Internal Error due to overloaded generic method? #13515
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Slightly more minimal repro: from __future__ import annotations
from typing import Protocol, TypeVar, overload
_KT_contra = TypeVar("_KT_contra", contravariant=True)
_VT_co = TypeVar("_VT_co", covariant=True)
_T = TypeVar("_T")
class MappingProtocol(Protocol[_KT_contra, _VT_co]):
@overload
def get(self, key: _KT_contra) -> _VT_co | None: ...
@overload
def get(self, key: _KT_contra, default: _VT_co | _T) -> _VT_co | _T: ...
def do_thing(stuff: MappingProtocol[_KT_contra, _VT_co]) -> None: ...
do_thing({"foo": None})https://mypy-play.net/?mypy=latest&python=3.10&flags=strict&gist=cebf8bc0e851ea6fa3b52d6d3639096d |
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Thanks! I will take a look today. |
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So, I was finally able to dig into this issue. What happens?
But, the question is: why does it happen? Right now I still have no idea. |
ilevkivskyi
added a commit
that referenced
this issue
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.
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Bug Report
I ran into an internal error that seems to be related to type inference with an overloaded method. Apologies for the bland description but I don't know mypy internals well enough to debug further.
To Reproduce
Create a py file with the following code and run it through mypy with no arguments:
Running mypy on the file will crash at line 35 (in the
this_causes_mypy_to_crashmethod) even on the current dev build:Expected Behavior
Successfully run and tell me if I have any lint errors.
Actual Behavior
Crashes with Internal Error
Environment
mypy.ini: noneThe text was updated successfully, but these errors were encountered: