Upgrade React Native Fixture App

Overview

The fixture app lives in fixture/react-native/. It is the primary test vehicle for FlashList on iOS and Android. The web fixture (fixture/web/) uses Expo and is independent — check it builds after the upgrade but it does not need the same dependency changes.

Step 1 — Research the Target Version

1. Check the latest stable RN version:

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   npm view react-native@latest version

2. Use the rn-diff-purge repo to see the exact template diff between your current and target version:

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   https://raw.githubusercontent.com/react-native-community/rn-diff-purge/release/<version>/RnDiffApp/<file>

   Key files to fetch:

   • package.json — React version, CLI versions, dev dep versions
   • android/build.gradle — SDK versions, Kotlin version
   • android/app/build.gradle — plugin names, dependency patterns
   • android/gradle.properties — feature flags (newArch, hermes, edgeToEdge)
   • android/gradle/wrapper/gradle-wrapper.properties — Gradle version
   • android/settings.gradle — plugin management pattern
   • android/app/src/main/java/com/rndiffapp/MainApplication.kt — app initialization pattern
   • ios/Podfile — pod configuration, post_install hooks
   • ios/RnDiffApp/AppDelegate.swift — app delegate pattern
   • metro.config.js — Metro config API changes

3. Check third-party library compatibility with the target RN version:

   • react-native-reanimated — check compatibility table
   • react-native-gesture-handler — supports 3 latest RN minors
   • react-native-screens, react-native-safe-area-context — usually latest works
   • @react-navigation/* — check for breaking changes
   • Any image library (@d11/react-native-fast-image, etc.)

Step 2 — Update Dependencies

fixture/react-native/package.json

Update in this order:

1. react and react-native — match the template
2. @react-native/* dev packages — must match the RN minor (e.g., @react-native/babel-preset@0.84.1 for RN 0.84.1)
3. @react-native-community/cli* — match the template
4. Third-party native libraries — bump to versions compatible with the target RN
5. Any new peer dependencies (e.g., reanimated 4 requires react-native-worklets)

Babel config

Check if any Babel plugins moved packages. Example: reanimated 4 moved react-native-reanimated/plugin to react-native-worklets/plugin.

Metro config

Metro's internal module paths change between versions. Common breakage:

• metro-config/src/defaults/exclusionList — in newer Metro this moved to metro-config/private/defaults/exclusionList and exports a .default instead of a direct function
• Always verify the import works: node -e "console.log(typeof require('<path>'))"

Step 3 — Update Android

android/build.gradle

• buildToolsVersion, compileSdkVersion, targetSdkVersion — match template
• kotlinVersion — match template
• ndkVersion — match template (usually unchanged between minors)

android/gradle/wrapper/gradle-wrapper.properties

• Update Gradle distribution URL to match template

android/gradle.properties

• Remove deprecated flags (e.g., android.enableJetifier, FLIPPER_VERSION)
• Add new flags (e.g., edgeToEdgeEnabled)
• Update JVM args if template changed them

android/app/build.gradle

• Update plugin names if changed (e.g., kotlin-android → org.jetbrains.kotlin.android)
• Remove unused imports (e.g., import com.android.build.OutputFile)
• Check autolinkLibrariesWithApp() is present

android/settings.gradle

• Match template structure
• Remove manual project includes for pure-JS libraries (flash-list has no native Android code)

MainApplication.kt

• This changes significantly between major RN versions. Always diff against the template.
• Preserve custom code: AppPackage() registration and I18nUtil.allowRTL() for RTL support.
• Key pattern changes across versions:
  • 0.79: SoLoader.init() + DefaultNewArchitectureEntryPoint.load() + ReactNativeHost
  • 0.84: loadReactNative(this) + getDefaultReactHost() with lazy delegate (no ReactNativeHost)

Step 4 — Update iOS

ios/Podfile

• Match template structure
• Remove deprecated env vars (e.g., ENV['RCT_NEW_ARCH_ENABLED'] when new arch is the default)
• Remove deprecated helper calls (e.g., get_default_flags())
• Keep project-specific customizations (use_frameworks! :linkage => :static if needed)

ios/FlatListPro.xcodeproj/project.pbxproj

• Update IPHONEOS_DEPLOYMENT_TARGET to match the RN minimum (e.g., 15.1 for RN 0.76+)
• Pod install will update header search paths and build settings automatically

ios/FlatListPro/Info.plist

• Add any new required plist keys (e.g., RCTNewArchEnabled)

Clean install

cd fixture/react-native
rm -rf node_modules yarn.lock
yarn install
cd ios && rm -rf Pods Podfile.lock && pod install && cd ..

Step 5 — Build and Verify

Build the flash-list library first

yarn build   # from repo root — compiles src/ → dist/

iOS

cd fixture/react-native
xcodebuild -workspace ios/FlatListPro.xcworkspace -scheme FlatListPro \
  -configuration Debug -sdk iphonesimulator \
  -destination 'platform=iOS Simulator,name=iPhone 16 Pro' build

Android

cd fixture/react-native
yarn react-native run-android

Web

cd fixture/web && yarn install && npx expo export --platform web

Step 6 — Run Tests

Unit tests

yarn test   # from repo root — 181+ tests must pass

E2E tests (iOS)

cd fixture/react-native
yarn e2e:build:ios
yarn e2e:test:ios

Screenshot reference updates: Visual diff tests (e.g., Carousel orientation) will fail after an RN upgrade because rendering changes slightly. To regenerate references:

1. Delete the old reference directory (e.g., e2e/artifacts/ios/Carousel_landscape/)
2. Run the test — it creates a new reference and fails with "no reference present"
3. Run again — it passes using the new reference
4. Repeat for each failing screenshot (the test stops at the first missing reference per run)

Common Pitfalls

• Metro exclusionList import — Metro's internal API paths change between versions. Always verify the import resolves before starting Metro.
• Stale Metro on wrong port — Kill ALL Metro instances before testing. Another project's Metro on a different port can cause "version mismatch" errors if the app connects to it.
• react-native-reanimated major version — Major bumps (3→4) require Babel plugin changes and may add new peer dependencies (react-native-worklets).
• Gradle version jumps — RN upgrades often bump Gradle (e.g., 8.x→9.x). This can break custom Gradle scripts. Check build warnings for deprecations.
• IPHONEOS_DEPLOYMENT_TARGET — Must match or exceed the RN minimum. Pod install updates most settings, but the project-level target in pbxproj must be set manually.
• Info.plist new keys — Some RN versions require new plist entries (e.g., RCTNewArchEnabled). Check the template's Info.plist diff.
• Legacy arch removal — Starting with RN 0.82+, legacy architecture code is being removed. Ensure all dependencies support new arch.