Use `ParamSpec` in type hints for `synapse.logging.context` (#12150)

Signed-off-by: Sean Quah <seanq@element.io>

5 files changed, 37 insertions, 25 deletions

diff --git a/changelog.d/12150.misc b/changelog.d/12150.misc
new file mode 100644
index 0000000000..2d2706dac7
--- /dev/null
+++ b/changelog.d/12150.misc
@@ -0,0 +1 @@
+Use `ParamSpec` in type hints for `synapse.logging.context`.
diff --git a/synapse/handlers/initial_sync.py b/synapse/handlers/initial_sync.py
index 316cfae24f..a7db8feb57 100644
--- a/synapse/handlers/initial_sync.py
+++ b/synapse/handlers/initial_sync.py
@@ -153,8 +153,9 @@ class InitialSyncHandler:
 
         public_room_ids = await self.store.get_public_room_ids()
 
-        limit = pagin_config.limit
-        if limit is None:
+        if pagin_config.limit is not None:
+            limit = pagin_config.limit
+        else:
             limit = 10
 
         serializer_options = SerializeEventConfig(as_client_event=as_client_event)
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index c31c2960ad..88cd8a9e1c 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -29,7 +29,6 @@ import warnings
 from types import TracebackType
 from typing import (
     TYPE_CHECKING,
-    Any,
     Awaitable,
     Callable,
     Optional,
@@ -41,7 +40,7 @@ from typing import (
 )
 
 import attr
-from typing_extensions import Literal
+from typing_extensions import Literal, ParamSpec
 
 from twisted.internet import defer, threads
 from twisted.python.threadpool import ThreadPool
@@ -719,32 +718,33 @@ def nested_logging_context(suffix: str) -> LoggingContext:
     )
 
 
+P = ParamSpec("P")
 R = TypeVar("R")
 
 
 @overload
 def preserve_fn(  # type: ignore[misc]
-    f: Callable[..., Awaitable[R]],
-) -> Callable[..., "defer.Deferred[R]"]:
+    f: Callable[P, Awaitable[R]],
+) -> Callable[P, "defer.Deferred[R]"]:
     # The `type: ignore[misc]` above suppresses
     # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
     ...
 
 
 @overload
-def preserve_fn(f: Callable[..., R]) -> Callable[..., "defer.Deferred[R]"]:
+def preserve_fn(f: Callable[P, R]) -> Callable[P, "defer.Deferred[R]"]:
     ...
 
 
 def preserve_fn(
     f: Union[
-        Callable[..., R],
-        Callable[..., Awaitable[R]],
+        Callable[P, R],
+        Callable[P, Awaitable[R]],
     ]
-) -> Callable[..., "defer.Deferred[R]"]:
+) -> Callable[P, "defer.Deferred[R]"]:
     """Function decorator which wraps the function with run_in_background"""
 
-    def g(*args: Any, **kwargs: Any) -> "defer.Deferred[R]":
+    def g(*args: P.args, **kwargs: P.kwargs) -> "defer.Deferred[R]":
         return run_in_background(f, *args, **kwargs)
 
     return g
@@ -752,7 +752,7 @@ def preserve_fn(
 
 @overload
 def run_in_background(  # type: ignore[misc]
-    f: Callable[..., Awaitable[R]], *args: Any, **kwargs: Any
+    f: Callable[P, Awaitable[R]], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     # The `type: ignore[misc]` above suppresses
     # "Overloaded function signatures 1 and 2 overlap with incompatible return types"
@@ -761,18 +761,22 @@ def run_in_background(  # type: ignore[misc]
 
 @overload
 def run_in_background(
-    f: Callable[..., R], *args: Any, **kwargs: Any
+    f: Callable[P, R], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     ...
 
 
-def run_in_background(
+def run_in_background(  # type: ignore[misc]
+    # The `type: ignore[misc]` above suppresses
+    # "Overloaded function implementation does not accept all possible arguments of signature 1"
+    # "Overloaded function implementation does not accept all possible arguments of signature 2"
+    # which seems like a bug in mypy.
     f: Union[
-        Callable[..., R],
-        Callable[..., Awaitable[R]],
+        Callable[P, R],
+        Callable[P, Awaitable[R]],
     ],
-    *args: Any,
-    **kwargs: Any,
+    *args: P.args,
+    **kwargs: P.kwargs,
 ) -> "defer.Deferred[R]":
     """Calls a function, ensuring that the current context is restored after
     return from the function, and that the sentinel context is set once the
@@ -872,7 +876,7 @@ def _set_context_cb(result: ResultT, context: LoggingContext) -> ResultT:
 
 
 def defer_to_thread(
-    reactor: "ISynapseReactor", f: Callable[..., R], *args: Any, **kwargs: Any
+    reactor: "ISynapseReactor", f: Callable[P, R], *args: P.args, **kwargs: P.kwargs
 ) -> "defer.Deferred[R]":
     """
     Calls the function `f` using a thread from the reactor's default threadpool and
@@ -908,9 +912,9 @@ def defer_to_thread(
 def defer_to_threadpool(
     reactor: "ISynapseReactor",
     threadpool: ThreadPool,
-    f: Callable[..., R],
-    *args: Any,
-    **kwargs: Any,
+    f: Callable[P, R],
+    *args: P.args,
+    **kwargs: P.kwargs,
 ) -> "defer.Deferred[R]":
     """
     A wrapper for twisted.internet.threads.deferToThreadpool, which handles
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index b40a7bbb76..1dd39f06cf 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -76,7 +76,8 @@ REQUIREMENTS = [
     "netaddr>=0.7.18",
     "Jinja2>=2.9",
     "bleach>=1.4.3",
-    "typing-extensions>=3.7.4",
+    # We use `ParamSpec`, which was added in `typing-extensions` 3.10.0.0.
+    "typing-extensions>=3.10.0",
     # We enforce that we have a `cryptography` version that bundles an `openssl`
     # with the latest security patches.
     "cryptography>=3.4.7",
diff --git a/synapse/rest/media/v1/storage_provider.py b/synapse/rest/media/v1/storage_provider.py
index 18bf977d3d..1c9b71d69c 100644
--- a/synapse/rest/media/v1/storage_provider.py
+++ b/synapse/rest/media/v1/storage_provider.py
@@ -16,7 +16,7 @@ import abc
 import logging
 import os
 import shutil
-from typing import TYPE_CHECKING, Optional
+from typing import TYPE_CHECKING, Callable, Optional
 
 from synapse.config._base import Config
 from synapse.logging.context import defer_to_thread, run_in_background
@@ -150,8 +150,13 @@ class FileStorageProviderBackend(StorageProvider):
         dirname = os.path.dirname(backup_fname)
         os.makedirs(dirname, exist_ok=True)
 
+        # mypy needs help inferring the type of the second parameter, which is generic
+        shutil_copyfile: Callable[[str, str], str] = shutil.copyfile
         await defer_to_thread(
-            self.hs.get_reactor(), shutil.copyfile, primary_fname, backup_fname
+            self.hs.get_reactor(),
+            shutil_copyfile,
+            primary_fname,
+            backup_fname,
         )
 
     async def fetch(self, path: str, file_info: FileInfo) -> Optional[Responder]: