Optionally, undo several consequential deletion in one step.

* lisp/simple.el (kill-append): Remove undo boundary depending on ...
(kill-append-merge-undo): New user option.

2 files changed, 26 insertions, 1 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 8c2fb12da4e..3f7896fd1c5 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2014-06-23  Sam Steingold  <sds@gnu.org>
+
+        * simple.el (kill-append): Remove undo boundary depending on ...
+        (kill-append-merge-undo): New user option.
+
 2014-06-23  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * simple.el (handle-shift-selection, exchange-point-and-mark)
diff --git a/lisp/simple.el b/lisp/simple.el
index 9983943298f..a8689aaf2e3 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -3742,14 +3742,34 @@ argument should still be a \"useful\" string for such uses."
   (if interprogram-cut-function
       (funcall interprogram-cut-function string)))
 
+;; It has been argued that this should work similar to `self-insert-command'
+;; which merges insertions in undo-list in groups of 20 (hard-coded in cmds.c).
+(defcustom kill-append-merge-undo nil
+  "Whether appending to kill ring also makes \\[undo] restore both pieces of text simultaneously."
+  :type 'boolean
+  :group 'killing
+  :version "24.5")
+
 (defun kill-append (string before-p)
   "Append STRING to the end of the latest kill in the kill ring.
 If BEFORE-P is non-nil, prepend STRING to the kill.
+Also removes the last undo boundary in the current buffer,
+ depending on `kill-append-merge-undo'.
 If `interprogram-cut-function' is set, pass the resulting kill to it."
   (let* ((cur (car kill-ring)))
     (kill-new (if before-p (concat string cur) (concat cur string))
               (or (= (length cur) 0)
-                  (equal nil (get-text-property 0 'yank-handler cur))))))
+                  (equal nil (get-text-property 0 'yank-handler cur))))
+    (when (and kill-append-merge-undo (not buffer-read-only))
+      (let ((prev buffer-undo-list)
+            (next (cdr buffer-undo-list)))
+        ;; find the next undo boundary
+        (while (car next)
+          (pop next)
+          (pop prev))
+        ;; remove this undo boundary
+        (when prev
+          (setcdr prev (cdr next)))))))
 
 (defcustom yank-pop-change-selection nil
   "Whether rotating the kill ring changes the window system selection.