(undo): Remove positions from buffer-undo-list up to

the next undo boundary only.

1 files changed, 18 insertions, 7 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index 8d2a5707898..e276b1dea32 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -961,13 +961,24 @@ as an argument limits undo to changes within the current region."
     ;; Don't specify a position in the undo record for the undo command.
     ;; Instead, undoing this should move point to where the change is.
     (let ((tail buffer-undo-list)
-          done)
-      (while (and tail (not done) (not (null (car tail))))
-        (if (integerp (car tail))
-            (progn
-              (setq done t)
-              (setq buffer-undo-list (delq (car tail) buffer-undo-list))))
-        (setq tail (cdr tail))))
+          (prev nil))
+      (while (car tail)
+        (when (integerp (car tail))
+          (let ((pos (car tail)))
+            (if (null prev)
+                (setq buffer-undo-list (cdr tail))
+              (setcdr prev (cdr tail)))
+            (setq tail (cdr tail))
+            (while (car tail)
+              (if (eq pos (car tail))
+                  (if prev
+                      (setcdr prev (cdr tail))
+                    (setq buffer-undo-list (cdr tail)))
+                (setq prev tail))
+              (setq tail (cdr tail)))
+            (setq tail nil)))
+        (setq prev tail tail (cdr tail))))
+
     (and modified (not (buffer-modified-p))
          (delete-auto-save-file-if-necessary recent-save)))
   ;; If we do get all the way thru, make this-command indicate that.