invalid-argument-type for annotated `self` argument when a generic context exists

[Glyphack]

This came up as part of astral-sh/ruff#18007. Since it can be reproduced on main I created a separate issue & PR to check ecosystem changes.

Normally annotated self accepts instance of that class a valid argument:

from typing import Self

class C:
    def m(self: Self, x: int) -> None: ...

c: C = C()
c.m(1)

But if the method has generics then this would not work:

from typing import Self
class C:
    def m[S](self: Self, x: S) -> None: ...

c: C[int] = C()
# error: [invalid-argument-type] "Argument to bound method `m` is incorrect: Expected `Self@m`, found `C`"
c.m(1)

[sharkdp]

c: C[int] = C()

I know it's not the key issue here, but it also looks like a bug that you're allowed to declare this as C[int] when C itself is not a generic class. You can probably remove that annotation from your example.

[sharkdp]

In the following example, we can see how Self vanishes from the generic context when using a PEP 695 typevar:

https://play.ty.dev/7208eaba-cf11-4352-9c9c-46f6968f3aa3

from typing import Self, TypeVar, reveal_type
from ty_extensions import generic_context

_T = TypeVar("_T")


class C:
    def method_with_non_generic_param(self: Self, x: int) -> None: ...
    def method_with_legacy_typevar(self: Self, x: _T) -> None: ...
    def method_with_pep695_typevar[T](self: Self, x: T) -> None: ...


reveal_type(generic_context(C.method_with_non_generic_param))  # tuple[Self@method_with_non_generic_param]
reveal_type(generic_context(C.method_with_legacy_typevar))  # tuple[Self@method_with_legacy_typevar, _T@method_with_legacy_typevar]
reveal_type(generic_context(C.method_with_pep695_typevar))  # tuple[T@method_with_pep695_typevar]