Transitive dependencies on proto libraries with `strip_import_prefix` don't work

[tpudlik]

🐞 bug report

Affected Rule

The issue is caused by the rule: py_proto_library

Is this a regression?

No, this was never supported.

Description

If a proto_library A with strip_import_prefix depends on another proto_library B with strip_import_prefix, then the _virtual_imports locations for both A and B must be added to the PYTHONPATH (i.e., to the imports attribute for the generated py_library).

Currently, only the _virtual_imports for A are added to PYTHONPATH.

You can work around this by adding the py_proto_library for B directly to the deps of the py_library that depends on the py_proto_library for A, but it's clearly confusing.

🔬 Minimal Reproduction

This commit adds a unit test that reproduces the issue (as well as a proposed change to py_proto_library.bzl that fixes it): 214bb7c

🔥 Exception or Error

  File "/usr/local/google/home/tpudlik/.cache/bazel/_bazel_tpudlik/1d5247c3691bed961cc8f7244214476e/sandbox/linux-sandbox/210/execroot/rules_python_py_proto_library_example/bazel-out/k8-fastbuild/bin/message_test.runfiles/rules_python_py_proto_library_example/example.com/another_pr
oto/_virtual_imports/message_proto/another_proto/message_pb2.py", line 14, in                                                                                                                                                                                                     
    from proto import pricetag_pb2 as proto_dot_pricetag__pb2                                                                                                                                                                                                                             
ModuleNotFoundError: No module named 'proto'

🌍 Your Environment

Operating System:

  
Linux
  

Output of bazel version:

  
6.2.0
  

Rules_python version:

  
2b05d9fba8cd7406c6c73549885210ba4771cc9e