Stub out the DB2API module

Author: David Robertson

synapse/storage/engines/_base.py

@@ -15,7 +15,7 @@
 from enum import IntEnum
 from typing import Generic, Optional, TypeVar
 
-from synapse.storage.types import Connection
+from synapse.storage.types import Connection, DBAPI2Module
 
 
 class IsolationLevel(IntEnum):
@@ -32,7 +32,7 @@ class IncorrectDatabaseSetup(RuntimeError):
 
 
 class BaseDatabaseEngine(Generic[ConnectionType], metaclass=abc.ABCMeta):
-    def __init__(self, module):
+    def __init__(self, module: DBAPI2Module):
         self.module = module
 
     @property

synapse/storage/types.py

@@ -94,3 +94,23 @@ def __exit__(
         traceback: Optional[TracebackType],
     ) -> Optional[bool]:
         ...
+
+
+class DBAPI2Module(Protocol):
+    """The module-level attributes that we use from PEP 249.
+
+    This is NOT a comprehensive stub for the entire DBAPI2."""
+
+    __name__: str
+
+    Warning: Type[Exception]
+    Error: Type[Exception]
+    DatabaseError: Type[Exception]
+    OperationalError: Type[Exception]
+    IntegrityError: Type[Exception]
+
+    def connect(self, **parameters: object) -> Connection:
+        ...
+
+
+__all__ = ["Cursor", "Connection", "DBAPI2Module"]