grammars: handle x{n} and fix x{n,n}

Author: Olivier Chafik

common/grammar-parser.cpp

@@ -199,7 +199,8 @@ namespace grammar_parser {
                 sub_rule.push_back({LLAMA_GRETYPE_RULE_REF, star_rule_id});
             } else {
                 uint32_t last_rec_rule_id = 0;
-                for (int i = 0, n = max_times - min_times; i < n; i++) {
+                auto n_opt = max_times - min_times;
+                for (int i = 0; i < n_opt; i++) {
                     uint32_t rec_rule_id = generate_symbol_id(state, rule_name + "_" + std::to_string(i + 1));
                     if (i == 0) {
                         add_rule(state, rec_rule_id, {
@@ -217,7 +218,9 @@ namespace grammar_parser {
                     }
                     last_rec_rule_id = rec_rule_id;
                 }
-                sub_rule.push_back({LLAMA_GRETYPE_RULE_REF, last_rec_rule_id});
+                if (n_opt > 0) {
+                    sub_rule.push_back({LLAMA_GRETYPE_RULE_REF, last_rec_rule_id});
+                }
             }
             sub_rule.push_back({LLAMA_GRETYPE_END, 0});
             add_rule(state, sub_rule_id, sub_rule);
@@ -291,24 +294,34 @@ namespace grammar_parser {
                 pos = parse_space(pos + 1, is_nested);
                 size_t min_times = 0;
                 int max_times = -1;
+
                 if (is_digit_char(*pos)) {
                     const char * int_end = parse_int(pos);
                     min_times = std::stoul(std::string(pos, int_end - pos));
                     pos = parse_space(int_end, is_nested);
+                } else if (*pos != ',') {
+                    throw std::runtime_error(std::string("expecting an int or ',' at ") + pos);
                 }
-                if (*pos != ',') {
+
+                if (*pos == '}') {
+                    max_times = min_times;
+                    pos = parse_space(pos + 1, is_nested);
+                } else if (*pos == ',') {
+                    pos = parse_space(pos + 1, is_nested);
+
+                    if (is_digit_char(*pos)) {
+                        const char * int_end = parse_int(pos);
+                        max_times = std::stoul(std::string(pos, int_end - pos));
+                        pos = parse_space(int_end, is_nested);
+                    }
+
+                    if (*pos != '}') {
+                        throw std::runtime_error(std::string("expecting '}' at ") + pos);
+                    }
+                    pos = parse_space(pos + 1, is_nested);
+                } else {
                     throw std::runtime_error(std::string("expecting ',' at ") + pos);
                 }
-                pos = parse_space(pos + 1, is_nested);
-                if (is_digit_char(*pos)) {
-                    const char * int_end = parse_int(pos);
-                    max_times = std::stoul(std::string(pos, int_end - pos));
-                    pos = parse_space(int_end, is_nested);
-                }
-                if (*pos != '}') {
-                    throw std::runtime_error(std::string("expecting '}' at ") + pos);
-                }
-                pos = parse_space(pos + 1, is_nested);
                 handle_repetitions(min_times, max_times);
             } else {
                 break;