1 files changed, 21 insertions, 14 deletions

diff --git a/lisp/vc/ediff-diff.el b/lisp/vc/ediff-diff.el
index 07b853817d1..24647de576d 100644
--- a/lisp/vc/ediff-diff.el
+++ b/lisp/vc/ediff-diff.el
@@ -942,6 +942,9 @@ one optional arguments, diff-number to refine.")
         (c-prev-pt nil)
         (anc-prev 1)
         diff-list shift-A shift-B shift-C
+        (A-idx "1")
+        (B-idx (if three-way-comp "2" "3"))
+        (C-idx (if three-way-comp "3" "2"))
         )
 
     ;; diff list contains word numbers or points, depending on word-mode
@@ -979,23 +982,23 @@ one optional arguments, diff-number to refine.")
        (let ((agreement (buffer-substring (match-beginning 1) (match-end 1))))
          ;; if the files A and B are the same and not 3way-comparison,
          ;; ignore the difference
-         (if (or three-way-comp (not (string-equal agreement "3")))
-             (let* ((a-begin (car (ediff-get-diff3-group "1")))
-                    (a-end  (nth 1 (ediff-get-diff3-group "1")))
-                    (b-begin (car (ediff-get-diff3-group "2")))
-                    (b-end (nth 1 (ediff-get-diff3-group "2")))
-                    (c-or-anc-begin (car (ediff-get-diff3-group "3")))
-                    (c-or-anc-end (nth 1 (ediff-get-diff3-group "3")))
+         (if (or three-way-comp (not (string-equal agreement C-idx)))
+             (let* ((a-begin (car (ediff-get-diff3-group A-idx)))
+                    (a-end  (nth 1 (ediff-get-diff3-group A-idx)))
+                    (b-begin (car (ediff-get-diff3-group B-idx)))
+                    (b-end (nth 1 (ediff-get-diff3-group B-idx)))
+                    (c-or-anc-begin (car (ediff-get-diff3-group C-idx)))
+                    (c-or-anc-end (nth 1 (ediff-get-diff3-group C-idx)))
                     (state-of-merge
-                     (cond ((string-equal agreement "1") 'prefer-A)
-                           ((string-equal agreement "2") 'prefer-B)
+                     (cond ((string-equal agreement A-idx) 'prefer-A)
+                           ((string-equal agreement B-idx) 'prefer-B)
                            (t ediff-default-variant)))
                     (state-of-diff-merge
                      (if (memq state-of-merge '(default-A prefer-A)) 'B 'A))
                     (state-of-diff-comparison
-                     (cond ((string-equal agreement "1") 'A)
-                           ((string-equal agreement "2") 'B)
-                           ((string-equal agreement "3") 'C)))
+                     (cond ((string-equal agreement A-idx) 'A)
+                           ((string-equal agreement B-idx) 'B)
+                           ((string-equal agreement C-idx) 'C)))
                     state-of-ancestor
                     c-begin c-end
                     a-begin-pt a-end-pt
@@ -1108,8 +1111,12 @@ one optional arguments, diff-number to refine.")
             (get-buffer-create (ediff-unique-buffer-name "*ediff-diff" "*"))))
 
   (message "Computing differences ...")
-  (ediff-exec-process ediff-diff3-program ediff-diff-buffer 'synchronize
-                      ediff-actual-diff3-options file-A file-B file-C)
+  (apply #'ediff-exec-process ediff-diff3-program ediff-diff-buffer 'synchronize
+         ediff-actual-diff3-options
+         (cons file-A (if ediff-merge-with-ancestor-job
+                          ;; Ancestor must be the middle file
+                          (list file-C file-B)
+                          (list file-B file-C))))
 
   (ediff-prepare-error-list ediff-diff3-ok-lines-regexp ediff-diff-buffer)
   ;;(message "Computing differences ... done")