Make it work when using a type annotation on the model_config (#6136)

pydantic/_internal/_fields.py

@@ -92,6 +92,11 @@ def collect_model_fields(  # noqa: C901
 
     class_vars: set[str] = set()
     for ann_name, ann_type in type_hints.items():
+        if ann_name == 'model_config':
+            # We never want to treat `model_config` as a field
+            # Note: we may need to change this logic if/when we introduce a `BareModel` class with no
+            # protected namespaces (where `model_config` might be allowed as a field name)
+            continue
         for protected_namespace in config_wrapper.protected_namespaces:
             if ann_name.startswith(protected_namespace):
                 raise NameError(f'Field "{ann_name}" has conflict with protected namespace "{protected_namespace}"')

tests/test_config.py

@@ -622,3 +622,13 @@ def test_config_wrapper_get_item():
     assert config_wrapper.title == 'test'
     with pytest.raises(AttributeError, match="Config has no attribute 'test'"):
         config_wrapper.test
+
+
+def test_config_inheritance_with_annotations():
+    class Parent(BaseModel):
+        model_config: ConfigDict = {'extra': 'allow'}
+
+    class Child(Parent):
+        model_config: ConfigDict = {'str_to_lower': True}
+
+    assert Child.model_config == {'extra': 'allow', 'str_to_lower': True}