3.14.0a1 urljoin regression wrt //

[hroncok]

Bug report

Bug description:

The tests of lxml do (simplified):

from urllib.parse import urljoin
urljoin('file:', '/foo/bar')

• On Python 3.13.0 and earlier, the result of the urljoin call is file:///foo/bar.
• On Python 3.14.0a1, the result of the urljoin call is file:/foo/bar.

This change of behavior was introduced in fc897fc #123273 cc @serhiy-storchaka

The NEWS entry in that change does not seem to indicate this change was intentional.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Linux

[ZeroIntensity]

Duplicate of #125926

[hroncok]

That seemed like a different problem to me, but perhaps the cause is the same, yes.

[serhiy-storchaka]

This is not a duplicate of #125926.

But file:///foo/bar and file:/foo/bar are equivalent URIs. And we can argue that since file: and /foo/bar have undefined authority, the result should have undefined authority as well. This is a result of the algorithm in RFC 3986, Section 5.2.2, although it need an absolute base URI.

[ZeroIntensity]

I marked this as duplicate because it seemed like there was some underlying issue introduced into urljoin. I was assuming they will both be fixed by the same PR, but I guess not, sorry!