In terms of matching existing expectations, it occurs to me that the clearest way to make these "act like generated code" is to pretend that they were codegen'd, and create a synthetic target for them. It would be a bit of a re-architecture of deferred sources, but essentially, have a unpacked_sources target with a lang parameter (similar to thrift_library), and have the UnpackJars task create a synthetic target of the appropriate type paired to the unpacked_sources target.