Hi rules_python team

I use your rules for a long time now. With WORKSPACE style, I use pip as follows:

pip_parse(
    name = "py_deps",
    extra_pip_args = [
        "--index-url=/home/user/local_pip_mirror",
        "--no-cache-dir",
    ],
    python_interpreter = "python3",
    python_interpreter_target = interpreter,
    requirements_lock = ":requirements_lock.txt",
)

The folder /home/user/local_pip_mirror gets populated with pypi-mirror download --requirement requirements_lock.txt

So I have a nice and clean way to use offline build. I could never get it running directly with bazel fetch and stuff. But this solution was very nice because no internet was involved at all.

I am in the way of upgrading to bzlmod. I saw many bug reports for making offline build work, but I honestly gave up with bazel vendor and stuff again. The simplest way in my opinion is to just use a local pip mirror. For that I tried the following:

pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip")
pip.parse(         
    experimental_index_url = "/home/user/local_pip_mirror",
    hub_name = "py_deps",
    python_version = python_version,
    requirements_lock = "//:requirements_lock.txt",
)                        
use_repo(pip, "py_deps")

at the moment, experimental_index_url must be a https:// url to work.

This MR changes it so that local paths are also a possible experimental_index_url.

For my project, the proposed changes are in effect and working great.

It is not perfect, but I think it is an important addition to aid the bzlmod migration.