Inconsistent narrowing for `builtins.type` and `typing.Type`

The following difference is due to Mypy handling typing.Type via TypeType, for which it does not try to create an intersection, and builtins.type as an Instance, for which it does:

# flags: --python-version 3.9 --warn-unreachable

from typing import Type

t1: Type
t2: type
class C: ...

if isinstance(t1, C):
    reveal_type(t1)  # E: Statement is unreachable
if isinstance(t2, C):
    reveal_type(t2)  # N: Revealed type is "__main__.<subclass of "type" and "C">"

I encountered this problem when working on #16330, which affects type checking a sphinx function.

Interestingly, things are consistent when annotating explicitly with Any:

# flags: --python-version 3.9 --warn-unreachable

from typing import Any, Type

t1: Type[Any]
t2: type[Any]
class C: ...

if isinstance(t1, C):
    reveal_type(t1)  # E: Statement is unreachable
if isinstance(t2, C):
    reveal_type(t2)  # E: Statement is unreachable

So, Mypy maybe misunderstands t2: type?

Inizia con il reproducer nell’issue usando le impostazioni indicate per Python 3.9 e --warn-unreachable. Traccia come Mypy restringe typing.Type tramite TypeType rispetto a builtins.type tramite Instance, quindi confronta il comportamento con gli esempi espliciti di Any. Il lavoro è concluso quando il restringimento incoerente è risolto e i casi mostrati producono diagnostica e tipi rivelati coerenti.