merge-recursive: Fix rename/rename(1to2) resolution for virtual merge base

When renaming one file to two files, we really should be doing a content
merge.  Also, in the recursive case, undoing the renames and recording the
merged file in the index with the source of the rename (while deleting
both destinations) allows the renames to be re-detected in the
non-recursive merge and will result in fewer spurious conflicts.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -984,17 +984,6 @@ static void conflict_rename_rename_1to2(struct merge_options *o,
 	       src, pair1->two->path, branch1,
 	       src, pair2->two->path, branch2,
 	       o->call_depth ? " (left unresolved)" : "");
-	if (o->call_depth) {
-		/*
-		 * FIXME: Why remove file from cache, and then
-		 * immediately readd it?  Why not just overwrite using
-		 * update_file only?  Also...this is buggy for
-		 * rename/add-source situations...
-		 */
-		remove_file_from_cache(src);
-		update_file(o, 0, pair1->one->sha1, pair1->one->mode, src);
-	}
-
 	if (dir_in_way(ren1_dst, !o->call_depth)) {
 		dst_name1 = del[delp++] = unique_path(o, ren1_dst, branch1);
 		output(o, 1, "%s is a directory in %s adding as %s instead",
@@ -1006,14 +995,21 @@ static void conflict_rename_rename_1to2(struct merge_options *o,
 		       ren2_dst, branch1, dst_name2);
 	}
 	if (o->call_depth) {
-		remove_file_from_cache(dst_name1);
-		remove_file_from_cache(dst_name2);
+		struct merge_file_info mfi;
+		mfi = merge_file(o, src,
+				 pair1->one->sha1, pair1->one->mode,
+				 pair1->two->sha1, pair1->two->mode,
+				 pair2->two->sha1, pair2->two->mode,
+				 branch1, branch2);
 		/*
-		 * Uncomment to leave the conflicting names in the resulting tree
-		 *
-		 * update_file(o, 0, pair1->two->sha1, pair1->two->mode, dst_name1);
-		 * update_file(o, 0, pair2->two->sha1, pair2->two->mode, dst_name2);
+		 * FIXME: For rename/add-source conflicts (if we could detect
+		 * such), this is wrong.  We should instead find a unique
+		 * pathname and then either rename the add-source file to that
+		 * unique path, or use that unique path instead of src here.
 		 */
+		update_file(o, 0, mfi.sha, mfi.mode, src);
+		remove_file_from_cache(ren1_dst);
+		remove_file_from_cache(ren2_dst);
 	} else {
 		update_stages(ren1_dst, NULL, pair1->two, NULL);
 		update_stages(ren2_dst, NULL, NULL, pair2->two);

t/t6036-recursive-corner-cases.sh

@@ -633,7 +633,7 @@ test_expect_success 'setup rename/rename(1to2)/modify followed by what looks lik
 	git tag E
 '
 
-test_expect_failure 'handle rename/rename(1to2)/modify followed by what looks like rename/rename(2to1)/modify' '
+test_expect_success 'handle rename/rename(1to2)/modify followed by what looks like rename/rename(2to1)/modify' '
 	git checkout D^0 &&
 
 	git merge -s recursive E^0 &&