Improve typing of start_new_thread when called without kwargs (#11446)

stdlib/_dummy_thread.pyi

@@ -1,13 +1,19 @@
 from collections.abc import Callable
 from types import TracebackType
-from typing import Any, NoReturn
+from typing import Any, NoReturn, overload
+from typing_extensions import TypeVarTuple, Unpack
 
 __all__ = ["error", "start_new_thread", "exit", "get_ident", "allocate_lock", "interrupt_main", "LockType", "RLock"]
 
+_Ts = TypeVarTuple("_Ts")
+
 TIMEOUT_MAX: int
 error = RuntimeError
 
-def start_new_thread(function: Callable[..., object], args: tuple[Any, ...], kwargs: dict[str, Any] = {}) -> None: ...
+@overload
+def start_new_thread(function: Callable[[Unpack[_Ts]], object], args: tuple[Unpack[_Ts]]) -> None: ...
+@overload
+def start_new_thread(function: Callable[..., object], args: tuple[Any, ...], kwargs: dict[str, Any]) -> None: ...
 def exit() -> NoReturn: ...
 def get_ident() -> int: ...
 def allocate_lock() -> LockType: ...

stdlib/_thread.pyi

@@ -3,7 +3,10 @@ from _typeshed import structseq
 from collections.abc import Callable
 from threading import Thread
 from types import TracebackType
-from typing import Any, Final, NoReturn, final
+from typing import Any, Final, NoReturn, final, overload
+from typing_extensions import TypeVarTuple, Unpack
+
+_Ts = TypeVarTuple("_Ts")
 
 error = RuntimeError
 
@@ -18,7 +21,10 @@ class LockType:
         self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None
     ) -> None: ...
 
-def start_new_thread(function: Callable[..., object], args: tuple[Any, ...], kwargs: dict[str, Any] = ...) -> int: ...
+@overload
+def start_new_thread(function: Callable[[Unpack[_Ts]], object], args: tuple[Unpack[_Ts]]) -> int: ...
+@overload
+def start_new_thread(function: Callable[..., object], args: tuple[Any, ...], kwargs: dict[str, Any]) -> int: ...
 def interrupt_main() -> None: ...
 def exit() -> NoReturn: ...
 def allocate_lock() -> LockType: ...