bug#54296: Add buffer-matching functionality

[Philip Kaludercic <philipk@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Philip Kaludercic <philipk@posteo.net>
>> Cc: larsi@gnus.org,  54296@debbugs.gnu.org
>> Date: Mon, 14 Mar 2022 08:21:56 +0000
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Philip Kaludercic <philipk@posteo.net>
>> >> Cc: larsi@gnus.org,  54296@debbugs.gnu.org
>> >> Date: Sun, 13 Mar 2022 20:40:49 +0000
>> >> 
>> >> Eli Zaretskii <eliz@gnu.org> writes:
>> >> 
>> >> >> From: Philip Kaludercic <philipk@posteo.net>
>> >> >> Cc: larsi@gnus.org,  54296@debbugs.gnu.org
>> >> >> Date: Fri, 11 Mar 2022 16:21:06 +0000
>> >> >> 
>> >> >> > I think we want in general avoid comparison with major-mode, and
>> >> >> > prefer derived-mode instead, and if so, IMO we had better did as we
>> >> >> > say and not exposed comparison to major mode unless we absolutely
>> >> >> > must.
>> >> >> 
>> >> >> Would it be enough to clarify this point in the documentation string?
>> >> >
>> >> > What would you like to clarify?
>> >> 
>> >> To clarify that the usage of (major-mode . foo-mode) might not be what
>> >> the user intends, and that in most cases derived-mode is preferable.
>> >
>> > I suggested to "clarify" that by not providing the 'major-mode'
>> > predicate at all.  I still don't think I understand why it is so
>> > important that we should provide a special case for it.
>> 
>> It is not inherently important, it is just that if the predicate would
>> also be used in project.el, then compatibility would have to be broken,
>> as the distinction between `major-mode' and `derived-mode' exists there.
>
> Then project.el could use the predicate route, right?  It's quite a
> special case, AFAIU, so having a special solution is OK.

The issue isn't that the default value couldn't be updated, but that if
anyone has e.g. been using `project-kill-buffer-conditions' over the
last 1½ years and has relied on the specific distinction between
`major-mode' and `derived-mode', they would run in to unexpected
results, that might result in more buffers being killed than intended,
potentially data being lost that the user might not expect because of an
update.

-- 
	Philip Kaludercic