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[regression] Files with mixed strict-optional forget None'able argument (with ParamSpec decorator) #16246
Closed as not planned
Description
Bug Report
I am in the progress of introducing strict_optional in my project. Some files have strict_optional disabled, others enabled.
Updating from mypy 1.5.1 to 1.6.0 caused some false positives when passing None to x | None arguments that are called across module boundaries.
To Reproduce
module_a.py:
# mypy: no-strict-optional
from typing import Callable, ParamSpec, TypeVar
P = ParamSpec("P")
T = TypeVar("T")
def paramspec_decorator(func: Callable[P, T]) -> Callable[P, T]:
return func
@paramspec_decorator
def example_func(arg: str | None) -> None:
print(arg)module_b.py:
from module_a import example_func
example_func(None)Expected Behavior
example_func should accept None argument.
Actual Behavior
% mypy --strict module_b.py
module_b.py:3: error: Argument 1 to "example_func" has incompatible type "None"; expected "str" [arg-type]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 1.6.0
- Mypy command-line flags:
--strict - Python version used: 3.11.5
Activity
[-][regression] Files with mixed `strict-optional` forget None'abe argument (with ParamSpec decorator)[/-][+][regression] Files with mixed `strict-optional` forget None'able argument (with ParamSpec decorator)[/+]ilevkivskyi commentedon Oct 11, 2023
I understand this behavior may be surprising, but this is not a bug actually. This behavior is consistent with how e.g. regular type variables (and other types) always behaved with
no-strict-optional, see #15932 where this was originally reported.ParamSpecwas accidentally special.Note this flag doesn't mean "do not report errors related to
Nonein this file" (because it is actually not a well defined thing), but rather "in this fileNoneis considered as subtype of all types".intgr commentedon Oct 13, 2023
Fair enough, this can be solved on my end by migrating more files to
strict_optional=true.