worktree: fix "add -B"

Current code does not update "symref" when -B is used. This string
contains the new HEAD. Because it's empty "git worktree add -B" fails at
symbolic-ref step.

Because branch creation is already done before calling add_worktree(),
-B is equivalent to -b from add_worktree() point of view. We do not need
the special case for -B.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/worktree.c

@@ -201,9 +201,7 @@ static int add_worktree(const char *path, const char *refname,
 		die(_("'%s' already exists"), path);
 
 	/* is 'refname' a branch or commit? */
-	if (opts->force_new_branch) /* definitely a branch */
-		;
-	else if (!opts->detach && !strbuf_check_branch_ref(&symref, refname) &&
+	if (!opts->detach && !strbuf_check_branch_ref(&symref, refname) &&
 		 ref_exists(symref.buf)) { /* it's a branch */
 		if (!opts->force)
 			die_if_checked_out(symref.buf);

t/t2025-worktree-add.sh

@@ -193,6 +193,14 @@ test_expect_success '"add" -B/--detach mutually exclusive' '
 	test_must_fail git worktree add -B poodle --detach bamboo master
 '
 
+test_expect_success 'add -B' '
+	git worktree add -B poodle bamboo2 master^ &&
+	git -C bamboo2 symbolic-ref HEAD >actual &&
+	echo refs/heads/poodle >expected &&
+	test_cmp expected actual &&
+	test_cmp_rev master^ poodle
+'
+
 test_expect_success 'local clone from linked checkout' '
 	git clone --local here here-clone &&
 	( cd here-clone && git fsck )