When are firebase_analytics, firebase_core, firebase_crashlytics and firebase_performance leaving KGP behind ?

[RoarGronmo]

I still get theese warnings, even I have moved to AGP for android.

[   +1 ms] WARNING: Your app uses the following plugins that apply Kotlin Gradle Plugin (KGP): firebase_analytics, firebase_core, firebase_crashlytics, firebase_performance
[   +1 ms] Future versions of Flutter will fail to build if your app uses plugins that apply KGP.
[        ] Please check the changelogs of these plugins and upgrade to a version that supports Built-in Kotlin.
[        ] If no such version exists, report the issue to the plugin. If necessary, here is a guide on filing
[        ] an issue against a plugin: https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-app-developers#report-incompatible-kotlin-gradle-plugin-usage-to-plugin-authors
[        ] If you are a plugin author, please migrate your plugin to Built-in Kotlin using this guide: https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-plugin-authors

When is it scheduled to leave KGP ?

[kgeminicdev]

With AGP 9 and built-in Kotlin on, these plugins already don't apply KGP. The warning is coming from how Flutter detects it: it doesn't run the plugin's build script, it searches the text of android/build.gradle with a regex (kgpRegexGroovy in FlutterPluginUtils.kt). The current FlutterFire build.gradle files still contain the line, but behind a condition:

// AGP 9+ has built-in Kotlin support unless Flutter opts out via android.builtInKotlin=false.
def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0] as int
def builtInKotlin = providers.gradleProperty("android.builtInKotlin")
        .map { it.toBoolean() }
        .orElse(agpMajor >= 9)
        .get()
if (agpMajor < 9 || !builtInKotlin) {
    apply plugin: 'kotlin-android'
}

I ran Flutter's regex against the build.gradle of all four plugins on FlutterFire main. It matches that indented apply plugin: 'kotlin-android' line in each one, so all four get listed even when the if is false.

A maintainer explained the same thing here. The line is kept so AGP 8 and android.builtInKotlin=false keep working, and it will be removed "as part of the full built-in Kotlin migration when we raise the minimum Flutter SDK". No date or version has been announced, so for now it's a warning, not a build failure.

One thing to check on your side: android/gradle.properties. The Flutter app template adds

android.builtInKotlin=false

If you still have that, the condition above is true, and the Firebase plugins (and Flutter itself, for your app module) really do apply KGP. Once your app is migrated to built-in Kotlin (guide), set it to true or remove it. The warning will still list these plugins until FlutterFire removes the line, but they won't actually apply KGP.