GNU bug report logs - #33341
27.0.50; Undo log merging and change groups

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Subject: bug#33341: closed (Re: bug#33341: 27.0.50; Undo log merging and
 change groups)
Date: Fri, 27 Nov 2020 17:44:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#33341: 27.0.50; Undo log merging and change groups

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 33341 <at> debbugs.gnu.org.

-- 
33341: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=33341
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 33341-done <at> debbugs.gnu.org, Lars Ingebrigtsen <larsi <at> gnus.org>
Subject: Re: bug#33341: 27.0.50; Undo log merging and change groups
Date: Fri, 27 Nov 2020 18:43:09 +0100

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> diff --git a/lisp/subr.el b/lisp/subr.el
> index e009dcc2b9..1cf3a49fe4 100644
> --- a/lisp/subr.el
> +++ b/lisp/subr.el
> [...]
> +	(undo-boundary)))))

Confirmed that it's fixed with that commit.

Thanks!

Michael.

[Message part 3 (message/rfc822, inline)]

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: 27.0.50; Undo log merging and change groups
Date: Sun, 11 Nov 2018 08:50:43 +0100

Hello,

I have been playing with the undo change group functions.  I found
`cancel-change-group' does not always work as expected.  For example, if
you define

(defun my-test-change-groups ()
  (interactive)
  (insert "0\n")
  (let ((g (prepare-change-group)))
    (activate-change-group g)
    (insert "b\n")
    (insert "c\n")
    (cancel-change-group g)))

and call that command in some random buffer, the final
`cancel-change-group' has no effect (i.e. nothing is reverted).  In
other, similar examples, `cancel-change-group' seems to revert more than
it should.

To cite (CC'd) Stefan's remark in emacs-help, "the undo entries for
(insert "0\n"), (insert "b\n"), and (insert "c\n") are merged into a
single entry in the undo log (as a form of optimization).  The
change-group code should prevent such a merge, e.g. by adding some dummy
undo element which will work like a "fence"".


Thanks,

Michael.




In GNU Emacs 27.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version 3.24.1)
 of 2018-11-11 built on drachen
Repository revision: c1095b03a933d55fe1cd357881f1ca6e16e06362
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description: Debian GNU/Linux buster/sid

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