json: remove recursion in opt_repetitions (avoids Python stack overflow)

common/json-schema-to-grammar.cpp

@@ -8,6 +8,7 @@
 #include <unordered_map>
 #include <unordered_set>
 #include <vector>
+#include "ggml.h"
 
 using json = nlohmann::ordered_json;
 
@@ -36,6 +37,23 @@ static std::string build_repetition(const std::string & item_rule, int min_items
     }
 
     std::function<std::string(int, bool)> opt_repetitions = [&](int up_to_n, bool prefix_with_sep) -> std::string {
+        auto content = prefix_with_sep && !separator_rule.empty() ? separator_rule + " " + item_rule : item_rule;
+
+        if (up_to_n == 0) {
+            return "";
+        } else if (up_to_n == 1) {
+            return "(" + content + ")?";
+        } else if (!separator_rule.empty() && !prefix_with_sep) {
+            return "(" + content + " " + opt_repetitions(up_to_n - 1, true) + ")?";
+        } else {
+            std::string res = repeat("(" + content + " ", up_to_n);
+            // strip trailing space
+            GGML_ASSERT(!res.empty());
+            res = res.substr(0, res.length() - 1);
+            res += repeat(")?", up_to_n);
+            return res;
+        }
+
         if (up_to_n == 0) {
             return "";
         }

examples/json_schema_to_grammar.py

@@ -22,13 +22,21 @@ def _build_repetition(item_rule, min_items, max_items, separator_rule=None, item
             result = (f' {separator_rule} ' if separator_rule else ' ').join([item_rule] * min_items)
 
     def opt_repetitions(up_to_n, prefix_with_sep=False):
+        '''
+            - n=4, no sep:             '(a (a (a (a)?)?)?)?'
+            - n=4, sep=',', prefix:    '("," a ("," a ("," a ("," a)?)?)?)?'
+            - n=4, sep=',', no prefix: '(a ("," a ("," a ("," a)?)?)?)?'
+        '''
+
+        content = f'{separator_rule} {item_rule}' if prefix_with_sep and separator_rule else item_rule
         if up_to_n == 0:
             return ''
-
-        res = separator_rule + ' ' + item_rule if separator_rule and prefix_with_sep else item_rule
-        if up_to_n > 1:
-            res += ' ' + opt_repetitions(up_to_n - 1, prefix_with_sep=True)
-        return f'({res})?'
+        elif up_to_n == 1:
+            return f'({content})?'
+        elif separator_rule and not prefix_with_sep:
+            return f'({content} {opt_repetitions(up_to_n - 1, prefix_with_sep=True)})?'
+        else:
+            return (f'({content} ' * up_to_n).rstrip() + (')?' * up_to_n)
 
     if min_items > 0 and max_items != min_items:
         result += ' '

examples/server/public/json-schema-to-grammar.mjs

@@ -24,14 +24,16 @@ function _buildRepetition(itemRule, minItems, maxItems, opts={}) {
   }
 
   const optRepetitions = (upToN, prefixWithSep=false) => {
+    const content = separatorRule !== '' && prefixWithSep ? `${separatorRule} ${itemRule}` : itemRule;
     if (upToN === 0) {
       return '';
+    } else if (upToN === 1) {
+      return `(${content})?`;
+    } else if (separatorRule !== '' && !prefixWithSep) {
+      return `(${content} ${optRepetitions(upToN - 1, true)})?`;
+    } else {
+      return Array.from({ length: upToN }, () => `(${content}`).join(' ').trim() + Array.from({ length: upToN }, () => ')?').join('');
     }
-    let res = separatorRule !== '' && prefixWithSep ? separatorRule + ' ' + itemRule : itemRule;
-    if (upToN > 1) {
-      res += ' ' + optRepetitions(upToN - 1, true);
-    }
-    return `(${res})?`;
   };
 
   if (minItems > 0 && maxItems !== minItems) {