Allow environment variables expansion in pyproject.toml

[ShaiAvr]

A feature I'd really like to see implemented is the ability to expand environment variables in the pyproject.toml file. My use-case is as follows: I am working on a library to simplify my work on other projects. In the future, I'd like to publish the library to PyPi. When I work on my projects, however, I want to use my library as a local editable dependency so I can quickly make changes and see them applied. So I have an example project with the following pyproject.toml:

[project]
name = "demo"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = [
    "my-lib",
]

[tool.uv.sources]
my-lib = { path = "/path/to/my/library/my-lib", editable = true }

The problem is I am using an absolute path for my library, so I need to modify it if I work on multiple computers, and it's not something I'd want to push to GitHub. A better solution would be to have an environment variable that defines the location of the library on my local machine: MY_LIB_PATH="/path/to/my/library/my-lib". That way, I can define the environment variable as necessary on different machines and my pyproject.toml file will simply use this variable:

[project]
name = "demo"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = [
    "my-lib",
]

[tool.uv.sources]
my-lib = { path = "${MY_LIB_PATH}", editable = true }

This isn't possible at the moment, and I think expanding environment variables in the pyproject.toml file could solve my use case and other similar use cases.

[woutervh]

I would reference a local symlink src/my-lib --> /absolute/path/to/my-lib

[ShaiAvr]

@woutervh I don’t think a symbolic link should be uploaded to git. The contents of the link won’t be portable.

[charliermarsh]

Similar (but not identical) to #5734.