Have Gazelle generate `py_proto_library` targets

[dougthor42]

🚀 feature request

Relevant Rules

gazelle

Description

As far as I know, there is no gazelle support for making py_proto_library targets.

Describe the solution you'd like

gazelle_binary(
    name = "gazelle_multilang",
    languages = [
        "@rules_python_gazelle_plugin//python",
        "@rules_python_gazelle_plugin//python_proto",  // or something
        "@bazel_gazelle//language/proto",
    ],
    visibility = ["//visibility:public"],
)

Thoughts, notes, addendums, provisios, questions, etc.

• [Gazelle][proto] How to automatically resolve protobuf target #1703 mentions things a bit
• Should this be part of rules_python_gazelle_plugin? Or part of bazel-contrib/bazel-gazelle? Or maybe protocolbuffers/protobuf given that the py_proto_library target is now maintained by them?
• Separate "language" (as the above example) or just a directive such as # gazelle:python_proto_generation True?
• Would we require people to also have gazelle generate the proto_library targets (like the example does) or no?
  • If yes, how do we ensure that the proto_library targets are made first?

As #1703 (comment) says: we'd basically just look at what bazel-gazelle does and copy that here, modulo some name changes.

Describe alternatives you've considered

Bespoke, artisanal, hand-crafted py_proto_library targets.

[shaldengeki]

👋 One thing to consider is that the golang extension to Gazelle is responsible for resolving deps on proto targets. In fact there's some logic in the gazelle proto extension that's special-cased to feed dependency information for well-known protos to the golang plugin. Probably a good idea to update that to include Python, once this is implemented.

So I'd by default go with that approach. I also think it's a better UX; folks won't have to install a second plugin just to handle proto. This implies we'd want a directive -- I'd argue for # gazelle:py_generate_proto, since the directive in golang is called go_generate_proto and we already use py as the language name in Gazelle.

As for how we'd ensure that proto_library are generated, I think that'll be easy - the gazelle docs say that users should put proto-dependent extensions after the proto extension in the languages list.

(BTW, @dougthor42 - I'm interested in working on this, if you're not -- let me know.)

[dougthor42]

That all sounds good to me! And yes I don't have the bandwidth to work on this, so please feel free to pick it up.

[shaldengeki]

Great! I'll pick it up, then -- I might ping you or the other rules_python folks in the next couple days if I need clarification on how the existing plugin works.