Bug Report: Semantics Assertion Failure with `FTextField`

[haijd]

Description

When using FResizable component in a Flutter application, the app triggers continuous semantics-related assertion failures that cascade into rendering pipeline errors. This makes the application unstable and fills the console with error messages.

Environment

• Forui Version: 0.17.0
• Flutter Version: 3.10.4+
• Dart SDK: ^3.10.4
• Platform: Linux (also likely affects other platforms)
• Framework: Using Rinf for Flutter-Rust interop

Error Messages

Primary Error

'package:flutter/src/semantics/semantics.dart': Failed assertion: line 4392 pos 16:
'node.parent == null || !node.parent!.isPartOfNodeMerging || node.isMergedIntoParent': is not true.

Secondary Errors (Cascading)

'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16:
'debugFrameWasSentToEngine': is not true.

'package:flutter/src/semantics/semantics.dart': Failed assertion: line 4406 pos 14:
'node.parent?._dirty != true': is not true.

Stack Trace

#2      SemanticsOwner.sendSemanticsUpdate (package:flutter/src/semantics/semantics.dart:4392:16)
#3      PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1512:24)
#4      PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1514:15)
#5      RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:636:25)
#6      WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:1264:13)
#7      RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:495:5)
#8      SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1434:15)
#9      SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1347:9)
#10     SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:1057:9)

Steps to Reproduce

Minimal Code Example

import 'package:flutter/cupertino.dart';
import 'package:forui/forui.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return CupertinoApp(
      builder: (context, child) {
        return FAnimatedTheme(
          data: FThemes.zinc.light,
          child: child!,
        );
      },
      home: const HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    final media = MediaQuery.of(context);
    final initWidth = media.size.width / 2;

    return FResizable(
      axis: Axis.horizontal,
      divider: FResizableDivider.divider,
      children: [
        FResizableRegion(
          initialExtent: initWidth,
          minExtent: 256,
          builder: (context, data, _) => Container(color: const Color(0xFFE0E0E0)),
        ),
        FResizableRegion(
          initialExtent: initWidth,
          minExtent: 482,
          builder: (context, data, _) => Container(color: const Color(0xFFF5F5F5)),
        )
      ],
    );
  }
}

Steps

1. Create a new Flutter project with forui: ^0.17.0
2. Add the minimal code above
3. Run the application: flutter run
4. Observe the console output showing continuous assertion failures

Expected Behavior

The FResizable component should render without triggering semantics assertion failures.

Actual Behavior

• Application starts but immediately triggers semantics assertion failures
• Errors continue to appear repeatedly (hundreds of times)
• The errors cascade from semantics to rendering pipeline
• Application may still function but is unstable

Workaround

The issue can be temporarily bypassed by excluding the semantics tree at the app level:

CupertinoApp(
  builder: (context, child) {
    return FAnimatedTheme(
      data: FThemes.zinc.light,
      child: ExcludeSemantics(
        child: child!,
      ),
    );
  },
  home: const HomePage(),
)

Note: This workaround disables accessibility features for the entire application.

Root Cause Hypothesis

The FResizable component appears to have an issue with how it manages its semantics tree during initialization or rendering. The error suggests that a semantics node is being merged into a parent incorrectly, or the parent-child relationship in the semantics tree is inconsistent.

Impact

• Severity: High - Makes applications unstable and unusable without workaround
• Accessibility: Workaround requires disabling semantics, breaking screen readers
• User Experience: Console spam makes debugging other issues difficult

Additional Context

This issue was discovered while building a desktop application using Forui components. The error appears immediately on application launch and persists throughout the app lifecycle.

Related Components

• FResizable
• FResizableRegion
• FResizableDivider
• Possibly FAnimatedTheme (though less likely)

---

Would appreciate any guidance on this issue. Happy to provide additional information or test fixes if needed.

[Pante]

Thanks for taking the time to file a really detailed issue!

I don't have access to a Linux machine, I've tried running the provided example on macOS but can't seem to reproduce the issue.

