Add option for --active flag to be used as default

[Nick-Hemenway]

Summary

There seems to be a lot of interest in enabling uv to reference virtual environments located in a central location on your computer (as opposed to in a .venv folder located in the project's directory) (See #1495). It doesn't appear that there's an immediate plan to support this functionality (at least not through an interface that resembles those of virtualenvwrapper, pyenv, or poetry).

There's a bit of workaround, however. A user can use an external virtual environment by creating it, activating it, and then adding a --active flag to each invocation of uv. It might look something like this:

>>> uv venv ~/.virtualenvs/my_venv
>>> source ~/.virtualenvs/my_venv/Scripts/activate
>>> uv add --active numpy pandas jupyterlab
>>> uv remove --active pandas
>>> uv sync --active

This workflow is fine, but it's kind of tedious remembering to add the --active flag all the time. Especially because if you forget to add the flag, uv will automatically create a new .venv folder in your project directory that you have to delete.

My request is to please add the option (perhaps through an environment variable?) to make the --active flag the default behavior. If enabled as the default, it would make sense to raise an error message if a user tries to call uv add (or similar applicable commands) without a virtual environment currently active.

Example

No response

[zanieb]

Duplicate of #11273