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:1.27'
        jmhAnnotationProcessor 'org.openjdk.jmh:jmh-generator-annprocess:1.27'
    }

    // 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)
}

...

I came across the fact that if you want to write benchmarks in Kotlin (not the code being checked, but the code of the benchmarks themselves), then annotationProcessor will not be enough. The code will be generated only by annotations in the Java code. Kotlin will be ignored. But you can use kapt instead, the code will be generated immediately and Java and Kotlin.

Here you can see an example where benchmarks are written immediately in both Kotlin and Java.

Actually an annotation processor is not required in case of JMH. JMH has a special org.openjdk.jmh.generators.bytecode.JmhBytecodeGenerator. Here you can see how to make a task in gradle that will generate code without using annotationProcessor and kapt. Not as the best solution, I want to share for those who may be useful.

@mrbald I found the annotationProcessor not working for scala but only for java. Any suggestion?