The error message caused by setting the covariant type variable of TypeVar to functions should be more specific #20360
Description
*Memo:
mypy --strict test.py- mypy 1.18.2
- Python 3.14.0
- Windows 11
Setting the covariant type variable of TypeVar to functions' parameters gets the error message except for __init__, __new__, and instance method's self as shown below:
from typing import TypeVar, Generic, cast, Type
class MyCls(Generic[T]):
# ↓↓↓↓↓↓↓↓↓↓↓↓↓ No error
def __init__(self: T, x: T) -> None: ...
# ↓↓↓↓↓↓↓↓↓↓↓↓ No error
def __new__(cls: T, x: T) -> MyCls[T]:
instance = super().__new__(cast(Type[MyCls[T]], cls))
return instance
# ↓↓↓↓↓↓↓ No error
def ins1(self: T) -> None: ...
# ↓↓↓↓ Error
def ins2(self, x: T) -> None: ...
@classmethod
def cls(cls: T, x: T) -> None: ...
# ↑↑↑↑↑↑↑↑↑↑↑↑ Error
@staticmethod
def sta(x: T) -> None: ...
# ↑↑↑↑ Error
def func(x: T) -> None: ...error: Cannot use a covariant type variable as a parameter
So, the error message should be more specific like below:
error: Cannot use a covariant type variable as a parameter except for __init__, __new__, and instance method's self