GNU bug report logs - #12581
24.2.50: redo+ fails to modify edit menu

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Konstantinos Efstathiou <konstantinos <at> efstathiou.gr>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2.50: redo+ fails to modify edit menu
Date: Fri, 5 Oct 2012 23:00:43 +0200

In the latest versions from the repository it is impossible to load redo+.el
(version 1.15 available from ELPA). The command (require 'redo+)
fails with (error "Attempt to modify read-only object").

I have tracked this down to the command

(setcar (cdr (memq :enable (assq 'undo menu-bar-edit-menu))) nil)

that fails with the same error. Actually redo+ attempts to setcar to 
something else but obviously the problem is that for some reason

(car (cdr (memq :enable (assq 'undo menu-bar-edit-menu)))

is now read-only while it used to be modifiable.

Is this a bug or expected behavior? Should redo+ be modified?

Message #10 received at 12581-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Konstantinos Efstathiou <konstantinos <at> efstathiou.gr>
Cc: 12581-done <at> debbugs.gnu.org
Subject: Re: bug#12581: 24.2.50: redo+ fails to modify edit menu
Date: Fri, 05 Oct 2012 17:55:27 -0400

> I have tracked this down to the command
> (setcar (cdr (memq :enable (assq 'undo menu-bar-edit-menu))) nil)
[...]
> that fails with the same error. Actually redo+ attempts to setcar to
> something else but obviously the problem is that for some reason
[...]
> Is this a bug or expected behavior? Should redo+ be modified?

It's not a bug, AFAIC.  You can change redo+ to use something like:

   (define-key menu-bar-edit-menu [undo]
     ;; We use `cdr+assq' instead of `lookup-key' because lookup-key
     ;; would return the actual binding inside the menu-item, whereas
     ;; we want the whole menu-item (IOW we don't want the get_keyelt
     ;; part of lookup-key).  We could use
     ;; (catch 'found
     ;;   (map-keymap (lambda (k v)
     ;;                 (if (eq k 'undo) (throw 'found v)))
     ;;               menu-bar-edit-menu))
     ;; instead.
     (let ((elem (copy-sequence (cdr (assq 'undo menu-bar-edit-menu)))))
       (setcar (cdr (memq :enable elem)) <your-exp-here>)
       elem))

       
-- Stefan

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