uv export should not need to have python installed

[mjpieters]

We are running a CI pipeline that includes a mend.io license compliance scanner, which looks for a requirements.txt file (it doesn't yet support uv.lock as an input file). We run the mend scanner in a minimal docker container with no Python installed. I can trivially install uv into that container, but without a python installation, I can't export the lock file to requirements.txt file:

$ uv --version
uv 0.4.27
$ uv export --output-file requirements.txt
error: No interpreter found for Python >=3.12 in managed installations or system path

Python should not be necessary here, all that is needed is that uv produces a requirements.txt file for another tool to then process.

The same applies to the tree command; uv has all the information needed already, a Python interpreter should not be necessary.

[zanieb]

I think we could do this with --frozen by making this block conditional

uv/crates/uv/src/commands/project/export.rs

Lines 84 to 95 in 291c4c4

	let interpreter = ProjectInterpreter::discover(
	project.workspace(),
	python.as_deref().map(PythonRequest::parse),
	python_preference,
	python_downloads,
	connectivity,
	native_tls,
	cache,
	printer,
	)
	.await?
	.into_interpreter();

Otherwise, we need an interpreter to check if the lockfile is up to date.

[charliermarsh]

(In uv tree, we need an interpreter unless the user passes --universal.)

[zanieb]

Are you talking about uv pip tree? Nevermind, I see we show the tree for the current platform by default.

[mjpieters]

Right, it didn't occur to me that tree would be platform dependant. I'm happy to ignore uv tree in this bug report, I am much more concerned with uv export in CI environments.