fix: type Markable is reduced to Any by mypy

This change simplifies the definition of `Markable` so that type information
is not lost and fixes the selection of the overloaded method to use.

Author: terencehonles

src/_pytest/mark/structures.py

@@ -3,6 +3,7 @@
 import warnings
 from typing import Any
 from typing import Callable
+from typing import cast
 from typing import Collection
 from typing import Iterable
 from typing import Iterator
@@ -266,7 +267,7 @@ def combined_with(self, other: "Mark") -> "Mark":
 # A generic parameter designating an object to which a Mark may
 # be applied -- a test function (callable) or class.
 # Note: a lambda is not allowed, but this can't be represented.
-Markable = TypeVar("Markable", bound=Union[Callable[..., object], type])
+Markable = TypeVar("Markable", bound=Callable[..., Any])
 
 
 @attr.s(init=False, auto_attribs=True)
@@ -348,21 +349,21 @@ def with_args(self, *args: object, **kwargs: object) -> "MarkDecorator":
     # return type. Not much we can do about that. Thankfully mypy picks
     # the first match so it works out even if we break the rules.
     @overload
-    def __call__(self, arg: Markable) -> Markable:  # type: ignore[misc]
+    def __call__(self, arg: Markable) -> Markable:
         pass
 
     @overload
-    def __call__(self, *args: object, **kwargs: object) -> "MarkDecorator":
+    def __call__(self, *args: Any, **kwargs: Any) -> "MarkDecorator":
         pass
 
-    def __call__(self, *args: object, **kwargs: object):
+    def __call__(self, *args: Any, **kwargs: Any) -> Union[Markable, "MarkDecorator"]:
         """Call the MarkDecorator."""
         if args and not kwargs:
             func = args[0]
             is_class = inspect.isclass(func)
             if len(args) == 1 and (istestfunc(func) or is_class):
                 store_mark(func, self.mark)
-                return func
+                return cast(Markable, func)
         return self.with_args(*args, **kwargs)