Enable reading uv.toml from venv

[JonneDatanen]

Resolves: #8107

Summary

Sometimes I would like to have per-venv uv.toml so that there could be e.g. multiple venv's with different constraints where different projects are run/tested. System/user wide configuration forbids doing many venv's and project settings doesn't allow running with different set of constraints.

Having configuration files within the venv is also a feature that pip supports: https://pip.pypa.io/en/stable/topics/configuration/#location

Test Plan

Manually tested by creating venv and adding uv.toml there -> constraints were resolved correctly.

[zanieb]

I think we're pretty hesitant to do this. When we recreate a virtual environment, we delete the entire directory. It doesn't seem like a good place for additional state, like settings.

What does

project settings doesn't allow running with different set of constraints

mean?

[JonneDatanen]

What does

project settings doesn't allow running with different set of constraints

mean?

We have some "fixed" python production environments. E.g.:

• prod-env0 -> python==3.8, numpy==1.17.0, pandas==0.24.0, ...
• prod-env1 -> python==3.10, numpy==1.24.4, pandas==1.4.4, ...
• prod-env2 -> python==3.12, numpy==2.13.0, pandas==2.2.2, ...
• etc...

And then we have e.g. python package foo that we ci-test and guarantee to run smoothly in e.g. env1 and env2.

That means that we want to give some set of hard constraints while installing foo, but:

• They cannot be in pyproject.toml as the constraints are different based on the env we are testing/running the package
• They cannot be in ~/.config/uv.toml as the same user might want to test in different venv's

So for our use case it is better to have venv-specific configs, that can be generated (with script, prod-env init 0) after I create new venv. Currently we have that kind of script for pip, but I would definitely like to switch to uv pip if pip-like venv specific uv.toml would be possible.

Of course this doesn't maybe fit nicely to uv sync/uv lock way of working, but having this in uv pip would be nice