ensure "sqlalchemy" info set for all considered classes

Fixed issue in mypy plugin where columns on a mixin would not be correctly
interpreted if the mapped class relied upon a ``__tablename__`` routine
that came from a superclass.

Fixes: #6937
Change-Id: I74aed4862d0545008ee67f781aaa794ab6866926

2 files changed, 7 insertions, 0 deletions

diff --git a/lib/sqlalchemy/ext/mypy/decl_class.py b/lib/sqlalchemy/ext/mypy/decl_class.py
index 23c78aa51..b85ec0f69 100644
--- a/lib/sqlalchemy/ext/mypy/decl_class.py
+++ b/lib/sqlalchemy/ext/mypy/decl_class.py
@@ -61,6 +61,9 @@ def scan_declarative_assignments_and_apply_types(
         List[util.SQLAlchemyAttribute]
     ] = util.get_mapped_attributes(info, api)
 
+    # used by assign.add_additional_orm_attributes among others
+    util.establish_as_sqlalchemy(info)
+
     if mapped_attributes is not None:
         # ensure that a class that's mapped is always picked up by
         # its mapped() decorator or declarative metaclass before
diff --git a/lib/sqlalchemy/ext/mypy/util.py b/lib/sqlalchemy/ext/mypy/util.py
index 614805d77..a3825f175 100644
--- a/lib/sqlalchemy/ext/mypy/util.py
+++ b/lib/sqlalchemy/ext/mypy/util.py
@@ -99,6 +99,10 @@ def _get_info_mro_metadata(info: TypeInfo, key: str) -> Optional[Any]:
     return None
 
 
+def establish_as_sqlalchemy(info: TypeInfo) -> None:
+    info.metadata.setdefault("sqlalchemy", {})
+
+
 def set_is_base(info: TypeInfo) -> None:
     _set_info_metadata(info, "is_base", True)