Fix scrollable to clear inner semantics node if it does not use two p… (#120996)

* Fix scrollable to clear inner semantics node if it does not use two panel

* g

* add more check

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

@@ -1659,6 +1659,7 @@ class _RenderScrollSemantics extends RenderProxyBox {
   @override
   void assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) {
     if (children.isEmpty || !children.first.isTagged(RenderViewport.useTwoPaneSemantics)) {
+      _innerNode = null;
       super.assembleSemanticsNode(node, config, children);
       return;
     }

packages/flutter/test/widgets/scrollable_test.dart

@@ -11,6 +11,8 @@ import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import 'semantics_tester.dart';
+
 Future<void> pumpTest(
   WidgetTester tester,
   TargetPlatform? platform, {
@@ -1643,6 +1645,51 @@ void main() {
     await tester.pump(const Duration(milliseconds: 4800));
     expect(getScrollOffset(tester), closeTo(333.2944, 0.0001));
   });
+
+  testWidgets('Swapping viewports in a scrollable does not crash', (WidgetTester tester) async {
+    final SemanticsTester semantics = SemanticsTester(tester);
+    final GlobalKey key = GlobalKey();
+    final GlobalKey key1 = GlobalKey();
+    Widget buildScrollable(bool withViewPort) {
+      return Scrollable(
+        key: key,
+        viewportBuilder: (BuildContext context, ViewportOffset position) {
+          if (withViewPort) {
+            return Viewport(
+              slivers: <Widget>[
+                SliverToBoxAdapter(child: Semantics(key: key1, container: true, child: const Text('text1')))
+              ],
+              offset: ViewportOffset.zero(),
+            );
+          }
+          return Semantics(key: key1, container: true, child: const Text('text1'));
+        },
+      );
+    }
+    // This should cache the inner node in Scrollable with the children text1.
+    await tester.pumpWidget(
+      MaterialApp(
+        home: buildScrollable(true),
+      ),
+    );
+    expect(semantics, includesNodeWith(tags: <SemanticsTag>{RenderViewport.useTwoPaneSemantics}));
+    // This does not use two panel, this should clear cached inner node.
+    await tester.pumpWidget(
+      MaterialApp(
+        home: buildScrollable(false),
+      ),
+    );
+    expect(semantics, isNot(includesNodeWith(tags: <SemanticsTag>{RenderViewport.useTwoPaneSemantics})));
+    // If the inner node was cleared in the previous step, this should not crash.
+    await tester.pumpWidget(
+      MaterialApp(
+        home: buildScrollable(true),
+      ),
+    );
+    expect(semantics, includesNodeWith(tags: <SemanticsTag>{RenderViewport.useTwoPaneSemantics}));
+    expect(tester.takeException(), isNull);
+    semantics.dispose();
+  });
 }
 
 // ignore: must_be_immutable

packages/flutter/test/widgets/semantics_tester.dart

@@ -487,6 +487,7 @@ class SemanticsTester {
     TextDirection? textDirection,
     List<SemanticsAction>? actions,
     List<SemanticsFlag>? flags,
+    Set<SemanticsTag>? tags,
     double? scrollPosition,
     double? scrollExtentMax,
     double? scrollExtentMin,
@@ -536,6 +537,12 @@ class SemanticsTester {
           return false;
         }
       }
+      if (tags != null) {
+        final Set<SemanticsTag>? actualTags = node.getSemanticsData().tags;
+        if (!setEquals<SemanticsTag>(actualTags, tags)) {
+          return false;
+        }
+      }
       if (scrollPosition != null && !nearEqual(node.scrollPosition, scrollPosition, 0.1)) {
         return false;
       }
@@ -796,6 +803,7 @@ class _IncludesNodeWith extends Matcher {
     this.textDirection,
     this.actions,
     this.flags,
+    this.tags,
     this.scrollPosition,
     this.scrollExtentMax,
     this.scrollExtentMin,
@@ -806,6 +814,7 @@ class _IncludesNodeWith extends Matcher {
        value != null ||
        actions != null ||
        flags != null ||
+       tags != null ||
        scrollPosition != null ||
        scrollExtentMax != null ||
        scrollExtentMin != null ||
@@ -821,6 +830,7 @@ class _IncludesNodeWith extends Matcher {
   final TextDirection? textDirection;
   final List<SemanticsAction>? actions;
   final List<SemanticsFlag>? flags;
+  final Set<SemanticsTag>? tags;
   final double? scrollPosition;
   final double? scrollExtentMax;
   final double? scrollExtentMin;
@@ -839,6 +849,7 @@ class _IncludesNodeWith extends Matcher {
       textDirection: textDirection,
       actions: actions,
       flags: flags,
+      tags: tags,
       scrollPosition: scrollPosition,
       scrollExtentMax: scrollExtentMax,
       scrollExtentMin: scrollExtentMin,
@@ -865,6 +876,7 @@ class _IncludesNodeWith extends Matcher {
       if (textDirection != null) ' (${textDirection!.name})',
       if (actions != null) 'actions "${actions!.join(', ')}"',
       if (flags != null) 'flags "${flags!.join(', ')}"',
+      if (tags != null) 'tags "${tags!.join(', ')}"',
       if (scrollPosition != null) 'scrollPosition "$scrollPosition"',
       if (scrollExtentMax != null) 'scrollExtentMax "$scrollExtentMax"',
       if (scrollExtentMin != null) 'scrollExtentMin "$scrollExtentMin"',
@@ -889,6 +901,7 @@ Matcher includesNodeWith({
   TextDirection? textDirection,
   List<SemanticsAction>? actions,
   List<SemanticsFlag>? flags,
+  Set<SemanticsTag>? tags,
   double? scrollPosition,
   double? scrollExtentMax,
   double? scrollExtentMin,
@@ -905,6 +918,7 @@ Matcher includesNodeWith({
     textDirection: textDirection,
     actions: actions,
     flags: flags,
+    tags: tags,
     scrollPosition: scrollPosition,
     scrollExtentMax: scrollExtentMax,
     scrollExtentMin: scrollExtentMin,