[web] Stop iOS auto-zoom by sizing semantic inputs at 16px by flutter-zl · Pull Request #192328 · flutter/flutter

flutter-zl · 2026-09-05T00:23:10Z

Fixes #192327 and #129233.

Problem

The semantic <input> and <textarea> never get a font size, so they fall back to the browser default, 11px on iOS. iOS auto-zooms any focused editable element under 16px, so tapping a TextField zoomed the page to 1.45x and left it there.
The framework's own text style never reached the element either. It arrives before the element is attached, so it is stored, and activate() replayed it before enabling the strategy, which made updateElementStyle skip writing it.
Font size, family, weight and spacing were all dropped. That is ensureSemantics() makes TextField font related properties in dev tools empty #129233.

Fix

Set the size on the element itself, to max(frameworkFontSize, 16) on iOS, at element creation and after every style sync. It cannot live in the global stylesheet because a later style update writes the framework font as an inline
font shorthand, which outranks any stylesheet rule. It assigns rather than only raises because on the first-focus path that shorthand is skipped and nothing else sets a size, so raising alone would leave a 24px field at 16px.

Nothing visible changes: the semantics tree is painted at filter: opacity(0%). Guarded by isIosSafari; Android was device-tested and does not auto-zoom.

Demo


Before	https://flutter-demo-50-before.web.app
After	https://flutter-demo-50-after.web.app

iOS auto-zoom. On an iPhone with semantics enabled, tap the 12px field. A default Material field is already 16px and cannot trigger the bug. Before, vvScale jumps to 1.45 and stays until you pinch out. After, it stays 1.00.

#129233. In desktop Chrome, click into the 24px field, then run:

[...document.querySelectorAll('flt-semantics-host input, flt-semantics-host textarea')]
  .map((e, i) => `${i} inline=${e.style.fontSize || 'NONE'} computed=${getComputedStyle(e).fontSize}`)
  .join('\n')

Index 3 is the 24px field. Before: inline=NONE computed=13.3333px. After: inline=24px computed=24px. Only the focused field carries a style, so the others correctly report NONE.

gemini-code-assist

Code Review

This pull request adds a CSS rule to set the font size of semantic inputs and textareas to 16px on iOS Safari, preventing the browser from auto-zooming upon focus, and introduces corresponding unit tests. Feedback suggests adding explicit newlines to the generated CSS string for better readability in DevTools, and moving the cleanup of the temporary style element in the test to a finally block to prevent resource leaks in case of assertion failures.

mdebbar · 2026-09-09T17:49:29Z

  /// Because style is supplied by the "flutter/textinput" channel and the DOM
  /// element is supplied by the semantics tree, the existence of both at the
  /// same time is not guaranteed.
  void _syncStyle() {


_syncStyle is called in activate before super.enable(...) which means the style won't be applied.

Good catch. Upated.

This also fixes #129233. On desktop Chrome, a focused 24px field now reports inline=24px, previously NONE.

mdebbar · 2026-09-09T17:58:56Z

+  final double effectiveFontSize =
+      frameworkFontSize == null || frameworkFontSize < _iosMinimumEditableFontSize
+      ? _iosMinimumEditableFontSize
+      : frameworkFontSize;


Minor suggestion:

Suggested change

final double effectiveFontSize =

frameworkFontSize == null || frameworkFontSize < _iosMinimumEditableFontSize

? _iosMinimumEditableFontSize

: frameworkFontSize;

final double effectiveFontSize = math.max(

_iosMinimumEditableFontSize,

frameworkFontSize ?? 0.0,

);

mdebbar · 2026-09-09T19:48:17Z

+      debugEmulateIosSafari = false;
+      semantics().semanticsEnabled = false;
+      domDocument.activeElement?.blur();


Let's make sure the text editing state is properly cleaned up:

Suggested change

debugEmulateIosSafari = false;

semantics().semanticsEnabled = false;

domDocument.activeElement?.blur();

if (strategy.isEnabled) {

strategy.disable();

}

cleanForms();

debugEmulateIosSafari = false;

semantics().semanticsEnabled = false;

domDocument.activeElement?.blur();

mdebbar · 2026-09-09T19:52:04Z

+      // This is the enabled path, where the shorthand really is written. The
+      // value persists past blur, so without the floor a later refocus would
+      // zoom.
+      expect(textField.editableElement.style.fontSize, '16px');


Should we make sure that other styles are also applied?

