Fix visual overflow when overscrolling RenderShrinkWrappingViewport (#91620)

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

@@ -1919,7 +1919,10 @@ class RenderShrinkWrappingViewport extends RenderViewportBase<SliverLogicalConta
     assert(correctedOffset.isFinite);
     _maxScrollExtent = 0.0;
     _shrinkWrapExtent = 0.0;
-    _hasVisualOverflow = false;
+    // Since the viewport is shrinkwrapped, we know that any negative overscroll
+    // into the potentially infinite mainAxisExtent will overflow the end of
+    // the viewport.
+    _hasVisualOverflow = correctedOffset < 0.0;
     switch (cacheExtentStyle) {
       case CacheExtentStyle.pixel:
         _calculatedCacheExtent = cacheExtent;
@@ -1928,6 +1931,7 @@ class RenderShrinkWrappingViewport extends RenderViewportBase<SliverLogicalConta
         _calculatedCacheExtent = mainAxisExtent * _cacheExtent;
         break;
     }
+
     return layoutChildSequence(
       child: firstChild,
       scrollOffset: math.max(0.0, correctedOffset),

packages/flutter/test/rendering/viewport_test.dart

@@ -1846,7 +1846,8 @@ void main() {
     });
   });
 
-  Widget _buildShrinkWrap({
+  group('Overscrolling RenderShrinkWrappingViewport', () {
+    Widget _buildSimpleShrinkWrap({
       ScrollController? controller,
       Axis scrollDirection = Axis.vertical,
       ScrollPhysics? physics,
@@ -1868,19 +1869,27 @@ void main() {
       );
     }
 
-  testWidgets('Constrained Shrinkwrapping viewport will not overflow on overscroll', (WidgetTester tester) async {
-    // Regression test for https://github.com/flutter/flutter/issues/89717
-    final  ScrollController controller = ScrollController();
-    await tester.pumpWidget(
-        Directionality(
+    Widget _buildClippingShrinkWrap(
+      ScrollController controller, {
+      bool constrain = false,
+    }) {
+      return Directionality(
         textDirection: TextDirection.ltr,
         child: MediaQuery(
           data: const MediaQueryData(),
+          child: Container(
+            color: const Color(0xFF000000),
             child: Column(
               children: <Widget>[
-                Container(height: 100, color: const Color(0x00000000)),
+                // Translucent boxes above and below the shrinkwrapped viewport
+                // make it easily discernible if the viewport is not being
+                // clipped properly.
+                Opacity(
+                  opacity: 0.5,
+                  child: Container(height: 100, color: const Color(0xFF00B0FF)),
+                ),
                 Container(
-                  height: 150,
+                  height: constrain ? 150 : null,
                   color: const Color(0xFFF44336),
                   child: ListView.builder(
                     controller: controller,
@@ -1890,37 +1899,77 @@ void main() {
                     itemCount: 10,
                   ),
                 ),
-                Container(height: 100, color: const Color(0x00000000)),
+                Opacity(
+                  opacity: 0.5,
+                  child: Container(height: 100, color: const Color(0xFF00B0FF)),
+                ),
               ],
             ),
           ),
-        )
+        ),
+      );
+    }
+
+    testWidgets('constrained viewport correctly clips overflow', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/89717
+      final  ScrollController controller = ScrollController();
+      await tester.pumpWidget(
+        _buildClippingShrinkWrap(controller, constrain: true)
       );
       expect(controller.offset, 0.0);
       expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+      expect(tester.getTopLeft(find.text('Item 9')).dy, 226.0);
 
       // Overscroll
       final TestGesture overscrollGesture = await tester.startGesture(tester.getCenter(find.text('Item 0')));
-    await overscrollGesture.moveBy(const Offset(0, 25));
+      await overscrollGesture.moveBy(const Offset(0, 100));
       await tester.pump();
-    expect(controller.offset, -25.0);
-    expect(tester.getTopLeft(find.text('Item 0')).dy, 125.0);
+      expect(controller.offset, -100.0);
+      expect(tester.getTopLeft(find.text('Item 0')).dy, 200.0);
       await expectLater(
         find.byType(Directionality),
-      matchesGoldenFile('shrinkwrapped_overscroll.png'),
+        matchesGoldenFile('shrinkwrap_clipped_constrained_overscroll.png'),
       );
       await overscrollGesture.up();
       await tester.pumpAndSettle();
       expect(controller.offset, 0.0);
       expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+      expect(tester.getTopLeft(find.text('Item 9')).dy, 226.0);
     });
 
