improve typing in inspect (#6020)

stdlib/inspect.pyi

@@ -117,10 +117,14 @@ if sys.version_info >= (3, 10):
 else:
     def signature(obj: Callable[..., Any], *, follow_wrapped: bool = ...) -> Signature: ...
 
+class _void: ...
+class _empty: ...
+
 class Signature:
-    def __init__(self, parameters: Sequence[Parameter] | None = ..., *, return_annotation: Any = ...) -> None: ...
-    # TODO: can we be more specific here?
-    empty: object
+    def __init__(
+        self, parameters: Sequence[Parameter] | None = ..., *, return_annotation: Any = ..., __validate_parameters__: bool = ...
+    ) -> None: ...
+    empty: _empty
     @property
     def parameters(self) -> types.MappingProxyType[str, Parameter]: ...
     # TODO: can we be more specific here?
@@ -128,7 +132,9 @@ class Signature:
     def return_annotation(self) -> Any: ...
     def bind(self, *args: Any, **kwargs: Any) -> BoundArguments: ...
     def bind_partial(self, *args: Any, **kwargs: Any) -> BoundArguments: ...
-    def replace(self: Self, *, parameters: Sequence[Parameter] | None = ..., return_annotation: Any = ...) -> Self: ...
+    def replace(
+        self: Self, *, parameters: Sequence[Parameter] | Type[_void] | None = ..., return_annotation: Any = ...
+    ) -> Self: ...
     if sys.version_info >= (3, 10):
         @classmethod
         def from_callable(
@@ -166,7 +172,7 @@ class _ParameterKind(enum.IntEnum):
 
 class Parameter:
     def __init__(self, name: str, kind: _ParameterKind, *, default: Any = ..., annotation: Any = ...) -> None: ...
-    empty: Any
+    empty: _empty
     name: str
     default: Any
     annotation: Any
@@ -178,7 +184,12 @@ class Parameter:
     KEYWORD_ONLY: ClassVar[Literal[_ParameterKind.KEYWORD_ONLY]]
     VAR_KEYWORD: ClassVar[Literal[_ParameterKind.VAR_KEYWORD]]
     def replace(
-        self: Self, *, name: str | None = ..., kind: _ParameterKind | None = ..., default: Any = ..., annotation: Any = ...
+        self: Self,
+        *,
+        name: str | Type[_void] = ...,
+        kind: _ParameterKind | Type[_void] = ...,
+        default: Any = ...,
+        annotation: Any = ...,
     ) -> Self: ...
 
 class BoundArguments:

tests/stubtest_allowlists/py3_common.txt

@@ -96,13 +96,13 @@ importlib.abc.Loader.exec_module  # See Lib/importlib/_abc.py. Might be defined
 importlib.abc.MetaPathFinder.find_spec  # Not defined on the actual class, but expected to exist.
 importlib.abc.PathEntryFinder.find_spec  # Not defined on the actual class, but expected to exist.
 importlib.machinery.ExtensionFileLoader.get_filename  # Wrapped with _check_name decorator which changes runtime signature
+inspect.Parameter.empty  # set as private marker _empty
 inspect.Parameter.KEYWORD_ONLY
 inspect.Parameter.POSITIONAL_ONLY
 inspect.Parameter.POSITIONAL_OR_KEYWORD
 inspect.Parameter.VAR_KEYWORD
 inspect.Parameter.VAR_POSITIONAL
-inspect.Parameter.replace
-inspect.Signature.replace
+inspect.Signature.empty  # set as private marker _empty
 io.BufferedRandom.truncate
 io.BufferedReader.seek
 io.BufferedReader.truncate