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Re: Undo discard prompt (was: [T. V. Raman] read-only modes should be us


From: Luc Teirlinck
Subject: Re: Undo discard prompt (was: [T. V. Raman] read-only modes should be using buffer-disable-undo?)
Date: Sun, 23 Jan 2005 10:44:05 -0600 (CST)

Stefan Monnier wrote:

   > however the recent updates in simple.el that cause the yes/no dialog 
   > to ask about discarding undo information does pop up in shell-mode --- 

   BTW, I just wanted to say that since this undo-discard prompt was introduced
   I've bumped into it also in "normal" circumstances (just manual buffer
   editing) and have found it to be just really annoying (half the time it
   occurred in the middle of some kbd-macro and breaks the sequence of steps).

It seems strange that you would routinely accumulate one large single
undo entry in the process of manual buffer editing.  Are you sure that
there is no inappropriate undo management involved somewhere?  Are
keyboard macros what causes the problem?

   I vote to replace the prompt with a warning.

   Or even to just revert to the 21.3 behavior (I haven't actually seen anyone
   really complain about that good ol' behavior.  What was wrong with it?).

I believe that we should at the very least offer a customizable option
to silently discard the undo entry without querying.

The prompt has turned out to be a great debugging tool, but it indeed
can be a real nuisance.  For CVS users it is OK, because they can
always report the incident.  Up till now, all such incidents really
where due to very bad undo management.  This gets taken care of and
the user can update his CVS.  End of problem.  Right now, 21.4 users
that run into the problem will be stuck with it and if they encounter
the popup routinely during normal editing, it could indeed be
sufficient a nuisance that they might decide to stick with 21.3,
unless we provide some way to disable the popups.

In as far as what was wrong with previous behavior:

If I understood correctly there first was a problem with Emacs
crashing as a result of running out of memory due to one single undo
entry growing completely out of control.  (If I understood correctly,
there are situations where Emacs can crash due to memory overflow, in
spite of the safeguards to prevent that.)  It was then decided to
discard the last undo entry when it grew too large.  But then somebody
complained about not being able to undo the last command in spite of
the guarantees given in the documentation that you can always at least
undo one single command.  If I understood correctly, the only really
safe thing to do when confronted with the prompt is answer "Yes",
because otherwise you risk a crash, after which you can not undo the
last command anyway.  Currently, the prompt does not warn about that.

Sincerely,

Luc.




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