(diff-unified->context): Use the new `apply' undo entry kind

if applicable, so as to save undo-log space.

1 files changed, 23 insertions, 2 deletions

diff --git a/lisp/diff-mode.el b/lisp/diff-mode.el
index ecd32f4c331..3c0208d5b27 100644
--- a/lisp/diff-mode.el
+++ b/lisp/diff-mode.el
@@ -701,7 +701,12 @@ else cover the whole bufer."
             (let ((line1 (match-string 4))
                   (lines1 (match-string 5))
                   (line2 (match-string 6))
-                  (lines2 (match-string 7)))
+                  (lines2 (match-string 7))
+                  ;; Variables to use the special undo function.
+                  (old-undo buffer-undo-list)
+                  (old-end (marker-position end))
+                  (start (match-beginning 0))
+                  (reversible t))
               (replace-match
                (concat "***************\n*** " line1 ","
                        (number-to-string (+ (string-to-number line1)
@@ -743,6 +748,14 @@ else cover the whole bufer."
                   (if (not (save-excursion (re-search-forward "^+" nil t)))
                       (delete-region (point) (point-max))
                     (let ((modif nil) (delete nil))
+                      (if (save-excursion (re-search-forward "^\\+.*\n-" nil t))
+                          ;; Normally, lines in a substitution come with
+                          ;; first the removals and then the additions, and
+                          ;; the context->unified function follows this
+                          ;; convention, of course.  Yet, other alternatives
+                          ;; are valid as well, but they preclude the use of
+                          ;; context->unified as an undo command.
+                          (setq reversible nil))
                       (while (not (eobp))
                         (case (char-after)
                           (?\s (insert " ") (setq modif nil) (backward-char 1))
@@ -761,7 +774,15 @@ else cover the whole bufer."
                           (forward-line 1)
                           (when delete
                             (delete-region last-pt (point))
-                            (setq delete nil)))))))))))))))
+                            (setq delete nil)))))))
+                (unless (or (not reversible) (eq buffer-undo-list t))
+                  ;; Drop the many undo entries and replace them with
+                  ;; a single entry that uses diff-context->unified to do
+                  ;; the work.
+                  (setq buffer-undo-list
+                        (cons (list 'apply (- old-end end) start (point-max)
+                                    'diff-context->unified start (point-max))
+                              old-undo)))))))))))
 
 (defun diff-context->unified (start end &optional to-context)
   "Convert context diffs to unified diffs.