Make __pydantic_extra__ = None when extra='forbid' (#725)

Author: dmontagu

src/validators/model_fields.rs

@@ -263,7 +263,9 @@ impl Validator for ModelFieldsValidator {
                             }
                         }
                     }
-                    model_extra_dict_op = Some(model_extra_dict);
+                    if matches!(self.extra_behavior, ExtraBehavior::Allow) {
+                        model_extra_dict_op = Some(model_extra_dict);
+                    }
                 }
             }};
         }
@@ -279,9 +281,9 @@ impl Validator for ModelFieldsValidator {
         } else {
             let fields_set = PySet::new(py, &fields_set_vec)?;
 
-            // if we have extra=allow, but we didn't create a dict because we were validate attributes, set it now
-            // so __pydantic_extra__ is always a dict if extra=allow
-            if model_extra_dict_op.is_none() && matches!(self.extra_behavior, ExtraBehavior::Allow) {
+            // if we have extra=allow, but we didn't create a dict because we were validating
+            // from attributes, set it now so __pydantic_extra__ is always a dict if extra=allow
+            if matches!(self.extra_behavior, ExtraBehavior::Allow) && model_extra_dict_op.is_none() {
                 model_extra_dict_op = Some(PyDict::new(py));
             };
 

tests/validators/test_model_fields.py

@@ -1445,7 +1445,7 @@ def test_alias_extra_forbid(py_and_json: PyAndJson):
             'fields': {'field_a': {'type': 'model-field', 'validation_alias': 'FieldA', 'schema': {'type': 'int'}}},
         }
     )
-    assert v.validate_test({'FieldA': 1}) == ({'field_a': 1}, {}, {'field_a'})
+    assert v.validate_test({'FieldA': 1}) == ({'field_a': 1}, None, {'field_a'})
 
 
 def test_with_default_factory():