Fix typechecking with twisted trunk (#16121)

.github/workflows/twisted_trunk.yml

@@ -54,8 +54,8 @@ jobs:
           poetry remove twisted
           poetry add --extras tls git+https://github.com/twisted/twisted.git#${{ inputs.twisted_ref || 'trunk' }}
           poetry install --no-interaction --extras "all test"
-      - name: Remove warn_unused_ignores from mypy config
-        run: sed '/warn_unused_ignores = True/d' -i mypy.ini
+      - name: Remove unhelpful options from mypy config
+        run: sed -e '/warn_unused_ignores = True/d' -e '/warn_redundant_casts = True/d' -i mypy.ini
       - run: poetry run mypy
 
   trial:

changelog.d/16121.misc

@@ -0,0 +1 @@
+Attempt to fix the twisted trunk job.

synapse/handlers/message.py

@@ -1474,10 +1474,10 @@ 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]
-        result, _ = await make_deferred_yieldable(
-            gather_results(
-                (
+        #
+        # 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,
@@ -1488,9 +1488,9 @@ class EventCreationHandler:
             run_in_background(
                 self.cache_joined_hosts_for_events, events_and_context
             ).addErrback(log_failure, "cache_joined_hosts_for_event failed"),
-                ),
-                consumeErrors=True,
         )
+        result, _ = await make_deferred_yieldable(
+            gather_results(deferreds, consumeErrors=True)
         ).addErrback(unwrapFirstError)
 
         return result

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

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]]

tests/util/test_async_helpers.py

@@ -60,11 +60,9 @@ class ObservableDeferredTest(TestCase):
         observer1.addBoth(check_called_first)
 
         # store the results
-        results: List[Optional[ObservableDeferred[int]]] = [None, None]
+        results: List[Optional[int]] = [None, None]
 
-        def check_val(
-            res: ObservableDeferred[int], idx: int
-        ) -> ObservableDeferred[int]:
+        def check_val(res: int, idx: int) -> int:
             results[idx] = res
             return res
 
@@ -93,14 +91,14 @@ class ObservableDeferredTest(TestCase):
         observer1.addBoth(check_called_first)
 
         # store the results
-        results: List[Optional[ObservableDeferred[str]]] = [None, None]
+        results: List[Optional[Failure]] = [None, None]
 
-        def check_val(res: ObservableDeferred[str], idx: int) -> None:
+        def check_failure(res: Failure, idx: int) -> None:
             results[idx] = res
             return None
 
-        observer1.addErrback(check_val, 0)
-        observer2.addErrback(check_val, 1)
+        observer1.addErrback(check_failure, 0)
+        observer2.addErrback(check_failure, 1)
 
         try:
             raise Exception("gah!")