Type[T] -> T has a strange behaviour

This bug report is coming from https://github.com/python/mypy/issues/8946 and https://github.com/ltworf/typedload/issues/132

Basically the pattern

def f(t: Type[T]) -> T: ...

Works for some types but not others, and I can't see a pattern. For example it will work for a NamedTuple but not for a Tuple.

See this example:

from typing import *
from dataclasses import dataclass
T = TypeVar('T')

@dataclass
class P:
    a: int

class Q(NamedTuple):
    a: int

def create(t: Type[T]) -> T:    ...

# These ones work
reveal_type(create(int))
reveal_type(create(str))
reveal_type(create(List[int]))
reveal_type(create(Dict[int, int]))
reveal_type(create(Q))
reveal_type(create(P))

# These do not
reveal_type(create(Tuple[int]))
reveal_type(create(Union[int,str]))
reveal_type(create(Optional[int]))

Now in the older mypy, the ones that do not work would just be understood as Any, which is absolutely not the intended behaviour. In the latest release instead they fail with error: Argument 1 to "create" has incompatible type "object"; expected "Type[<nothing>]" (and I have no idea of what this means).

Anyway in my view, all of the examples provided should work.

In case I'm wrong, then none of them should work, and probably a way to achieve this is needed.

Background: I am working on a library to load json-like things into more typed classes, and it promises to either return an object of the wanted type, or fail with an exception.

提供された Python 再現コードから始め、各 reveal_type 呼び出しに対して mypy を実行し、動作するケースを Tuple[int]、Union[int, str]、Optional[int] と比較します。それらの呼び出しで Type[T] と TypeVar[T] がどのように推論されるかを追跡します。例で一貫した意図どおりの推論型が得られるか、またはサポートされる動作が明確に文書化され、回帰テストでカバーされれば完了です。