read info/{attributes,exclude} only when in repository

The low-level attribute and gitignore code will try to look
in $GIT_DIR/info for any repo-level configuration files,
even if we have not actually determined that we are in a
repository (e.g., running "git grep --no-index"). In such a
case they end up looking for ".git/info/attributes", etc.

This is generally harmless, as such a file is unlikely to
exist outside of a repository, but it's still conceptually
the wrong thing to do.

Let's detect this situation explicitly and skip reading the
file (i.e., the same behavior we'd get if we were in a
repository and the file did not exist).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

attr.c

@@ -531,7 +531,11 @@ static void bootstrap_attr_stack(void)
 		debug_push(elem);
 	}
 
-	elem = read_attr_from_file(git_path_info_attributes(), 1);
+	if (startup_info->have_repository)
+		elem = read_attr_from_file(git_path_info_attributes(), 1);
+	else
+		elem = NULL;
+
 	if (!elem)
 		elem = xcalloc(1, sizeof(*elem));
 	elem->origin = NULL;