Add final type hint to synapse.server. (#15035)

synapse/server.py

@@ -21,7 +21,7 @@
 import abc
 import functools
 import logging
-from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, TypeVar, cast
+from typing import TYPE_CHECKING, Callable, Dict, List, Optional, TypeVar, cast
 
 from twisted.internet.interfaces import IOpenSSLContextFactory
 from twisted.internet.tcp import Port
@@ -144,10 +144,10 @@ if TYPE_CHECKING:
     from synapse.handlers.saml import SamlHandler
 
 
-T = TypeVar("T", bound=Callable[..., Any])
+T = TypeVar("T")
 
 
-def cache_in_self(builder: T) -> T:
+def cache_in_self(builder: Callable[["HomeServer"], T]) -> Callable[["HomeServer"], T]:
     """Wraps a function called e.g. `get_foo`, checking if `self.foo` exists and
     returning if so. If not, calls the given function and sets `self.foo` to it.
 
@@ -166,7 +166,7 @@ def cache_in_self(builder: T) -> T:
     building = [False]
 
     @functools.wraps(builder)
-    def _get(self):
+    def _get(self: "HomeServer") -> T:
         try:
             return getattr(self, depname)
         except AttributeError:
@@ -185,9 +185,7 @@ def cache_in_self(builder: T) -> T:
 
         return dep
 
-    # We cast here as we need to tell mypy that `_get` has the same signature as
-    # `builder`.
-    return cast(T, _get)
+    return _get
 
 
 class HomeServer(metaclass=abc.ABCMeta):