JMH gradle without plugin for multi-module projects

build.gradle

...

subprojects {
    ...

    apply plugin: 'java'
    apply plugin: 'scala'

    sourceCompatibility = 1.8
    targetCompatibility = 1.8

    sourceSets.main {
        java.srcDirs = ['src/main/java']
        scala.srcDirs = ['src/main/scala']
        scala.include '**/*.*'
    }

    sourceSets.test {
        java.srcDirs = ['src/test/java']
        scala.srcDirs = ['src/test/scala']
        scala.include '**/*.*'
    }

    // https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_source_sets
    sourceSets {
        jmh {
            java.srcDirs = ['src/jmh/java']
            scala.srcDirs = ['src/jmh/scala']
            resources.srcDirs = ['src/jmh/resources']
            compileClasspath += sourceSets.main.runtimeClasspath
        }
    }

    dependencies {
        ...

        jmhImplementation 'org.openjdk.jmh:jmh-core:1.21'
        jmhImplementation 'org.openjdk.jmh:jmh-generator-annprocess:1.21'
    }

    // https://docs.gradle.org/current/dsl/org.gradle.api.tasks.JavaExec.html
    task jmh(type: JavaExec, dependsOn: jmhClasses) {
        main = 'org.openjdk.jmh.Main'
        classpath = sourceSets.jmh.compileClasspath + sourceSets.jmh.runtimeClasspath

        // To enable the built-in stacktrace sampling profiler
        // args = ['-prof', 'stack']
    }

    // to make sure benchmarks always get compiled
    classes.finalizedBy(jmhClasses)
}

...