Improve `mypy` hinting on `RootModel` with `oneOf` about datamodel-code-generator

[woodruffw]

For a concrete example of this failing, see this CI job.

This happens because of a generated type that looks like this:

class DsseSchema(RootModel[Union[DsseV001Schema1, DsseV001Schema2]]):
    model_config = ConfigDict(
        populate_by_name=True,
    )
    root: Union[DsseV001Schema1, DsseV001Schema2] = Field(
        ...,
        description="log entry schema for dsse envelopes",
        title="DSSE Schema",
    )

...which then gets instantiated like this:

proposed_entry = rekor_types.Dsse(
    spec=rekor_types.dsse.DsseSchema(
        proposed_content=rekor_types.dsse.ProposedContent(
            envelope=content.to_json(),
            verifiers=[b64_cert.decode()],
        ),
    ),
)

...which fails, since Dsse's constructor is not inferred to be the superset of DsseV001Schema1 | DsseV001Schema2.

[koxudaxi]

@woodruffw
Thank you for exploring the solution.
Is your error related to the issue? #1921

I would like to know, if you know, if your solution is version-constrained on the Pydantic side?
Can it be used with 2.5, etc.?

[woodruffw]

Thanks for your response @koxudaxi! #1921 looks like a different issue -- in my case the generated code is syntactically and semantically sound, but just doesn't work with the patterns mypy and Pydantic both understand for kwarg inference 🙂

I would like to know, if you know, if your solution is version-constrained on the Pydantic side?
Can it be used with 2.5, etc.?

Yes, I believe it can be used with anything in 2.x!