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 500 popular React Native libraries against the AGP 9 defaults. 152 failed
with the new DSL enabled, and 144 of those failed on exactly this collision — by
far the most common blocker. Affects @phantom/react-native-webview here.

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

Summary by CodeRabbit

• Compatibility
  • Improved Android build compatibility with projects using Android Gradle Plugin 9’s built-in Kotlin integration.
  • Retained support for configurations that require the Kotlin plugin to be applied separately.

[coderabbitai]

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Reviewing files that changed from the base of the PR and between ebd8509 and 368e5d0.

📒 Files selected for processing (1)

• android/build.gradle

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📝 Walkthrough

Walkthrough

The Android build now skips kotlin-android when a kotlin extension already exists. It continues to apply the plugin for configurations without that extension.

Changes

Kotlin plugin compatibility

Layer / File(s)	Summary
Conditional Kotlin plugin application android/build.gradle	The build checks for the kotlin extension before applying kotlin-android.

Suggested reviewers: jamonholmgren, titozzz

Merge Risk: ⚪ Minimal · up to 368e5

The Android build now avoids applying Kotlin support twice while retaining the existing plugin behavior where Kotlin is not already available. No current merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: skipping the explicit Kotlin plugin when AGP registers the kotlin extension.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Create PR with unit tests

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