bug#54296: Add buffer-matching functionality

[Dmitry Gutov <dgutov@yandex.ru>]

On 14.06.2022 21:47, Eli Zaretskii wrote:

>>> Do you agree with Philip that deprecating or removing major-mode would
>>> be a problem for users of project-kill-buffer-conditions etc.?
>>
>> Yes. I also mentioned that here:
>> https://lists.gnu.org/archive/html/emacs-devel/2022-06/msg00650.html
> 
> So then everything is okay, AFAIU, because eventually Philip left that
> in the code.  Right?

No, he didn't.

He tried to migrate project-kill-buffer-conditions to the new format, 
with predicted unfortunate side-effects. And an unpredicted one (which 
is easier to fix, though).

See commit 1a3bad431d.

>>> I kinda gave up because Philip felt extremely uneasy with dropping
>>> major-mode, leaving us with just derived-mode, but I still think we
>>> shouldn't encourage Lisp programs to use major-mode.  So if you don't
>>> think it would be a problem, I'd be happier if we removed major-mode
>>> and used derived-mode instead.
>>
>> If I didn't think Philip's point had merit, I wouldn't have brought it
>> up now.
> 
> OK, but I didn't press my POV, so where's the problem, and why the
> emotions?

Your POV was the one that got implemented. buffer-match-p has 
'major-mode' but not 'derived-mode'. And 'major-mode' behaves like 
'derived-mode' behaved in project-kill-buffer-conditions.