prefix_path: show gitdir if worktree unavailable

If there is no worktree at present, we can still hint the user about
Git's current directory by showing them the absolute path to the Git
directory. Even though the Git directory doesn't make it as easy to
locate the worktree in question, it can still help a user figure out
what's going on while developing a script.

This fixes a segmentation fault introduced in e0020b2f
("prefix_path: show gitdir when arg is outside repo", 2020-02-14).

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
[jc: added minimum tests, with help from Szeder Gábor]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/setup.c b/setup.c
index 17814a0..f489728 100644
--- a/setup.c
+++ b/setup.c
@@ -120,9 +120,13 @@ char *prefix_path_gently(const char *prefix, int len,
 char *prefix_path(const char *prefix, int len, const char *path)
 {
 	char *r = prefix_path_gently(prefix, len, NULL, path);
-	if (!r)
+	if (!r) {
+		const char *hint_path = get_git_work_tree();
+		if (!hint_path)
+			hint_path = get_git_dir();
 		die(_("'%s' is outside repository at '%s'"), path,
-		    absolute_path(get_git_work_tree()));
+		    absolute_path(hint_path));
+	}
 	return r;
 }