False Positive for covariant when using T | None
#4613
Comments
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Could a pylance team member please transfer to the pyright project? This is a core type checker issue. |
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Here's a simplified repro: from typing import TypeVar, Protocol
T = TypeVar("T")
T_co = TypeVar("T_co", covariant=True)
class FalsePositive(Protocol[T]):
var: T | None
class Positive(Protocol[T_co]):
var: T_co | NoneAnd here's an even simpler repro that demonstrates the underlying problem: from typing import TypeVar
T = TypeVar("T")
def func(x: list[T | None]) -> T | None:
y: list[object | None] = x # This should generate an error but does not
return x[0] |
erictraut
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Jul 17, 2023
…one` type to `object | None` in an invariant context. This same bug led to issues with the validation of TypeVar variance within a Protocol. This addresses microsoft/pylance-release#4613.
erictraut
added a commit
to microsoft/pyright
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Jul 17, 2023
…one` type to `object | None` in an invariant context. This same bug led to issues with the validation of TypeVar variance within a Protocol. This addresses microsoft/pylance-release#4613. (#5518) Co-authored-by: Eric Traut <erictr@microsoft.com>
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Thanks for the bug report. This will be fixed in the next release of pyright and a future release of pylance. |
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Thank you, do I close it now? |
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Please leave it open. The pylance team will close it once it's in a released version of pylance. |
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Environment data
Code Snippet
Expected behavior
Only the class
Positiveto give a warning thatType variable "T_co" used in generic protocol "Positive" should be invariant, just like mypy.Actual behavior
Opposite is true, class
Positivedoes not give a warning. ClassFalsePositivegives a warning thatType variable "T" used in generic protocol "FalsePositive" should be covariant.Logs
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