bug#65797: 29.0.92; func-arity should not return (0 . many) with apply-partially

[Eli Zaretskii]

> Cc: 65797@debbugs.gnu.org
> Date: Thu, 07 Sep 2023 21:40:28 -0700
> From:  Joseph Turner via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> > - Replace `&optional arg` with `&rest args` and pass those args via
> >   `apply`, so the number of args passed doesn't depend on the function
> >   but on the caller.
> 
> I like this idea. See patch.
> 
> > - Always pass both args to the function (i.e. as documented in the
> >   docstring).
> 
> This isn't backwards compatible, is it?

Neither is what you propose, AFAIU.  We are in effect changing a
public API in incompatible ways.