Fix typechecking with twisted trunk (#16121)

3 files changed, 27 insertions, 26 deletions

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index a74db1dccf..3184bfb047 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1474,23 +1474,23 @@ class EventCreationHandler:
 
         # We now persist the event (and update the cache in parallel, since we
         # don't want to block on it).
-        event, context = events_and_context[0]
+        #
+        # Note: mypy gets confused if we inline dl and check with twisted#11770.
+        # Some kind of bug in mypy's deduction?
+        deferreds = (
+            run_in_background(
+                self._persist_events,
+                requester=requester,
+                events_and_context=events_and_context,
+                ratelimit=ratelimit,
+                extra_users=extra_users,
+            ),
+            run_in_background(
+                self.cache_joined_hosts_for_events, events_and_context
+            ).addErrback(log_failure, "cache_joined_hosts_for_event failed"),
+        )
         result, _ = await make_deferred_yieldable(
-            gather_results(
-                (
-                    run_in_background(
-                        self._persist_events,
-                        requester=requester,
-                        events_and_context=events_and_context,
-                        ratelimit=ratelimit,
-                        extra_users=extra_users,
-                    ),
-                    run_in_background(
-                        self.cache_joined_hosts_for_events, events_and_context
-                    ).addErrback(log_failure, "cache_joined_hosts_for_event failed"),
-                ),
-                consumeErrors=True,
-            )
+            gather_results(deferreds, consumeErrors=True)
         ).addErrback(unwrapFirstError)
 
         return result
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index f62bea968f..64c6ae4512 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -809,23 +809,24 @@ def run_in_background(  # type: ignore[misc]
 
     # `res` may be a coroutine, `Deferred`, some other kind of awaitable, or a plain
     # value. Convert it to a `Deferred`.
+    d: "defer.Deferred[R]"
     if isinstance(res, typing.Coroutine):
         # Wrap the coroutine in a `Deferred`.
-        res = defer.ensureDeferred(res)
+        d = defer.ensureDeferred(res)
     elif isinstance(res, defer.Deferred):
-        pass
+        d = res
     elif isinstance(res, Awaitable):
         # `res` is probably some kind of completed awaitable, such as a `DoneAwaitable`
         # or `Future` from `make_awaitable`.
-        res = defer.ensureDeferred(_unwrap_awaitable(res))
+        d = defer.ensureDeferred(_unwrap_awaitable(res))
     else:
         # `res` is a plain value. Wrap it in a `Deferred`.
-        res = defer.succeed(res)
+        d = defer.succeed(res)
 
-    if res.called and not res.paused:
+    if d.called and not d.paused:
         # The function should have maintained the logcontext, so we can
         # optimise out the messing about
-        return res
+        return d
 
     # The function may have reset the context before returning, so
     # we need to restore it now.
@@ -843,8 +844,8 @@ def run_in_background(  # type: ignore[misc]
     # which is supposed to have a single entry and exit point. But
     # by spawning off another deferred, we are effectively
     # adding a new exit point.)
-    res.addBoth(_set_context_cb, ctx)
-    return res
+    d.addBoth(_set_context_cb, ctx)
+    return d
 
 
 T = TypeVar("T")
@@ -877,7 +878,7 @@ def make_deferred_yieldable(deferred: "defer.Deferred[T]") -> "defer.Deferred[T]
 ResultT = TypeVar("ResultT")
 
 
-def _set_context_cb(result: ResultT, context: LoggingContext) -> ResultT:
+def _set_context_cb(result: ResultT, context: LoggingContextOrSentinel) -> ResultT:
     """A callback function which just sets the logging context"""
     set_current_context(context)
     return result
diff --git a/synapse/util/caches/deferred_cache.py b/synapse/util/caches/deferred_cache.py
index bf7bd351e0..029eedcc6f 100644
--- a/synapse/util/caches/deferred_cache.py
+++ b/synapse/util/caches/deferred_cache.py
@@ -470,7 +470,7 @@ class CacheMultipleEntries(CacheEntry[KT, VT]):
     def deferred(self, key: KT) -> "defer.Deferred[VT]":
         if not self._deferred:
             self._deferred = ObservableDeferred(defer.Deferred(), consumeErrors=True)
-        return self._deferred.observe().addCallback(lambda res: res.get(key))
+        return self._deferred.observe().addCallback(lambda res: res[key])
 
     def add_invalidation_callback(
         self, key: KT, callback: Optional[Callable[[], None]]