Join of actual Class with Type[Class] results in `object`

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Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
python
领域
compilers

调研方向

Start with the provided Python reproducer and trace mypy's handling of the conditional-expression type join involving the actual Foo class and Type[Foo]. Run the example to confirm the revealed type and call error; done means the expression is inferred as Type[Foo], Foo can be called, and the existing reversed-order and cls or Foo cases remain covered.

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描述

bug priority-1-normal

This file:

from typing import Type, Optional

class Foo:
    pass

def make_foo(cls: Optional[Type[Foo]] = None) -> Foo:
    x = Foo if cls is None else cls
    reveal_type(x)
    return x()

gives the following:

typeofclass.py:10: error: Revealed type is 'builtins.object' 
typeofclass.py:11: error: "object" not callable

This example is superficially related to #3487, in that it uses an if/else expression to make mypy perform a type join, but the distinct bug here is that joining Foo (the actual class object) with Type[Foo] should result in Type[Foo], but instead results in object.

This is related to the fact that class objects are typed as callables instead of as Type[Class].

Oddly reversing Foo if cls is None else cls to cls if cls is not None else Foo results in builtin.type instead of object, which is still wrong, but differently wrong.

Using cls or Foo results in Type[Foo].

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