Wrong types and crash with polymorphic Callable #10244
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It no longer crashes with mypy 0.971, but type checking is still wrong. Interestingly, it can be worked around replacing class Cont(Generic[R]):
@abstractmethod
def run(self, x: X) -> R:
...
def f(c: Cont[R]) -> R:
reveal_type(c.run)
return c.run(3)I have also noticed that revealed type is different this time. Let's add @dataclass
class Box(Generic[T]):
inner: T
@dataclass
class Cont(Generic[R]):
run: Box[Callable[[X], R]]
def f(c: Cont[R]) -> R:
reveal_type(c.run.inner)
return c.run.inner(3)Parameter type is |
This was referenced Nov 14, 2022
ilevkivskyi
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Nov 16, 2022
Fixes #10244 Fixes #13515 This fixes only the crash part, I am going to fix also the embarrassing type variable clash in a separate PR, since it is completely unrelated issue. The crash happens because solver can call `is_suptype()` on the constraint bounds, and those can contain `<Erased>`. Then if it is a generic callable type (e.g. `def [S] (S) -> T` when used as a context is erased to `def [S] (S) -> <Erased>`), `is_subtype()` will try unifying them, causing the crash when applying unified arguments. My fix is to simply allow subtyping between callable types that contain `<Erased>`, we anyway allow checking subtpying between all other types with `<Erased>` components. And this technically can be useful, e.g. `[T <: DerivedGen1[<Erased>], T <: DerivedGen2[<Erased>]]` will be solved as `T <: NonGenBase`. Btw this crash technically has nothing to do with dataclasses, but it looks like there is no other way in mypy to define a callable with generic callable as argument type, if I try: ```python def foo(x: Callable[[S], T]) -> T: ... ``` to repro the crash, mypy instead interprets `foo` as `def [S, T] (x: Callable[[S], T]) -> T`, i.e. the argument type is not generic. I also tried callback protocols, but they also don't repro the crash (at least I can't find a repro), because protocols use variance for subtyping, before actually checking member types.
ilevkivskyi
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Nov 16, 2022
Addresses the non-crash part of #10244 (and similar situations). The `freshen_function_type_vars()` use in `checkmember.py` was inconsistent: * It needs to be applied to attributes too, not just methods * It needs to be a visitor, since generic callable can appear in a nested position The downsides are ~2% performance regression, and people will see more large ids in `reveal_type()` (since refreshing functions uses a global unique counter). But since this is a correctness issue that can cause really bizarre error messages, I think it is totally worth it.
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Crash Report
First of all, the code that makess mypy crash:
Adding type annotation at the last line
c: Cont[str] = Cont(Box(const_two))prevents the crash.There's another problem - mypy gets types in function
fwrong. Herec.run.innerreturns typeR, while mypy insists it must by int.Traceback
To Reproduce
Full source code is in the description.
Your Environment
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