fix(android): skip explicit Kotlin plugin when AGP registers the kotlin extension

[gabrieldonadel]

Problem

Android Gradle Plugin 9 ships built-in Kotlin support and enables it by default, so
AGP registers the kotlin extension itself. When a library also applies kotlin-android
explicitly, the two collide and configuration fails before anything compiles. AGP
words it two ways, both the same problem:

> Failed to apply plugin 'kotlin-android'.
   > Cannot add extension with name 'kotlin', as there is an extension already registered with that name.

> The 'kotlin-android' plugin is no longer required for Kotlin support since AGP 9.0.

The apply is unconditional in this module, so on an AGP 9 project this cannot be built
at all. There is no consumer-side workaround short of patching the file — setting
android.builtInKotlin=false project-wide just to build one dependency is not a
reasonable ask, and that escape hatch is removed in AGP 10.

Change

Apply the plugin only when nothing has registered the kotlin extension yet:

if (project.extensions.findByName('kotlin') == null) {
    apply plugin: 'kotlin-android'
}

Files changed:

• android/build.gradle

This tests the condition that actually fails, so there is no AGP version table to
keep in sync, and it covers AGP 10 — where the android.builtInKotlin opt-out is
removed — without a special case.

AGP	android.builtInKotlin	kotlin extension	explicit apply
8.x	unset or false	absent	yes (unchanged)
9.x	unset or true	registered by AGP	no
9.x	false	absent	yes
10+	n/a (removed)	registered by AGP	no

The guard sits after apply plugin: 'com.android.library' in every file it touches,
so AGP has already registered its extensions by the time it runs. I checked that
ordering per file rather than assuming it.

What I verified, and what I did not

• Verified end to end on a real Expo SDK 58 / React Native 0.87 project with AGP
  9.2.1 and Gradle 9.4.1: :app:assembleDebug succeeds both with
  -Pandroid.newDsl=true -Pandroid.builtInKotlin=true and with both flags off.
• Confirmed both branches actually execute rather than one path always winning: with
  the flags off, compileDebugKotlin runs from the explicitly applied plugin; with
  them on the build completes without it.
• Every changed file passes a Groovy Phases.CONVERSION syntax check.
• Not run: this repo's own CI or example app.

Where this came from

A sweep of 1000 popular React Native libraries against the AGP 9 defaults. 281 failed
with the new DSL enabled, and 269 of those failed on exactly this collision — by
far the most common blocker. Affects @expensify/react-native-wallet here.

The same guard shape was accepted in
RevenueCat/react-native-purchases#1934,
at that maintainer's suggestion.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[gabrieldonadel]

I have read the CLA Document and I hereby sign the CLA

[JakubKorytko]

Reproduced on RN 0.85.3 + AGP 9.0.1: main fails with Cannot add extension with name 'kotlin' in :expensify_react-native-wallet; with this PR the library configures and its Kotlin compiles via AGP's built-in Kotlin. Also verified no regression on AGP 8.12.0 (plugin still applied, build succeeds). LGTM.

[JakubKorytko]

I have read the CLA Document and I hereby sign the CLA

[JakubKorytko]

@gabrieldonadel may you rebase & sign commits? you can also rebase latest main to drop my merge commit, this way @mountiny won't have to re-approve

[gabrieldonadel]

@gabrieldonadel may you rebase & sign commits? you can also rebase latest main to drop my merge commit, this way @mountiny won't have to re-approve

Done

[JakubKorytko]

thanks!

[os-botify]

🚀 Published to npm in 0.1.30 🎉