mdebbar

Roll Flutter from 63b9518f16bc to 2553f89be1ef (62 revisions) flutter/flutter@63b9518...2553f89 2026-09-12 [email protected] Roll clang to 07d67299a15ce03b053736e2d31a668ee0576987 (flutter/flutter#192607) 2026-09-12 [email protected] Roll Dart SDK from b24b352c29db to 7863887acbfb (3 revisions) (flutter/flutter#192665) 2026-09-12 [email protected] fix(tree): et format --all (flutter/flutter#192669) 2026-09-12 [email protected] Support activity-alias in Android launcher activity detection (flutter/flutter#187251) 2026-09-12 [email protected] fix: regenerate gradle lockfiles for external_textures integration test (flutter/flutter#192657) 2026-09-12 [email protected] Roll Skia from 51aa02b2c195 to e5e96533b732 (4 revisions) (flutter/flutter#192646) 2026-09-12 [email protected] [WebParagraph] Fix text pixelation, glyph clipping, and snapping offsets to avoid subpixel raster caching (flutter/flutter#191736) 2026-09-12 [email protected] fix(tests): Add ruby dep to Mac windowing_test (flutter/flutter#192656) 2026-09-12 [email protected] Remove some `unawaited_futures` outdated ignores (flutter/flutter#192026) 2026-09-11 [email protected] Bump Dart to 3.13, reformat, re-enable formatting check (flutter/flutter#192649) 2026-09-11 [email protected] [android] Isolate API-34 high contrast listener in AccessibilityBridge behind Api34Impl (flutter/flutter#192502) 2026-09-11 [email protected] Update style guide for Dart 3.13 (flutter/flutter#192639) 2026-09-11 [email protected] ci(bringups): remove bringup from these tests (flutter/flutter#192637) 2026-09-11 [email protected] Unmark new_gallery_windows_impeller__transition_perf as bringup (flutter/flutter#192633) 2026-09-11 [email protected] Unmark new_gallery_windows_skia__transition_perf as bringup (flutter/flutter#192635) 2026-09-11 [email protected] Roll Skia from f446aec4ce9e to 51aa02b2c195 (2 revisions) (flutter/flutter#192631) 2026-09-11 [email protected] fix(ci): mac verify binaries still racing (flutter/flutter#192634) 2026-09-11 [email protected] Roll Packages from 8a35b16 to 9caa77c (8 revisions) (flutter/flutter#192630) 2026-09-11 [email protected] Roll Dart SDK from a76fee2722e0 to b24b352c29db (2 revisions) (flutter/flutter#192627) 2026-09-11 [email protected] [tool] Migrate PackagesCommand and Pub to modular dependency injection (flutter/flutter#192460) 2026-09-11 [email protected] [tool] Migrate Darwin framework commands to modular dependency injection (flutter/flutter#192252) 2026-09-11 [email protected] [tool] Migrate Upgrade, Downgrade, and UpdatePackages commands to modular dependency injection (flutter/flutter#190787) 2026-09-11 [email protected] Roll Skia from b3fa80a0e168 to f446aec4ce9e (55 revisions) (flutter/flutter#192620) 2026-09-11 [email protected] Roll Dart SDK from d20d59cfa664 to a76fee2722e0 (2 revisions) (flutter/flutter#192616) 2026-09-11 [email protected] remove deeplink integration tests from bringup (flutter/flutter#192459) 2026-09-11 [email protected] Revert: [devicelab] Clean up Chrome profile directories and trap abort signals in web benchmarks (flutter/flutter#192615) 2026-09-11 [email protected] Roll Fuchsia Linux SDK from C0j8F-_Iy-OQZ6YyI... to m69nfK-wnHaMTe8P9... 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flutter-dashboard Bot added the CICD Run CI/CD label Sep 5, 2026

github-actions Bot added engine flutter/engine related. See also e: labels. platform-web Web applications specifically team-web Owned by Web platform team labels Sep 5, 2026

gemini-code-assist Bot reviewed Sep 5, 2026

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Comment thread engine/src/flutter/lib/web_ui/lib/src/engine/view_embedder/style_manager.dart Outdated

Comment thread engine/src/flutter/lib/web_ui/test/engine/global_styles_test.dart Outdated

github-actions Bot added a: text input Entering text in a text field or keyboard related problems a: accessibility Accessibility, e.g. VoiceOver or TalkBack. (aka a11y) labels Sep 8, 2026

[web] Stop iOS auto-zoom by sizing semantic inputs at 16px

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flutter-zl force-pushed the issue_192327_fix branch from 7e7aa62 to 00f6217 Compare September 8, 2026 21:33

flutter-zl added 2 commits September 8, 2026 14:40

Merge branch 'master' into issue_192327_fix

39059f2

Merge branch 'master' into issue_192327_fix

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flutter-zl requested review from Renzo-Olivares, chunhtai and mdebbar September 9, 2026 16:55

mdebbar reviewed Sep 9, 2026

View reviewed changes

[web] Apply the framework text style to the semantic text field

86e99ab

flutter-zl requested a review from mdebbar September 9, 2026 22:03

Merge branch 'master' into issue_192327_fix

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mdebbar approved these changes Sep 10, 2026

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Merged via the queue into flutter:master with commit 0414680 Sep 10, 2026
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flutter-zl mentioned this pull request Sep 10, 2026

ensureSemantics() makes TextField font related properties in dev tools empty #129233

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Renzo-Olivares mentioned this pull request Sep 11, 2026

Flutter Notable Commits - 2026 #181433

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Roll Flutter from 63b9518f16bc to 2553f89be1ef (62 revisions) flutter/packages#12853

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Roll Flutter from 63b9518f16bc to 2553f89be1ef (62 revisions) flutter/packages#12855

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kevmoo mentioned this pull request Oct 7, 2026

[ui/accessibility] Update web-accessibility.md for Flutter 3.50 WCAG 2.1 AA improvements and fix duplicated sentence flutter/website#13963

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[web] Stop iOS auto-zoom by sizing semantic inputs at 16px - #192328

[web] Stop iOS auto-zoom by sizing semantic inputs at 16px#192328
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