GNU bug report logs - #26061
26.0.50; cancel-change-group fails with "unrelated state" error if used after an undo

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Andreas Politz <politza <at> hochschule-trier.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.0.50;
 cancel-change-group fails with "unrelated state" error if used after
 an undo
Date: Sat, 11 Mar 2017 19:01:28 +0100

Save the following in some file foo.el:

#+BEGIN_SRC emacs-lisp
(defun bug ()
  (interactive)
  (catch 'done
    (atomic-change-group
      (insert "bug")
      (throw 'done nil))))

(setq debug-on-error t)
(switch-to-buffer (get-buffer-create "*bug*"))
(setq unread-command-events
      (list
       ;; insert abc
       ?a ?b ?c
       ;; undo once
       ?\C-/
       ;; call bug
       ?\M-x ?b ?u ?g ?\C-j))
#+END_SRC

, then start Emacs like this:

$ emacs -Q -l foo.el

Debugger entered--Lisp error: (error "Undoing to some unrelated state")
  signal(error ("Undoing to some unrelated state"))
  error("Undoing to some unrelated state")
  cancel-change-group(((#<buffer *bug*> nil)))

--

-ap

Message #8 received at 26061 <at> debbugs.gnu.org (full text, mbox):

From: Braun Gábor <braungb88 <at> gmail.com>
To: 26061 <at> debbugs.gnu.org
Subject: Consider merging with 26287 and 34405
Date: Thu, 21 Nov 2019 10:53:09 +0100

This seems to be a candidate to merge with 26287 and 34405,
the latter two being already merged.

All three bugs have similar Lisp code
(catch ... (atomic-change-group ... (throw ...)))
producing an "unrelated state" error after undo.

Best wishes,

	Gábor

Message #11 received at 26061 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Braun Gábor <braungb88 <at> gmail.com>
Cc: 26061 <at> debbugs.gnu.org
Subject: Re: bug#26061: Consider merging with 26287 and 34405
Date: Thu, 21 Nov 2019 12:47:38 +0100

Braun Gábor <braungb88 <at> gmail.com> writes:

> This seems to be a candidate to merge with 26287 and 34405,
> the latter two being already merged.
>
> All three bugs have similar Lisp code
> (catch ... (atomic-change-group ... (throw ...)))
> producing an "unrelated state" error after undo.

Yup; I've merged the bugs now.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #16 received at 26061 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Braun Gábor <braungb88 <at> gmail.com>
Cc: 34405 <at> debbugs.gnu.org, 26061 <at> debbugs.gnu.org
Subject: Re: bug#26061: 26.0.50; cancel-change-group fails with "unrelated
 state" error if used after an undo
Date: Sat, 14 Aug 2021 15:58:41 +0200

Braun Gábor <braungb88 <at> gmail.com> writes:

> -------------------- File test.el ----------------------------------
> ;; -*- lexical-binding: t; -*-
> (defun test-fun ()
>   "Test atomic change group, no visible effect."
>   (interactive)
>   (catch 'test
>     (atomic-change-group
>       (save-excursion
>         (goto-char (point-min))
>         (insert "!!! TEST: you shouldn't see this !!!")
>         (throw 'test t)))))
>
> (global-set-key [(control c) ?a] #'test-fun)
> --------------------------------------------------------------------
>
> Start emacs by the command
>
> emacs -Q -l test.el
>
> Press the following keys: a C-_ C-c a
>
> A "!!! TEST: you shouldn't see this !!!" gets inserted at the top of
> buffer *scratch*, and the message "Undoing to some unrelated state"
> appears in the echo area.

I can reproduce this problem in Emacs 26.1, but it seems to be gone in
Emacs 27.1 (and 28), so I'm going to go ahead and guess that this has
been fixed in the years since this was reported, and I'm closing this
bug report.  If this is still a problem in recent Emacs versions, please
respond to the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #21 received at 26061 <at> debbugs.gnu.org (full text, mbox):

From: Braun Gábor <braungb88 <at> gmail.com>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 34405 <at> debbugs.gnu.org, 26061 <at> debbugs.gnu.org
Subject: Re: bug#26061: 26.0.50;
 cancel-change-group fails with "unrelated state" error if used after
 an undo
Date: Mon, 16 Aug 2021 14:01:01 +0200

> I can reproduce this problem in Emacs 26.1, but it seems to be gone in
> Emacs 27.1 (and 28), so I'm going to go ahead and guess that this has
> been fixed

I can see the fix in the following snippet of `cancel-change-group' in 
Emacs 27.1 code.  The faulty logic with `last-command' and `undo-start' 
has been gone.  (... denotes omitted code.)

    (let (...
	      ;; Use `pending-undo-list' temporarily since `undo-more' needs
	      ;; it, but restore it afterwards so as not to mess with an
	      ;; ongoing sequence of `undo's.
	      (pending-undo-list
	       ;; Use `buffer-undo-list' unconditionally (bug#39680).
	       buffer-undo-list))

Thank you for checking in recent Emacs versions.

Best wishes,

	Gábor

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