improve error raise for dialect/pool events w/ async engine

Fixed issues where a descriptive error message was not raised for some
classes of event listening with an async engine, which should instead be a
sync engine instance.

Change-Id: I00b9f4fe9373ef5fd5464fac10651cc4024f648e

1 files changed, 8 insertions, 2 deletions

diff --git a/lib/sqlalchemy/engine/events.py b/lib/sqlalchemy/engine/events.py
index 0cbf56a6d..699faf489 100644
--- a/lib/sqlalchemy/engine/events.py
+++ b/lib/sqlalchemy/engine/events.py
@@ -779,7 +779,7 @@ class DialectEvents(event.Events[Dialect]):
     @classmethod
     def _accept_with(
         cls, target: Union[Engine, Type[Engine], Dialect, Type[Dialect]]
-    ) -> Union[Dialect, Type[Dialect]]:
+    ) -> Optional[Union[Dialect, Type[Dialect]]]:
         if isinstance(target, type):
             if issubclass(target, Engine):
                 return Dialect
@@ -787,8 +787,14 @@ class DialectEvents(event.Events[Dialect]):
                 return target
         elif isinstance(target, Engine):
             return target.dialect
-        else:
+        elif isinstance(target, Dialect):
             return target
+        elif hasattr(target, "dispatch") and hasattr(
+            target.dispatch._events, "_no_async_engine_events"
+        ):
+            target.dispatch._events._no_async_engine_events()
+        else:
+            return None
 
     def do_connect(
         self,