mypy_stubs issues

[brandonchinn178]

I'm encountering a few issues with mypy_stubs:

1. Stubs included transitively aren't being included:

   mypy_stubs(name = "kafka_stub", srcs = ["kafka.pyi"])
   
   py_library(name = "dep", srcs = ["dep.py"], deps = [":kafka_stub"])
   
   py_binary(name = "main", srcs = ["main.py"], deps = [":dep"])

   With this setup, building main fails because dep.py is included in the mypy invocation, but kafka.pyi isn't transitively included in stub_files, which means kafka.pyi isn't making it into mypypath

2. A tree of stub files isn't included in the mypy path correctly. Currently, the integration only adds the mypy_stubs' files' immediate directory into MYPYPATH, but that won't resolve nested structures like a/__init__.py and a/b/__init__.py

   • I also suspect that having a/__init__.py and b/__init__.py would also error currently

Current workaround

I'm currently adding a patch file doing the equivalent of the following:

# transitively include stubs
for deps in transitive_srcs_depsets:
    for f in deps.to_list():
        if f.extension == "pyi":
            stub_files.append(f)

# only add stub root
mypypath_parts += [src_f.dirname for src_f in stub_files if src_f.basename == "__stubs_root__.pyi"]

and then adding __stubs_root__.pyi to every mypy_stubs target