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ensureSemantics() breaks Tap*Details emitted from GestureDetector on mouse click on web #188859
Description
Steps to reproduce
Run the code sample below on the web (specifically I'm running in Chrome on Windows). Click around the screen with your mouse. Remove/add the ensureSemantics() invocation if required for comparison.
This is causing fleaflet/flutter_map#2176. There are some similarities to #146063 which has been open for 2 years and linked to flutter-team-archive/engine#47360 which has been closed.
Expected results
The position should be accurate, as is without running ensureSemantics().
Actual results
The printed information does not change depending on the cursor position (the position is always the center of the screen). Note that the kind is "unknown" rather than mouse.
Code sample
Code sample
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
void main() {
runApp(const MyApp());
SemanticsBinding.instance.ensureSemantics();
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: GestureDetector(
onTapDown: print,
child: const SizedBox.expand(
child: ColoredBox(color: Colors.black),
),
),
),
);
}
}
Flutter Doctor output
Doctor output
[√] Flutter (Channel beta, 3.46.0-0.2.pre, on Microsoft Windows [Version 10.0.26220.8754], locale en-GB) [518ms]
• Flutter version 3.46.0-0.2.pre on channel beta at C:\Users\lukas\flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 0f5a2c4694 (5 days ago), 2026-06-25 22:15:21 -0700
• Engine revision a24b1ea55d
• Dart version 3.13.0 (build 3.13.0-167.1.beta)
• DevTools version 2.59.0
• Feature flags: enable-web, no-enable-linux-desktop, no-enable-macos-desktop, enable-windows-desktop, enable-android, enable-ios, cli-animations, enable-native-assets, enable-swift-package-manager, omit-legacy-version-file, enable-lldb-debugging,
enable-uiscene-migration
[√] Windows Version (11 Home Insider Preview 64-bit, 25H2, 2009) [1,614ms]
[!] Android toolchain - develop for Android devices (Android SDK version 36.0.0-rc3) [3.4s]
• Android SDK at C:\Users\lukas\AppData\Local\Android\sdk
• Emulator version 35.2.10.0 (build_id 12414864) (CL:N/A)
• Platform android-36, build-tools 36.0.0-rc3
• Java binary at: C:\Program Files\Android\Android Studio\jbr\bin\java
This is the JDK bundled with the latest Android Studio installation on this machine.
To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
• Java version OpenJDK Runtime Environment (build 21.0.5+-13047016-b750.29)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses
[√] Chrome - develop for the web [162ms]
• CHROME_EXECUTABLE = C:\Program Files\Google\Chrome Dev\Application\chrome.exe
[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.14.13 (August 2025)) [162ms]
• Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
• Visual Studio Community 2022 version 17.14.36414.22
• Windows 10 SDK version 10.0.26100.0
[√] Connected device (3 available) [341ms]
• Windows (desktop) • windows • windows-x64 • Microsoft Windows [Version 10.0.26220.8754]
• Chrome (web) • chrome • web-javascript • unknown
• Edge (web) • edge • web-javascript • Microsoft Edge 150.0.4078.42
[√] Network resources [320ms]
• All expected network resources are available.
! Doctor found issues in 1 category.
Activity
[-]`ensureSemantics()` breaks `TapDownDetails` emitted from `GestureDetector` on mouse click on web[/-][+]`ensureSemantics()` breaks `Tap*Details` emitted from `GestureDetector` on mouse click on web[/+]mbcorona commentedon Jul 1, 2026
Hi @JaffaKetchup , thanks for reporting and providing a code sample.
This appears closely related to #146063 (and its duplicate #177314), which likely shares the same root cause in the web engine's semantics/pointer path
Routing to the web team to evaluate.
flutter-triage-bot commentedon Aug 15, 2026
This issue is missing a priority label. Please set a priority label when adding the
triaged-weblabel.ensureSemantics()inhibitsMapOptions.onTapfiring from mouse click on web platform fleaflet/flutter_map#2176[web] Don't debounce physical mouse clicks in ClickDebouncer
kevmoo commentedon Oct 8, 2026
Closing #192641 unmerged and leaving notes here so the investigation isn't lost.
Why the PR approach doesn't work. The fix forwarded
pointerType == 'mouse'input pastClickDebouncer. On Chrome that also captures every screen-reader activation: Blink'ssimulated_event_util.cchardcodespointerType = "mouse",pointerId = kMouseId,isTrusted = true, and border-box-center coordinates forSimulatedClickCreationScope::kFromAccessibility, andevent_dispatcher.ccemits the fullpointerdown → mousedown → pointerup → mouseup → clicksequence. There is no DOM-level discriminator between a real mouse click and AT activation on Chrome. (WebKit is different:AccessibilityObject::press()emitsmousedown/mouseup/clickonly, withpointerType = ""on the loneclick, so the debouncer is never entered on Safari.) Net effect of the PR on Chrome:Semantics(onTap:)nodes without a gesture recognizer under their centroid stop responding to screen readers. Not acceptable.Design direction from review (@yjbanov): keep debouncing, and instead attach the pointer position (and ideally device kind) to
SemanticsAction.tapso the framework can synthesizeTap*Detailswith the real coordinates. That's a cross-cutting change — new action args indart:uiSemanticsAction,SemanticsOwner.performAction→ tap-detail synthesis in the framework, andweb_uiClickDebouncerpopulating them from the queuedpointerdown/pointerup— with a decision needed for what non-web platforms send. It's bigger than a bug fix and I'm not pursuing it right now.Independent observation worth keeping: the debouncer imposes ~200ms press latency on every
flt-tappablenode underensureSemantics()for mouse users, on every browser. That's a latency issue rather than an a11y correctness issue and could be tracked separately if someone wants it.Possibly same root cause, not reproduced: #146063, #177314.
fix: prefer pointer events over semantics tap for mouse clicks on web (…