worktree add: trim slashes when deriving branch name from path

worktree_basename() sets `n` to the length of `path` without trailing
path separators, not to the length of the basename.  This matters when
deriving a branch name from a path with more than one component.  E.g.:

   path: /new/worktree/
   s:         ^
   n:    |-----------|

So here xstrndup(s, n) copies up to 13 characters from "worktree/",
effectively to the end of the string, including the trailing dash.

Path separators are not allowed at the end of branch names, so strip
them off by calculating the basename length and extracting just that
part.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/worktree.c

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 214de50..e5b7d6f 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -768,7 +768,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	int n;
 	int branch_exists;
 	const char *s = worktree_basename(path, &n);
-	char *branchname = xstrndup(s, n);
+	char *branchname = xmemdupz(s, path + n - s);
 	struct strbuf ref = STRBUF_INIT;
 
 	branch_exists = !check_branch_ref(&ref, branchname) &&
@@ -877,7 +877,7 @@ static int add(int ac, const char **av, const char *prefix,
 	if (opts.orphan && !new_branch) {
 		int n;
 		const char *s = worktree_basename(path, &n);
-		new_branch = new_branch_to_free = xstrndup(s, n);
+		new_branch = new_branch_to_free = xmemdupz(s, path + n - s);
 	} else if (opts.orphan) {
 		; /* no-op */
 	} else if (opts.detach) {

t/t2400-worktree-add.sh

diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 4ffdd56..9542a17 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -298,6 +298,11 @@
 	test_cmp_rev HEAD bat
 '
 
+test_expect_success '"add" with trailing slash and <branch> omitted' '
+	git worktree add waffle/bit/ &&
+	test_cmp_rev HEAD bit
+'
+
 test_expect_success '"add" checks out existing branch of dwimd name' '
 	git branch dwim HEAD~1 &&
 	git worktree add dwim &&
@@ -388,6 +393,14 @@
 	test_cmp expected actual
 '
 
+test_expect_success '"add --orphan with trailing slash (no -b)"' '
+	test_when_finished "git worktree remove -f -f neworphan" &&
+	git worktree add --orphan ./neworphan/ &&
+	echo refs/heads/neworphan >expected &&
+	git -C neworphan symbolic-ref HEAD >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success '"add --orphan --quiet"' '
 	test_when_finished "git worktree remove -f -f orphandir" &&
 	git worktree add --quiet --orphan -b neworphan orphandir 2>log.actual &&