fix: type hints on BaseConfig (#1618)

closes #1614

changes/1614-PrettyWood.md

@@ -0,0 +1 @@
+Ensure `SchemaExtraCallable` is always defined to get type hints on BaseConfig.

pydantic/main.py

@@ -66,6 +66,10 @@ def __call__(self, schema: Dict[str, Any], model_class: Type['Model']) -> None:
             pass
 
 
+else:
+    SchemaExtraCallable = Callable[..., None]
+
+
 try:
     import cython  # type: ignore
 except ImportError:

tests/test_main.py

@@ -1,6 +1,6 @@
 import sys
 from enum import Enum
-from typing import Any, Callable, ClassVar, Dict, List, Mapping, Optional, Type
+from typing import Any, Callable, ClassVar, Dict, List, Mapping, Optional, Type, get_type_hints
 from uuid import UUID, uuid4
 
 import pytest
@@ -1133,3 +1133,10 @@ class Model2(BaseModel):
         Model1.parse_obj({})
     with pytest.raises(ValidationError):
         Model2.parse_obj({})
+
+
+def test_base_config_type_hinting():
+    class M(BaseModel):
+        a: int
+
+    get_type_hints(M.__config__)