bug#77853: 30.1; python-inferior-mode: completion regression

[Eli Zaretskii]

> From: Christian Sattler <sattler.christian@gmail.com>
> Date: Wed, 16 Apr 2025 21:59:01 +0200
> 
> Completing a non-existing prefix attempts to complete it as a filename.
> 
> Steps to reproduce:
> 
> 1. touch test.file
> 2. emacs -Q
> 3. M-x run-python
> 4. test
> 5. M-x python-shell-completion-complete-or-indent
> 
> Outcome: incorrectly completes to test.file.
> 
> This regression was introduced in commit 0b9c714. The function
> python-shell-completion-at-point now returns nil instead of an empty
> list of candidates. This causes the next element of
> completion-at-point-functions list to be tried. This is
> comint-completion-at-point and completes filenames, which does not
> make sense in this context.

Thanks.

Liu Hui and kobarity, any suggestions for how to fix that?  The fix
should be safe enough for the release branch, since the regression was
introduced by Emacs 30.1.