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JukkaL opened this issue Mar 23, 2022 · 2 comments · Fixed by #12435
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Let overload item have a wider return type than implementation #12434

JukkaL opened this issue Mar 23, 2022 · 2 comments · Fixed by #12435
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@JukkaL
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feature topic-overloads

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@JukkaL
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JukkaL commented Mar 23, 2022

A wider return type can be useful if a decorator gets a more precise error type as part of a typeshed update.

@wrobell reported this concrete example in #12021 (comment):

import typing as tp
from contextlib import asynccontextmanager

T = tp.TypeVar('T')

@tp.overload
def f() -> tp.AsyncContextManager[int]:
    ...

@tp.overload
def f(cls: type[T]) -> tp.AsyncContextManager[T]:
    ...

@asynccontextmanager
async def f(cls=int):
    yield 1

Mypy 0.940 got a more precise type for @asynccontextmanager, and this resulted in apparent false positives:

tp.py:14: error: Overloaded function implementation cannot produce return type of signature 1
tp.py:14: error: Overloaded function implementation cannot produce return type of signature 2

I think that we can allow an overload item to have a more general return type than the implementation, for convenience.
@JukkaL JukkaL added the feature label Mar 23, 2022
@JukkaL JukkaL self-assigned this Mar 23, 2022
JukkaL added a commit that referenced this issue Mar 23, 2022
@JukkaL
Let overload item have a wider return type than implementation
59ed20e 
A wider return type can be useful if a decorator used for the overload
implementation gets a more precise return type as part of a typeshed
update.

Closes #12434.
@JukkaL JukkaL mentioned this issue Mar 23, 2022
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8000
@pranavrajpal
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This seems like the same issue as #11373.

JukkaL added a commit that referenced this issue Mar 24, 2022
@JukkaL
Let overload item have a wider return type than implementation (#12435)
1772a4c 
A wider return type can be useful if a decorator used for the overload
implementation gets a more precise return type as part of a typeshed
update.

Closes #12434.
@JukkaL
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JukkaL commented Mar 24, 2022

@pranavrajpal Correct! I also closed #11373.

JukkaL added a commit that referenced this issue Mar 24, 2022
@JukkaL
Let overload item have a wider return type than implementation (#12435)
1c83668 
A wider return type can be useful if a decorator used for the overload
implementation gets a more precise return type as part of a typeshed
update.

Closes #12434.
@KotlinIsland KotlinIsland mentioned this issue Apr 26, 2022
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Let overload item have a wider return type than implementation python/mypy
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@JukkaL @AlexWaygood @pranavrajpal
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