Add enum and type to the JSON schema for single item literals

[dmontagu]

Closes #8905

However, I think we should be careful about merging this, as any change to the JSON schema usually comes with some complaints. In particular, it's probably a good idea to track down the initial commit adding the use of constant and determine if it might be a problem to include the duplicate information about the enum value.

Probably also a good idea to make sure this doesn't break swagger UI in some way.

Another option, whether this causes any problems we can find or not, would be to expose the change by way of some config setting which would ensure that people wouldn't be affected unless they opted in, but then they also wouldn't benefit from improvements to integration with some JSON schema tools... 🤷‍♂️ not sure what's best.

[dmontagu]

Not sure what the relnotes tag should be. I did relnotes-change since it's arguably not a bugfix but not sure what's best.

[codspeed-hq]

CodSpeed Performance Report

Merging #8944 will not alter performance

_{Comparing dmontagu/add-enum-to-json-schema-single-item-literal (02ab56d) with main (af41c8e)}

Summary

✅ 10 untouched benchmarks

[sydney-runkle]

Looks great, thanks @dmontagu

[fi11er]

After updating to 2.7 we issued a problem with generating frontend api for schema

We have some objects, specified by discriminator:

class ProfileBase(BaseModel):
    guid: str
    model_type: str


class ProfileFoo(ProfileBase):
    model_type: Literal["FOO"]
    # some foo specific fields


class ProfileBar(ProfileBase):
    model_type: Literal["BAR"]
    # some bar specific fields


Profile = Annotated[
    Union[ProfileFoo, ProfileBar],
    Field(discriminator="model_type")
]


router = APIRouter(prefix="/profiles")


@router.get("/")
def list_profiles() -> list[Profile]:
    return []

On frontend swagger-typescript-api is used for code generation
https://github.com/acacode/swagger-typescript-api

Here is exampe of generated code:

/** Model Type */
export enum ProfileFooModelTypeEnum {
  FOO = 'FOO',
}

/** ProfileFoo */
export interface ProfileFoo {
  /** Guid */
  guid: string;
  /** Model Type */
  model_type: ProfileFooModelTypeEnum;
  // For pydantic<2.7 it was like this:
  // model_type: 'FOO';
}


// here is generated api request
// discrimitator field is string, but object field is enum 
listProfiles: (params: RequestParams = {}) =>
      this.request<
        (
          | ({
              model_type: 'FOO';
            } & ProfileFoo)
          | ({
              model_type: 'BAR';
            } & ProfileBar)
        )[],
        AppExceptionSchema
      >({
        path: `/profiles/`,
        method: 'GET',
        secure: true,
        format: 'json',
        ...params,
      }),

For generated api there is a type mismatch, because discriminator field is string and object field is enum.

This looks like a bug. Can we remove enum field for Literal with one value, or at least add some flag for this option?

[sydney-runkle]

Hi @fi11er,

Thanks for the report - please open another issue with said description and we'll be sure to take a look!