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bug#33341: 27.0.50; Undo log merging and change groups
From: |
Michael Heerdegen |
Subject: |
bug#33341: 27.0.50; Undo log merging and change groups |
Date: |
Sun, 11 Nov 2018 08:50:43 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
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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Michael Heerdegen <=