Just to rule out any other issues, can you try running:

import 'package:flutter/cupertino.dart';
import 'package:forui/forui.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return CupertinoApp(
      builder: (context, child) {
        return FAnimatedTheme(
          data: FThemes.zinc.light,
          child: child!,
        );
      },
      home: const HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    final media = MediaQuery.of(context);
    final initWidth = media.size.width / 2;

    return FResizable(
      axis: Axis.horizontal,
      divider: FResizableDivider.divider,
      children: [
        FResizableRegion(
          initialExtent: initWidth,
          builder: (context, data, _) => Container(color: const Color(0xFFE0E0E0)),
        ),
        FResizableRegion(
          initialExtent: initWidth,
          builder: (context, data, _) => Container(color: const Color(0xFFF5F5F5)),
        )
      ],
    );
  }
}

[haijd]

Yes, this issue only occurs on Linux systems; it does not occur on macOS. 在 2026年1月5日星期一，Matthias Ngeo ***@***.***> 写道：

…

*Pante* left a comment (duobaseio/forui#808) <#808 (comment)> Thanks for taking the time to file a really detailed issue! I don't have access to a Linux machine, I've tried running the provided example on macOS but can't seem to reproduce the issue. Just to rule out any other issues, can you try running: import 'package:flutter/cupertino.dart';import 'package:forui/forui.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); @OverRide Widget build(BuildContext context) { return CupertinoApp( builder: (context, child) { return FAnimatedTheme( data: FThemes.zinc.light, child: child!, ); }, home: const HomePage(), ); } } class HomePage extends StatelessWidget { const HomePage({super.key}); @OverRide Widget build(BuildContext context) { final media = MediaQuery.of(context); final initWidth = media.size.width / 2; return FResizable( axis: Axis.horizontal, divider: FResizableDivider.divider, children: [ FResizableRegion( initialExtent: initWidth, builder: (context, data, _) => Container(color: const Color(0xFFE0E0E0)), ), FResizableRegion( initialExtent: initWidth, builder: (context, data, _) => Container(color: const Color(0xFFF5F5F5)), ) ], ); } } — Reply to this email directly, view it on GitHub <#808 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAXJZQIH66YXQKVIOSXQM3D4FJ6BDAVCNFSM6AAAAACQXBZ3XGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTOMJQHA2TGMRVGI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Pante]

Can I confirm, does the code snippet below work on your Linux machine?

import 'package:flutter/cupertino.dart';
import 'package:forui/forui.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return CupertinoApp(
      builder: (context, child) {
        return FAnimatedTheme(
          data: FThemes.zinc.light,
          child: child!,
        );
      },
      home: const HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    final media = MediaQuery.of(context);
    final initWidth = media.size.width / 2;

    return FResizable(
      axis: Axis.horizontal,
      divider: FResizableDivider.divider,
      children: [
        FResizableRegion(
          initialExtent: initWidth,
          builder: (context, data, _) => Container(color: const Color(0xFFE0E0E0)),
        ),
        FResizableRegion(
          initialExtent: initWidth,
          builder: (context, data, _) => Container(color: const Color(0xFFF5F5F5)),
        )
      ],
    );
  }
}```

[haijd]

This is a snippet I extracted from my code. It runs on Linux systems, but during execution, it spams the terminal with the following warning messages: ``` 'package:flutter/src/semantics/semantics.dart': Failed assertion: line 4392 pos 16: 'node.parent == null || !node.parent!.isPartOfNodeMerging || node.isMergedIntoParent': is not true. ``` Basically, every operation will output dozens or even over a hundred similar messages. Matthias Ngeo ***@***.***> 于2026年1月6日周二 09:49写道：

…

*Pante* left a comment (duobaseio/forui#808) <#808 (comment)> Can I confirm, does the code snippet below work on your Linux machine? import 'package:flutter/cupertino.dart';import 'package:forui/forui.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); @OverRide Widget build(BuildContext context) { return CupertinoApp( builder: (context, child) { return FAnimatedTheme( data: FThemes.zinc.light, child: child!, ); }, home: const HomePage(), ); } } class HomePage extends StatelessWidget { const HomePage({super.key}); @OverRide Widget build(BuildContext context) { final media = MediaQuery.of(context); final initWidth = media.size.width / 2; return FResizable( axis: Axis.horizontal, divider: FResizableDivider.divider, children: [ FResizableRegion( initialExtent: initWidth, builder: (context, data, _) => Container(color: const Color(0xFFE0E0E0)), ), FResizableRegion( initialExtent: initWidth, builder: (context, data, _) => Container(color: const Color(0xFFF5F5F5)), ) ], ); } }``` — Reply to this email directly, view it on GitHub <#808 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAXJZQOQNUNS5LCE7OBGK234FMIDFAVCNFSM6AAAAACQXBZ3XGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTOMJSG44DEMBTGA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Pante]

