[spec] overload subtyping rules are too strict.

The typing spec states that, when A and B are potentially overloaded methods

If a callable B is overloaded with two or more signatures, it is assignable to callable A if at least one of the overloaded signatures in B is assignable to A

If a callable A is overloaded with two or more signatures, callable B is assignable to A if B is assignable to all of the signatures in A

However, this definition seems to be too strict. Consider the following example:

from typing import Protocol, Self, overload

class IntScalarOurs(Protocol):
    def __add__(self, other: int | Self, /) -> Self: ...

class IntScalarTheirs(Protocol):
    @overload
    def __add__(self, other: int, /) -> Self: ...
    @overload
    def __add__(self, other: Self, /) -> Self: ...

These two protocols specify the exact same runtime behavior. Yet, following the rules of the spec, IntScalarOurs is assignable to IntScalarTheirs, but IntScalarTheirs is not assignable to IntScalarOurs.

From a pure set-theoretic POV, it seems that subtyping functions should follow a very simply rule based on the domain.

$f <: g$ if and only if $\text{dom}(f) ⊇ \text{dom}(g)$ and $f(x) <: g(x)$ for all $x∈\text{dom}(g)$

What is currently specced appears to be a lemma for a sufficient condition, but not a necessary one.
Individual type-checkers can of course use such lemmas if the general case is too difficult to check/implement (and communicate that to their users), but shouldn't the spec be biased towards the theoretically principled point of view, when applicable?

Related Discussions

https://github.com/python/typing/discussions/1782

Bắt đầu với các quy tắc kiểu con của overload trong phần callables của đặc tả typing và xem lại cuộc thảo luận liên quan tại typing/discussions/1782. So sánh các quy tắc đã nêu với ví dụ IntScalarOurs và IntScalarTheirs, sau đó xác định xem đặc tả có cần một bản sửa đổi mang tính nguyên tắc hay một quy tắc về điều kiện đủ được làm rõ hay không.