Inconsistent errors reported for protocol matching #13850

from typing import Generic, Protocol, TypeVar, overload

_T_co = TypeVar("_T_co", covariant=True)

class _NestedSequence(Protocol[_T_co]):
    @overload
    def __getitem__(self, index: int) -> _T_co | "_NestedSequence[_T_co]":
        ...

    @overload
    def __getitem__(self, index: slice) -> "_NestedSequence[_T_co]":
        ...

    # def __contains__(self, __s: object, /) -> bool:
    #     ...

class MySequence(Generic[_T_co]):
    @overload
    def __getitem__(self, index: int) -> _T_co:
        ...

    @overload
    def __getitem__(self, index: slice) -> "MySequence[_T_co]":
        ...

    def __getitem__(self, index: slice | int) -> "MySequence[_T_co]" | _T_co:
        ...

    def __contains__(self, __s: object, /) -> bool:
        ...

class MySequenceCopy(Generic[_T_co]):
    @overload
    def __getitem__(self, index: int) -> _T_co:
        ...

    @overload
    def __getitem__(self, index: slice) -> "MySequenceCopy[_T_co]":
        ...

    def __getitem__(self, index: slice | int) -> "MySequenceCopy[_T_co]" | _T_co:
        ...

    def __contains__(self, __s: object, /) -> bool:
        ...

def func1_1(x: MySequence[int]):
    _: _NestedSequence[int] = x  # (no error)

def func1_1_copy(x: MySequence[int]):
    _: _NestedSequence[int] = x  # error: Incompatible types in assignment

def func1_2(x: MySequence[MySequence[int]]):
    _: _NestedSequence[int] = x  # (no error)

def func2_1(x: MySequenceCopy[int]):
    _: _NestedSequence[int] = x  # error: Incompatible types in assignment

def func2_1_copy(x: MySequenceCopy[int]):
    _: _NestedSequence[int] = x  # error: Incompatible types in assignment

def func2_2(x: MySequenceCopy[MySequenceCopy[int]]):
    _: _NestedSequence[int] = x  # error: Incompatible types in assignment

a: _NestedSequence[int] = [[1, 2, 3]]  # error: List item 0/1/2 has incompatible type "int"; expected "_NestedSequence[int]"