bug#33341: 27.0.50; Undo log merging and change groups

[Michael Heerdegen]

Michael Heerdegen <michael_heerdegen@web.de> writes:

#+begin_src emacs-lisp
(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)))
#+end_src

Adding an explicit `undo-boundary' call before preparing the change
group fixes the problem for me.  Should `prepare-change-group' do
something like that implicitly?

Michael.