commit 5ab6c7bce1f6e9ebeaf9e66d1145a17289ad0223
author Kate Lovett <katelovett@google.com> Fri Oct 01 11:08:02 2021 -0500
committer GitHub <noreply@github.com> Fri Oct 01 09:08:02 2021 -0700
tree 4371d0bd778b49ec41cbda1389c251e83ace1751
parent 778876597a61644cfc4e8ae4a4c99f5322a2c15e

Fix overflow edge case in overscrolled RenderShrinkWrappingViewport (#90419)

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

diff --git a/packages/flutter/lib/src/rendering/viewport.dart b/packages/flutter/lib/src/rendering/viewport.dart
index 3e32b4a..9da485d 100644
--- a/packages/flutter/lib/src/rendering/viewport.dart
+++ b/packages/flutter/lib/src/rendering/viewport.dart
@@ -1933,7 +1933,7 @@
       scrollOffset: math.max(0.0, correctedOffset),
       overlap: math.min(0.0, correctedOffset),
       layoutOffset: math.max(0.0, -correctedOffset),
-      remainingPaintExtent: mainAxisExtent,
+      remainingPaintExtent: mainAxisExtent + math.min(0.0, correctedOffset),
       mainAxisExtent: mainAxisExtent,
       crossAxisExtent: crossAxisExtent,
       growthDirection: GrowthDirection.forward,

packages/flutter/test/rendering/viewport_test.dart

diff --git a/packages/flutter/test/rendering/viewport_test.dart b/packages/flutter/test/rendering/viewport_test.dart
index 913eb57..2cfe466 100644
--- a/packages/flutter/test/rendering/viewport_test.dart
+++ b/packages/flutter/test/rendering/viewport_test.dart
@@ -7,6 +7,8 @@
 // initialize a binding, which rendering_tester will attempt to re-initialize
 // (or vice versa).
 
+@Tags(<String>['reduced-test-set'])
+
 import 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
@@ -1867,6 +1869,53 @@
     );
   }
 
+  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(
+          textDirection: TextDirection.ltr,
+          child: MediaQuery(
+            data: const MediaQueryData(),
+            child: Column(
+              children: <Widget>[
+                Container(height: 100, color: const Color(0x00000000)),
+                Container(
+                  height: 150,
+                  color: const Color(0xFFF44336),
+                  child: ListView.builder(
+                    controller: controller,
+                    shrinkWrap: true,
+                    physics: const BouncingScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
+                    itemBuilder: (BuildContext context, int index) => Text('Item $index'),
+                    itemCount: 10,
+                  ),
+                ),
+                Container(height: 100, color: const Color(0x00000000)),
+              ],
+            ),
+          ),
+        )
+    );
+    expect(controller.offset, 0.0);
+    expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+
+    // Overscroll
+    final TestGesture overscrollGesture = await tester.startGesture(tester.getCenter(find.text('Item 0')));
+    await overscrollGesture.moveBy(const Offset(0, 25));
+    await tester.pump();
+    expect(controller.offset, -25.0);
+    expect(tester.getTopLeft(find.text('Item 0')).dy, 125.0);
+    await expectLater(
+      find.byType(Directionality),
+      matchesGoldenFile('shrinkwrapped_overscroll.png'),
+    );
+    await overscrollGesture.up();
+    await tester.pumpAndSettle();
+    expect(controller.offset, 0.0);
+    expect(tester.getTopLeft(find.text('Item 0')).dy, 100.0);
+  });
+
   testWidgets('Shrinkwrap 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