Use stable IDs for TextSpan SemanticsNodes (#52769)

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:ui' as ui show Gradient, Shader, TextBox, PlaceholderAlignment, TextHeightBehavior;
 
@@ -844,6 +845,12 @@ class RenderParagraph extends RenderBox
     }
   }
 
+  // Caches [SemanticsNode]s created during [assembleSemanticsNode] so they
+  // can be re-used when [assembleSemanticsNode] is called again. This ensures
+  // stable ids for the [SemanticsNode]s of [TextSpan]s across
+  // [assembleSemanticsNode] invocations.
+  Queue<SemanticsNode> _cachedChildNodes;
+
   @override
   void assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) {
     assert(_semanticsInfo != null && _semanticsInfo.isNotEmpty);
@@ -854,6 +861,7 @@ class RenderParagraph extends RenderBox
     int start = 0;
     int placeholderIndex = 0;
     RenderBox child = firstChild;
+    final Queue<SemanticsNode> newChildCache = Queue<SemanticsNode>();
     for (final InlineSpanSemanticsInformation info in _combineSemanticsInfo()) {
       final TextDirection initialDirection = currentDirection;
       final TextSelection selection = TextSelection(
@@ -914,17 +922,27 @@ class RenderParagraph extends RenderBox
             assert(false);
           }
         }
-        newChildren.add(
-          SemanticsNode()
-            ..updateWith(config: configuration)
-            ..rect = currentRect,
-        );
+        final SemanticsNode newChild = (_cachedChildNodes?.isNotEmpty == true)
+            ? _cachedChildNodes.removeFirst()
+            : SemanticsNode();
+        newChild
+          ..updateWith(config: configuration)
+          ..rect = currentRect;
+        newChildCache.addLast(newChild);
+        newChildren.add(newChild);
       }
       start += info.text.length;
     }
+    _cachedChildNodes = newChildCache;
     node.updateWith(config: config, childrenInInversePaintOrder: newChildren);
   }
 
+  @override
+  void clearSemantics() {
+    super.clearSemantics();
+    _cachedChildNodes = null;
+  }
+
   @override
   List<DiagnosticsNode> debugDescribeChildren() {
     return <DiagnosticsNode>[

packages/flutter/test/widgets/text_semantics_test.dart

@@ -0,0 +1,133 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+
+import 'semantics_tester.dart';
+
+void main() {
+  testWidgets('SemanticsNode ids are stable', (WidgetTester tester) async {
+    // Regression test for b/151732341.
+    final SemanticsTester semantics = SemanticsTester(tester);
+    await tester.pumpWidget(Directionality(
+    textDirection: TextDirection.ltr,
+      child: Text.rich(
+        TextSpan(
+          text: 'Hallo ',
+          recognizer: TapGestureRecognizer()..onTap = () {},
+          children: <TextSpan>[
+            TextSpan(
+              text: 'Welt ',
+              recognizer: TapGestureRecognizer()..onTap = () {},
+            ),
+            TextSpan(
+              text: '!!!',
+              recognizer: TapGestureRecognizer()..onTap = () {},
+            ),
+          ],
+        ),
+      ),
+    ));
+    expect(find.text('Hallo Welt !!!'), findsOneWidget);
+    final SemanticsNode node = tester.getSemantics(find.text('Hallo Welt !!!'));
+    final Map<String, int> labelToNodeId = <String, int>{};
+    node.visitChildren((SemanticsNode node) {
+      labelToNodeId[node.label] = node.id;
+       return true;
+    });
+    expect(node.id, 1);
+    expect(labelToNodeId['Hallo '], 2);
+    expect(labelToNodeId['Welt '], 3);
+    expect(labelToNodeId['!!!'], 4);
+    expect(labelToNodeId.length, 3);
+
+    // Rebuild semantics.
+    tester.renderObject(find.text('Hallo Welt !!!')).markNeedsSemanticsUpdate();
+    await tester.pump();
+
+    final SemanticsNode nodeAfterRebuild = tester.getSemantics(find.text('Hallo Welt !!!'));
+    final Map<String, int> labelToNodeIdAfterRebuild = <String, int>{};
+    nodeAfterRebuild.visitChildren((SemanticsNode node) {
+      labelToNodeIdAfterRebuild[node.label] = node.id;
+      return true;
+    });
+
+    // Node IDs are stable.
+    expect(nodeAfterRebuild.id, node.id);
+    expect(labelToNodeIdAfterRebuild['Hallo '], labelToNodeId['Hallo ']);
+    expect(labelToNodeIdAfterRebuild['Welt '], labelToNodeId['Welt ']);
+    expect(labelToNodeIdAfterRebuild['!!!'], labelToNodeId['!!!']);
+    expect(labelToNodeIdAfterRebuild.length, 3);
+
+    // Remove one node.
+    await tester.pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: Text.rich(
+        TextSpan(
+          text: 'Hallo ',
+          recognizer: TapGestureRecognizer()..onTap = () {},
+          children: <TextSpan>[
+            TextSpan(
+              text: 'Welt ',
+              recognizer: TapGestureRecognizer()..onTap = () {},
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    final SemanticsNode nodeAfterRemoval = tester.getSemantics(find.text('Hallo Welt '));
+    final Map<String, int> labelToNodeIdAfterRemoval = <String, int>{};
+    nodeAfterRemoval.visitChildren((SemanticsNode node) {
+      labelToNodeIdAfterRemoval[node.label] = node.id;
+      return true;
+    });
+
+    // Node IDs are stable.
+    expect(nodeAfterRemoval.id, node.id);
+    expect(labelToNodeIdAfterRemoval['Hallo '], labelToNodeId['Hallo ']);
+    expect(labelToNodeIdAfterRemoval['Welt '], labelToNodeId['Welt ']);
+    expect(labelToNodeIdAfterRemoval.length, 2);
+
+    await tester.pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: Text.rich(
+        TextSpan(
+          text: 'Hallo ',
+          recognizer: TapGestureRecognizer()..onTap = () {},
+          children: <TextSpan>[
+            TextSpan(
+              text: 'Welt ',
+              recognizer: TapGestureRecognizer()..onTap = () {},
+            ),
+            TextSpan(
+              text: '!!!',
+              recognizer: TapGestureRecognizer()..onTap = () {},
+            ),
+          ],
+        ),
+      ),
+    ));
+    expect(find.text('Hallo Welt !!!'), findsOneWidget);
+    final SemanticsNode nodeAfterAddition = tester.getSemantics(find.text('Hallo Welt !!!'));
+    final Map<String, int> labelToNodeIdAfterAddition = <String, int>{};
+    nodeAfterAddition.visitChildren((SemanticsNode node) {
+      labelToNodeIdAfterAddition[node.label] = node.id;
+      return true;
+    });
+
+    // New node gets a new ID.
+    expect(nodeAfterAddition.id, node.id);
+    expect(labelToNodeIdAfterAddition['Hallo '], labelToNodeId['Hallo ']);
+    expect(labelToNodeIdAfterAddition['Welt '], labelToNodeId['Welt ']);
+    expect(labelToNodeIdAfterAddition['!!!'], isNot(labelToNodeId['!!!']));
+    expect(labelToNodeIdAfterAddition['!!!'], isNotNull);
+    expect(labelToNodeIdAfterAddition.length, 3);
+
+    semantics.dispose();
+  });
+}