Pyright raises type error when supplying an attr field with both default and a validator

[bavalpey]

Describe the bug
Pyright incorrectly reports an error when supplying both a validator and a default to attrs.field
This does not seem to be a bug with the attrs package, as using mypy reports no issues.

Code or Screenshots

import attrs
@attrs.define
class Foo:
    a: bool = attrs.field(default=False, validator=attrs.validators.instance_of(bool))

Interestingly, if the validator is surrounded with parenthesis (which should have no effect), pyright reports no error:

import attrs
@attrs.define
class Foo:
    a: bool = attrs.field(default=False, validator=(attrs.validators.instance_of(bool)))

VS Code extension or command-line
command-line, version 1.1.367

[erictraut]

Thanks for the bug report.

You've actually identified two separate bugs. The first is related to your observation that the behavior changes when you add parens. As you noted, this should have no impact on type evaluation. This bug was easy to address, and the fix will be in the next release.

The second issue is more difficult to fix and is related to the way that pyright's constraint solver is designed. The constraint solver is responsible for "solving" type variables for a generic function call. The bug you've identified here is related to two other open issues: #5855 and #8048. This fix will likely take much longer. In the meantime, if you want to work around it, you can swap the order of the two arguments. Place the validator first, then default.

[bavalpey]

In the meantime, if you want to work around it, you can swap the order of the two arguments. Place the validator first, then default.

This doesn't actually fix the error. I was actually fixing it by using the parenthesis. I couldn't figure out a way to fix it other than with an ignore directive.