[WIP] use uv for resolving Pants plugins

[tdyas]

Use uv for resolving Pants plugins. Enabled via new --experimental-use-uv-for-plugin-resolution option.

[benjyw]

Interesting approach. Fair to say that uv itself is a side quest here? IIUC the real goal is to not need a scheduler, which means not using any existing pex-running rules. So at that point we must use some CLI tool directly, and uv is an interesting choice? But we could also use pip or even pex, I would guess? We just can't use existing pex machinery.

[tdyas]

Interesting approach. Fair to say that uv itself is a side quest here? IIUC the real goal is to not need a scheduler, which means not using any existing pex-running rules. So at that point we must use some CLI tool directly, and uv is an interesting choice? But we could also use pip or even pex, I would guess? We just can't use existing pex machinery.

Correct, some tool needs to be invoked, it need not be uv. For context, uv was not my first choice. I tried to use pex with this approach in #21986, but generating the necessary magic shell scripts used by the VenvPex support is confusing me currently. Suggestions there are very much welcome.

So uv is a side quest but it turned out to be much simpler than trying to replicate the existing plugin resolution experience with pex outside of the Python backend logic.

[benjyw]

Getting some experience with uv is probably a good idea...

[grihabor]

You can parametrize a fixture instead:

@pytest.fixture(params=[False, True], ids=["pip", "uv"])
def use_uv(request) -> bool:
    return request.param

def test_1(use_uv: bool): ...
def test_2(use_uv: bool): ...

see the docs here https://docs.pytest.org/en/6.2.x/fixture.html#parametrizing-fixtures