContext?.findRenderObject();
+      if (scrollSemanticsRenderObject != null)
+        scrollSemanticsRenderObject.markNeedsSemanticsUpdate();
+    }
+    return false;
+  }
+
   // DESCRIPTION
 
   @override
@@ -757,12 +765,15 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
     );
 
     if (!widget.excludeFromSemantics) {
-      result = _ScrollSemantics(
-        key: _scrollSemanticsKey,
-        position: position,
-        allowImplicitScrolling: _physics!.allowImplicitScrolling,
-        semanticChildCount: widget.semanticChildCount,
-        child: result,
+      result = NotificationListener<ScrollMetricsNotification>(
+        onNotification: _handleScrollMetricsNotification,
+        child: _ScrollSemantics(
+          key: _scrollSemanticsKey,
+          position: position,
+          allowImplicitScrolling: _physics!.allowImplicitScrolling,
+          semanticChildCount: widget.semanticChildCount,
+          child: result,
+        )
       );
     }
 

packages/flutter/test/widgets/page_view_test.dart

@@ -787,7 +787,7 @@ void main() {
     ));
     expect(controller.page, 0);
     controller.jumpToPage(2);
-    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 1);
+    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 2);
     expect(controller.page, 2);
     await tester.pumpWidget(
       PageStorage(

packages/flutter/test/widgets/range_maintaining_scroll_physics_test.dart

@@ -122,7 +122,7 @@ void main() {
     final TestGesture drag1 = await tester.startGesture(const Offset(10.0, 500.0));
     expect(await tester.pumpAndSettle(), 1); // Nothing to animate
     await drag1.moveTo(const Offset(10.0, 0.0));
-    expect(await tester.pumpAndSettle(), 1); // Nothing to animate
+    expect(await tester.pumpAndSettle(), 2); // Nothing to animate, only one semantics update
     await drag1.up();
     expect(await tester.pumpAndSettle(), 1); // Nothing to animate
     expect(position.pixels, moreOrLessEquals(500.0));
@@ -132,14 +132,14 @@ void main() {
     final TestGesture drag2 = await tester.startGesture(const Offset(10.0, 500.0));
     expect(await tester.pumpAndSettle(), 1); // Nothing to animate
     await drag2.moveTo(const Offset(10.0, 100.0));
-    expect(await tester.pumpAndSettle(), 1); // Nothing to animate
+    expect(await tester.pumpAndSettle(), 2); // Nothing to animate, only one semantics update
     expect(position.maxScrollExtent, 900.0);
     expect(position.pixels, lessThanOrEqualTo(900.0));
     expect(position.activity, isInstanceOf<DragScrollActivity>());
 
     final _ExpandingBoxState expandingBoxState = tester.state<_ExpandingBoxState>(find.byType(ExpandingBox));
     expandingBoxState.toggleSize();
-    expect(await tester.pumpAndSettle(), 1); // Nothing to animate
+    expect(await tester.pumpAndSettle(), 2); // Nothing to animate, only one semantics update
     expect(position.activity, isInstanceOf<DragScrollActivity>());
     expect(position.minScrollExtent, 0.0);
     expect(position.maxScrollExtent, 100.0);
@@ -150,7 +150,7 @@ void main() {
     expect(position.minScrollExtent, 0.0);
     expect(position.maxScrollExtent, 100.0);
     expect(position.pixels, 50.0);
-    expect(await tester.pumpAndSettle(), 1); // Nothing to animate
+    expect(await tester.pumpAndSettle(), 2); // Nothing to animate, only one semantics update
     expect(position.minScrollExtent, 0.0);
     expect(position.maxScrollExtent, 100.0);
     expect(position.pixels, 50.0);

packages/flutter/test/widgets/scroll_activity_test.dart

@@ -23,7 +23,7 @@ void main() {
     await tester.pump();
     await tester.pumpWidget(MaterialApp(home: ListView(controller: controller, children: children(31))));
     expect(controller.position.pixels, thirty + 200.0); // same distance past the end
-    expect(await tester.pumpAndSettle(), 7); // now it goes ballistic...
+    expect(await tester.pumpAndSettle(), 8); // now it goes ballistic...
     expect(controller.position.pixels, thirty + 100.0); // and ends up at the end
   });
 

