Tuple comparison does not check comparability of element types

[ktbarrett]

Bug Report

When comparing tuples, the comparability of the element isn't taken into account.

To Reproduce

from typing import *

class SupportsGT(Protocol):
    def __gt__(self, other: Any, /) -> bool:
        ...

a = cast(tuple[SupportsGT, ...], ...)
b = cast(tuple[object, ...], ...)
c = a < b  # no issue!

Expected Behavior

There is no matching a_elem.__lt__(b_elem) so this should fail.

Actual Behavior

No error.

Your Environment

Python 3.12
Mypy 1.19.1

[A5rocks]

I haven't looked at typeshed source to confirm my guess, but my first guess is that this is a typeshed issue...

[A5rocks]

Hm, typeshed doesn't seem to allow this. Maybe I'm misinterpreting this signature

https://github.com/python/typeshed/blob/50ec9108eb191ab96d9ab766e506a7c680d5f3d6/stdlib/builtins.pyi#L1052

but it seems to me like tuple[object] shouldn't be allowed here for _T_co=SupportsGT. (so this is a mypy issue)

---

On the other hand, I don't see typeshed checking whether the contained types have a __lt__, so in general mypy not checking comparability is expected.

[ktbarrett]

Ive also checked ty which does the typeshed check correctly and complain. I haven't checked others yet. Seems like a bit of both. But Im not sure if its possible to bound the element wise comparison using the current type system. But mypy's behavior here seems incorrect. Perhaps this is because the bound TypeVar is a Protocol? I can check a bit more once I get into work.

[A5rocks]

ty's behavior is not based on typeshed btw, it's a special case.