nested_type Callable-branch is brittle on values lacking __qualname__/__module__

[datvo06]

Failing tests that should pass

import pytest
from effectful.internals.unification import nested_type


def test_nested_type_marker_decorator_widens_to_class():
    """MarkDecorator lacks `__qualname__`; `typing.get_overloads` raises
    AttributeError instead of widening to `Box(MarkDecorator)`."""
    assert nested_type(pytest.mark.parametrize).value is type(pytest.mark.parametrize)


def test_nested_type_method_descriptor_widens_to_class():
    """method_descriptor lacks `__module__`; same shape."""
    assert nested_type(dict.get).value is type(dict.get)


def test_nested_type_unresolvable_forward_ref_widens():
    """An Operation whose default carries a stringified annotation that
    does not resolve in scope. `inspect.signature` → `__signature__` →
    `typing.get_type_hints` raises NameError instead of widening to
    `Box(Operation)`."""

    def _hidden_module():
        class ClientSession:
            pass

        def real(x: "ClientSession") -> int:
            ...

        return real

    from effectful.ops.syntax import defop

    op = defop(_hidden_module())
    assert nested_type(op).value is type(op)

Invariant being violated

IIUC, and this invariant PR #613,: nested_type is part of the canonicalize-widening family: When introspection cannot construct a more precise TypeExpression, the documented fallback is Box(type(value)), not a raise. The Callable branch in effectful/internals/unification.py currently honors this for ValueError but lets AttributeError/NameError/TypeError from typing.get_overloads and inspect.signature escape.

This affected downstream #670 in trying to create reader tools for similar cases to the above.

[eb8680]

The first two cases are clear bugs with simple fixes, but the third one is more subtle. What happens if you remove the quotes around ClientSession in the annotation? Does it still fail?

[eb8680]

Related to #577

[datvo06]

The first two cases are clear bugs with simple fixes, but the third one is more subtle. What happens if you remove the quotes around ClientSession in the annotation? Does it still fail?

Yes. In that case,

>>> nested_type(op).value
effectful.ops.types.Operation[[__main__._hidden_module.<locals>.ClientSession], int]
>>> type(op)
<class 'effectful.ops.types.Operation'>
>>> canonicalize(type(op))
<class 'effectful.ops.types.Operation'>

[eb8680]

Well, that's different behavior than the NameError in the original test. I would argue the third case should be handled in nested_type by calling typing.get_type_hints or inspect.signature as a probe. If that fails with a NameError, it should return type(value). If it succeeds, nested_type should return whatever it currently returns.

[datvo06]

Right, because in that ClientSession example, nested_type can/does know how to construct a more precise type expression.