Importing `annotations` from `__future__` causes a StructureHandlerNotFoundError

• cattrs version: 22.1.0
• Python version: 3.10.1
• Operating System: Ubuntu

Description

Importing annotations from __future__ causes a StructureHandlerNotFoundError, whereas my registered structure function works fine when I do not import annotations from __future__.

What I Did

I ran a Python script with the following contents:

# from __future__ import annotations

from typing import Any

import attr
from cattrs import Converter


@attr.frozen
class C:
    a: int


def structure_int(val: str, type_: Any) -> int:
    return int(val)


c = Converter()
c.register_structure_hook(int, structure_int)

result = c.structure_attrs_fromtuple(["1"], C)
print(result)

When the first line is commented out, it works fine and prints the following as expected:

C(a=1)

When the first line is not commented out, it causes the following error:

Traceback (most recent call last):
  File ".../.config/JetBrains/PyCharmCE2022.1/scratches/scratch_7.py", line 21, in <module>
    result = c.structure_attrs_fromtuple(["1"], C)
  File ".../.pyenv/versions/edgar-3.10/lib/python3.10/site-packages/cattrs/converters.py", line 403, in structure_attrs_fromtuple
    converted = self._structure_attribute(a, value)
  File ".../.pyenv/versions/edgar-3.10/lib/python3.10/site-packages/cattrs/converters.py", line 422, in _structure_attribute
    return self._structure_func.dispatch(type_)(value, type_)
  File ".../.pyenv/versions/edgar-3.10/lib/python3.10/site-packages/cattrs/converters.py", line 344, in _structure_error
    raise StructureHandlerNotFoundError(msg, type_=cl)
cattrs.errors.StructureHandlerNotFoundError: Unsupported type: 'int'. Register a structure hook for it.

Reproduce the example with and without from __future__ import annotations, then inspect cattrs/converters.py around structure_attrs_fromtuple, _structure_attribute, and _structure_error from the traceback. Trace how the attribute annotation is resolved and why the registered int hook is not reached. Done means the future-annotations variant structures C(a=1) and the regression is covered by a test.