When using --target, exceptions can leave a temp directory behind

Right, the problem with target_temp_dir is that it’s created conditionally - so sometimes it’s a context manager, and other times it’s None. So we can’t “just” enter it earlier, as you can’t do with None.

When we drop Python 2, we could fix this with contextlib.ExitStack. This isn’t worth vendoring the contextlib backport just for Python 2, though. We could also write our own MaybeContextManager class that wraps an optional context manager, but again that’s a lot of work.

I’m going to make the call that this should be handled in a follow-up PR, and for now just allow left-over temp directories in the test.

_Originally posted by @pfmoore in https://github.com/pypa/pip/pull/8462#issuecomment-649349135_

[pfmoore]

@pfmoore, I think you’ve already fixed it in f162236 😄

I thought it rang a bell 😄

Too many issues in the tracker, not enough cells in my brain…

[uranusjr]

Gosh, I knew I’ve seen that CommandContextMixIn implementation before. I thought I was hallucinating or something.