bug#64989: 29.1; Comment or uncomment lines in elisp-mode will show message in minibuffer

[Eli Zaretskii <eliz@gnu.org>]

Ping!  Stefan, any suggestions?

> Cc: 64989@debbugs.gnu.org
> Date: Tue, 01 Aug 2023 16:20:20 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> 
> > From: Eason Huang <aqua0210@foxmail.com>
> > Date: Tue, 01 Aug 2023 19:13:59 +0800
> > 
> > Hello Emacs,
> > 
> > When update to the new released Emacs 29.1, I found that when comment or
> > uncomment lines in emacs-lisp-mode will show message in minibuffer as
> > below:
> > ```
> > combine-change-calls: buffer-undo-list broken
> > ```
> > Steps to reproduce:
> > 1. create a test.el file with any Elisp code. such as:
> > ```
> > (message "Test")
> > ```
> > 2. start emacs and open the test.el file with `emacs -Q ~/test.el`
> > 3. Use C-x C-; (comment-line) to comment the code in test.el
> > 4. Now you will see the message mentioned above.
> 
> Thanks.
> 
> Stefan, I think this is due to the commit below:
> 
> | Author:     Stefan Monnier <monnier@iro.umontreal.ca>
> | AuthorDate: Fri Jan 13 17:38:04 2023 -0500
> | Commit:     Stefan Monnier <monnier@iro.umontreal.ca>
> | CommitDate: Fri Jan 13 17:38:04 2023 -0500
> |
> |     * lisp/subr.el (combine-change-calls-1): Fix bug#60467
> |
> |     Don't stop at timestamps.  Strip them for now, to be on the safe side.
> |     Don't merge into `master` where we'll use a better fix.
> 
> My "partial bisecting" indicates that the bug was introduced between
> Dec 31, 2022 and Jan 31, 2023, and the above is the only commit
> in-between that could matter.
> 
> If indeed this is the culprit, can we perhaps backport the "better
> fix" from master to the emacs-29 branch?