Skill: React Native Build Expert

This skill provides deep expertise in React Native iOS and Android build systems. Activate when: user mentions build errors, pod install, gradle, Xcode, signing, APK, or IPA.

Advanced Debugging Techniques

iOS: Reading Xcode Build Logs

• •Open Xcode -> Report Navigator (Cmd+9) -> latest build
• •Filter by "Errors" to isolate the root cause
• •The real error is usually the FIRST error in the log, not the last

Android: Reading Gradle Output

• •Run with --stacktrace for full trace: ./gradlew assembleDebug --stacktrace
• •Run with --info for dependency resolution: ./gradlew dependencies
• •The root cause is usually near "FAILURE: Build failed with an exception"

Identifying the Package Manager

• •yarn.lock -> Yarn
• •pnpm-lock.yaml -> pnpm
• •package-lock.json -> npm
• •Using wrong package manager after package.json change is a common source of corruption

React Native Upgrade Issues

After npx react-native upgrade:

1. •Check for conflicts in ios/ and android/ directories
2. •Verify Podfile matches the template for the new version
3. •Verify build.gradle AGP version matches new requirements
4. •Run pod install and a Gradle sync

Hermes Deep Dive

• •Hermes is the JavaScript engine optimized for React Native (default from RN 0.71)
• •hermes-engine is installed as a CocoaPod
• •If Hermes build fails: clean DerivedData, delete Pods/, reinstall
• •Hermes improves startup time by pre-compiling JS to bytecode during build

New Architecture (Fabric + TurboModules)

• •Enabled by default in RN 0.76+
• •Requires all native libraries to be migrated
• •To check if a library supports it: look for codegenConfig in its package.json
• •Fallback: set newArchEnabled=false in gradle.properties until libraries catch up

Common Environment Variables

# Android
export ANDROID_HOME=$HOME/Library/Android/sdk
export PATH=$PATH:$ANDROID_HOME/emulator
export PATH=$PATH:$ANDROID_HOME/platform-tools

# Java (macOS)
export JAVA_HOME=$(/usr/libexec/java_home -v 17)

# React Native New Architecture
export RN_NEW_ARCH_ENABLED=1  # or 0 to disable

Version Compatibility Matrix

Android Gradle Plugin (AGP) vs Gradle

Xcode vs iOS Deployment Target