Built-in Kotlin migration for plugin authors

This guide outlines the migration steps specifically for plugin authors.

The following steps assume you can update your plugin's Flutter SDK minimum to 3.44. If you can't update the Flutter SDK minimum to 3.44, follow the instructions to support Flutter versions earlier than 3.44.

First, find the kotlin-android plugin (or the org.jetbrains.kotlin.android plugin). It is likely located in the plugins block of the <plugin-project>/build.gradle or the <plugin-project>/build.gradle.kts file. If you use the legacy apply syntax, it will be located in the Groovy-based <plugin-project>/build.gradle file, as this syntax isn't supported in Kotlin DSL.

The following examples demonstrate how to migrate a Flutter plugin:

plugins {
    id("com.android.library")
    id("kotlin-android")
    // ...
}
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}
​
// ...

plugins {
    id("com.android.library")
    id("kotlin-android")
    // ...
}
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}

kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}

plugins {
    id("com.android.library")
    // ...
}
​
android {
    // ...
}
​
kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}
​
// ...

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
// ...
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}
​
// ...

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
 ...
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}

kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}

apply plugin: 'com.android.library'
// ...
​
android {
    // ...
}
​
kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}
​
// ...

Using the kotlin.compilerOptions {} DSL block requires a minimum Kotlin Gradle Plugin (KGP) version of 2.0.0. Beginning with Flutter 3.44, the minimum required KGP version is 2.0.0. To ensure that apps using your plugin can safely migrate to built-in Kotlin, you should require a minimum Flutter version of 3.44 for this plugin version.

Since you are updating the minimum Flutter version, you must also update the minimum associated Dart version.

Update the minimum Flutter version and the minimum Dart version:

...
​
environment:
  sdk: ^<previous-dart-minimum>
  sdk: ^3.12.0
  flutter: ">=<previous-flutter-minimum>"
  flutter: ">=3.44.0"
​
...

Here is how the file will likely end up:

# ...
​
environment:
  sdk: ^3.12.0
  flutter: ">=3.44.0"
​
# ...

If you updated your plugin's Flutter SDK minimum to 3.44, skip this section and proceed to updating the plugin's CHANGELOG.md.

If you can't update the plugin's Flutter SDK minimum to 3.44, you must make the following changes to <plugin-project>/android/build.gradle or <plugin-project>/android/build.gradle.kts to support apps on AGP versions less than 9 and versions on 9 or later.

plugins {
    id("com.android.library")
    id("kotlin-android")
    // ...
}
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}
​
// ...

plugins {
    id("com.android.library")
    id("kotlin-android")
    // ...
}
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}

val agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.substringBefore('.').toInt()
​
if (agpMajor < 9) {
    apply(plugin = "org.jetbrains.kotlin.android")
}

project.extensions.configure(org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension::class.java) {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}

plugins {
    id("com.android.library")
    // ...
}
​
val agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.substringBefore('.').toInt()
​
if (agpMajor < 9) {
    apply(plugin = "org.jetbrains.kotlin.android")
}
​
android {
    // ...
}
​
project.extensions.configure(org.jetbrains.kotlin.gradle.dsl.KotlinAndroidProjectExtension::class.java) {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}
​
// ...

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}
​
// ...

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
​
android {
    // ...
    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_17.toString()
    }
    // ...
}

def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0] as int
​
if (agpMajor < 9) {
   apply plugin: 'kotlin-android'
}

kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}

apply plugin: 'com.android.library'
​
def agpMajor = com.android.Version.ANDROID_GRADLE_PLUGIN_VERSION.tokenize('.')[0] as int
if (agpMajor < 9) {
    apply plugin: 'kotlin-android'
}
​
android {
    // ...
}
​
kotlin {
    compilerOptions {
        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
    }
}
​
// ...

Include your changes in the CHANGELOG.md file of the newly released plugin version:

## <new-plugin-release-version>
​
- Updates the minimum supported SDK version to Flutter 3.44/Dart 3.12.
- Migrates to built-in Kotlin.
​
 ...

Execute flutter run or flutter build apk to confirm that your plugin example app builds and launches on a connected Android device or emulator.

If your plugin example app also applies KGP, then you will also have to migrate the example app. To migrate your example app, follow the migration guide for app developers.