SliverOffstage Fix (#45580)

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

@@ -2124,7 +2124,14 @@ class RenderSliverOffstage extends RenderSliver with RenderObjectWithChildMixin<
   void performLayout() {
     assert(child != null);
     child.layout(constraints, parentUsesSize: true);
+    if (!offstage)
       geometry = child.geometry;
+    else
+      geometry = const SliverGeometry(
+        scrollExtent: 0.0,
+        visible: false,
+        maxPaintExtent: 0.0,
+      );
   }
 
   @override
@@ -2159,7 +2166,7 @@ class RenderSliverOffstage extends RenderSliver with RenderObjectWithChildMixin<
   void paint(PaintingContext context, Offset offset) {
     if (offstage)
       return;
-    super.paint(context, offset);
+    context.paintChild(child, offset);
   }
 
   @override

packages/flutter/test/widgets/slivers_test.dart

@@ -454,6 +454,10 @@ void main() {
 
       expect(semantics.nodesWith(label: 'a'), hasLength(0));
       expect(find.byType(Text), findsNothing);
+      final RenderViewport renderViewport = tester.renderObject(find.byType(Viewport));
+      final RenderSliver renderSliver = renderViewport.lastChild;
+      expect(renderSliver.geometry.scrollExtent, 0.0);
+      expect(find.byType(SliverOffstage), findsNothing);
     });
 
     testWidgets('offstage false', (WidgetTester tester) async {
@@ -469,6 +473,10 @@ void main() {
 
       expect(semantics.nodesWith(label: 'a'), hasLength(1));
       expect(find.byType(Text), findsOneWidget);
+      final RenderViewport renderViewport = tester.renderObject(find.byType(Viewport));
+      final RenderSliver renderSliver = renderViewport.lastChild;
+      expect(renderSliver.geometry.scrollExtent, 14.0);
+      expect(find.byType(SliverOffstage), paints..paragraph());
     });
   });