Remove unnecessary maybeDeferred calls (#8044)

changelog.d/8044.misc

@@ -0,0 +1 @@
+Convert various parts of the codebase to async/await.

synapse/rest/client/v2_alpha/register.py

@@ -665,7 +665,7 @@ class RegisterRestServlet(RestServlet):
             (object) params: registration parameters, from which we pull
                 device_id, initial_device_name and inhibit_login
         Returns:
-            defer.Deferred: (object) dictionary for response from /register
+            (object) dictionary for response from /register
         """
         result = {"user_id": user_id, "home_server": self.hs.hostname}
         if not params.get("inhibit_login", False):

synapse/rest/consent/consent_resource.py

@@ -22,8 +22,6 @@ from os import path
 import jinja2
 from jinja2 import TemplateNotFound
 
-from twisted.internet import defer
-
 from synapse.api.errors import NotFoundError, StoreError, SynapseError
 from synapse.config import ConfigError
 from synapse.http.server import DirectServeHtmlResource, respond_with_html
@@ -135,7 +133,7 @@ class ConsentResource(DirectServeHtmlResource):
             else:
                 qualified_user_id = UserID(username, self.hs.hostname).to_string()
 
-            u = await defer.maybeDeferred(self.store.get_user_by_id, qualified_user_id)
+            u = await self.store.get_user_by_id(qualified_user_id)
             if u is None:
                 raise NotFoundError("Unknown user")
 

synapse/rest/media/v1/preview_url_resource.py

@@ -28,7 +28,6 @@ from urllib import parse as urlparse
 
 import attr
 
-from twisted.internet import defer
 from twisted.internet.error import DNSLookupError
 
 from synapse.api.errors import Codes, SynapseError
@@ -228,7 +227,7 @@ class PreviewUrlResource(DirectServeJsonResource):
         else:
             logger.info("Returning cached response")
 
-        og = await make_deferred_yieldable(defer.maybeDeferred(observable.observe))
+        og = await make_deferred_yieldable(observable.observe())
         respond_with_json_bytes(request, 200, og, send_cors=True)
 
     async def _do_preview(self, url: str, user: str, ts: int) -> bytes:

synapse/util/caches/descriptors.py

@@ -192,7 +192,7 @@ class Cache(object):
         callbacks = [callback] if callback else []
         self.check_thread()
         observable = ObservableDeferred(value, consumeErrors=True)
-        observer = defer.maybeDeferred(observable.observe)
+        observer = observable.observe()
         entry = CacheEntry(deferred=observable, callbacks=callbacks)
 
         existing_entry = self._pending_deferred_cache.pop(key, None)