Fix up type hints for Twisted 21.7 (#10490)

Mostly this involves decorating a few Deferred declarations with extra type hints. We wrap the types in quotes to avoid runtime errors when running against older versions of Twisted that don't have generics on Deferred.

changelog.d/10490.misc

@@ -0,0 +1 @@
+Fix up type annotations to work with Twisted 21.7.

synapse/http/client.py

@@ -847,7 +847,7 @@ class _ReadBodyWithMaxSizeProtocol(protocol.Protocol):
 
 def read_body_with_max_size(
     response: IResponse, stream: ByteWriteable, max_size: Optional[int]
-) -> defer.Deferred:
+) -> "defer.Deferred[int]":
     """
     Read a HTTP response body to a file-object. Optionally enforcing a maximum file size.
 
@@ -862,7 +862,7 @@ def read_body_with_max_size(
     Returns:
         A Deferred which resolves to the length of the read body.
     """
-    d = defer.Deferred()
+    d: "defer.Deferred[int]" = defer.Deferred()
 
     # If the Content-Length header gives a size larger than the maximum allowed
     # size, do not bother downloading the body.

synapse/replication/tcp/client.py

@@ -285,7 +285,7 @@ class ReplicationDataHandler:
 
         # Create a new deferred that times out after N seconds, as we don't want
         # to wedge here forever.
-        deferred = Deferred()
+        deferred: "Deferred[None]" = Deferred()
         deferred = timeout_deferred(
             deferred, _WAIT_FOR_REPLICATION_TIMEOUT_SECONDS, self._reactor
         )

synapse/util/async_helpers.py

@@ -49,6 +49,8 @@ from synapse.util import Clock, unwrapFirstError
 
 logger = logging.getLogger(__name__)
 
+_T = TypeVar("_T")
+
 
 class ObservableDeferred:
     """Wraps a deferred object so that we can add observer deferreds. These
@@ -121,7 +123,7 @@ class ObservableDeferred:
         effect the underlying deferred.
         """
         if not self._result:
-            d = defer.Deferred()
+            d: "defer.Deferred[Any]" = defer.Deferred()
 
             def remove(r):
                 self._observers.discard(d)
@@ -415,7 +417,7 @@ class ReadWriteLock:
         self.key_to_current_writer: Dict[str, defer.Deferred] = {}
 
     async def read(self, key: str) -> ContextManager:
-        new_defer = defer.Deferred()
+        new_defer: "defer.Deferred[None]" = defer.Deferred()
 
         curr_readers = self.key_to_current_readers.setdefault(key, set())
         curr_writer = self.key_to_current_writer.get(key, None)
@@ -438,7 +440,7 @@ class ReadWriteLock:
         return _ctx_manager()
 
     async def write(self, key: str) -> ContextManager:
-        new_defer = defer.Deferred()
+        new_defer: "defer.Deferred[None]" = defer.Deferred()
 
         curr_readers = self.key_to_current_readers.get(key, set())
         curr_writer = self.key_to_current_writer.get(key, None)
@@ -471,10 +473,8 @@ R = TypeVar("R")
 
 
 def timeout_deferred(
-    deferred: defer.Deferred,
-    timeout: float,
-    reactor: IReactorTime,
-) -> defer.Deferred:
+    deferred: "defer.Deferred[_T]", timeout: float, reactor: IReactorTime
+) -> "defer.Deferred[_T]":
     """The in built twisted `Deferred.addTimeout` fails to time out deferreds
     that have a canceller that throws exceptions. This method creates a new
     deferred that wraps and times out the given deferred, correctly handling
@@ -497,7 +497,7 @@ def timeout_deferred(
     Returns:
         A new Deferred, which will errback with defer.TimeoutError on timeout.
     """
-    new_d = defer.Deferred()
+    new_d: "defer.Deferred[_T]" = defer.Deferred()
 
     timed_out = [False]
 

synapse/util/caches/deferred_cache.py

@@ -16,7 +16,16 @@
 
 import enum
 import threading
-from typing import Callable, Generic, Iterable, MutableMapping, Optional, TypeVar, Union
+from typing import (
+    Callable,
+    Generic,
+    Iterable,
+    MutableMapping,
+    Optional,
+    TypeVar,
+    Union,
+    cast,
+)
 
 from prometheus_client import Gauge
 
@@ -166,7 +175,7 @@ class DeferredCache(Generic[KT, VT]):
     def set(
         self,
         key: KT,
-        value: defer.Deferred,
+        value: "defer.Deferred[VT]",
         callback: Optional[Callable[[], None]] = None,
     ) -> defer.Deferred:
         """Adds a new entry to the cache (or updates an existing one).
@@ -214,7 +223,7 @@ class DeferredCache(Generic[KT, VT]):
         if value.called:
             result = value.result
             if not isinstance(result, failure.Failure):
-                self.cache.set(key, result, callbacks)
+                self.cache.set(key, cast(VT, result), callbacks)
             return value
 
         # otherwise, we'll add an entry to the _pending_deferred_cache for now,

synapse/util/caches/descriptors.py

@@ -413,7 +413,7 @@ class DeferredCacheListDescriptor(_CacheDescriptorBase):
                 # relevant result for that key.
                 deferreds_map = {}
                 for arg in missing:
-                    deferred = defer.Deferred()
+                    deferred: "defer.Deferred[Any]" = defer.Deferred()
                     deferreds_map[arg] = deferred
                     key = arg_to_cache_key(arg)
                     cache.set(key, deferred, callback=invalidate_callback)