[Bug]: maxFontSizeMultiplier is not being respected

[mysport12]

Description

The maxFontSizeMultiplier prop is not being respected for Text and TextInput components. When accessibility settings are changed to increase the display text, the font size increases beyond the multiplier set.

Steps to reproduce

• Init a new project from the CLI template
• Add a few Text/TextInput components to the screen
• Prevent some from scaling and allow others to scale with the maxFontSizeMultiplier prop passed
• Change OS accessibility settings from display text size and observe bug

React Native Version

0.76.1

Affected Platforms

Runtime - Android, Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx react-native info

System:
  OS: macOS 15.0.1
  CPU: (12) arm64 Apple M3 Pro
  Memory: 107.84 MB / 36.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 23.1.0
    path: /opt/homebrew/bin/node
  Yarn:
    version: 4.5.1
    path: /opt/homebrew/bin/yarn
  npm:
    version: 10.9.0
    path: /opt/homebrew/bin/npm
  Watchman:
    version: 2024.10.28.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /Users/craig/.rvm/gems/ruby-3.3.5/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.1
      - iOS 18.1
      - macOS 15.1
      - tvOS 18.1
      - visionOS 2.1
      - watchOS 11.1
  Android SDK:
    API Levels:
      - "23"
      - "24"
      - "25"
      - "26"
      - "27"
      - "28"
      - "29"
      - "30"
      - "31"
      - "33"
      - "34"
      - "35"
    Build Tools:
      - 28.0.3
      - 29.0.2
      - 29.0.3
      - 30.0.1
      - 30.0.2
      - 30.0.3
      - 31.0.0
      - 33.0.0
      - 33.0.1
      - 33.0.2
      - 34.0.0
      - 35.0.0
    System Images:
      - android-28 | Google Play Intel x86 Atom
      - android-29 | Google APIs Intel x86 Atom
      - android-29 | Google Play Intel x86 Atom
      - android-30 | Google APIs Intel x86 Atom
      - android-30 | Google APIs Intel x86_64 Atom
      - android-30 | Google Play Intel x86 Atom
      - android-30 | Google Play Intel x86 Atom_64
      - android-33 | Google APIs ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2024.2 AI-242.23339.11.2421.12550806
  Xcode:
    version: 16.1/16B40
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.12
    path: /usr/bin/javac
  Ruby:
    version: 3.3.5
    path: /Users/craig/.rvm/rubies/ruby-3.3.5/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.0.0
    wanted: 15.0.0
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.76.1
    wanted: 0.76.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

No logs

Reproducer

https://github.com/mysport12/maxFontSizeMultiplierBug

Screenshots and Videos

[cortinico]

The maxFontSizeMultiplier prop is not being respected for Text and TextInput components. When accessibility settings are changed to increase the display text, the font size increases beyond the multiplier set.

Is this working well if you turn off the New Architecture? Asking to understand if this is a Fabric regression or not

[mysport12]

@cortinico It is working properly on the legacy architecture in 0.75.4.

[cortinico]

@cortinico It is working properly on the legacy architecture in 0.75.4.

And how about legacy arch on 0.76?

[mysport12]

Yes, I can confirm it is working on 0.76.1 with the legacy arch.

[RickardZrinski]

I've added support (RickardZrinski@140d9eb) and hoping to open a pull request tomorrow. Just need to do some more manual testing / compare with the old architecture and do some screenshots for the PR.

Edit: still working on it :)

[hungnd-casso]

I've added support (RickardZrinski@140d9eb) and hoping to open a pull request tomorrow. Just need to do some more manual testing / compare with the old architecture and do some screenshots for the PR.

Edit: still working on it :)

[RickardZrinski]

Everything is working on Android and iOS, except that there is some weirdness happening on the new architecture with reapplying changes made in Settings when switching back to the app (e.g. you've changed font size in accessibility settings but you need to restart the app for it to apply).

I don't think this issue is specific to my PR but rather a general issue in the new architecture. Though I'll need to verify that to be sure.

Edit: yeah, the reapplying of settings is a general issue on the new architecture. On iOS you can switch back and forth to your app after changing Settings and usually after the second roundtrip it gets applied. On Android it does apply after returning from Settings, but line height (seemingly) is messed up until you restart the app. I should probably open an issue on this...