GH-128520: pathlib ABCs: raise text encoding warnings at correct stack level

[barneygale]

Ensure that warnings about unspecified text encodings are emitted from ReadablePath.read_text(), WritablePath.write_text() and magic_open() with the correct stack level set.

These classes/functions are still private, so there's no public change of behaviour.

• Issue: Make pathlib ABCs usable by zipfile.Path #128520

[JelleZijlstra]

Looks good. Do we run any tests/buildbots with warn_default_encoding on?

An alternative way to write the tests would be to run a subprocess that has the flag on.

[barneygale]

Thanks!

I can't see any indication that any build bots enable warn_default_encoding, but I'm not sure how to confirm!

FWIW, when I backport this to the pathlib-abc pypi package, I'll add PYTHONWARNDEFAULTENCODING = 1 to tox.ini. There's a similar setup in the zipp package and the zipfile.Path tests

[JelleZijlstra]

I'd prefer if these tests are exercised in some way in CPython's own CI but up to you if you prefer a different approach; feel free to merge as is.

[barneygale]

Thanks Jelle.

I'll get these tests running in CPython CI in a follow-up PR, because I suspect the same fix will be useful in the zipfile.Path tests, and that'll need to land upstream in zipp first.