"required" JSON keys are validated against "additionalProperties" if …

…they are missing from "properties" (#1029)

When `required` properties don't have a
schema in `properties`, validate against `additionalProperties`

guidance/library/_json.py

@@ -447,16 +447,24 @@ def _gen_json_object(
     required: Sequence[str],
     definitions: Mapping[str, Callable[[], GrammarFunction]],
 ):
-    if any(k not in properties for k in required):
-        raise ValueError(f"Required properties not in properties: {set(required) - set(properties)}")
-
-    grammars = tuple(f'"{name}":' + _gen_json(json_schema=schema, definitions=definitions) for name, schema in properties.items())
-    required_items = tuple(name in required for name in properties)
+    # "required" keys will be validated against "properties" if they're present, otherwise against "additionalProperties".
+    # If "additionalProperties" is False, then required keys must be in "properties".
+    if any(k not in properties for k in required) and additional_properties is False:
+        raise ValueError(
+            f"Required properties not in properties but additionalProperties is False."
+            f" Missing required properties: {list(r for r in required if r not in properties)}"
+        )
+    items = [
+        # First iterate over the properties in order
+        *properties.items(),
+        # If there are any keys in required that weren't specified by properties, add them in order at the end,
+        # where we will validate against the additional_properties schema
+        *((key, additional_properties) for key in required if key not in properties),
+    ]
+    grammars = tuple(f'"{name}":' + _gen_json(json_schema=schema, definitions=definitions) for name, schema in items)
+    required_items = tuple(name in required for name, _ in items)
 
     if additional_properties is not False:
-        if additional_properties is True:
-            # True means that anything goes
-            additional_properties = {}
         additional_item_grammar =  _gen_json_string() + ':' + _gen_json(json_schema=additional_properties, definitions=definitions)
         additional_items_grammar = sequence(additional_item_grammar + ',') + additional_item_grammar
         grammars += (additional_items_grammar,)

tests/unit/library/test_json.py

@@ -614,6 +614,36 @@ def test_bad_object(self, bad_string, good_bytes, failure_byte, allowed_bytes, m
         )
 
 
+class TestObjectWithMissingRequired:
+    def test_required_is_required(self):
+        schema = {"type": "object", "properties": {"a": {"type": "integer"}}, "required": ["b"]}
+        generate_and_check({"b": 1}, schema)
+        generate_and_check({"a": 1, "b": "xyz"}, schema)
+        check_match_failure(
+            bad_string=_to_compact_json(
+                {"a": 1}
+            ),
+            schema_obj=schema,
+        )
+
+    def test_validated_against_additionalProperties(self):
+        schema = {"type": "object", "properties": {"a": {"type": "integer"}}, "required": ["b"], "additionalProperties": {"type": "integer"}}
+        generate_and_check({"b": 1}, schema)
+        generate_and_check({"a": 1, "b": 42}, schema)
+        check_match_failure(
+            bad_string=_to_compact_json(
+                {"a": 1, "b": "string"}
+            ),
+            schema_obj=schema,
+        )
+
+    def test_false_additionalProperties_fails(self):
+        schema = {"type": "object", "properties": {"a": {"type": "integer"}}, "required": ["b", "c"], "additionalProperties": False}
+        with pytest.raises(ValueError) as ve:
+            _ = gen_json(schema=schema)
+        assert ve.value.args[0] == "Required properties not in properties but additionalProperties is False. Missing required properties: ['b', 'c']"
+
+
 class TestSimpleArray:
     # These are array without references
     @pytest.mark.parametrize("target_obj", [[], [0], [34, 56], [1, 2, 3], [9, 8, 7, 6]])