feat(gazelle): Gazelle resolves module-level imports of py_proto_library

[shaldengeki]

Closes #1703. (I think this is only asking for module-level imports.)

This adds support in Gazelle for resolving module-level imports of py_proto_library rules. Note that this does not support:

1. Imports of module contents, like messages, services, or enums,
2. Imports of other rules, like GRPC

See the tests for examples of how this works. I would ideally like to implement the first one as well, but I think the "right" way to do that is to use something that's only present in Gazelle 0.38. So that'll have to wait on an upgrade of Gazelle in this repo; in the meanwhile, I think this is worth landing.

[dougthor42]

Nit: LF@EO, here and elsewhere.

[dougthor42]

I'm not sure I understand this test case - can you elaborate? Unless I'm blind, it looks like you're resolving the same thing that gazelle would resolve by default. So... what's that testing?

I would assume that using a resolve directive would typically be for cases where, say, the bar_py_pb2 py_proto_library doesn't exist but we want Gazelle to resolve import test2_generates_using_resolve.bar.bar_pb2 to something else.

Yes, I'm quite blind I guess.

Could you adjust the resolve directive to be easier to ID that it's resolving to a target that doesn't exist? Maybe:

# gazelle:resolve py test2_generates_using_resolve.bar.bar_pb2 //some:target

[dougthor42]

Can we add a test case with # gazelle:proto file mode?

One proto_library per .proto --> one py_proto_library per proto_library --> the final py_library will have multiple deps.

[dougthor42]

What's Rel in this context?

[dougthor42]

This is not always true. Depending on # gazelle:python_root, any one of these is possible:

//some/path/foo:foo_py_pb2
foo.foo_pb2                     # python_root is //some/path
path.foo.foo_pb2                # python_root is //some
some.path.foo.foo_pb2           # python_root is project root, default case.

I think we'll need a test case for # gazelle:python_root.

.
+ src/
  + BUILD.bazel        # gazelle:python_root
  + my_pkg/
    + protos/
      + foo.proto
      + BUILD.bazel
    + subpkg/
    + __init__.py
    + main.py
    + foo.py
    + BUILD.bazel
pyproject.toml
deploy.py
BUILD.bazel

In the above tree, src/my_pkg/main.py will have:

import my_pkg.foo as foo
import my_pkg.subpkg.bar as bar
import my_pkg.proto.foo_pb2 as foo_pb2

While the target will be:

# src/my_pkg/BUILD.bazel
py_library(
    name = "main",
    srcs = ["main.py"],
    imports = "..",
    deps = [
        "//src/my_pkg:foo",
        "//src/my_pkg/subpkg:bar",
        "//src/my_pkg/proto:foo_py_pb2",
    ],
)

Specifically: the Bazel target will include information (src) not found in the python import string.

[dougthor42]

Future work: if the proto import is guarded with if TYPE_CHECKING, then only include the _pb2.pyi file in the pyi_deps target attribute.