merge-recursive: Provide more info in conflict markers with file renames

Whenever there are merge conflicts in file contents, we would mark the
different sides of the conflict with the two branches being merged.
However, when there is a rename involved as well, the branchname is not
sufficient to specify where the conflicting content came from.  In such
cases, mark the two sides of the conflict with branchname:filename rather
than just branchname.

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

merge-recursive.c

@@ -1353,6 +1353,7 @@ static int merge_content(struct merge_options *o,
 			 struct rename_conflict_info *rename_conflict_info)
 {
 	const char *reason = "content";
+	char *side1 = NULL, *side2 = NULL;
 	struct merge_file_info mfi;
 	struct diff_filespec one, a, b;
 	unsigned df_conflict_remains = 0;
@@ -1369,10 +1370,31 @@ static int merge_content(struct merge_options *o,
 	hashcpy(b.sha1, b_sha);
 	b.mode = b_mode;
 
-	mfi = merge_file(o, &one, &a, &b, o->branch1, o->branch2);
-	if (rename_conflict_info && dir_in_way(path, !o->call_depth)) {
-		df_conflict_remains = 1;
+	if (rename_conflict_info) {
+		const char *path1, *path2;
+		struct diff_filepair *pair1 = rename_conflict_info->pair1;
+
+		path1 = (o->branch1 == rename_conflict_info->branch1) ?
+			pair1->two->path : pair1->one->path;
+		/* If rename_conflict_info->pair2 != NULL, we are in
+		 * RENAME_ONE_FILE_TO_ONE case.  Otherwise, we have a
+		 * normal rename.
+		 */
+		path2 = (rename_conflict_info->pair2 ||
+			 o->branch2 == rename_conflict_info->branch1) ?
+			pair1->two->path : pair1->one->path;
+		side1 = xmalloc(strlen(o->branch1) + strlen(path1) + 2);
+		side2 = xmalloc(strlen(o->branch2) + strlen(path2) + 2);
+		sprintf(side1, "%s:%s", o->branch1, path1);
+		sprintf(side2, "%s:%s", o->branch2, path2);
+
+		if (dir_in_way(path, !o->call_depth))
+			df_conflict_remains = 1;
 	}
+	mfi = merge_file(o, &one, &a, &b,
+			 side1 ? side1 : o->branch1, side2 ? side2 : o->branch2);
+	free(side1);
+	free(side2);
 
 	if (mfi.clean && !df_conflict_remains &&
 	    sha_eq(mfi.sha, a_sha) && mfi.mode == a.mode)

t/t6022-merge-rename.sh

@@ -351,11 +351,11 @@ cat >expected <<\EOF &&
 8
 9
 10
-<<<<<<< HEAD
+<<<<<<< HEAD:dir
 12
 =======
 11
->>>>>>> dir-not-in-way
+>>>>>>> dir-not-in-way:sub/file
 EOF
 
 test_expect_success 'Rename+D/F conflict; renamed file cannot merge, dir not in way' '
@@ -405,11 +405,11 @@ cat >expected <<\EOF &&
 8
 9
 10
-<<<<<<< HEAD
+<<<<<<< HEAD:sub/file
 11
 =======
 12
->>>>>>> renamed-file-has-conflicts
+>>>>>>> renamed-file-has-conflicts:dir
 EOF
 
 test_expect_success 'Same as previous, but merged other way' '
@@ -700,4 +700,71 @@ test_expect_success 'merge rename + small change' '
 	test $(git rev-parse HEAD:renamed_file) = $(git rev-parse HEAD~1:file)
 '
 
+test_expect_success 'setup for use of extended merge markers' '
+	git rm -rf . &&
+	git clean -fdqx &&
+	rm -rf .git &&
+	git init &&
+
+	printf "1\n2\n3\n4\n5\n6\n7\n8\n" >original_file &&
+	git add original_file &&
+	git commit -mA &&
+
+	git checkout -b rename &&
+	echo 9 >>original_file &&
+	git add original_file &&
+	git mv original_file renamed_file &&
+	git commit -mB &&
+
+	git checkout master &&
+	echo 8.5 >>original_file &&
+	git add original_file &&
+	git commit -mC
+'
+
+cat >expected <<\EOF &&
+1
+2
+3
+4
+5
+6
+7
+8
+<<<<<<< HEAD:renamed_file
+9
+=======
+8.5
+>>>>>>> master^0:original_file
+EOF
+
+test_expect_success 'merge master into rename has correct extended markers' '
+	git checkout rename^0 &&
+	test_must_fail git merge -s recursive master^0 &&
+	test_cmp expected renamed_file
+'
+
+cat >expected <<\EOF &&
+1
+2
+3
+4
+5
+6
+7
+8
+<<<<<<< HEAD:original_file
+8.5
+=======
+9
+>>>>>>> rename^0:renamed_file
+EOF
+
+test_expect_success 'merge rename into master has correct extended markers' '
+	git reset --hard &&
+	git checkout master^0 &&
+	test_must_fail git merge -s recursive rename^0 &&
+	test_cmp expected renamed_file
+'
+
 test_done

t/t6042-merge-rename-corner-cases.sh

@@ -258,7 +258,7 @@ test_expect_success 'rename/directory conflict + clean content merge' '
 	test -f newfile~HEAD
 '
 
-test_expect_failure 'rename/directory conflict + content merge conflict' '
+test_expect_success 'rename/directory conflict + content merge conflict' '
 	git reset --hard &&
 	git reset --hard &&
 	git clean -fdqx &&