Then, a python_library which depends on the protobuf_library will get all of the Protoc runtime libraries (including the JarLibrary) when using TransitiveTargets.

I argue that it’s not worth the complexity to pre-filter out that

JarLibrary

. Unlike codegen of sources, which has a real performance cost of running Protoc, adding an extra dependency is cheap. And it’s already very common for call sites to filter out irrelevant dependencies