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bug#33341: 27.0.50; Undo log merging and change groups
From: |
Stefan Monnier |
Subject: |
bug#33341: 27.0.50; Undo log merging and change groups |
Date: |
Fri, 27 Nov 2020 09:44:27 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
> (defun my-test-change-groups ()
> (interactive)
> (insert "0\n")
> ;; (undo-boundary)
> (let ((g (prepare-change-group)))
> (activate-change-group g)
> (insert "b\n")
> (insert "c\n")
> (cancel-change-group g)))
I see it's a bug indeed: the problem is that `insert` optimizes the undo
entries by reusing a previous undo entry is that was
a consecutive insertion, so when you get to `cancel-change-group` the
`buffer-undo-list` only has a single entry that represent the
combination of all 3 insertions.
I just pushed the patch below which should fix it.
Stefan
diff --git a/lisp/subr.el b/lisp/subr.el
index e009dcc2b9..1cf3a49fe4 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -3036,7 +3036,10 @@ activate-change-group
(dolist (elt handle)
(with-current-buffer (car elt)
(if (eq buffer-undo-list t)
- (setq buffer-undo-list nil)))))
+ (setq buffer-undo-list nil)
+ ;; Add a boundary to make sure the upcoming changes won't be
+ ;; merged with any previous changes (bug#33341).
+ (undo-boundary)))))
(defun accept-change-group (handle)
"Finish a change group made with `prepare-change-group' (which see).
diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index 67f7fc9749..e3f798d11c 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -551,5 +551,17 @@ subr-replace-regexp-in-string
(should (equal (replace-regexp-in-string "\\`\\|x" "z" "--xx--")
"z--zz--")))
+(ert-deftest subr-tests--change-group-33341 ()
+ (with-temp-buffer
+ (buffer-enable-undo)
+ (insert "0\n")
+ ;; (undo-boundary)
+ (let ((g (prepare-change-group)))
+ (activate-change-group g)
+ (insert "b\n")
+ (insert "c\n")
+ (cancel-change-group g))
+ (should (equal (buffer-string) "0\n"))))
+
(provide 'subr-tests)
;;; subr-tests.el ends here