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False positive: comparison-overlap with dataclasses.Field.default_factory and dataclasses.MISSING #12124
Description
Bug Report
In code which is checking if a field has a default, a check to see if Field.default_factory is MISSING will be misreported as a comparison-overlap error if mypy --strict is used.
To Reproduce
In foo.py:
from dataclasses import MISSING, Field
from typing import Any
def is_required(x: Field[Any]) -> bool:
return x.default is MISSING and x.default_factory is MISSINGExpected Behavior
This check should pass. One of the valid values for default_factory is MISSING.
Actual Behavior
With the above reproduction,
$ mypy --strict foo.py
foo.py:5: error: Non-overlapping identity check (left operand type: "_DefaultFactory[Any]", right operand type: "_MISSING_TYPE")
Found 1 error in 1 file (checked 1 source file)Your Environment
- Mypy version used:
0.931andmaster(0.940+dev.84b977876aa76bfebf5fe49d11ebd202e4a60a33) - Mypy command-line flags:
--strict - Mypy configuration options from
mypy.ini(and other config files): None
Activity
erictraut commentedon Feb 4, 2022
This looks like a bug in the typeshed stub
dataclasses.pyi. The type annotations forField.defaultandField.default_factoryshould probably be unions that include the type_MISSING_TYPE.sirosen commentedon Feb 4, 2022
Good point! I didn't think to look at typeshed -- I thought
mypywas doing something weird.I'll put in a PR to update it. Assuming that's right and my patch is accepted, I'll close this when that's merged.
hauntsaninja commentedon Feb 4, 2022
There isn't any action for mypy, so closing. Current plan is to use the literal trick in typeshed: python/typeshed#7127