Re: undoing changes automatically

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> I don't know if anyone has as yet used atomic-change-group.
>> I'd be interested to know if it actually works well for you.

> While testing various error scenarios in bibtex.el that should be
> handled by atomic-change-group, I once got the error message

>   cancel-change-group: Undoing to some unrelated state

> followed by

>   cancel-change-group: Wrong type argument: listp, t

> I wanted to debug this error, but I couldn't reproduce it.

> I looked at the code of cancel-change-group.  It's not clear to me
> what "Undoing to some unrelated state" means.  I'd expect that
> atomic-change-group should not produce any errors by itself.

I guess the message means that cancel-change-group couldn't find the
path (through undo entries) going from the current state to the
original state.  More specifically, it means that the current undo-log
does not contains as one of its nthcdr the head of the original
undo logs.  That might be the case if the changes to undo are too
numerous and the undo-log has been truncated to the point where the
undo-info needed to revert the change are not present any more.


        Stefan