Fix `minimumFontScale` with `adjustsFontSizeToFit` in the New Architecture by conner1reimers · Pull Request #58492 · react/react-native

conner1reimers · 2026-09-11T20:05:35Z

Summary:

minimumFontScale has no effect when used with adjustsFontSizeToFit under the New Architecture on either platform (#50248). Text shrinks all the way down to the hard-coded floor regardless of the requested scale.

The root cause is the same on both platforms. Fabric's ParagraphAttributes carries minimumFontSize, but no <Text> or <TextInput> prop ever sets it, so it is always NaN:

iOS: RCTTextLayoutManager falls back to a 4pt minimum whenever minimumFontSize is NaN, so the floor is always 4pt.
Android: the C++ side serializes minimumFontSize into MapBuffer key 6, and TextLayoutManager.adjustSpannableFontToFit() treats that value as an absolute minimum font size, falling back to 4dp when it is NaN. Same result: the floor is always 4dp.

This PR serializes minimumFontScale (the field already existed) into a new MapBuffer key (10). Each platform then derives the minimum font size from that scale. minimumFontSize and MapBuffer key 6 are left as they are and deprecated in favor of minimumFontScale; an explicit minimumFontSize still takes precedence over the scale on both platforms, so existing callers keep working unchanged. The legacy renderers based the scale on the outermost text's font size; using the largest font size in the attributed string follows the approach from #43543.

iOS: RCTTextLayoutManager finds the largest font size in the attributed string and computes the minimum as MAX(minimumFontScale * largestFontSize, 4.0).
Android: adjustSpannableFontToFit() finds the largest ReactAbsoluteSizeSpan first and uses max(minimumFontScale * largestFontSize, 4dp). This uses the same scale-based calculation as the original Android implementation in Implement adjustsFontSizeToFit on Android #26389, although the legacy renderer based it on the outer text's effective font size rather than the largest span. A NaN or non-positive scale keeps the bare 4dp floor. Both the measurement path (createLayout()) and the view path (ReactTextViewManager -> ReactTextView.onDraw()) go through this one function, so only its interpretation of the value changes. PA_KEY_MINIMUM_FONT_SCALE is added as key 10, ReactTextView.setMinimumFontSize() is kept and marked @Deprecated, and setMinimumFontScale() is added alongside it (the ReactAndroid.api dump was also updated).
Android: ReactTextView.updateView() no longer clears the ellipsize location when adjustsFontSizeToFit is set. With the floor effectively pinned at 4dp that branch was dead, since text always fit. Now that a floor can stop the text from shrinking, text that still overflows at the floor gets the requested ellipsizeMode instead of being clipped, matching iOS.

The 4pt/4dp floor is kept on both platforms. minimumFontScale still has an @platform ios annotation in TextProps.js, so that annotation is removed since it's supported on Android as well.

Depends on #58529, which removes the unused maximumFontSize attribute and introduces the largest-font-size helper this PR uses on iOS; I'll rebase this PR onto it once it lands.

This supersedes #54072 (iOS only) and #43543.

Fixes #50248.

Changelog:

[GENERAL] [FIXED] - Fix minimumFontScale with adjustsFontSizeToFit in the New Architecture

Test Plan:

Unit tests

Updated ParagraphAttributesTest.cpp to cover minimumFontScale.
Added TextLayoutManagerMinimumFontScaleTest.kt covering the scale calculation, the 4dp floor, the precedence of an explicit minimumFontSize over the scale, and text that already fits.
Added a ReactTextViewTest.kt case verifying that adjustsFontSizeToFit preserves the ellipsize location.
Regenerated the C++ API snapshots (yarn cxx-api-build) for the new MapBuffer key.

./gradlew :packages:react-native:ReactAndroid:testDebugUnitTest --tests 'com.facebook.react.views.text.*'

All 47 com.facebook.react.views.text tests pass.

RNTester

Added a minimumFontScale={0.5} line to the adjustsFontSizeToFit section of the Text example on both platforms ("Can limit how small the text becomes with minimumFontScale"). Before this change the line shrinks past the requested floor; after it stops at 50% of the original font size and is ellipsized.

Each screenshot below was captured on the same machine, on an iPhone 17 simulator and an Android API 35 emulator. "Before" is this branch's base commit with only the new RNTester example applied.

	Before	After
iOS
Android

…itecture Fabric's ParagraphAttributes carried `minimumFontSize` and `maximumFontSize`, which no `<Text>` prop can set, so RCTTextLayoutManager always fell back to a 4pt floor and ignored `minimumFontScale`. Replace those two fields with the existing `minimumFontScale` (default 0) everywhere it is parsed, diffed and serialized, and derive the floor in RCTTextLayoutManager the way the legacy renderer did: MAX(minimumFontScale * largest font size in the attributed string, 4.0). MapBuffer key 6 now carries the scale instead of an absolute size; key 7 is no longer written. Updates ParagraphAttributesTest for the removed fields and adds an RNTester example exercising `minimumFontScale`.

