@@ -9,7 +9,7 @@ git-merge-index - Run a merge for files needing merging
 SYNOPSIS
 --------
 [verse]
-'git merge-index' [-o] [-q] <merge-program> (-a | [--] <file>*)
+'git merge-index' [-o] [-q] (<merge-program> | --use=merge-one-file) (-a | [--] <file>*)
 
 DESCRIPTION
 -----------

@@ -44,8 +44,9 @@ code.
 Typically this is run with a script calling Git's imitation of
 the 'merge' command from the RCS package.
 
-A sample script called 'git merge-one-file' is included in the
-distribution.
+A sample script called 'git merge-one-file' used to be included in the
+distribution. This program must now be called with
+'--use=merge-one-file'.
 
 ALERT ALERT ALERT! The Git "merge object order" is different from the
 RCS 'merge' program merge object order. In the above ordering, the

@@ -1,4 +1,5 @@
 #include "builtin.h"
+#include "lockfile.h"
 #include "merge-strategies.h"
 #include "run-command.h"
 

@@ -37,7 +38,10 @@ static int merge_one_file_spawn(struct index_state *istate,
 int cmd_merge_index(int argc, const char **argv, const char *prefix)
 {
 	int i, force_file = 0, err = 0, one_shot = 0, quiet = 0;
+	merge_fn merge_action = merge_one_file_spawn;
+	struct lock_file lock = LOCK_INIT;
 	struct repository *r = the_repository;
+	const char *use_internal = NULL;
 
 	/* Without this we cannot rely on waitpid() to tell
 	 * what happened to our children.

@@ -45,7 +49,7 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 	signal(SIGCHLD, SIG_DFL);
 
 	if (argc < 3)
-		usage("git merge-index [-o] [-q] <merge-program> (-a | [--] [<filename>...])");
+		usage("git merge-index [-o] [-q] (<merge-program> | --use=merge-one-file) (-a | [--] [<filename>...])");
 
 	if (repo_read_index(r) < 0)
 		die("invalid index");

@@ -61,6 +65,14 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 	}
 
 	pgm = argv[i++];
+	setup_work_tree();
+
+	if (skip_prefix(pgm, "--use=", &use_internal)) {
+		if (!strcmp(use_internal, "merge-one-file"))
+			pgm = "git-merge-one-file";
+		else
+			die(_("git merge-index: unknown internal program %s"), use_internal);
+	}
 
 	for (; i < argc; i++) {
 		const char *arg = argv[i];

@@ -71,13 +83,20 @@ int cmd_merge_index(int argc, const char **argv, const char *prefix)
 			}
 			if (!strcmp(arg, "-a")) {
 				err |= merge_all_index(r->index, one_shot, quiet,
-						       merge_one_file_spawn, NULL);
+						       merge_action, NULL);
 				continue;
 			}
 			die("git merge-index: unknown option %s", arg);
 		}
 		err |= merge_index_path(r->index, one_shot, quiet, arg,
-					merge_one_file_spawn, NULL);
+					merge_action, NULL);
+	}
+
+	if (is_lock_file_locked(&lock)) {
+		if (err)
+			rollback_lock_file(&lock);
+		else
+			return write_locked_index(r->index, &lock, COMMIT_LOCK);
 	}
 
 	return err;

@@ -100,7 +100,7 @@ do
 	if test $? -ne 0
 	then
 		gettextln "Simple merge did not work, trying automatic merge."
-		git merge-index -o git-merge-one-file -a ||
+		git merge-index -o --use=merge-one-file -a ||
 		OCTOPUS_FAILURE=1
 		next=$(git write-tree 2>/dev/null)
 	fi

@@ -45,7 +45,7 @@ then
 	exit 0
 else
 	echo "Simple merge failed, trying Automatic merge."
-	if git merge-index -o git-merge-one-file -a
+	if git merge-index -o --use=merge-one-file -a
 	then
 		exit 0
 	else

@@ -50,8 +50,8 @@ test_expect_success 'read-tree does not resolve content merge' '
 	test_cmp expect unmerged
 '
 
-test_expect_success 'git merge-index git-merge-one-file resolves' '
-	git merge-index git-merge-one-file -a &&
+test_expect_success 'git merge-index --use=merge-one-file resolves' '
+	git merge-index --use=merge-one-file -a &&
 	git diff-files --name-only --diff-filter=U >unmerged &&
 	test_must_be_empty unmerged &&
 	test_cmp expect-merged file &&

@@ -83,7 +83,7 @@ test_expect_success 'merge-one-file respects GIT_WORK_TREE' '
 	 export GIT_WORK_TREE &&
 	 GIT_INDEX_FILE=$PWD/merge.index &&
 	 export GIT_INDEX_FILE &&
-	 git merge-index git-merge-one-file -a &&
+	 git merge-index --use=merge-one-file -a &&
 	 git cat-file blob :file >work/file-index
 	) &&
 	test_cmp expect-merged bare.git/work/file &&

@@ -98,7 +98,7 @@ test_expect_success 'merge-one-file respects core.worktree' '
 	 export GIT_DIR &&
 	 git config core.worktree "$PWD/child" &&
 	 git read-tree -i -m base ten two &&
-	 git merge-index git-merge-one-file -a &&
+	 git merge-index --use=merge-one-file -a &&
 	 git cat-file blob :file >file-index
 	) &&
 	test_cmp expect-merged subdir/child/file &&