(🐞) No error when overload implementation has incompatible return type

from typing import overload

@overload
def foo(a: int) -> int: ...

@overload
def foo(a: float) -> int: ...

def foo(a: object) -> object:  # no error
    return object()

playground

While the strictest of solutions would be to enforce the return type be an intersection of the overload return types, that would result in being overly strict to the point of being unusable. I suggest enforcing the return type to be a union of the overloads, this is not typesafe, but is much safer than not checking it at all.

首先，在链接的 mypy playground 中复现该示例，并跟踪它所执行的 overload 实现返回类型检查。将完成定义为：针对实现的不兼容返回类型生成诊断，同时保留所述的 overload 预期行为。