pip wheel --no-clean does not prevent clean

[mhsmith]

Environment

• pip version: 10.0.1
• Python version: 3.6
• OS: Linux

Description
WheelBuilder in https://github.com/pypa/pip/blob/master/src/pip/_internal/wheel.py takes a no_clean argument, but doesn't do anything with it. As a result, setup.py clean is unconditionally executed whether the build is successful or not.

I just had a 20 minute build process fail at the last step, after which pip deleted the entire build directory, making it impossible to investigate the problem. You might want to consider whether this is a good default behaviour. But in any case, --no-clean should actually prevent the clean.

#2779 is related, but involves a different area.

[ziebam]

Using the --no-clean flag on the current pip version (21.3.dev0) works correctly. I'm not sure which PR fixed it, but I think this issue can be closed.

[sbidoul]

--no-clean controls the cleanup of temporary directories created by pip.
But there is indeed an unconditional call to setup.py clean after a setup.py bdist_wheel failure.
I'm not sure why it is so. That is legacy behaviour which does not occur for projects using pyproject.toml.

[ziebam]

Would a simple check (i.e. if not req.use_pep517: -> if not req.use_pep517 and [check here that --no-clean isn't set]: suffice or is it a more involved fix? In the first case I'd be willing to provide a PR.

[sbidoul]

Maybe ? Or we could simply just stop calling setup.py clean. Not sure.