ExpansionTile semantics assertion with nested WidgetSpan title in Flutter 3.44.2

Steps to reproduce

Create a minimal Flutter package.
Add the test below as test/expansion_tile_semantics_test.dart.
Run flutter test.
Observe that the test fails on Flutter 3.44.2.
The same pattern previously passed on Flutter 3.38.10.

Expected results

The widget test should complete without framework assertions. ExpansionTile should be able to build and pump when its title contains a Text.rich with a nested WidgetSpan.

Actual results

Flutter throws a framework semantics assertion during tester.pumpWidget:

'package:flutter/src/rendering/object.dart': Failed assertion: line 5460 pos 12: '!conflict': is not true.

The failure happens during PipelineOwner.flushSemantics.

Code sample

pubspec.yaml

name: flutter_semantics_repro
description: Minimal Flutter semantics repro.
publish_to: none

environment:
  sdk: '>=3.8.0 <4.0.0'

dependencies:
  flutter:
    sdk: flutter

dev_dependencies:
  flutter_test:
    sdk: flutter

test/expansion_tile_semantics_test.dart

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('ExpansionTile title allows nested block-like WidgetSpan',
      (tester) async {
    await tester.pumpWidget(
      MaterialApp(
        home: Scaffold(
          body: Text.rich(
            TextSpan(
              children: [
                WidgetSpan(
                  child: ExpansionTile(
                    title: Text.rich(
                      TextSpan(
                        children: [
                          WidgetSpan(
                            child: Text.rich(
                              const TextSpan(
                                style: TextStyle(
                                  fontSize: 32,
                                  fontWeight: FontWeight.bold,
                                ),
                                text: 'Header',
                              ),
                            ),
                          ),
                        ],
                      ),
                    ),
                    children: const [Text('These are the details.')],
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  });

  testWidgets('ExpansionTile title allows plain Text', (tester) async {
    await tester.pumpWidget(
      const MaterialApp(
        home: Scaffold(
          body: ExpansionTile(
            title: Text('Header'),
            children: [Text('These are the details.')],
          ),
        ),
      ),
    );
  });
}

Screenshots or Video

No response

Logs

Screenshots / Video demonstration

Not applicable.

Logs

$ flutter test
00:00 +0: loading /tmp/flutter_semantics_repro/test/expansion_tile_semantics_test.dart
00:00 +0: ExpansionTile title allows nested block-like WidgetSpan
══╡ EXCEPTION CAUGHT BY SCHEDULER LIBRARY ╞═════════════════════════════════════════════════════════
The following assertion was thrown during a scheduler callback:
'package:flutter/src/rendering/object.dart': Failed assertion: line 5460 pos 12: '!conflict': is not
true.

Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
  https://github.com/flutter/flutter/issues/new?template=02_bug.yml

When the exception was thrown, this was the stack:
#2      _IncompleteSemanticsFragment.markSiblingConfigurationConflict (package:flutter/src/rendering/object.dart:5460:12)
#3      _RenderObjectSemantics._marksConflictsInMergeGroup (package:flutter/src/rendering/object.dart:6517:16)
#4      _RenderObjectSemantics.updateChildren (package:flutter/src/rendering/object.dart:5837:5)
#5      _RenderObjectSemantics._didUpdateParentData (package:flutter/src/rendering/object.dart:6071:5)
#6      _RenderObjectSemantics._collectChildMergeUpAndSiblingGroup (package:flutter/src/rendering/object.dart:5995:22)
#7      _RenderObjectSemantics.updateChildren (package:flutter/src/rendering/object.dart:5825:50)
...
#101    PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1489:25)
#102    PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1653:15)
#103    AutomatedTestWidgetsFlutterBinding.drawFrame (package:flutter_test/src/binding.dart:2444:35)
#104    RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:509:5)
#105    SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1430:15)
#106    SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1345:9)
#107    AutomatedTestWidgetsFlutterBinding.pump.<anonymous closure> (package:flutter_test/src/binding.dart:2260:9)
#110    TestAsyncUtils.guard (package:flutter/src/test_async_utils.dart:74:41)
#111    AutomatedTestWidgetsFlutterBinding.pump (package:flutter_test/src/binding.dart:2249:27)
#112    WidgetTester.pumpWidget.<anonymous closure> (package:flutter_test/src/widget_tester.dart:598:22)
#115    TestAsyncUtils.guard (package:flutter_test/src/test_async_utils.dart:74:41)
#116    WidgetTester.pumpWidget (package:flutter_test/src/widget_tester.dart:595:27)
#117    main.<anonymous closure> (file:///tmp/flutter_semantics_repro/test/expansion_tile_semantics_test.dart:7:18)
#118    testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:192:29)
<asynchronous suspension>
#119    TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:1952:5)
<asynchronous suspension>
<asynchronous suspension>
(elided 7 frames from class _AssertionError, dart:async, and package:stack_trace)
════════════════════════════════════════════════════════════════════════════════════════════════════
00:00 +0 -1: ExpansionTile title allows nested block-like WidgetSpan [E]
  Test failed. See exception logs above.
  The test description was: ExpansionTile title allows nested block-like WidgetSpan

