Using shadowJar with FG's jarJar

build.gradle

afterEvaluate {
    tasks.named('jarJar') {
        enabled = false
    }
    tasks.named('reobfJarJar') {
        enabled = false
    }
}

tasks.register('fullJar', net.minecraftforge.gradle.userdev.tasks.JarJar) {
    group = 'build'

    archiveClassifier = ''
    from tasks.named('shadowJar').map { zipTree(it.archiveFile) }
    configuration project.configurations.jarJar

    doFirst {
        manifest.inheritFrom tasks.shadowJar.manifest.effectiveManifest
    }
}

reobf {
    shadowJar {}
    fullJar {}
}