Subject: Re: bug#65797: `buffer-match-p` should not use `func-arity`

From: Stefan Monnier <[email-masked]>
Date: Thu, 14 Sep 2023 09:47:07 -0400

>>> FWIW The intention here was to be able and specify simpler conditions
>>> that don't have to handle the alist.
>> You mean for `display-buffer-alist`?
>> Do you have examples that rely on this?
> From the core?  No, I cannot think of an example, but any user
> configuration may make use of this feature.

>From the core would have been good, but from elsewhere (including
random .emacs config you may find on the web) would be helpful to gauge
how important that could be.

> I am not sure if I just missed it, but is there no technical solution
> around the advice issue?  Couldn't `func-arity' check if the actual
> function and the advice function have the same arity, and return the
> right value in that case?  My impression is that in 99% of the cases,
> advice isn't used to increase or decrease the arity of a function.

There are various 99% solutions, yes.
There is no 100% solution, OTOH :-(
So the documented behavior is inherently unreliable.

        Stefan