dir: do not traverse mount points

It was already decided in ef22148 (clean: do not traverse mount points,
2018-12-07) that we shouldn't traverse NTFS junctions/bind mounts when
using `git clean`, partly because they're sometimes used in worktrees.
But the same check wasn't applied to `remove_dir_recurse()` in `dir.c`,
which `git worktree remove` uses. So removing a worktree suffers the
same problem we had previously with `git clean`.

Let's add the same guard from ef22148.

Signed-off-by: Maks Kuznia <makskuznia244@gmail.com>

dir.c

@@ -3411,6 +3411,13 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
 		return 0;
 	}
 
+	if (is_mount_point(path)) {
+		/* Do not descend and nuke a mount point or junction. */
+		if (kept_up)
+			*kept_up = 1;
+		return 0;
+	}
+
 	flag &= ~REMOVE_DIR_KEEP_TOPLEVEL;
 	dir = opendir(path->buf);
 	if (!dir) {

t/t2403-worktree-move.sh

@@ -271,4 +271,13 @@ test_expect_success 'move worktree with relative path to absolute path' '
 	test_cmp expect .git/worktrees/absolute/gitdir
 '
 
+test_expect_success MINGW 'worktree remove does not traverse mount points' '
+	mkdir target &&
+	>target/dont-remove-me &&
+	git worktree add --detach wt-junction &&
+	cmd //c "mklink /j wt-junction\\mnt target" &&
+	git worktree remove --force wt-junction &&
+	test_path_is_file target/dont-remove-me
+'
+
 test_done