-unsigned int utf8_hash_case_bytes (const char *, size_t n, unsigned int basis);
-unsigned int utf8_hash_case_string (const char *, unsigned int basis);
+unsigned int utf8_hash_case_bytes (const char *, size_t n, unsigned int basis) WARN_UNUSED_RESULT;
+unsigned int utf8_hash_case_string (const char *, unsigned int basis) WARN_UNUSED_RESULT;
+unsigned int utf8_hash_case_substring (struct substring, unsigned int basis)
+ WARN_UNUSED_RESULT;