Support venv --prompt

[methane]

Summary

This PR adds the --prompt option to venv subcommand.

The default behavior for uv venv is to create a virtual environment in the current directory with .venv name. This is different from venv / virtualenv where a user always needs to provide the virtual environment path. This allows us to define our own behavior in the default scenario (uv venv). We've decided to use the current directory's name in that case.

Workflows:

Command	Virtual Environment Name	Prompt
uv venv	.venv (default)	Current directory name
uv venv project	project	project
uv venv --prompt .	.venv	Current directory name
uv venv --prompt foobar	.venv	foobar
uv venv project --prompt foobar	project	foobar

Fixes #1445

Test Plan

This is my first Rust code and I don't know how to write tests yet.
I just checked the behavior manually:

$ cargo build
$ mkdir t
$ cd t
$ ../target/debug/uv venv -p 3.11
$ rg -w t .venv/bin/acti*
.venv/bin/activate.csh
13:setenv VIRTUAL_ENV '/Users/inada-n/work/uv/t/.venv'
20:if ('t' != "") then
21:    setenv VIRTUAL_ENV_PROMPT 't'
23:    setenv VIRTUAL_ENV_PROMPT "$VIRTUAL_ENV:t:q"
38:    # in which case, $prompt is undefined and we wouldn't

.venv/bin/activate
48:VIRTUAL_ENV='/Users/inada-n/work/uv/t/.venv'
59:    VIRTUAL_ENV_PROMPT="t"

.venv/bin/activate.fish
61:set -gx VIRTUAL_ENV '/Users/inada-n/work/uv/t/.venv'
73:if test -n 't'
74:    set -gx VIRTUAL_ENV_PROMPT 't'

.venv/bin/activate.ps1
40:if ("t" -ne "") {
41:    $env:VIRTUAL_ENV_PROMPT = "t"

.venv/bin/activate.nu
6:# but then simply `deactivate` won't work because it is just an alias to hide
35:    let virtual_env = '/Users/inada-n/work/uv/t/.venv'
50:    let virtual_env_prompt = (if ('t' | is-empty) {
53:        't'

[zanieb]

Thanks for your pull request! I have some comments to start.

I'm not sure what the best way to test this is either, you can see our current venv tests at https://github.com/astral-sh/uv/blob/main/crates/uv/tests/venv.rs — I'd look into adding a snapshot there.

Here's a resource about our snapshotting tool: https://insta.rs/docs/cli/

[zanieb]

Also congrats on your first Rust pull request ❤️

[dhruvmanila]

Thanks for creating this PR!

I was just playing around with venv / virtualenv when I saw this PR. That helped me understand what the original behavior is which means you don't need to fiddle around with other tools ;)

There are a few changes required to be compatible with the --prompt flag from other tools.

From the implementation side, I'm not exactly sure but you might want to play around with either using Option<&str> or Option<String> type for the prompt parameter in the gourgeist::create_bare_venv function. This is because we need to get the prompt value from the current working directory if it's Some(".") which could lead into ownership problems. Feel free to ping me if you face any, I'm happy to help :)

[methane]

When name is specified

~/work/uv/t (git)-[support-prompt] % ../target/debug/uv venv -p 3.11 hoge
Using Python 3.11.7 interpreter at /opt/homebrew/opt/python@3.11/bin/python3.11
Creating virtualenv at: hoge
~/work/uv/t (git)-[support-prompt] % grep prompt hoge/pyvenv.cfg
prompt = hoge

When name is omitted (.venv)

~/work/uv/t (git)-[support-prompt] % ../target/debug/uv venv -p 3.11
Using Python 3.11.7 interpreter at /opt/homebrew/opt/python@3.11/bin/python3.11
Creating virtualenv at: .venv
~/work/uv/t (git)-[support-prompt] % grep prompt .venv/pyvenv.cfg
prompt = t

stale

[MichaReiser]

Nice. We now also support batch files. Could you add the same logic to the activation.bat file?

[dhruvmanila]

I like the default behavior that you proposed. With that in mind, this is the final set of review comments and then it should be good to go.

It's mainly a simplification of using Option to avoid using is_empty for every entry in pyvenv.cfg. This is to keep the invariant that other entries are always going to be written to the file while prompt is optional.

Thanks for your patience!

[dhruvmanila]

@methane Thanks a lot for initiating this effort! I made some small tweaks at the end to accommodate Micha's recommendation:

1. Expanding the CLI flag documentation
2. Using a custom enum Prompt
3. Updated the PR description to list down the workflow

Congrats on landing your first PR and welcome to Astral! 🥳

[frague59]

Great job guys !