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From: phillip.lord@newcastle.ac.uk (Phillip Lord)
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: Emacs-Devel devel <emacs-devel@gnu.org>
Subject: Re: disabling undo boundaries
Date: Tue, 19 May 2015 22:48:51 +0100	[thread overview]
Message-ID: <87y4kkkzlo.fsf@newcastle.ac.uk> (raw)
In-Reply-To: <jwv382sichw.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Tue, 19 May 2015 15:42:42 -0400")

Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> Just wanted to bump this. I am still not sure why this is a good
>> behaviour. My own feeling is that the "undo-boundary when a buffer
>> change happens" logic may not have been implemented for this reason, but
>> as a belts-and-braces way of detecting the end of a command -- after
>> all, buffer changes (followed by an undoable event) normally happen
>> between commands rather than within.
>
> For process filters, I think the "right way" would be to add an
> undo-boundary every N insertions.

"undo" for a process filter seems to be quite a difficult one to me. In
many cases ("M-x compile") undo is just switched off. For things like
M-x shell undo is on and makes sense. My initial guess would be that
"undo the last command and all the output from that command" would seem
the most intuitive.


>> I did start working on this, but haven't got it functional yet. One
>> problem is that if I record the cons cell at the head of
>> buffer-undo-list, I have to search the whole buffer-undo-list to see if
>> it is there (unless I get a match). A cons cell with a nil gets added
>> for every self-insert-command and then removed again, so this tends to
>> happen quite a lot.
>
> Sounds rather ugly.  Let's see how far we can go with the option of
> changing the current behavior rather than trying to add workarounds in
> your code.

Agreed. I'd rather fix the core Emacs behaviour than workaround it, so
it works better for everyone. Of course, I have to acknowledge that my
public spirited behaviour is partly motivated by the workaround being a
PITA.

> Could you describe the exact case that bothers you, so we could start by
> thinking what should be the ideal behavior for that one?


Yes. Any after-change-function that changes another buffer breaks undo.

My "noisy-change" package which just logs the before and
after-change-function args is an example of this.

https://raw.githubusercontent.com/phillord/lentic/master/noisy-change.el

My real use case is lentic.

Ideal behaviour: is just not to do it. Uncommenting all the
"undo_boundary" calls in undo.c seems to achieve this for me, although
obviously that's a blunt fix.

Phil




  reply	other threads:[~2015-05-19 21:48 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-10 21:43 disabling undo boundaries Phillip Lord
2015-05-11  1:42 ` Stefan Monnier
2015-05-11 11:46   ` Phillip Lord
2015-05-11 14:45     ` Stefan Monnier
2015-05-11 16:31       ` Phillip Lord
2015-05-11 19:30         ` Stefan Monnier
2015-05-11 20:42           ` Phillip Lord
2015-05-11 22:23             ` Stefan Monnier
2015-05-12 11:52               ` Phillip Lord
2015-05-12 20:15                 ` Stefan Monnier
2015-05-12 20:59                   ` Phillip Lord
2015-05-13 12:32                     ` Stefan Monnier
2015-05-13 15:40                       ` Phillip Lord
2015-05-14 15:28                         ` Stefan Monnier
2015-05-15 12:27                           ` Phillip Lord
2015-05-15 18:08                             ` Stefan Monnier
2015-05-15 19:49                               ` Phillip Lord
2015-05-15 23:45                                 ` Stefan Monnier
2015-05-16 13:31                                   ` Phillip Lord
2015-05-19 11:59                                     ` Phillip Lord
2015-05-19 19:42                                       ` Stefan Monnier
2015-05-19 21:48                                         ` Phillip Lord [this message]
2015-05-20  2:00                                           ` Stefan Monnier
2015-05-20  7:45                                             ` Phillip Lord
2015-05-20 12:53                                               ` Stefan Monnier
2015-05-21 11:15                                                 ` Phillip Lord
2015-05-21 15:44                                                   ` Stefan Monnier
2015-05-21 17:03                                                     ` Phillip Lord
2015-05-27 11:46                                                       ` Phillip Lord
2015-06-29  0:46                                                         ` Stefan Monnier
2015-08-04 14:18                                                           ` Phillip Lord
2015-08-06 21:02                                                             ` Phillip Lord
2015-08-06 22:20                                                             ` Stefan Monnier
2015-08-07 13:40                                                               ` Phillip Lord
2015-08-07 13:59                                                                 ` David Kastrup
2015-08-07 21:10                                                                   ` Phillip Lord
2015-08-08  5:39                                                                     ` David Kastrup
2015-08-08  9:58                                                                       ` Phillip Lord
2015-08-07 17:10                                                                 ` Stefan Monnier
2015-08-08 21:28                                                                   ` Stefan Monnier
2015-08-09 15:39                                                                     ` Phillip Lord
2015-08-09 16:30                                                                       ` Stefan Monnier
2015-08-09 16:50                                                                         ` Phillip Lord
2015-08-09 17:40                                                                           ` Stefan Monnier
2015-08-10  9:27                                                                             ` Phillip Lord
2015-08-10 21:21                                                                               ` Phillip Lord
2015-08-12 21:15                                                                               ` Stefan Monnier
2015-08-12 22:34                                                                                 ` Phillip Lord
2015-08-13  2:23                                                                                   ` Stefan Monnier
2015-08-21  9:40                                                                                     ` Phillip Lord
2015-08-07 23:49                                                     ` Davis Herring
2015-08-08 10:01                                                       ` Phillip Lord

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