r8-expo-config

name: r8-expo-config description: "Configures R8 minification, ProGuard rules, and Gradle JVM memory for Expo managed workflow Android builds. Use when the user asks about R8, ProGuard, build minification, shrinking, obfuscation, Gradle memory, EAS build hangs, or OOM errors during Android builds." context: fork user-invocable: true

Skill: R8 & Expo Config Plugin

This project uses Expo managed workflow — the android/ folder is not committed. All Gradle and R8 configuration is applied via a config plugin that runs during expo prebuild.

Architecture

proguard-rules.pro          ← source of truth for ProGuard rules
plugins/withR8Config.js     ← Expo config plugin (applies rules + Gradle props)
app.config.js               ← registers the plugin
eas.json                    ← build profiles (production uses app-bundle + R8)

Never edit android/gradle.properties or android/app/proguard-rules.pro directly — they are regenerated on every prebuild.

Config Plugin (plugins/withR8Config.js)

Uses withGradleProperties to inject into gradle.properties and withDangerousMod to copy proguard-rules.pro into android/app/.

Gradle properties set by the plugin

Memory budget rule

GitHub Actions runners have 7GB RAM. Keep JVM heap + Metaspace ≤ 5GB total to leave headroom for OS, Node.js, and EAS CLI. The current setting (4GB heap + 1GB Metaspace = 5GB) is the safe maximum. If builds hang, reduce Xmx — do NOT increase it.

Preview builds (arm64-v8a only)

When APP_VARIANT=preview, the plugin adds:

reactNativeArchitectures=arm64-v8a

This halves build time for preview APKs by skipping x86_64.

ProGuard Rules (proguard-rules.pro)

Keep rules are required for:

• React Native core (com.facebook.react.**)
• Hermes engine (com.facebook.hermes.**, com.facebook.jni.**)
• Expo modules (expo.modules.**)
• expo-sqlite (org.sqlite.**)
• Kotlin runtime (kotlin.**, kotlinx.**)
• BuildConfig (com.heywood8.monkeep.BuildConfig)

Always use -dontwarn alongside -keep for Expo Kotlin canary classes to suppress false-positive warnings.

Modifying R8 Configuration

To change Gradle JVM memory

Edit plugins/withR8Config.js, property org.gradle.jvmargs. Keep total ≤ 5GB for CI.

To add a new ProGuard keep rule

Add to proguard-rules.pro in the project root. It is automatically copied to android/app/ during prebuild.

To add a new Gradle property

Add it to the properties object in plugins/withR8Config.js:

const properties = {
  'your.new.property': 'value',
  // ...existing props
};

Verification Commands

# Regenerate android/ and verify plugin ran
npx expo prebuild --clean
cat android/gradle.properties | grep -E "(Minify|Shrink|jvmargs)"
cat android/app/proguard-rules.pro | head -5

# Local release build (requires Android SDK)
cd android && ./gradlew :app:bundleRelease
ls -lh app/build/outputs/mapping/release/mapping.txt

Troubleshooting

Build hangs on GitHub Actions → Reduce Xmx in org.gradle.jvmargs. Check for OOM in logs.

ProGuard rules not applied → Confirm ./plugins/withR8Config.js is listed in plugins array in app.config.js.

Missing class warnings → Add -dontwarn your.package.** to proguard-rules.pro.

Crash deobfuscation → Download mapping.txt from EAS dashboard, then:

$ANDROID_HOME/cmdline-tools/latest/bin/retrace mapping.txt stacktrace.txt

References

• Full setup docs: docs/R8_CICD_SETUP.md
• R8 shrink code
• Expo Config Plugins
• EAS Build profiles