feat(gazelle) For package mode, resolve dependencies when imports are relative to the package path

[yushan26]

When # gazelle:python_generation_mode package is enabled, relative imports are currently not being added to the deps field of the generated target.

For example, given the following Python code:

from .library import add as _add
from .library import divide as _divide
from .library import multiply as _multiply
from .library import subtract as _subtract

The expected py_library rule should include a dependency on the local library package:

py_library(
    name = "py_default_library",
    srcs = ["__init__.py"],
    visibility = ["//visibility:public"],
    deps = [
        "//example/library:py_default_library",
    ],
)

However, the actual generated rule is missing the deps entry:

py_library(
    name = "py_default_library",
    srcs = ["__init__.py"],
    visibility = ["//visibility:public"],
)

This change updates file_parser.go to ensure that relative imports (those starting with a .) are parsed and preserved. In Resolve(), logic is added to correctly interpret relative paths:

A single dot (.) refers to the current package.

Multiple dots (.., ..., etc.) traverse up parent directories.

The relative import is resolved against the current label.Pkg path that imports the module and converted into an path relative to the root before dependency resolution.

As a result, dependencies for relative imports are now correctly added to the deps field in package generation mode.

Added a directive # gazelle:experimental_allow_relative_imports true to allow this feature to be opt in.

[linzhp]

LGTM. @aignas Can you take a look?

[aignas]

Don't have time right now to look into gazelle PRs at a great detail, so I'll defer this one to @dougthor42, Thanks @linzhp, for the initial review!

[dougthor42]

@yushan26 can you take a look at the discussion in #2203? There are some edge case issues that I'd like to know if you've addressed. It looks like you're focusing on the "importing a class/function identifier" case. Does this also support importing relative modules?

from ..my_library import some_function  # looks like you've got this covered
from ...my_library.foo import some_function  # this too
from .library import other_module
from .. import some_module
from .. import some_function  # eg the function is exposed in ../__init__.py

Also, if we add support for relative imports, we need to make sure that it works when # gazelle:python_generation_mode file.

[linzhp]

Also, if we add support for relative imports

To clarify, relative imports are already supported before this PR (see this test), but it's partially broken in package mode (on importing another package) and not supported in file mode. This PR fixes the package mode. I am leaning towards fixing the file mode in a separate PR, unless you feel strongly about fixing both of them in one PR.

[yushan26]

Yea good point. Updated the test case to support the scenario and updated the function.

[dougthor42]

I am leaning towards fixing the file mode in a separate PR

SGTM.

---

Other requests:

1. Please update the PR title to follow the guidelines.
2. Please update the changelog.

[yushan26]

@dougthor42 Thanks for the review. I also included the directive # gazelle:experimental_allow_relative_imports to allow opt-in instead.