Fix schema references in discriminated unions

[adriangb]

Fixes #7611 (comment) (I hope)

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[adriangb]

@Fokko can you try this branch? I tried it locally and can import files I could not before but don't know how to get your unit tests to run (missing env vars, etc.)

[Fokko]

@adriangb Thanks for the quick turnaround, this fixed it: apache/iceberg#8646

[dmontagu]

I think the following example reproduces the issue that this PR is trying to solve:

from typing import Literal, Annotated

from pydantic import BaseModel, Field, RootModel


class Model1(BaseModel):
    kind: Literal['1'] = '1'
    two: 'Model2 | None'


class Model2(BaseModel):
    kind: Literal['2'] = '2'
    one: Model1 | None


class Root1(RootModel[Model1]):
    pass


class Root2(RootModel[Model2]):
    pass


class Outer(BaseModel):
    first: Annotated[Root1 | Root2, Field(discriminator='kind')]
    second: Annotated[Root1 | Root2, Field(discriminator='kind')]

[Fokko]

@dmontagu Yes, that looks like it. We use the discriminator to distinguish between the different versions.