I want to build a rule that is very similar to cc_proto_library. The key features are that it would apply an aspect to all the transitive proto_library dependencies and generate .cc and .h files for all of the dependencies. In addition it would generate actions that would compile these into object files.
While I understand how I can do the file generation, I don't see how to easily do the object generation. The native module is not available for rule (or aspect) implementations, and I cannot use a macro on top of the aspect as I need the object files to be generated in the same package as the proto_library so that it is generated only once.
cc_proto_library can do this I believe because it is not written in Skylark and thus has access to more primitives. Is there anyway to do this with just Skylark?
This is unfortunately currently not possible. There is no Skylark API to the C++ rules/actions (what we call C++ sandwich). We have plans to implement this in Q1 2018. There are many tracking issues, this one looks the most relevant: https://github.com/bazelbuild/bazel/issues/2163.