00:00 +0 -1: ExpansionTile title allows plain Text
00:00 +1 -1: Some tests failed.

Flutter Doctor output

Doctor output

[✓] Flutter (Channel stable, 3.44.2, on Ubuntu 26.04 LTS 7.0.0-22-generic, locale en_US.UTF-8) [23ms]
    • Flutter version 3.44.2 on channel stable at /home/[email protected]/fvm/versions/3.44.2
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision c9a6c48423 (11 days ago), 2026-06-10 15:52:41 -0700
    • Engine revision 77e2e94772
    • Dart version 3.12.2
    • DevTools version 2.57.0
    • Feature flags: no-enable-web, enable-linux-desktop, no-enable-macos-desktop, no-enable-windows-desktop, no-enable-android, no-enable-ios, cli-animations, enable-native-assets, enable-swift-package-manager, omit-legacy-version-file, enable-lldb-debugging, enable-uiscene-migration

[✓] Linux toolchain - develop for Linux desktop [265ms]
    • Ubuntu clang version 21.1.8 (6ubuntu1)
    • cmake version 4.2.3
    • ninja version 1.13.2
    • pkg-config version 2.5.1
    • OpenGL core renderer: AMD Radeon 890M Graphics (radeonsi, strix1, ACO, DRM 3.64, 7.0.0-22-generic)
    • OpenGL core version: 4.6 (Core Profile) Mesa 26.0.3-1ubuntu1
    • OpenGL core shading language version: 4.60
    • OpenGL ES renderer: AMD Radeon 890M Graphics (radeonsi, strix1, ACO, DRM 3.64, 7.0.0-22-generic)
    • OpenGL ES version: OpenGL ES 3.2 Mesa 26.0.3-1ubuntu1
    • OpenGL ES shading language version: OpenGL ES GLSL ES 3.20
    • GL_EXT_framebuffer_blit: yes
    • GL_EXT_texture_format_BGRA8888: yes

[✓] Connected device (1 available) [12ms]
    • Linux (desktop) • linux • linux-x64 • Ubuntu 26.04 LTS 7.0.0-22-generic

[✓] Network resources [196ms]
    • All expected network resources are available.

• No issues found!

@d-loose

@d-loose Thanks for the detailed report and the minimal reproduction. I was able to reproduce the reported assertion on Flutter 3.44.2 using the provided test case. The issue includes a reproducible example and logs, making it actionable for further investigation. Routing this issue to the team-accessibility for further investigation

This issue is missing a priority label. Please set a priority label when adding the triaged-accessibility label.

[material_ui] Fix ExpansionTile WidgetSpan semantics assertion (flutt…

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

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`ExpansionTile` semantics assertion with nested `WidgetSpan` title in Flutter 3.44.2 #188298

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ExpansionTile semantics assertion with nested WidgetSpan title in Flutter 3.44.2 #188298

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suryaKommana2662 commented on Jun 22, 2026

flutter-triage-bot commented on Jul 1, 2026

github-actions commented on Oct 23, 2026

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`ExpansionTile` semantics assertion with nested `WidgetSpan` title in Flutter 3.44.2 #188298