Fix serialization of Enum and Path

[radoering]

Resolves: #202

[RonnyPfannschmidt]

Just for being pedantic what happens if msg is dict of name to enum

Although i wouldn't expect people to use that people are always in for horrible surprises

[radoering]

It seems to work - probably because attr.asdict() handles dicts per default by converting their elements: https://github.com/python-attrs/attrs/blob/a296a129c60f5c736165086621f03c10a4d14065/src/attr/_funcs.py#L104-L126

[nicoddemus]

Thanks for the PR @radoering!

Please take a look at my comment.

[nicoddemus]

I think we should not special-case Enum and Path, seems subTest parameters are reported as::

• The msg parameter is always converted to string using str().
• The dict contents are converted to string using repr().

The example below uses a custom class to demonstrate that.

import unittest
from enum import StrEnum, auto, Enum


class MyEnum(Enum):
    A = 1
    B = 2

class C:
    def __str__(self):
        return "C:str"
    def __repr__(self):
        return "C:repr"


class MyUnitTest(unittest.TestCase):

    def test_enum_values(self):
        for value in (C(), MyEnum.B):
            with self.subTest(value, p=value):
                assert False

if __name__ == '__main__':
    unittest.main()

test_enum_values (__main__.MyUnitTest.test_enum_values) ...
  test_enum_values (__main__.MyUnitTest.test_enum_values) [C:str] (p=C:repr) ... FAIL
  test_enum_values (__main__.MyUnitTest.test_enum_values) [MyEnum.B] (p=<MyEnum.B: 2>) ... FAIL

Ideally, we should find a way to perform the same conversions (str for msg and repr for the rest) during serialization.

[radoering]

I think we should not special-case Enum and Path

That seems to be tricky. I tried to kind of invert the logic:

        def serialize(inst: type, field: attr.Attribute, value: Any) -> Any:
            if (
                value is None
                or attr.has(value.__class__)
                or isinstance(value, (tuple, list, set, frozenset, dict))
            ):
                return value
            elif isinstance(value, str):
                return str(value)
            return repr(value)

which results in

(p='C:repr') SUBFAIL tests/test_.py::MyUnitTest::test_enum_values - AssertionError: assert False
(p='<MyEnum.B: 2>') SUBFAIL tests/test_.py::MyUnitTest::test_enum_values - AssertionError: assert False

which is close but has additional apostrophes around the representations.

Further, it is quite brittle to list all types that should not be special-cased.

[nicoddemus]

I believe we should instead see how unittest.subTest produces this output:

test_enum_values (__main__.MyUnitTest.test_enum_values) ...
  test_enum_values (__main__.MyUnitTest.test_enum_values) [C:str] (p=C:repr) ... FAIL
  test_enum_values (__main__.MyUnitTest.test_enum_values) [MyEnum.B] (p=<MyEnum.B: 2>) ... FAIL

And follow the same approach.

Further, it is quite brittle to list all types that should not be special-cased.

Definitely agree!