packages/flutter/test/widgets/scrollable_restoration_test.dart

@@ -446,7 +446,6 @@ void main() {
     expect(find.text('Tile 12'), findsNothing);
 
     final TestRestorationData initialData = await tester.getRestorationData();
-
     final TestGesture gesture = await tester.startGesture(tester.getCenter(find.byType(ListView)));
     await gesture.moveBy(const Offset(0, -525));
     await tester.pump();
@@ -457,12 +456,12 @@ void main() {
     expect(find.text('Tile 11'), findsOneWidget);
     expect(find.text('Tile 12'), findsOneWidget);
 
-    // Restoration data hasn't changed and no frame is scheduled.
+    // Restoration data hasn't changed.
     expect(await tester.getRestorationData(), initialData);
-    expect(tester.binding.hasScheduledFrame, isFalse);
 
     // Restoration data changes with up event.
     await gesture.up();
+    await tester.pump();
     expect(await tester.getRestorationData(), isNot(initialData));
   });
 }

packages/flutter/test/widgets/scrollable_test.dart

@@ -152,7 +152,7 @@ void main() {
     expect(getScrollOffset(tester), heldPosition);
     await gesture.up();
     // Once the hold is let go, it should still snap back to origin.
-    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 2);
+    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 3);
     expect(getScrollOffset(tester), 0.0);
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS,  TargetPlatform.macOS }));
 
@@ -1313,6 +1313,64 @@ void main() {
     await gesture.removePointer();
     await tester.pump();
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS, TargetPlatform.macOS, TargetPlatform.android }));
+
+  testWidgets('Updated content dimensions correctly reflect in semantics', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/40419.
+    final SemanticsHandle handle = tester.ensureSemantics();
+    final UniqueKey listView = UniqueKey();
+    await tester.pumpWidget(MaterialApp(
+      home: TickerMode(
+        enabled: true,
+        child: ListView.builder(
+          key: listView,
+          itemCount: 100,
+          itemBuilder: (BuildContext context, int index) {
+            return Text('Item $index');
+          },
+        ),
+      ),
+    ));
+
+    SemanticsNode scrollableNode = tester.getSemantics(find.descendant(of: find.byKey(listView), matching: find.byType(RawGestureDetector)));
+    SemanticsNode? syntheticScrollableNode;
+    scrollableNode.visitChildren((SemanticsNode node) {
+      syntheticScrollableNode = node;
+      return true;
+    });
+    expect(syntheticScrollableNode!.hasFlag(ui.SemanticsFlag.hasImplicitScrolling), isTrue);
+    // Disabled the ticker mode to trigger didChangeDependencies on Scrollable.
+    // This can happen when a route is push or pop from top.
+    // It will reconstruct the scroll position and apply content dimensions.
+    await tester.pumpWidget(MaterialApp(
+      home: TickerMode(
+        enabled: false,
+        child: ListView.builder(
+          key: listView,
+          itemCount: 100,
+          itemBuilder: (BuildContext context, int index) {
+            return Text('Item $index');
+          },
+        ),
+      ),
+    ));
+    await tester.pump();
+    // The correct workflow will be the following:
+    // 1. _RenderScrollSemantics receives a new scroll position without content
+    //    dimensions and creates a SemanticsNode without implicit scroll.
+    // 2. The content dimensions are applied to the scroll position during the
+    //    layout phase, and the scroll position marks the semantics node of
+    //    _RenderScrollSemantics dirty.
+    // 3. The _RenderScrollSemantics rebuilds its semantics node with implicit
+    //    scroll.
+    scrollableNode = tester.getSemantics(find.descendant(of: find.byKey(listView), matching: find.byType(RawGestureDetector)));
+    syntheticScrollableNode = null;
+    scrollableNode.visitChildren((SemanticsNode node) {
+      syntheticScrollableNode = node;
+      return true;
+    });
+    expect(syntheticScrollableNode!.hasFlag(ui.SemanticsFlag.hasImplicitScrolling), isTrue);
+    handle.dispose();
+  });
 }
 
 // ignore: must_be_immutable