Adding an external backend as an output formatter

Although the popular AsciidoctorJ backends are supported in this plugin suite, there is a good chance that one might want to use a backend that is not directly supported. For this there is a special output formatter of type AsciidoctorjGenericOutputFormatter.

import org.asciidoctor.gradle.model5.jvm.formatters.AsciidoctorjGenericOutputFormatter
import org.asciidoctor.gradle.model5.jvm.toolchains.AsciidoctorjToolchain

asciidoc {
  toolchains {
    asciidoctorj.registeredOutputFormatters {
      myBackend(AsciidoctorjGenericOutputFormatter) {
        backend = 'foo' (1)
        attributes( foo_color : 'black') (2)
        copyResources = false (3)
        enforcedDocType = 'book' (4)
        requires 'foo' (5)
        useGem 'foo', '1.2.3' (6)
        useModule( 'acme.foo:foo', '1.2.3') (7)
        useModule( dependencies.project(':my-backend')) (8)
      }
    }
  }
}

1	Set the name of the backend
2	Set the specific attributes that this backend might require.
3	Set whether the backend should copy resources.
4	If the backend requires a specific kind of document type, set it here, otherwise leave it alone.
5	If one or more `requires` need to be passed to the engine, define them here.
6	If the backend is only available as a GEM, add the name of the GEM and its version. To use this option, the `org.asciidoctor.jvm.gems` must be applied.
7	If the backend is available as a JAR artifact from a Maven or Ivy repository, provide the Maven module coordinates as well as something that will resolve to a version string.
8	If the backend is provided from the current project hierarchy, it can be referenced as a project dependency.