GNU bug report logs - #39680
27.0.60; electric-pair-mode broken by undo

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#39680: closed (27.0.60; electric-pair-mode broken by undo)
Date: Thu, 12 Mar 2020 14:05:01 +0000

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Your message dated Thu, 12 Mar 2020 10:04:11 -0400
with message-id <jwvimj9wtyt.fsf-monnier+emacs <at> gnu.org>
and subject line Re: bug#39680: 27.0.60; electric-pair-mode broken by undo
has caused the debbugs.gnu.org bug report #39680,
regarding 27.0.60; electric-pair-mode broken by undo
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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39680: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=39680
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From: Kévin Le Gouguec <kevin.legouguec <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: 27.0.60; electric-pair-mode broken by undo
Date: Wed, 19 Feb 2020 19:34:37 +0100

Hello,

Commit e66d5a1c45 (2019-02-19T00:00:44Z!monnier <at> iro.umontreal.ca) might
have introduced a bug.  From emacs -Q:

1. C-x b foo RET
2. M-x electric-pair-mode RET
3. (
    - A closing parenthesis has been inserted.
4. C-b C-f
    - This is to break undo grouping.
5. a
6. C-_
7. (

In Emacs 26.3, buffer foo contains "(())" and point is after the
innermost opening bracket.

In Emacs 27, buffer foo contains "()" and point is after the closing
bracket.  The *Messages* buffer shows:

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

NB: this can be reproduced with other electric-pair characters, e.g. ".
I found the bug in a Python buffer trying to write a tuple of strings: I
opened a parenthesis, forgot to add quotes, wrote a string, hit undo,
tried to insert a single quote… and got moved past the end parenthesis
instead.

I tried to write a non-regression test; unfortunately what I came up
with does not catch this bug reliably:

(ert-deftest electric-pair-undo-unrelated-state ()
  (with-temp-buffer
    (buffer-enable-undo)
    (electric-pair-mode)
    (let ((last-command-event ?\())
      (self-insert-command 1))
    (undo-boundary)
    (insert "hi there")
    (undo)
    (let ((last-command-event ?\())
      (self-insert-command 1))))

C-x C-e'ing the (with-temp-buffer …) form only triggers the error once
every two evaluations, for some reason.


Thank you for your time.


In GNU Emacs 28.0.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.24.13, cairo version 1.16.0)
 of 2020-02-19 built on my-little-tumbleweed
Repository revision: e1e1bd8f85c53fea9f61b6ec99b461ddd93461b9
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12007000
System Description: openSUSE Tumbleweed

Configured using:
 'configure --with-xwidgets --with-cairo'

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: acm <at> muc.de, 39680-done <at> debbugs.gnu.org, kevin.legouguec <at> gmail.com
Subject: Re: bug#39680: 27.0.60; electric-pair-mode broken by undo
Date: Thu, 12 Mar 2020 10:04:11 -0400

>> Eli, is the patch below OK for `emacs-27`?
> Yes, thanks.

Thanks, installed,


        Stefan

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