`allowFontScaling` is ignored on iOS when Fabric is enabled

[amgleitman]

Description

The allowFontScaling prop can normally be used to force text to stay the same size even when accessibility settings change the default font size. However, this property appears to have no effect when Fabric is enabled.

This was discovered when looking into implementing Dynamic Type ramps for Fabric as discussed in this proposal.

Version

main

Output of npx react-native info

info Fetching system and libraries information...
System:
 OS: macOS 12.6
 CPU: (10) arm64 Apple M1 Pro
 Memory: 148.70 MB / 32.00 GB
 Shell: 3.2.57 - /bin/bash
 Binaries:
 Node: 16.17.0 - ~/.nvm/versions/node/v16.17.0/bin/node
 Yarn: 1.22.19 - ~/.nvm/versions/node/v16.17.0/bin/yarn
 npm: 8.15.0 - ~/.nvm/versions/node/v16.17.0/bin/npm
 Watchman: 2022.09.19.00 - /opt/homebrew/bin/watchman
 Managers:
 CocoaPods: 1.11.3 - /opt/homebrew/bin/pod
 SDKs:
 iOS SDK:
 Platforms: DriverKit 21.4, iOS 16.0, macOS 12.3, tvOS 16.0, watchOS 9.0
 Android SDK: Not Found
 IDEs:
 Android Studio: Not Found
 Xcode: 14.0/14A309 - /usr/bin/xcodebuild
 Languages:
 Java: Not Found
 npmPackages:
 @react-native-community/cli: Not Found
 react: Not Found
 react-native: Not Found
 react-native-macos: Not Found
 npmGlobalPackages:
 *react-native*: Not Found

Steps to reproduce

1. Check out the main branch of facebook/react-native. (In my case, I got a repro against commit 4664292.)
2. Build RNTester and run it on an iOS simulator.
3. In the launched Simulator, adjust the accessibility settings to use the largest text size possible.
4. Look at the Text test page, specifically, the "This text will not scale..." paragraph in the section that talks about allowFontScaling.
5. Repeat steps 2-4, but this time, set fabric_enabled = false in packages/rn-tester/Podfile.
6. Compare the resulting screenshots.

Snack, code example, screenshot, or link to a repository

Screenshot with Fabric enabled: (Unexpected behavior)	Screenshot with Fabric disabled: (Expected behavior)

[sammy-SC]

@amgleitman thank you for the report!

e9b89b5 should fix it.