Add types to multiprocessing/reduction.pyi (#9171)

stdlib/multiprocessing/reduction.pyi

@@ -1,9 +1,14 @@
 import pickle
 import sys
-from _typeshed import HasFileno, Incomplete
+from _typeshed import HasFileno, SupportsWrite
 from abc import ABCMeta
+from builtins import type as Type  # alias to avoid name clash
+from collections.abc import Callable
 from copyreg import _DispatchTableType
+from multiprocessing import connection
+from pickle import _ReducedType
 from socket import socket
+from typing import Any
 from typing_extensions import Literal
 
 if sys.platform == "win32":
@@ -11,18 +16,20 @@ if sys.platform == "win32":
 else:
     __all__ = ["send_handle", "recv_handle", "ForkingPickler", "register", "dump", "DupFd", "sendfds", "recvfds"]
 
+HAVE_SEND_HANDLE: bool
+
 class ForkingPickler(pickle.Pickler):
     dispatch_table: _DispatchTableType
-    def __init__(self, *args) -> None: ...
+    def __init__(self, file: SupportsWrite[bytes], protocol: int | None = ...) -> None: ...
     @classmethod
-    def register(cls, type, reduce) -> None: ...
+    def register(cls, type: Type, reduce: Callable[[Any], _ReducedType]) -> None: ...
     @classmethod
-    def dumps(cls, obj, protocol: Incomplete | None = ...): ...
+    def dumps(cls, obj: Any, protocol: int | None = ...) -> memoryview: ...
     loads = pickle.loads
 
 register = ForkingPickler.register
 
-def dump(obj, file, protocol: Incomplete | None = ...) -> None: ...
+def dump(obj: Any, file: SupportsWrite[bytes], protocol: int | None = ...) -> None: ...
 
 if sys.platform == "win32":
     if sys.version_info >= (3, 8):
@@ -32,13 +39,13 @@ if sys.platform == "win32":
     else:
         def duplicate(handle: int, target_process: int | None = ..., inheritable: bool = ...) -> int: ...
 
-    def steal_handle(source_pid, handle): ...
-    def send_handle(conn, handle, destination_pid) -> None: ...
-    def recv_handle(conn): ...
+    def steal_handle(source_pid: int, handle: int) -> int: ...
+    def send_handle(conn: connection.PipeConnection, handle: int, destination_pid: int) -> None: ...
+    def recv_handle(conn: connection.PipeConnection) -> int: ...
 
     class DupHandle:
-        def __init__(self, handle, access, pid: Incomplete | None = ...) -> None: ...
-        def detach(self): ...
+        def __init__(self, handle: int, access: int, pid: int | None = ...) -> None: ...
+        def detach(self) -> int: ...
 
 else:
     if sys.platform == "darwin":
@@ -47,10 +54,11 @@ else:
         ACKNOWLEDGE: Literal[False]
 
     def recvfds(sock: socket, size: int) -> list[int]: ...
-    def send_handle(conn, handle, destination_pid) -> None: ...
+    # destination_pid is unused
+    def send_handle(conn: HasFileno, handle: int, destination_pid: object) -> None: ...
     def recv_handle(conn: HasFileno) -> int: ...
-    def sendfds(sock, fds) -> None: ...
-    def DupFd(fd): ...
+    def sendfds(sock: socket, fds: list[int]) -> None: ...
+    def DupFd(fd: int) -> Any: ...  # Return type is really hard to get right
 
 # These aliases are to work around pyright complaints.
 # Pyright doesn't like it when a class object is defined as an alias
@@ -84,4 +92,5 @@ class AbstractReducer(metaclass=ABCMeta):
         sendfds = _sendfds
         recvfds = _recvfds
         DupFd = _DupFd
-    def __init__(self, *args) -> None: ...
+    # *args are unused
+    def __init__(self, *args: object) -> None: ...