GNU bug report logs - #71277
30.0.50; last-prefix-arg lost when universal-argument used

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Sean Whitton <spwhitton <at> spwhitton.name>
Subject: bug#71277: closed (Re: bug#71277: 30.0.50; last-prefix-arg lost
 when universal-argument used)
Date: Thu, 30 May 2024 15:32:02 +0000

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Your bug report

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

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 71277 <at> debbugs.gnu.org.

-- 
71277: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=71277
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Sean Whitton <spwhitton <at> spwhitton.name>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>, 71277-done <at> debbugs.gnu.org
Subject: Re: bug#71277: 30.0.50; last-prefix-arg lost when
 universal-argument used
Date: Thu, 30 May 2024 16:31:23 +0100

Hello,

On Thu 30 May 2024 at 10:42am -04, Stefan Monnier wrote:

>>> 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.
>
> Hmm... I didn't know about `last-prefix-arg`.
> [ I'm not sure I like the idea of such a variable, but
>   well... it's there.  ]
> The patch looks fine to me, thank you.

Installed, thanks for the review.

-- 
Sean Whitton

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From: Sean Whitton <spwhitton <at> spwhitton.name>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; last-prefix-arg lost when universal-argument used
Date: Thu, 30 May 2024 12:47:29 +0100

Hello,

Consider

    (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:

-- >8 --
Subject: [PATCH] universal-argument--preserve: Preserve last-prefix-arg

* lisp/simple.el (universal-argument--preserve): Set
current-prefix-arg to last-prefix-arg in order to preserve
last-prefix-arg, too.
---
 lisp/simple.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/simple.el b/lisp/simple.el
index 44197c3189a..76fb81c9df5 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -5414,7 +5414,8 @@ universal-argument--description
 (add-hook 'prefix-command-preserve-state-hook
           #'universal-argument--preserve)
 (defun universal-argument--preserve ()
-  (setq prefix-arg current-prefix-arg))
+  (setq prefix-arg current-prefix-arg)
+  (setq current-prefix-arg last-prefix-arg))
 
 (defvar universal-argument-map
   (let ((map (make-sparse-keymap))
-- 
Sean Whitton

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