[PATCH v2 21/23] worktree: add: make -b/-B default to HEAD when <branch> is omitted

@@ -69,6 +69,7 @@ OPTIONS
 -B <new-branch>::
 	With `add`, create a new branch named `<new-branch>` starting at
 	`<branch>`, and check out `<new-branch>` into the new worktree.
+	If `<branch>` is omitted, it defaults to HEAD.
 	By default, `-b` refuses to create a new branch if it already
 	exists. `-B` overrides this safeguard, resetting `<new-branch>` to
 	`<branch>`.

@@ -284,11 +284,13 @@ static int add(int ac, const char **av, const char *prefix)
 	ac = parse_options(ac, av, prefix, options, worktree_usage, 0);
 	if (new_branch && new_branch_force)
 		die(_("-b and -B are mutually exclusive"));
-	if (ac != 2)
+	if (ac < 1 || ac > 2)
+		usage_with_options(worktree_usage, options);
+	if (ac < 2 && !new_branch && !new_branch_force)
 		usage_with_options(worktree_usage, options);
 
 	path = prefix ? prefix_filename(prefix, strlen(prefix), av[0]) : av[0];
-	branch = av[1];
+	branch = ac < 2 ? "HEAD" : av[1];
 
 	argv_array_push(&cmd, "checkout");
 	if (force)

@@ -140,4 +140,11 @@ test_expect_success '"add" from relative HEAD' '
 	test_cmp expected actual
 '
 
+test_expect_success '"add -b" with <branch> omitted' '
+	git rev-parse HEAD >expected &&
+	git worktree add -b burble flornk &&
+	git rev-parse burble >actual &&
+	test_cmp expected actual
+'
+
 test_done