Update mypy to 0.950 and fix complaints (#12650)

5 files changed, 43 insertions, 14 deletions

diff --git a/synapse/appservice/api.py b/synapse/appservice/api.py
index adc6b074da..d19f8dd996 100644
--- a/synapse/appservice/api.py
+++ b/synapse/appservice/api.py
@@ -17,6 +17,7 @@ import urllib.parse
 from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Tuple
 
 from prometheus_client import Counter
+from typing_extensions import TypeGuard
 
 from synapse.api.constants import EventTypes, Membership, ThirdPartyEntityKind
 from synapse.api.errors import CodeMessageException
@@ -66,7 +67,7 @@ def _is_valid_3pe_metadata(info: JsonDict) -> bool:
     return True
 
 
-def _is_valid_3pe_result(r: JsonDict, field: str) -> bool:
+def _is_valid_3pe_result(r: object, field: str) -> TypeGuard[JsonDict]:
     if not isinstance(r, dict):
         return False
 
diff --git a/synapse/config/appservice.py b/synapse/config/appservice.py
index b13cc6bb6e..24498e7944 100644
--- a/synapse/config/appservice.py
+++ b/synapse/config/appservice.py
@@ -55,7 +55,8 @@ def load_appservices(
 ) -> List[ApplicationService]:
     """Returns a list of Application Services from the config files."""
     if not isinstance(config_files, list):
-        logger.warning("Expected %s to be a list of AS config files.", config_files)
+        # type-ignore: this function gets arbitrary json value; we do use this path.
+        logger.warning("Expected %s to be a list of AS config files.", config_files)  # type: ignore[unreachable]
         return []
 
     # Dicts of value -> filename
diff --git a/synapse/events/presence_router.py b/synapse/events/presence_router.py
index a58f313e8b..98555c8c0c 100644
--- a/synapse/events/presence_router.py
+++ b/synapse/events/presence_router.py
@@ -147,7 +147,9 @@ class PresenceRouter:
         # run all the callbacks for get_users_for_states and combine the results
         for callback in self._get_users_for_states_callbacks:
             try:
-                result = await callback(state_updates)
+                # Note: result is an object here, because we don't trust modules to
+                # return the types they're supposed to.
+                result: object = await callback(state_updates)
             except Exception as e:
                 logger.warning("Failed to run module API callback %s: %s", callback, e)
                 continue
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 95a89ac01f..c28b792e6f 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1427,7 +1427,7 @@ class EventCreationHandler:
             # Validate a newly added alias or newly added alt_aliases.
 
             original_alias = None
-            original_alt_aliases: List[str] = []
+            original_alt_aliases: object = []
 
             original_event_id = event.unsigned.get("replaces_state")
             if original_event_id:
@@ -1455,6 +1455,7 @@ class EventCreationHandler:
             # If the old version of alt_aliases is of an unknown form,
             # completely replace it.
             if not isinstance(original_alt_aliases, (list, tuple)):
+                # TODO: check that the original_alt_aliases' entries are all strings
                 original_alt_aliases = []
 
             # Check that each alias is currently valid.
diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py
index f61396bb79..298809742a 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -28,11 +28,11 @@ from typing import (
     Type,
     TypeVar,
     Union,
-    cast,
 )
 
 from prometheus_client import Metric
 from prometheus_client.core import REGISTRY, Counter, Gauge
+from typing_extensions import ParamSpec
 
 from twisted.internet import defer
 
@@ -256,24 +256,48 @@ def run_as_background_process(
         return defer.ensureDeferred(run())
 
 
-F = TypeVar("F", bound=Callable[..., Awaitable[Optional[Any]]])
+P = ParamSpec("P")
 
 
-def wrap_as_background_process(desc: str) -> Callable[[F], F]:
-    """Decorator that wraps a function that gets called as a background
-    process.
+def wrap_as_background_process(
+    desc: str,
+) -> Callable[
+    [Callable[P, Awaitable[Optional[R]]]],
+    Callable[P, "defer.Deferred[Optional[R]]"],
+]:
+    """Decorator that wraps an asynchronous function `func`, returning a synchronous
+    decorated function. Calling the decorated version runs `func` as a background
+    process, forwarding all arguments verbatim.
+
+    That is,
+
+        @wrap_as_background_process
+        def func(*args): ...
+        func(1, 2, third=3)
+
+    is equivalent to:
+
+        def func(*args): ...
+        run_as_background_process(func, 1, 2, third=3)
 
-    Equivalent to calling the function with `run_as_background_process`
+    The former can be convenient if `func` needs to be run as a background process in
+    multiple places.
     """
 
-    def wrap_as_background_process_inner(func: F) -> F:
+    def wrap_as_background_process_inner(
+        func: Callable[P, Awaitable[Optional[R]]]
+    ) -> Callable[P, "defer.Deferred[Optional[R]]"]:
         @wraps(func)
         def wrap_as_background_process_inner_2(
-            *args: Any, **kwargs: Any
+            *args: P.args, **kwargs: P.kwargs
         ) -> "defer.Deferred[Optional[R]]":
-            return run_as_background_process(desc, func, *args, **kwargs)
+            # type-ignore: mypy is confusing kwargs with the bg_start_span kwarg.
+            #     Argument 4 to "run_as_background_process" has incompatible type
+            #     "**P.kwargs"; expected "bool"
+            # See https://github.com/python/mypy/issues/8862
+            return run_as_background_process(desc, func, *args, **kwargs)  # type: ignore[arg-type]
 
-        return cast(F, wrap_as_background_process_inner_2)
+        return wrap_as_background_process_inner_2
 
     return wrap_as_background_process_inner