bug#53764: 27.1; shouldn't ~/diary be in diary-mode?

[Francesco Potortì]

>>>>>Do we have a convenience function that says whether we have a match in
>>>>>auto-mode-alist?  `set-auto-mode--apply-alist' seems to be the closest I
>>>>>can find, and...  it's not that close.  :-/  But I guess it could be
>>>>>refactored out of there.
>>>>
>>>> This one seems to do the job:
>>>> (add-to-list 'auto-mode-alist
>>>>         (cons diary-file 'diary-mode)
>>>>               (lambda (a b) (equal (car a) (car b))))
>>>
>>>The user may have used a regexp like "diary$", "diary\\'", etc, so that
>>>doesn't work.
>>
>> Sorry, I don't get it.  I am suggeting to add the name of the actual file 
>> (the one in diary-file) to the mode alist.  Looking for possible matches is 
>> a (small) optimisation. Why do we need a completely reliable matching code?
>
>If you put it at the end, it won't hide any preexisting match.

Little matter, in my opinion.  If the user haa set up anything, that will 
match.  It's okay.  We don't want to hide anything.  We just want to improve 
user experience in the common case when the user has not read the source code 
and does not know about diary-mode.