GNU bug report logs - #60467
30.0.50; primitive-undo: Changes to be undone by function different from announced

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Message #59 received at 60467 <at> debbugs.gnu.org (full text, mbox):

From: Gregory Heytings <gregory <at> heytings.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 60467 <at> debbugs.gnu.org, Alan Mackenzie <acm <at> muc.de>,
 Eli Zaretskii <eliz <at> gnu.org>, yantar92 <at> posteo.net
Subject: Re: bug#60467: 30.0.50; primitive-undo: Changes to be undone by
 function different from announced
Date: Wed, 04 Jan 2023 00:16:39 +0000

>>> I don't even understand what this is supposed to do.
>> 
>> Yet you happily threw it away :-(
>
> Because there are no such precautions elsewhere in the code, and the 
> comment above ("In case garbage collection has removed OLD-BUL") does 
> not explain what its purpose is.  A few lines below, old-bul is used 
> without such a precaution.  Of course, if it has a purpose, it's okay to 
> keep it.
>

I didn't remember the main reason why I removed that (cdr ptr).  The 
reason is not only that the comment above it is wrong, but also that this 
(cdr ptr) condition itself is wrong: it makes that loop stop when the last 
element of the buffer-undo-list is reached.  When buffer-undo-list is 
initially nil, (funcall body) adds a number of entries in 
buffer-undo-list, and there is no reason to exit that loop without 
processing its last element.

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