grep: error out if --untracked is used with --cached

The options --untracked and --cached are not compatible, but if they are
used together, grep just silently ignores --cached and searches the
working tree. Error out, instead, to avoid any potential confusion.

Signed-off-by: Matheus Tavares <[email protected]>
Reviewed-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: matheustavares

builtin/grep.c

@@ -1157,6 +1157,9 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	if (!use_index && (untracked || cached))
 		die(_("--cached or --untracked cannot be used with --no-index"));
 
+	if (untracked && cached)
+		die(_("--untracked cannot be used with --cached"));
+
 	if (!use_index || untracked) {
 		int use_exclude = (opt_exclude < 0) ? use_index : !!opt_exclude;
 		hit = grep_directory(&opt, &pathspec, use_exclude, use_index);