gh-158998: Fix os.statx() ignoring follow_symlinks=False

[jjhelmus]

Set AT_SYMLINK_NOFOLLOW to prevent statx from following symlinks when follow_symlinks=False is passed to os.statx.

• Issue: os.statx() ignores follow_symlinks=False #158998

[jjhelmus]

Let me know if this change meet the criteria for needing tests or a NEWS item. I can add both if needed.

[cmaloney]

This will need both NEWS and a test (changes visible behavior of a feature that has been in a release). Pinged the contributor who added statx to hopefully review (haven’t reviewed the implementation myself yet)

[jbosboom]

The fix looks obviously correct. (Whoops!)

The tests should go in test_os.StatAttributeTests. Change check_statx_attributes to accept a follow_symlinks kwarg and pass it to the os.stat and os.statx calls, then add new test methods like test_statx_attributes that create a proper/broken symlink and pass follow_symlinks=False/True (four cases; can be four methods or one method with four subtests).

Ping me again for review when you've written the tests.

[jjhelmus]

I've added a the described tests and a NEWS item. @jbosboom was this what you were looking for in the tests?

[jbosboom]

check_statx_attributes only accidentally checks that os.statx raises in this case (because os.statx is called before os.stat). I think it's sufficient and clearer to call os.statx directly here.

[jbosboom]

I mean: replace self.check_statx_attributes -> os.statx on the line just after the lines shown in the comment. (Sorry, not used to GitHub's review/comment interface.)

[jjhelmus]

Agreed that calling statx here is clearer. I've updated the test.

[jbosboom]

LGTM except for one comment on the test, where you did what I asked for even though it doesn't make sense in one case.

Thanks for fixing this, and I'm sorry you had to fix it.

[jjhelmus]

Thanks for fixing this, and I'm sorry you had to fix it.

Happy to address this.
I discovered this when putting together the more ambitious syscall fallback for statx, #159043, which effects similar areas blocks.