bug#71277: 30.0.50; last-prefix-arg lost when universal-argument used

[Eli Zaretskii]

> Date: Thu, 30 May 2024 12:47:29 +0100
> From:  Sean Whitton via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
>     (defun counter ()
>       (interactive)
>       (when (eq last-command this-command)
>       (setq current-prefix-arg
>             (+ (prefix-numeric-value current-prefix-arg)
>                (prefix-numeric-value last-prefix-arg))))
>       (message "%s!" (prefix-numeric-value current-prefix-arg)))
>     (global-set-key "\M-." #'counter)
> 
> If you type M-. M-. M-. then you see "3!" as expected.
> 
> Similarly if you type "C-u M-. M-. M-." then you see "6!".
> 
> However, if you type "M-. M-. C-u M-." then you get "5!".
> 
> Unlses something is wrong with my arithmetic, this is not correct.
> You should get "6!" after the third example too.
> The use of C-u clobbers last-prefix-arg, basically.
> 
> I believe this will fix it:

Thanks, I'm adding Stefan to this discussion.