master c8b9922e26: ediff: Merges with ancestor: Fix computation of hunks and proposed merge

[Eli Zaretskii]

branch: master
commit c8b9922e26a42db46411d1dea4e78089adf6743e
Author: Olivier Certner <olce.emacs@certner.fr>
Commit: Eli Zaretskii <eliz@gnu.org>

    ediff: Merges with ancestor: Fix computation of hunks and proposed merge
    
    Hunks were not computed correctly because the diff3 command was
    invoked with arguments in an incorrect order.  The correct order is
    the local file first, the base (or "ancestor") second and the other
    file third.  This erroneous behavior had two consequences.  First, the
    output of diff3 would change, since it tries to merge chunks according
    to maximal matches between the second and first files, and the second
    and third files.  Second, ediff, more precisely, `ediff-do-merge',
    would consequently try to merge the reverse of the changes from the
    base to the other file.
    
    * lisp/vc/ediff-diff.el (ediff-setup-diff-regions3): In the arguments
    to `ediff-exec-process', swap the other file with the ancestor (only
    when merging with an ancestor).
    
    (ediff-extract-diffs3): Match the hunk data for the ancestor and the
    other file correctly.  The local variable `three-way-comp' indicates
    this is a merge with ancestors when it is nil.
    
    (Bug#59182)
---
 lisp/vc/ediff-diff.el | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/lisp/vc/ediff-diff.el b/lisp/vc/ediff-diff.el
index 07b853817d..24647de576 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")