android - compileKotlin block in build.gradle file throws error "Could not find method compileKotlin() for arguments [...]"

Question

I'm trying to configure Kotlin to work with Java 1.8 in my Android project. I've tried adding the compileKotlin block at the bottom of my build.gradle file, but I get an error if I do so.

The error that occurs is the following:

Error:(38, 0) Could not find method compileKotlin() for arguments [build_dvcqiof5pov8xt8flfud06cm3$_run_closure4@66047120] on project ':core' of type org.gradle.api.Project.

The project runs fine without this block. What am I missing? Here's the complete build.gradle file, it's pretty basic stuff:

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'


android {
    compileSdkVersion 25
    buildToolsVersion '25.0.2'


    defaultConfig {
        minSdkVersion 24
        targetSdkVersion 25
        versionCode 1
        versionName '1.0.0'

        testInstrumentationRunner 'android.support.test.runner.AndroidJUnitRunner'

    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
    compile 'com.google.android.support:wearable:2.0.2'
}

repositories {
    mavenCentral()
}

compileKotlin {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8

    kotlinOptions {
        jvmTarget = '1.8'
        apiVersion = '1.1'
        languageVersion = '1.1'
    }
}

Answer 1

The error you are getting means that there's no compileKotlin task in the project, and that's expected for Android projects.

The Kotlin compilation task names in Android projects contain the build variant names (those are combined from build type, product flavor and other settings and look like debug or releaseUnitTest -- the tasks are compileDebugKotlin and compileReleaseUnitTestKotlin respectively). There's no compileKotlin task, which is usually created for the main source set in ordinary Java + Kotlin projects.

Most probably, you want to configure all Kotlin compilation tasks in the project, and to do that, you can apply the block as follows:

tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8

    kotlinOptions {
        jvmTarget = '1.8'
        apiVersion = '1.1'
        languageVersion = '1.1'
    }
}