Add a type hint for `get_device_handler()` and fix incorrect types. (#14055)

This was the last untyped handler from the HomeServer object. Since
it was being treated as Any (and thus unchecked) it was being used
incorrectly in a few places.

1 files changed, 4 insertions, 0 deletions

diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py

index ca1c7a1866..6307fa9c5d 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -38,6 +38,7 @@ from synapse.api.errors import (
 )
 from synapse.appservice import ApplicationService
 from synapse.config.server import is_threepid_reserved
+from synapse.handlers.device import DeviceHandler
 from synapse.http.servlet import assert_params_in_dict
 from synapse.replication.http.login import RegisterDeviceReplicationServlet
 from synapse.replication.http.register import (
@@ -841,6 +842,9 @@ class RegistrationHandler:
         refresh_token = None
         refresh_token_id = None
 
+        # This can only run on the main process.
+        assert isinstance(self.device_handler, DeviceHandler)
+
         registered_device_id = await self.device_handler.check_device_registered(
             user_id,
             device_id,