Expand environment variables in URLs

[charliermarsh]

Summary

This PR enables users to express relative dependencies via environment variables. Like pip, PDM, Hatch, Rye, and others, we now allow users to express dependencies like:

flask @ file://${PROJECT_ROOT}/flask-3.0.0-py3-none-any.whl

In the compiled requirements file, we'll also preserve the unexpanded environment variable.

Closes #592.

[konstin]

Is it intentional that PROJECT_ROOT defined in the user env takes precedence over `PROJECT_ROOT?

[charliermarsh]

Yeah

[alelavelli]

How it is possible to dynamically read the local package content like in poetry with my-local-package = { path = "local/package/path", develop = true }?

Because for now, the only solution I found is to recompile the pypropject.toml with --refresh-package my-local-packageand then reinstall it

[charliermarsh]

@alelavelli -- Are you looking for uv pip install -e ./local/package/path?

[alelavelli]

@charliermarsh

Yes but directly from the pyproject.toml. Something like poetry:

[tool.poetry.dependencies]
my-local-package = {path = "../my-local-package", develop = true}

but with uv, like this:
[project]
dependencies = [
"my-package @ file:/path/to/my/package" # with something to say -e
]

[charliermarsh]

Unfortunately I think it's not possible in pyproject.toml, because it's just not part of the standard PEP 508 specification.