Fix the hitTest issue of reversed SliverMainAxisGroup. (#171073)

Fixes: #170999
Fixes: #171121

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

@@ -246,10 +246,17 @@ class RenderSliverMainAxisGroup extends RenderSliver
 
   @override
   double childMainAxisPosition(RenderSliver child) {
-    final Offset paintOffset = (child.parentData! as SliverPhysicalParentData).paintOffset;
-    return switch (constraints.axis) {
-      Axis.horizontal => paintOffset.dx,
-      Axis.vertical => paintOffset.dy,
+    final SliverPhysicalParentData childParentData = child.parentData! as SliverPhysicalParentData;
+    return switch (applyGrowthDirectionToAxisDirection(
+      child.constraints.axisDirection,
+      child.constraints.growthDirection,
+    )) {
+      AxisDirection.down => childParentData.paintOffset.dy,
+      AxisDirection.right => childParentData.paintOffset.dx,
+      AxisDirection.up =>
+        geometry!.paintExtent - child.geometry!.paintExtent - childParentData.paintOffset.dy,
+      AxisDirection.left =>
+        geometry!.paintExtent - child.geometry!.paintExtent - childParentData.paintOffset.dx,
     };
   }
 

packages/flutter/test/widgets/sliver_main_axis_group_test.dart

@@ -1063,6 +1063,34 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  testWidgets('SliverMainAxisGroup reverse hitTest', (WidgetTester tester) async {
+    bool onTapCalled = false;
+    await tester.pumpWidget(
+      _buildSliverMainAxisGroup(
+        reverse: true,
+        viewportHeight: 70,
+        slivers: <Widget>[
+          SliverToBoxAdapter(
+            child: GestureDetector(
+              behavior: HitTestBehavior.opaque,
+              onTap: () {
+                onTapCalled = true;
+              },
+              child: const SizedBox(height: 50),
+            ),
+          ),
+          const SliverToBoxAdapter(child: SizedBox(height: 20)),
+        ],
+      ),
+    );
+    await tester.tapAt(const Offset(0, 10));
+    await tester.pumpAndSettle();
+    expect(onTapCalled, isFalse);
+    await tester.tapAt(const Offset(0, 69));
+    await tester.pumpAndSettle();
+    expect(onTapCalled, isTrue);
+  });
+
   testWidgets('SliverMainAxisGroup with center', (WidgetTester tester) async {
     final ScrollController controller = ScrollController();
     addTearDown(controller.dispose);