Why is there no SourceSetOutput.sourcesDir for AnnotationProcessor generated source?

Is there a gap in the SourceSetOutput for specifying a directory for javac generated source? The -s option: http://docs.oracle.com/javase/8/docs/technotes/tools/windows/javac.html

We’re using an AnnotationProcessor to generate source for some source sets, and have to manually wire this support into the javac execution, as well as tweak things for the Eclipse plugin to account for these source directories in the .classpath.

The SourceSetOutput seems to support various other output directories (e.g. resources, classes) one would use via a Filer when processing annotations: http://docs.oracle.com/javase/8/docs/api/javax/annotation/processing/Filer.html

I’ve also read elsewhere treatment of generated source may be changing for Gradle 2.0?