Please revert the deprecation to declare additional feature variants on the `main` source set about gradle

[Vampire]

I think this should be the work-around if the deprecation is not going to be reverted:

plugins {
    `java-library`
    `maven-publish`
}

group = "showcase"
version = "0.1.0-SNAPSHOT"

publishing {
    val library by publications.registering(MavenPublication::class) {
        from(components["java"])
    }
}

val java9 by sourceSets.creating
java {
    targetCompatibility = JavaVersion.VERSION_1_8
    registerFeature("java9") {
        usingSourceSet(java9)
        capability("$group", name, "$version")
    }
}
val java9ApiElements by configurations.existing {
    attributes {
        attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, 9)
    }
}
val java9RuntimeElements by configurations.existing {
    attributes {
        attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, 9)
    }
}
val java9RuntimeOnly by configurations.existing
dependencies {
    java9RuntimeOnly("javax.cache:cache-api:1.1.1")
}

val apiElements by configurations.getting
val java9ApiElements by configurations.existing {
    outgoing.artifacts.clear()
    apiElements.artifacts.forEach(outgoing::artifact)
    extendsFrom(apiElements)
}
val runtimeElements by configurations.getting
val java9RuntimeElements by configurations.existing {
    outgoing.artifacts.clear()
    runtimeElements.artifacts.forEach(outgoing::artifact)
    extendsFrom(runtimeElements)
}

[ljacomet]

This issue needs a decision from the team responsible for that area. They have been informed. Response time may vary.