Difference in behaviour between overload and TypeVars when using functools.update_wrapper

[hajarmitage]

Bug Report

When calling functools.update_wrapper(f, g) where f has a type of TypeVar('T', Type1, Type2), mypy errors incorrectly, saying it expects Callable[[Never], Never] in that spot.

To Reproduce
https://mypy-play.net/?mypy=latest&python=3.12&gist=8b79db2fe7eb042e15122536a393dd43

Expected Behavior

I think f1 and f2 are identical functions. I expect both checks to succeed (as they did on mypy 1.9.0), or possibly both to fail (but if this is an error, I don't see why...).

Actual Behavior

update_wrapper(f1, g) succeeds and update_wrapper(f2, g) errors, with the message Argument 1 to "update_wrapper" has incompatible type "Callable[[T], T]"; expected "Callable[[Never], Never]" [arg-type]

Your Environment

• Mypy version used: 1.9.0 -> 1.10.0
• Python version used: 3.10, 3.12