java

configure<JavaPluginConvention> {
    sourceSets[SourceSet.MAIN_SOURCE_SET_NAME].java {
        srcDir("src/main/kotlin")
    }
}

plugins {
    java // so we can benefit from the `java` accessor below
}

fun Project.sourceSets(block: SourceSetContainer.() -> Unit) = the<JavaPluginConvention>().sourceSets.apply(block)
val SourceSetContainer.main: SourceSet get() = this["main"]
val SourceSetContainer.test: SourceSet get() = this["test"]
fun SourceSetContainer.main(block: SourceSet.() -> Unit) = main.apply(block)
fun SourceSetContainer.test(block: SourceSet.() -> Unit) = test.apply(block)
val SourceSet.kotlin: SourceDirectorySet get() = (this as HasConvention).convention.getPlugin<KotlinSourceSet>().kotlin

        sourceSets {
            main {
                println("${name.capitalize()} => Java : ${java.srcDirs}, Kotlin: ${kotlin.srcDirs}, Resource: ${resources.srcDirs}")
            }
            test {
                println("${name.capitalize()} => Java : ${java.srcDirs}, Kotlin: ${kotlin.srcDirs}, Resource: ${resources.srcDirs}")
            }
        }