GH-73991: Disallow copying directory into itself via pathlib.Path.copy()

[barneygale]

No news blurb because pathlib.Path.copy() is still new.

• Issue: Support moving across filesystems in pathlib.Path, as shutil.move() does #73991

[picnixz]

I think my interrogations are answered. Do we actually need to have a full coverage? I think that what we are covering currently is A' -> A' and A -> A' with A' a symlink to A but I'm not sure if we need to do more per our discussion on the perverse example (for instance, A' -> A'' where both are symlinks actually).

[barneygale]

Good shout! I've added tests for copying from one symlink to another.

[barneygale]

Hey @picnixz, do you think this is ready to merge?

[picnixz]

Sometimes I request reviews for myself in order not to forget them... and then I still forget about them >.< From what we decided, I think we are fine with the tests, but you could also increase the coverage by testing the follow_symlinks=False case. I'm fine with the current state of the PR though (by the way, any reason why you sometimes use a context manager for checking the error and sometimes not?)

[barneygale]

No worries! Thanks tons for the review, it's been very helpful

[picnixz]

No worries! Thanks tons for the review, it's been very helpful

It was a fun moment as well!