Internal error with TypeGuard and Literal-based union narrowing using StrEnum #18895
Comments
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master traceback: |
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This minimal patch should prevent crashing due to Note that |
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Hmm, I notice that if both typeguards use literals (instead of one using a union of literals), then we don't even put a union of Is having a union-of- |
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Hm, transposing a union-of-guards into guard-of-union sounds reasonable too. In the linked PR I settled on a slightly different approach, not as in the patch above: I propose to keep narrowing union members even for enum/literal-union overlap - why should cf. playground from enum import Enum
from typing_extensions import TypeIs, Literal
class Model(str, Enum):
A = 'a'
B = 'a'
def is_model_a(model: str) -> TypeIs[Literal[Model.A, "foo"]]:
return True
def handle(model: Model) -> None:
if is_model_a(model):
reveal_type(model) # N: Revealed type is "Union[Literal[__main__.Model.A], Literal['foo']]"
def is_int_or_list(model: object) -> TypeIs[int | list[int]]:
return True
def compare(x: int | str) -> None:
if is_int_or_list(x):
reveal_type(x) # N: Revealed type is "builtins.int"(yes, I can't invent a simpler test to show On my PR |
…apping with enum (#18897) Fixes #18895. The original implementation of that block was introduced as a performance optimization in #12032. It's in fact incorrect: it produces overly optimistic meets, assuming that *any* match among union items makes them *all* relevant. As discussed in #18895, this actually results in unexpected `meet` behaviour, as demonstrated by ```python from enum import Enum from typing_extensions import TypeIs, Literal class Model(str, Enum): A = 'a' B = 'a' def is_model_a(model: str) -> TypeIs[Literal[Model.A, "foo"]]: return True def handle(model: Model) -> None: if is_model_a(model): reveal_type(model) # N: Revealed type is "Union[Literal[__main__.Model.A], Literal['foo']]" def is_int_or_list(model: object) -> TypeIs[int | list[int]]: return True def compare(x: int | str) -> None: if is_int_or_list(x): reveal_type(x) # N: Revealed type is "builtins.int" ``` This patch restores filtering of union members, but keeps it running before the expensive `is_overlapping_types` check involving expansion.
Crash Report
When using TypeGuard to narrow a Literal-based union from a StrEnum, mypy raises an internal error.
I found a workaround, but I prefer my first implementation as it is more concise.
Traceback
To Reproduce
Your Environment
mypy.ini(and other config files):The text was updated successfully, but these errors were encountered: