Sequences of attrs validators

[AdrianSosic]

Bug Report

It's only a minor issue, but there was a recent fix on the attrs side to properly handle lists of validators. While code execution works, mypy is still giving a false positive.

To Reproduce

from attrs import define, field
from attrs.validators import deep_iterable, instance_of, min_len


@define
class A:
    x: list[str] = field(
        validator=deep_iterable(
            member_validator=[instance_of(str), min_len(1)],
            iterable_validator=[instance_of(list), min_len(1)],
        ),
    )

A(['a', 'b'])  # works

Expected Behavior

Should not raise any mypy errors.

Actual Behavior

dbg.py:9: error: Argument "member_validator" to "deep_iterable" has incompatible type "list[function]"; expected "Callable[[Any, Attribute[Never], Never], Any] | Sequence[Callable[[Any, Attribute[Never], Never], Any]]"  [arg-type]
dbg.py:10: error: Argument "iterable_validator" to "deep_iterable" has incompatible type "list[function]"; expected "Callable[[Any, Attribute[Never], Never], Any] | Sequence[Callable[[Any, Attribute[Never], Never], Any]] | None"  [arg-type]

Your Environment

• Mypy version used: 1.18.2
• Attrs version used: 25.4.0
• Python version used: 3.10

[A5rocks]

I think this is an artifact of the fact that mypy joins the entries of the list rather than uses a union. It should be possible to do something like:

my_validator_list: list[Callable[[Any, Attribute[str], str], Any]] = [instance_of(str), min_len(1)]

# the rest of your code, with [instance_of(str), min_len(1)] replaced by `my_validator_list`

and similar for iterable_validator. (fyi the typing for deep_iterable is suboptimal -- the type of member_validator's usage of _T is useless)

[A5rocks]

... Though arguably this should work because type context? I'm not sure.

[A5rocks]

#20025 fixes the iterable_validator error. (never mind, I misread. It doesn't) The other error is just how we join things together, and could be fixed in attrs's stubs by replacing the _T in deep_iterable with Any.