Bug: Broken union type generation since "polyfactory<2.6" (pydantic_factory)

[realitycheck]

Description

Value generation for union_field: str | list[str] types is broken since polyfactory<2.6.

Sample of broken results:

{'union_field': ['xHTRynXkQXaHKksrCLan', ['mlAkGEPvArmUXfHMUDvh']]}
{'union_field': ['AOQqrBoBIUXjkkDazQMu', ['EDNDtAdsaLdPVrSjwrDo']]}
{'union_field': ['cVPkYHEIYQOEVCbYEOiS', ['evgTnOLFzcVsbaZWjmim']]}

URL to code causing the issue

No response

MCVE

import pydantic

from polyfactory.factories.pydantic_factory import ModelFactory


class UnionModel(pydantic.BaseModel):
    union_field: str | list[str]


class UnionFactory(ModelFactory):
    __model__ = UnionModel

for _ in range(100):
    print(UnionFactory.process_kwargs())

Steps to reproduce

1. Install "polyfactory<2.6"
2. Run MCVE
3. Notice correct results (sample):

{'union_field': ['pxmZfDPIiXJBzmcMiDFC']}
{'union_field': ['qmaITGzIrhtIbwXSNCHF']}
{'union_field': ['FTTgnfVwmySLgdbylTkQ']}
{'union_field': ['EonBSyUuDseCjXhuzONc']}
{'union_field': ['QqBzlNBMKRrlLuEmiDBl']}
{'union_field': 'IfiTUXnKFaCgnrvCnEpi'}
{'union_field': ['GZaprKiCagdtrSNciVQa']}

4. Install "polyfactory>=2.6"
5. Run MCVE
6. Notice incorrect results (sample):

{'union_field': ['xHTRynXkQXaHKksrCLan', ['mlAkGEPvArmUXfHMUDvh']]}
{'union_field': ['AOQqrBoBIUXjkkDazQMu', ['EDNDtAdsaLdPVrSjwrDo']]}
{'union_field': ['cVPkYHEIYQOEVCbYEOiS', ['evgTnOLFzcVsbaZWjmim']]}

### Screenshots

_No response_

### Logs

_No response_

### Release Version

polyfactory>=2.6,<3

### Platform

- [ ] Linux
- [ ] Mac
- [ ] Windows
- [ ] Other (Please specify in the description above)

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[guacs]

Yeah this is definitely a bug. Thank you for reporting this :)

[adhtruong]

This seems like it's fixed on main now by #468. Below is the output of the original example

➜  polyfactory git:(main) ✗ pdm run python -m a
{'union_field': ['RWjcFtahQiPQtoUvVwEz']}
{'union_field': 'SSYSdEVUTbiyGUfWRlSn'}
{'union_field': ['cepYPKWhGknvHXGykLXm']}
{'union_field': ['gmVhBhPhYvhfGsfDRPrV']}
{'union_field': 'zbmGlcaQcjdHCEnYmxkd'}
{'union_field': 'PIXzWGqKEQdCoslhuHTN'}
{'union_field': 'xqVijCVLcMcEWuNZwItl'}
{'union_field': 'bGZVfMnctOfkRUONRqPj'}
{'union_field': ['fwrQzvnToUnFLEeyfVOO']}
{'union_field': 'OSrMqpcnTFtjhOqUIAMF'}

[guacs]

Seems it's not fixed yet in Pydantic v1 :/ I think we may have to just special case pydantic v1 as mentioned here.

[guacs]

Fixed in #491.