`url2pathname()` mishandles URL with Windows drive in netloc

[barneygale]

Bug report

Bug description:

Windows-specific regression in Python 3.14 caused by d783d7b

Some programs generate file URLs by adding a file:// prefix to a path. On Windows, this can result in URLs like file://C:/foo. Though these URLs are malformed, they were correctly handled by urllib.request.url2pathname() until 3.14.

>>> from urllib.request import url2pathname
>>> url2pathname('//C:/foo')
'\\\\C:\\foo'  # expected 'C:\\foo'

CPython versions tested on:

3.14

Operating systems tested on:

No response

Linked PRs

• GH-137059: url2pathname(): fix support for drive letter in netloc #137060

[serhiy-storchaka]

Note that there will also be issues if the path contains # (after #136874) or %. On Posix -- also if the path contains ?.