Delete pushers after calling on_logged_out module hook on device delete

Author: Mathieu Velten

changelog.d/15410.bugfix

@@ -0,0 +1 @@
+Fix untold assumption that `on_logged_out` module hooks will be called before pushers deletion.

docs/modules/password_auth_provider_callbacks.md

@@ -103,6 +103,9 @@ Called during a logout request for a user. It is passed the qualified user ID, t
 deactivated device (if any: access tokens are occasionally created without an associated
 device ID), and the (now deactivated) access token.
 
+Deleting the related pushers is done after calling `on_logged_out`, so you can rely on them
+to still be present.
+
 If multiple modules implement this callback, Synapse runs them all in order.
 
 ### `get_username_for_registration`

synapse/handlers/device.py

@@ -513,8 +513,6 @@ async def delete_devices(self, user_id: str, device_ids: List[str]) -> None:
             else:
                 raise
 
-        await self.hs.get_pusherpool().remove_pushers_by_devices(user_id, device_ids)
-
         # Delete data specific to each device. Not optimised as it is not
         # considered as part of a critical path.
         for device_id in device_ids:
@@ -533,6 +531,10 @@ async def delete_devices(self, user_id: str, device_ids: List[str]) -> None:
                     f"org.matrix.msc3890.local_notification_settings.{device_id}",
                 )
 
+        # Pushers are deleted after `delete_access_tokens_for_user` is called so that
+        # modules using `on_logged_out` hook can use them if needed.
+        await self.hs.get_pusherpool().remove_pushers_by_devices(user_id, device_ids)
+
         await self.notify_device_update(user_id, device_ids)
 
     async def update_device(self, user_id: str, device_id: str, content: dict) -> None: