Reland "Fix sliver geometry assert (#47027)"

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

@@ -1211,17 +1211,17 @@ abstract class RenderSliver extends RenderObject {
       }
     ));
     assert(() {
-      if (geometry.paintExtent > constraints.remainingPaintExtent) {
+      if (geometry.paintOrigin + geometry.paintExtent > constraints.remainingPaintExtent) {
         throw FlutterError.fromParts(<DiagnosticsNode>[
           ErrorSummary('SliverGeometry has a paintOffset that exceeds the remainingPaintExtent from the constraints.'),
           describeForError('The render object whose geometry violates the constraints is the following'),
           ..._debugCompareFloats(
             'remainingPaintExtent', constraints.remainingPaintExtent,
-            'paintExtent', geometry.paintExtent,
+            'paintOrigin + paintExtent', geometry.paintOrigin + geometry.paintExtent,
           ),
           ErrorDescription(
-            'The paintExtent must cause the child sliver to paint within the viewport, and so '
+            'The paintOrigin and paintExtent must cause the child sliver to paint '
-            'cannot exceed the remainingPaintExtent.',
+            'within the viewport, and so cannot exceed the remainingPaintExtent.',
           ),
         ]);
       }

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

@@ -373,14 +373,15 @@ abstract class RenderSliverPinnedPersistentHeader extends RenderSliverPersistent
     final bool overlapsContent = constraints.overlap > 0.0;
     excludeFromSemanticsScrolling = overlapsContent || (constraints.scrollOffset > maxExtent - minExtent);
     layoutChild(constraints.scrollOffset, maxExtent, overlapsContent: overlapsContent);
-    final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent) as double;
+    final double effectiveRemainingPaintExtent = math.max(0, constraints.remainingPaintExtent - constraints.overlap);
+    final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, effectiveRemainingPaintExtent) as double;
     final double stretchOffset = stretchConfiguration != null ?
       constraints.overlap.abs() :
       0.0;
     geometry = SliverGeometry(
       scrollExtent: maxExtent,
       paintOrigin: constraints.overlap,
-      paintExtent: math.min(childExtent, constraints.remainingPaintExtent),
+      paintExtent: math.min(childExtent, effectiveRemainingPaintExtent),
       layoutExtent: layoutExtent,
       maxPaintExtent: maxExtent + stretchOffset,
       maxScrollObstructionExtent: minExtent,

packages/flutter/test/cupertino/refresh_test.dart

@@ -1028,6 +1028,30 @@ void main() {
         debugDefaultTargetPlatformOverride = null;
       },
     );
+
+    testWidgets('Should not crash when dragged', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: CustomScrollView(
+            physics: const BouncingScrollPhysics(),
+            slivers: <Widget>[
+              CupertinoSliverRefreshControl(
+                onRefresh: () async => Future<void>.delayed(const Duration(days: 2000)),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      await tester.dragFrom(const Offset(100, 10), const Offset(0.0, 50.0), touchSlopY: 0);
+      await tester.pump();
+
+      await tester.dragFrom(const Offset(100, 10), const Offset(0, 500), touchSlopY: 0);
+      await tester.pump();
+
+      expect(tester.takeException(), isNull);
+    });
   };
 
   final VoidCallback stateMachineTestGroup = () {
@@ -1465,6 +1489,36 @@ void main() {
   // Test the internal state machine directly to make sure the UI aren't just
   // correct by coincidence.
   group('state machine test short list', stateMachineTestGroup);
+
+  testWidgets(
+    'Does not crash when paintExtent > remainingPaintExtent',
+    (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/46871.
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: CustomScrollView(
+            physics: const BouncingScrollPhysics(),
+            slivers: <Widget>[
+              const CupertinoSliverRefreshControl(),
+              SliverList(
+                delegate: SliverChildBuilderDelegate(
+                  (BuildContext context, int index) => const SizedBox(height: 100),
+                  childCount: 20,
+                ),
+              ),
+            ],
+          ),
+        ),
+      );
+
+      // Drag the content down far enough so that
+      // geometry.paintExent > constraints.maxPaintExtent
+      await tester.dragFrom(const Offset(10, 10), const Offset(0, 500));
+      await tester.pump();
+
+      expect(tester.takeException(), isNull);
+  });
 }
 
 class MockHelper extends Mock {