Fix: geoalchemy2.functions type stubs (#481)

geoalchemy2/_functions_helpers.py

@@ -46,7 +46,6 @@ def _generate_stubs() -> str:
 
     header = '''\
 # this file is automatically generated
-from typing import Any
 from typing import List
 
 from sqlalchemy.sql import functions
@@ -67,27 +66,21 @@ def _from_objects(self) -> List[bool]: ...  # type: ignore[override]
     stub_file_parts = [header]
 
     functions = _FUNCTIONS.copy()
-    functions.insert(0, ("ST_AsGeoJSON", str, ST_AsGeoJSON.__doc__))
+    functions.insert(0, ("ST_AsGeoJSON", None, ST_AsGeoJSON.__doc__))
 
     for name, type_, doc_parts in functions:
         doc = _replace_indent(_get_docstring(name, doc_parts, type_), "    ")
 
         if type_ is None:
-            type_str = "Any"
-        elif type_.__module__ == "builtins":
-            type_str = type_.__name__
+            type_str = ""
         else:
-            type_str = f"{type_.__module__}.{type_.__name__}"
+            type_str = f"\n\n    type = {type_.__module__}.{type_.__name__}()"
 
         signature = f'''\
-class _{name}(functions.GenericFunction):
+class {name}(GenericFunction):
     """
     {doc}
-    """
-
-    def __call__(self, *args: Any, **kwargs: Any) -> {type_str}: ...
-
-{name}: _{name}
+    """{type_str}
 '''
         stub_file_parts.append(signature)