-  testWidgets('Shrinkwrap allows overscrolling on default platforms - vertical', (WidgetTester tester) async {
+    testWidgets('correctly clips overflow without constraints', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/89717
+      final  ScrollController controller = ScrollController();
+      await tester.pumpWidget(
+        _buildClippingShrinkWrap(controller)
+      );
+      expect(controller.offset, 0.0);
+      expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+      expect(tester.getTopLeft(find.text('Item 9')).dy, 226.0);
+
+      // Overscroll
+      final TestGesture overscrollGesture = await tester.startGesture(tester.getCenter(find.text('Item 0')));
+      await overscrollGesture.moveBy(const Offset(0, 100));
+      await tester.pump();
+      expect(controller.offset, -100.0);
+      expect(tester.getTopLeft(find.text('Item 0')).dy, 200.0);
+      await expectLater(
+        find.byType(Directionality),
+        matchesGoldenFile('shrinkwrap_clipped_overscroll.png'),
+      );
+      await overscrollGesture.up();
+      await tester.pumpAndSettle();
+      expect(controller.offset, 0.0);
+      expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+      expect(tester.getTopLeft(find.text('Item 9')).dy, 226.0);
+    });
+
+    testWidgets('allows overscrolling on default platforms - vertical', (WidgetTester tester) async {
       // Regression test for https://github.com/flutter/flutter/issues/10949
       // Scrollables should overscroll by default on iOS and macOS
       final  ScrollController controller = ScrollController();
       await tester.pumpWidget(
-      _buildShrinkWrap(controller: controller),
+        _buildSimpleShrinkWrap(controller: controller),
       );
       expect(controller.offset, 0.0);
       expect(tester.getTopLeft(find.text('Item 0')).dy, 0.0);
@@ -1954,12 +2003,12 @@ void main() {
       expect(tester.getBottomLeft(find.text('Item 19')).dy, 600.0);
     }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS, TargetPlatform.macOS }));
 
-  testWidgets('Shrinkwrap allows overscrolling on default platforms - horizontal', (WidgetTester tester) async {
+    testWidgets('allows overscrolling on default platforms - horizontal', (WidgetTester tester) async {
       // Regression test for https://github.com/flutter/flutter/issues/10949
       // Scrollables should overscroll by default on iOS and macOS
       final  ScrollController controller = ScrollController();
       await tester.pumpWidget(
-      _buildShrinkWrap(controller: controller, scrollDirection: Axis.horizontal),
+        _buildSimpleShrinkWrap(controller: controller, scrollDirection: Axis.horizontal),
       );
       expect(controller.offset, 0.0);
       expect(tester.getTopLeft(find.text('Item 0')).dx, 0.0);
@@ -1993,12 +2042,12 @@ void main() {
       expect(tester.getTopRight(find.text('Item 19')).dx, 800.0);
     }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS, TargetPlatform.macOS }));
 
-  testWidgets('Shrinkwrap allows overscrolling per physics - vertical', (WidgetTester tester) async {
+    testWidgets('allows overscrolling per physics - vertical', (WidgetTester tester) async {
       // Regression test for https://github.com/flutter/flutter/issues/10949
       // Scrollables should overscroll when the scroll physics allow
       final  ScrollController controller = ScrollController();
       await tester.pumpWidget(
-      _buildShrinkWrap(controller: controller, physics: const BouncingScrollPhysics()),
+        _buildSimpleShrinkWrap(controller: controller, physics: const BouncingScrollPhysics()),
       );
       expect(controller.offset, 0.0);
       expect(tester.getTopLeft(find.text('Item 0')).dy, 0.0);
@@ -2032,12 +2081,12 @@ void main() {
       expect(tester.getBottomLeft(find.text('Item 19')).dy, 600.0);
     });
 
-  testWidgets('Shrinkwrap allows overscrolling per physics - horizontal', (WidgetTester tester) async {
+    testWidgets('allows overscrolling per physics - horizontal', (WidgetTester tester) async {
       // Regression test for https://github.com/flutter/flutter/issues/10949
       // Scrollables should overscroll when the scroll physics allow
       final  ScrollController controller = ScrollController();
       await tester.pumpWidget(
-      _buildShrinkWrap(
+        _buildSimpleShrinkWrap(
           controller: controller,
           scrollDirection: Axis.horizontal,
           physics: const BouncingScrollPhysics(),
@@ -2074,6 +2123,7 @@ void main() {
       expect(controller.offset, maxExtent);
       expect(tester.getTopRight(find.text('Item 19')).dx, 800.0);
     });
+  });
 
   testWidgets('Handles infinite constraints when TargetPlatform is iOS or macOS', (WidgetTester tester) async {
     // regression test for https://github.com/flutter/flutter/issues/45866