I think there's a slight misunderstanding at play. I modified the provided code snippet slightly to remove the regions' initialExtents. Ideally, we want to rule out that its a weird combination of initialExtent and some other internal factor which is erroring out and causing a cascading failure with the semantics assertions.

[haijd]

Sorry, I didn't notice that the `minExtent` property had already been removed from `FResizableRegion` in the code you provided. I will test again using the modified code. Matthias Ngeo ***@***.***> 于2026年1月7日周三 11:15写道：

…

*Pante* left a comment (duobaseio/forui#808) <#808 (comment)> I think there's a slight misunderstanding at play. I modified the provided code snippet slightly to remove the regions' initialExtents. Ideally, we want to rule out that its a weird combination of initialExtent and some other internal factor which is erroring out and causing a cascading failure with the semantics assertions. — Reply to this email directly, view it on GitHub <#808 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAXJZQLNJ5DMHENYOBP2IR34FR24JAVCNFSM6AAAAACQXBZ3XGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTOMJXGE2TQMJTG4> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Pante]

Thank you!

[haijd]

After repeated troubleshooting and testing, I discovered that the previous report was misleading. The problematic component is not `FResizableRegion`, but rather `FTextFormField.password`. If you use the following code (the `onTap` property is essential): ``` FTextFormField.password( label: Row( children: [ const Text('Password'), GestureDetector( onTap: _handleForgotPassword, child: const Text('Forgot Password?'), ), ], ), ), ``` The following problem will occur: ``` ══╡ EXCEPTION CAUGHT BY SCHEDULER LIBRARY ╞═════════════════════════════════════════════════════════ The following assertion was thrown during a scheduler callback: 'package:flutter/src/semantics/semantics.dart': Failed assertion: line 4392 pos 16: 'node.parent == null || !node.parent!.isPartOfNodeMerging || node.isMergedIntoParent': 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 SemanticsOwner.sendSemanticsUpdate (package:flutter/src/semantics/semantics.dart:4392:16) #3 PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1512:24) #4 PipelineOwner.flushSemantics (package:flutter/src/rendering/object.dart:1514:15) #5 RendererBinding.drawFrame (package:flutter/src/rendering/binding.dart:636:25) #6 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:1264:13) #7 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:495:5) #8 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1434:15) #9 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1347:9) #10 SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:1057:9) #11 PlatformDispatcher.scheduleWarmUpFrame.<anonymous closure> (dart:ui/platform_dispatcher.dart:906:16) #15 _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:193:12) (elided 5 frames from class _AssertionError, class _Timer, and dart:async-patch) ════════════════════════════════════════════════════════════════════════════════════════════════════ Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/semantics/semantics.dart': Failed assertion: line 4406 pos 14: 'node.parent?._dirty != true': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. Another exception was thrown: 'package:flutter/src/widgets/binding.dart': Failed assertion: line 1240 pos 16: 'debugFrameWasSentToEngine': is not true. ``` if I modify the code to the following, there will be no problem: ``` FTextFormField.password( label: Row( children: [ const Text('Password'), GestureDetector( child: const Text('Forgot Password?'), ), ], ), ), ``` Matthias Ngeo ***@***.***> 于2026年1月8日周四 12:47写道：

…

*Pante* left a comment (duobaseio/forui#808) <#808 (comment)> Thank you! — Reply to this email directly, view it on GitHub <#808 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAXJZQOF64HHOQ7ENHPQWJL4FXOPXAVCNFSM6AAAAACQXBZ3XGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTOMRRHA3DCNRSHE> . You are receiving this because you authored the thread.Message ID: ***@***.***>