Subject: Re: bug#10047: Looking for help debugging an undo issue

From: Phil Sainty <[email-masked]>
Date: Mon, 28 Nov 2011 23:49:24 +1300

> Your problem doesn't ring a bell, sorry.  The best options I can think
> of are:
> - log the value of buffer-undo-list at each step in some auxiliary
>    debugging buffer, for post-mortem analysis.
> - try to come up with a reproducible test case.

As it turned out, most of my code & context was irrelevant.
You should be able to reproduce the bug like this:

emacs -Q
M-: (add-hook 'post-command-hook 'align-current) RET
<backspace> (until the scratch buffer message is gone)
C-/ (or otherwise undo, until it fails with the message
"No further undo information")

It will probably occur after deleting far fewer characters
than that, but the point of failure seems variable. However,
in a half-dozen test runs just now, I've yet to have it
get as far as restoring the first half of the first line
before failing.

-Phil