Expo Android Build Doctor

Overview

Triage Android build failures in Expo (prebuild/dev-client) projects and apply targeted fixes with minimal churn. Focus on Kotlin/Gradle version alignment issues that block :app:compileDebugKotlin.

Workflow

1) Reproduce and isolate the failing task

• Prefer ./android/gradlew :app:compileDebugKotlin --stacktrace to avoid Expo CLI noise.
• Only treat errors as blockers; warnings like CXX5304 usually aren’t fatal.

2) If you see a Kotlin metadata/version mismatch

Trigger strings (any of these):

• Module was compiled with an incompatible version of Kotlin
• The binary version of its metadata is 2.1.0, expected version is 1.9.0
• Errors pointing at .../META-INF/*.kotlin_module inside a .jar

First: look for dependency overrides that upgraded Firebase/Play Services.

• Search for app-level/platform overrides like firebase-bom in android/app/build.gradle.
• If you’re using @react-native-firebase/*, avoid adding your own Firebase BoM + firebase-analytics in the app module; it can force newer transitive deps than your toolchain supports.

Then (if still needed): upgrade project Kotlin to match the dependency’s metadata.

For Expo/RN Android projects, align these in one pass:

• Root android/build.gradle (Kotlin version + kotlin-gradle-plugin)
• android/react-settings-plugin/build.gradle.kts (Kotlin JVM plugin)

Use the script:

• python3 skills/expo-android-build-doctor/scripts/bump_kotlin_version.py --version 2.1.0 --apply

Then rebuild:

• ./android/gradlew :app:compileDebugKotlin

If upgrading Kotlin causes Gradle evaluation errors (plugin incompatibility), revert and instead pin/downgrade the dependency that introduced newer Kotlin metadata.

If it still fails, identify what pulled in the Kotlin-2.x compiled artifact:

• ./android/gradlew :app:dependencies --configuration debugCompileClasspath

3) If you see Google Mobile Ads android_app_id warning

This warning is not a build failure but it will crash at runtime if you’re using the native SDK.

• Ensure app.json/app.config.* includes react-native-google-mobile-ads.android_app_id, or confirm you’re using the library’s Expo config plugin that injects it.

References

Read skills/expo-android-build-doctor/references/kotlin-metadata-mismatch.md when you need background or alternative mitigation options.