Add declarative_mixin

In support of
sqlalchemy/sqlalchemy#6147

Author: zzzeek

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = sqlalchemy2-stubs
-version = 0.0.1a4
+version = 0.0.1a5
 description = Typing Stubs for SQLAlchemy 1.4
 long_description = file: README.rst
 long_description_content_type = text/x-rst

sqlalchemy-stubs/orm/__init__.pyi

@@ -10,6 +10,7 @@ from .attributes import QueryableAttribute as QueryableAttribute
 from .context import QueryContext as QueryContext
 from .decl_api import as_declarative as as_declarative
 from .decl_api import declarative_base as declarative_base
+from .decl_api import declarative_mixin as declarative_mixin
 from .decl_api import declared_attr as declared_attr
 from .decl_api import has_inherited_table as has_inherited_table
 from .decl_api import registry as registry

sqlalchemy-stubs/orm/decl_api.pyi

@@ -25,16 +25,6 @@ from ..util import hybridproperty as hybridproperty
 _T = TypeVar("_T")
 
 def has_inherited_table(cls: type) -> bool: ...
-
-class DeclarativeMeta(type):
-    def __init__(
-        cls, classname: Any, bases: Any, dict_: Any, **kw: Any
-    ) -> None: ...
-    def __setattr__(cls, key: Any, value: Any) -> None: ...
-    def __delattr__(cls, key: Any) -> None: ...
-    metadata: MetaData
-    registry: _registry  # Avoid circural reference
-
 def synonym_for(name: Any, map_column: bool = ...): ...
 
 class declared_attr(interfaces._MappedAttribute, property, Generic[_T]):
@@ -50,6 +40,7 @@ class _stateful_declared_attr(declared_attr):
     def __init__(self, **kw: Any) -> None: ...
     def __call__(self, fn: Any): ...
 
+def declarative_mixin(cls: type) -> type: ...
 def declarative_base(
     bind: Optional[
         Any
@@ -98,4 +89,13 @@ class registry:
 
 _registry = registry
 
+class DeclarativeMeta(type):
+    def __init__(
+        cls, classname: Any, bases: Any, dict_: Any, **kw: Any
+    ) -> None: ...
+    def __setattr__(cls, key: Any, value: Any) -> None: ...
+    def __delattr__(cls, key: Any) -> None: ...
+    metadata: MetaData
+    registry: _registry  # Avoid circural reference
+
 def as_declarative(**kw: Any) -> Callable[[Type[_T]], Type[_T]]: ...