ZipFile.mkdir() combines the caller-provided mode into the entry's external attributes without clearing the file type bits, so those bits can mark the created entry as something other than a directory:

>>> import io, stat, zipfile
>>> with zipfile.ZipFile(io.BytesIO(), 'w') as zh:
...     zh.mkdir('foo/', 0o107777)
...     print(oct(stat.S_IFMT(zh.getinfo('foo/').external_attr >> 16)))
...
0o140000   # socket, not a directory

This PR sanitizes mode to its permission bits before combining it with S_IFDIR, matching what stat.S_IMODE() does, as suggested in the issue:

zinfo.external_attr = (0o40000 | (mode & 0o7777)) << 16

It also spells the default mode as 0o777 instead of 511 in the signature and documentation, for consistency with os.mkdir() (same value, clearer intent).

Included:

• Regression assertions in test_mkdir covering S_IFREG and S_IFLNK type bits in mode, plus an extractall() round-trip.
• Documentation update for ZipFile.mkdir() with a versionchanged note.
• NEWS entry.

• Issue: Improper sanitization and documentation for ZipFile.mkdir(mode) #154490