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

[Joseph Turner]

Eli Zaretskii <eliz@gnu.org> writes:

> I think one of the alternatives you proposed was backward-compatible
> (albeit not very elegant).  So my vote is for that alternative.

I'm in favor of the solution in the patch (from Stefan's suggestion):

> - 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.

The "&rest args" solution is clean and hack-free. It breaks
compatibility, but in unlikely cases:

- CONDITION pred accepts only a buffer argument, but additional ARG was
  passed (why would you do this?)

- CONDITION pred accepts two arguments, and no ARG was passed (this code
  would be broken anyway, right?)

Since buffer-match-p is new in Emacs 29, is it acceptable to assume that
code affected by this breakage can be updated?

Joseph