Subject: bug#1501: Emacs 22 loses undo buffer

From: Chong Yidong <[email-masked]>
Date: Sun, 07 Dec 2008 00:36:32 -0500

"Emerick Rogul" <[email-masked]> writes:

> That's clearly not the issue at all, since the header file is only 8k
> in total size.  What's more, I get the message after hitting the undo
> key sequence a couple of times.  Also, this works perfectly fine in
> Emacs 21.2, as I mentioned in my initial report.

In the key sequence you reported:

... C-k C-k C-k C-k C-k C-k C-k C-k C-k
C-k C-k C-k C-k C-k C-k C-k C-k C-k C-k C-k C-k C-k
[snip]
C-k C-k C-k C-k C-k C-k C-/ C-/ C-/ C-/ C-/ C-/ C-/
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/
C-/ ESC x r e p o r t - e m a <tab> <return>

it appears that you hit C-/ 22 times.  If Emacs kept 22 undo records,
and each undo record takes about 1 kilobyte, that is enough to hit the
default undo limit.  It might be that each undo record takes more space
in Emacs 23 than in Emacs 21, which is why you don't see the problem in
Emacs 21 (there are several reasons why this could happen, which could
be investigated).

I do observe the same behavior that you reported, using the key sequence
you supplied; furthermore, if I increase undo-limit to a larger number,
I find that Emacs can undo all the way back to the buffer's original
state.