Sliver padding overlap fix (#65323)

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

@@ -19,11 +19,9 @@ import 'sliver.dart';
 /// passed on to the child.
 ///
 /// {@template flutter.rendering.sliverPadding.limitation}
-/// Applying padding to anything but the most mundane sliver is likely to have
-/// undesired effects. For example, wrapping a [RenderSliverPinnedPersistentHeader]
-/// will cause the app bar to overlap earlier slivers (contrary to the normal
-/// behavior of pinned app bars), and while the app bar is pinned, the padding
-/// will scroll away.
+/// Applying padding in the main extent of the viewport to slivers that have scroll effects is likely to have
+/// undesired effects. For example, For example, wrapping a [SliverPersistentHeader] with
+/// `pinned:true` will cause only the appbar to stay pinned while the padding will scroll away.
 /// {@endtemplate}
 abstract class RenderSliverEdgeInsetsPadding extends RenderSliver with RenderObjectWithChildMixin<RenderSliver> {
   /// The amount to pad the child in each dimension.
@@ -129,11 +127,20 @@ abstract class RenderSliverEdgeInsetsPadding extends RenderSliver with RenderObj
       );
       return;
     }
+    final double beforePaddingPaintExtent = calculatePaintOffset(
+      constraints,
+      from: 0.0,
+      to: beforePadding,
+    );
+    double overlap = constraints.overlap;
+    if (overlap > 0) {
+      overlap = math.max(0.0, constraints.overlap - beforePaddingPaintExtent);
+    }
     child!.layout(
       constraints.copyWith(
         scrollOffset: math.max(0.0, constraints.scrollOffset - beforePadding),
         cacheOrigin: math.min(0.0, constraints.cacheOrigin + beforePadding),
-        overlap: 0.0,
+        overlap: overlap,
         remainingPaintExtent: constraints.remainingPaintExtent - calculatePaintOffset(constraints, from: 0.0, to: beforePadding),
         remainingCacheExtent: constraints.remainingCacheExtent - calculateCacheOffset(constraints, from: 0.0, to: beforePadding),
         crossAxisExtent: math.max(0.0, constraints.crossAxisExtent - crossAxisPadding),
@@ -148,11 +155,6 @@ abstract class RenderSliverEdgeInsetsPadding extends RenderSliver with RenderObj
       );
       return;
     }
-    final double beforePaddingPaintExtent = calculatePaintOffset(
-      constraints,
-      from: 0.0,
-      to: beforePadding,
-    );
     final double afterPaddingPaintExtent = calculatePaintOffset(
       constraints,
       from: beforePadding + childLayoutGeometry.scrollExtent,
@@ -175,6 +177,7 @@ abstract class RenderSliverEdgeInsetsPadding extends RenderSliver with RenderObj
       constraints.remainingPaintExtent,
     );
     geometry = SliverGeometry(
+      paintOrigin: childLayoutGeometry.paintOrigin,
       scrollExtent: mainAxisPadding + childLayoutGeometry.scrollExtent,
       paintExtent: paintExtent,
       layoutExtent: math.min(mainAxisPaddingPaintExtent + childLayoutGeometry.layoutExtent, paintExtent),

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

@@ -3004,11 +3004,7 @@ class SliverToBoxAdapter extends SingleChildRenderObjectWidget {
 /// is a basic sliver that insets another sliver by applying padding on each
 /// side.
 ///
-/// Applying padding to anything but the most mundane sliver is likely to have
-/// undesired effects. For example, wrapping a [SliverPersistentHeader] with
-/// `pinned:true` will cause the app bar to overlap earlier slivers (contrary to
-/// the normal behavior of pinned app bars), and while the app bar is pinned,
-/// the padding will scroll away.
+/// {@macro flutter.rendering.sliverPadding.limitation}
 ///
 /// See also:
 ///

packages/flutter/test/widgets/slivers_padding_test.dart

@@ -9,6 +9,18 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
+class _MockRenderSliver extends RenderSliver {
+  @override
+  void performLayout() {
+    geometry = const SliverGeometry(
+      paintOrigin: 10,
+      paintExtent: 10,
+      maxPaintExtent: 10,
+    );
+  }
+
+}
+
 Future<void> test(WidgetTester tester, double offset, EdgeInsetsGeometry padding, AxisDirection axisDirection, TextDirection textDirection) {
   return tester.pumpWidget(
     Directionality(
@@ -459,4 +471,79 @@ void main() {
       equals(570),
     );
   });
+
+  testWidgets('SliverPadding consumes only its padding from the overlap of its parent\'s constraints', (WidgetTester tester) async {
+    final _MockRenderSliver mock = _MockRenderSliver();
+    final RenderSliverPadding renderObject = RenderSliverPadding(
+      padding: const EdgeInsets.only(top: 20),
+    );
+    renderObject.child = mock;
+    renderObject.layout(const SliverConstraints(
+        viewportMainAxisExtent: 100.0,
+        overlap: 100.0,
+        cacheOrigin: 0.0,
+        scrollOffset: 0.0,
+        axisDirection: AxisDirection.down,
+        growthDirection: GrowthDirection.forward,
+        crossAxisExtent: 100.0,
+        crossAxisDirection: AxisDirection.right,
+        userScrollDirection: ScrollDirection.idle,
+        remainingPaintExtent: 100.0,
+        remainingCacheExtent: 100.0,
+        precedingScrollExtent: 0.0,
+      ),
+      parentUsesSize: true,
+    );
+    expect(mock.constraints.overlap, 80.0);
+  });
+
+  testWidgets('SliverPadding passes the overlap to the child if it\'s negative', (WidgetTester tester) async {
+    final _MockRenderSliver mock = _MockRenderSliver();
+    final RenderSliverPadding renderObject = RenderSliverPadding(
+      padding: const EdgeInsets.only(top: 20),
+    );
+    renderObject.child = mock;
+    renderObject.layout(const SliverConstraints(
+        viewportMainAxisExtent: 100.0,
+        overlap: -100.0,
+        cacheOrigin: 0.0,
+        scrollOffset: 0.0,
+        axisDirection: AxisDirection.down,
+        growthDirection: GrowthDirection.forward,
+        crossAxisExtent: 100.0,
+        crossAxisDirection: AxisDirection.right,
+        userScrollDirection: ScrollDirection.idle,
+        remainingPaintExtent: 100.0,
+        remainingCacheExtent: 100.0,
+        precedingScrollExtent: 0.0,
+      ),
+      parentUsesSize: true,
+    );
+    expect(mock.constraints.overlap, -100.0);
+  });
+
+  testWidgets('SliverPadding passes the paintOrigin of the child on', (WidgetTester tester) async {
+    final _MockRenderSliver mock = _MockRenderSliver();
+    final RenderSliverPadding renderObject = RenderSliverPadding(
+      padding: const EdgeInsets.only(top: 20),
+    );
+    renderObject.child = mock;
+    renderObject.layout(const SliverConstraints(
+        viewportMainAxisExtent: 100.0,
+        overlap: 100.0,
+        cacheOrigin: 0.0,
+        scrollOffset: 0.0,
+        axisDirection: AxisDirection.down,
+        growthDirection: GrowthDirection.forward,
+        crossAxisExtent: 100.0,
+        crossAxisDirection: AxisDirection.right,
+        userScrollDirection: ScrollDirection.idle,
+        remainingPaintExtent: 100.0,
+        remainingCacheExtent: 100.0,
+        precedingScrollExtent: 0.0,
+      ),
+      parentUsesSize: true,
+    );
+    expect(renderObject.geometry.paintOrigin, 10.0);
+  });
 }