…w Architecture TextLayoutManager read MapBuffer key 6 as an absolute minimum font size in pixels and fell back to 4dp when it was NaN. Since nothing on the JS side ever set `minimumFontSize`, Android always used the 4dp floor and `minimumFontScale` was ignored. Key 6 now carries `minimumFontScale`, so adjustSpannableFontToFit() finds the largest ReactAbsoluteSizeSpan first and derives the floor as max(minimumFontScale * largestFontSize, 4dp), matching iOS and the formula the original Android implementation (react#26389) used. A NaN or non-positive scale keeps the bare 4dp floor. Both the measurement path and the view path go through this one function, so only its interpretation of the value changes. Renames PA_KEY_MINIMUM_FONT_SIZE to PA_KEY_MINIMUM_FONT_SCALE, drops the unused PA_KEY_MAXIMUM_FONT_SIZE, and renames ReactTextView.setMinimumFontSize() to setMinimumFontScale() (public API dump updated). Adds Robolectric coverage for the floor computation, an RNTester example, and drops the `@platform ios` annotation from the `minimumFontScale` prop docs.

ReactTextView.updateView() cleared the ellipsize location whenever adjustsFontSizeToFit was on. Now that minimumFontScale can stop the text from shrinking further, text that still does not fit at the floor was clipped instead of ellipsized. iOS applies the ellipsize mode regardless of adjustsFontSizeToFit, so do the same here.

javache

Thanks for the PR! A few comments.

I think it would be good to split this up in different PR's

Removal of the undocumented / inconsistently supported maximumFontSize API
Adding minimumFontScale to Android, and deprecating minimumFontSize (backwards compat would be great if feasible)

javache · 2026-09-14T09:21:37Z

    applyTextAttributes();
  }

-  public void setMinimumFontSize(float minimumFontSize) {


This is a public API change - please avoid. Can you add back the old API as deprecated?

setMinimumFontSize() was added back as deprecated, and setMinimumFontScale() was added alongside it. minimumFontSize still takes precedence when explicitly set, so existing callers keep the old behavior.

javache · 2026-09-14T09:21:50Z

-        mNumberOfLines == ViewDefaults.NUMBER_OF_LINES || mAdjustsFontSizeToFit
-            ? null
-            : mEllipsizeLocation;


Why this behavioural chagne?

This is for the case where text reaches minimumFontScale and still doesn't fit. Android currently clears ellipsizeMode whenever adjustsFontSizeToFit is enabled, so that overflow gets clipped instead.

The original Android implementation did this to avoid some incorrect ellipsizing cases (#26389 (comment)), with overflow at the minimum scale being a known tradeoff. Since minimumFontScale is now actually respected, I kept this change so overflow at the floor uses the requested ellipsizeMode, which matches iOS.

It's kept as a separate commit, so I can split it out if you'd prefer.

javache · 2026-09-14T09:22:09Z

  const val PA_KEY_TEXT_ALIGN_VERTICAL: Int = 8
  const val PA_KEY_TEXT_WIDTH_MODE: Int = 9


nit: re-order

This has been fixed.

javache · 2026-09-14T09:25:15Z

  if (paragraphAttributes.adjustsFontSizeToFit) {
-    CGFloat minimumFontSize = !isnan(paragraphAttributes.minimumFontSize) ? paragraphAttributes.minimumFontSize : 4.0;
-    CGFloat maximumFontSize = !isnan(paragraphAttributes.maximumFontSize) ? paragraphAttributes.maximumFontSize : 96.0;
+    CGFloat maximumFontSize = [self _maximumFontSizeInAttributedString:attributedString];


Behavioural change

This was moved to #58529. The behavior change from the 96pt fallback is covered in that PR's summary.

…ffer key

…inimumFontScale()

conner1reimers · 2026-09-15T00:37:57Z

Thanks for the review! I've split this up as suggested:

Remove the unused maximumFontSize paragraph attribute #58529 removes the undocumented maximumFontSize attribute, including the 96pt iOS behavior.
This PR now just adds minimumFontScale support. minimumFontSize and its existing MapBuffer key are kept for compatibility. minimumFontSize was marked as deprecated, and minimumFontScale uses a new key. setMinimumFontSize() is also back and marked as deprecated.
The updateView() ellipsize change is still its own commit (e6a8a06); I added the reasoning in the inline thread.

I'll rebase this onto #58529 after it's merged, since both use the same largest-font-size helper on iOS. The RNTester screenshots in the description are still from the pre-split branch, but the behavior shown there is unchanged.

conner1reimers added 3 commits September 11, 2026 13:24

meta-cla Bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Sep 11, 2026

This was referenced Sep 11, 2026

[iOS] Fix minimumFontScale in New Architecture #54072

Closed

Fix adjustsFontSizeToFit on new arch #43543

Open

[0.77.1] minimumFontScale doesn't work in New Arch #50248

Open

facebook-github-tools Bot added the Shared with Meta Applied via automation to indicate that an Issue or Pull Request has been shared with the team. label Sep 11, 2026

javache requested changes Sep 14, 2026

View reviewed changes

conner1reimers added 3 commits September 14, 2026 17:31

Keep minimumFontSize and serialize minimumFontScale under a new MapBu…

1cb6e66

…ffer key

Restore ReactTextView.setMinimumFontSize() as deprecated and add setM…

7e2827e

…inimumFontScale()

Update C++ API snapshots for PA_KEY_MINIMUM_FONT_SCALE

3cd5ab0

conner1reimers mentioned this pull request Sep 14, 2026

Remove the unused maximumFontSize paragraph attribute #58529

Open

conner1reimers requested a review from javache September 15, 2026 00:38

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Fix `minimumFontScale` with `adjustsFontSizeToFit` in the New Architecture - #58492

Fix `minimumFontScale` with `adjustsFontSizeToFit` in the New Architecture#58492
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		const val PA_KEY_TEXT_ALIGN_VERTICAL: Int = 8
		const val PA_KEY_TEXT_WIDTH_MODE: Int = 9

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Changelog:

Test Plan:

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