/**
     * Kotlin-friendly sources config.
     */
    private fun AsciidoctorTask.sources(patternFunction: PatternSet.() -> Unit) {
        this.sources(object : Closure<Unit>(this) {
            override fun call() {
                (delegate as PatternSet).patternFunction()
            }
        })
    }

sources {
                include("index.adoc")
            }

delegateClosureOf()