json: better support for "type" unions (e.g. nullable arrays w/ typed items)

common/json-schema-to-grammar.cpp

@@ -820,7 +820,9 @@ class SchemaConverter {
         } else if (schema_type.is_array()) {
             std::vector<json> schema_types;
             for (const auto & t : schema_type) {
-                schema_types.push_back({{"type", t}});
+                json schema_copy(schema);
+                schema_copy["type"] = t;
+                schema_types.push_back(schema_copy);
             }
             return _add_rule(rule_name, _generate_union_rule(name, schema_types));
         } else if (schema.contains("const")) {

examples/json_schema_to_grammar.py

@@ -521,7 +521,7 @@ def visit(self, schema, name):
             return self._add_rule(rule_name, self._generate_union_rule(name, schema.get('oneOf') or schema['anyOf']))
 
         elif isinstance(schema_type, list):
-            return self._add_rule(rule_name, self._generate_union_rule(name, [{'type': t} for t in schema_type]))
+            return self._add_rule(rule_name, self._generate_union_rule(name, [{**schema, 'type': t} for t in schema_type]))
 
         elif 'const' in schema:
             return self._add_rule(rule_name, self._generate_constant_rule(schema['const']))

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

@@ -558,7 +558,7 @@ export class SchemaConverter {
     } else if (schema.oneOf || schema.anyOf) {
       return this._addRule(ruleName, this._generateUnionRule(name, schema.oneOf || schema.anyOf));
     } else if (Array.isArray(schemaType)) {
-      return this._addRule(ruleName, this._generateUnionRule(name, schemaType.map(t => ({ type: t }))));
+      return this._addRule(ruleName, this._generateUnionRule(name, schemaType.map(t => ({...schema, type: t}))));
     } else if ('const' in schema) {
       return this._addRule(ruleName, this._generateConstantRule(schema.const));
     } else if ('enum' in schema) {

tests/test-grammar-integration.cpp

@@ -1017,6 +1017,31 @@ static void test_json_schema() {
         }
     );
 
+    test_schema(
+        "",
+        // Schema
+        R"""(
+            {
+                "type": ["array", "null"],
+                "items": { "type": "string" }
+            }
+        )""",
+        // Passing strings
+        {
+            "null",
+            "[]",
+            "[\"123\"]",
+            "[\"foo\", \"bar\"]",
+        },
+        // Failing strings
+        {
+            "",
+            "[123]",
+            "\"foo\"",
+            "[\"foo\", 42]",
+        }
+    );
+
     test_schema(
         "min+max items",
         // Schema

tests/test-json-schema-to-grammar.cpp

@@ -502,6 +502,38 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
         )"""
     });
 
+    test({
+        SUCCESS,
+        "string array",
+        R"""({
+            "type": "array",
+            "prefixItems": { "type": "string" }
+        })""",
+        R"""(
+            char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
+            root ::= "[" space (string ("," space string)*)? "]" space
+            space ::= | " " | "\n" [ \t]{0,20}
+            string ::= "\"" char* "\"" space
+        )"""
+    });
+
+    test({
+        SUCCESS,
+        "nullable string array",
+        R"""({
+            "type": ["array", "null"],
+            "prefixItems": { "type": "string" }
+        })""",
+        R"""(
+            alternative-0 ::= "[" space (string ("," space string)*)? "]" space
+            char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
+            null ::= "null" space
+            root ::= alternative-0 | null
+            space ::= | " " | "\n" [ \t]{0,20}
+            string ::= "\"" char* "\"" space
+        )"""
+    });
+
     test({
         SUCCESS,
         "tuple1",