[BUG] [kotlin-server] Does not create type discriminator for oneOf

[rupert-jung-mw]

Description

It seems like the kotlin-server generator is not creating any type mappings as JSON annotations for Jackson when using oneOf + discriminator.

OpenAPI 3.1 (snippet)

# (within Model MyService)
      properties:
        serviceDetails:
          description: "Service specific details. Identified by the serviceType discriminator."
          oneOf:
            - $ref: '#/components/schemas/ServiceA'
            - $ref: '#/components/schemas/ServiceB'
          discriminator:
            propertyName: serviceType
            mapping:
              A: '#/components/schemas/ServiceA'
              B: '#/components/schemas/ServiceB'

Configuration (Maven) looks like this:

<configuration>
    <inputSpec>myfile.openapi.yaml</inputSpec>
    <generatorName>kotlin-server</generatorName>
    <skipValidateSpec>true</skipValidateSpec>
    <output>${project.build.directory}/generated-sources</output>
    <packageName>com.testing</packageName>
    <modelPackage>com.testing.myapi.dto</modelPackage>
    <apiPackage>com.testing.myapi.api</apiPackage>
    <generateApis>true</generateApis>
    <generateApiTests>false</generateApiTests>
    <generateModelTests>false</generateModelTests>
    <generateModelDocumentation>false</generateModelDocumentation>
    <generateSupportingFiles>false</generateSupportingFiles>
    <configOptions>
        <library>jaxrs-spec</library>
        <useJakartaEe>true</useJakartaEe>
        <useSwaggerAnnotations>false</useSwaggerAnnotations>
        <sourceFolder>src/main/java</sourceFolder>
        <dateLibrary>java8</dateLibrary>
        <serializationLibrary>jackson</serializationLibrary>
        <useBeanValidation>true</useBeanValidation>
        <openApiNullable>false</openApiNullable>
        <sortModelPropertiesByRequiredFlag>true</sortModelPropertiesByRequiredFlag>
        <sortParamsByRequiredFlag>true</sortParamsByRequiredFlag>
        <interfaceOnly>true</interfaceOnly>
    </configOptions>
</configuration>

Generated classes look like this:

data class ClassA(...): ServiceTOAllOfServiceDetails

data class ClassB(...): ServiceTOAllOfServiceDetails

interface MyClassAllOfServiceDetails

But there is no JSON type info generated.
I would expect something like

@JsonTypeInfo(use = NAME, include = PROPERTY, property = "serviceType")
@JsonSubTypes(
	JsonSubTypes.Type(value = ServiceA::class, name = "A"),
	JsonSubTypes.Type(value = ServiceB::class, name = "B"),
	
)
interface ServiceDetails 

So JSON in this form cannot be parsed:

{
    // ...
    "serviceDetails": {
        "serviceType": "A",
        // ...
    }
}

Error: Cannot construct instance of ServiceTOAllOfServiceDetails ... no Creators

openapi-generator version

7.24.0

OpenAPI declaration file content or url

(See above)

Generation Details

• Using kotlin-server generator with library `jax

Steps to reproduce

See above

Related merge requests

#22610

(I was under the impression, that this should actually work in 7.24.0)?

Thank you :)

[Mattias-Sehlstedt]

Please share more of your specification since there are several ways to express oneOf, and some of them the generator does not like. The entire schema carrying serviceDetails is necessary and it would also be good to include both the branches too.

Do you own the spec or is it someone else's? Generally models are only generated when they are concrete components and not inline definitions as serviceDetails is. There are settings for forcing and controlling inline schemas, but I do not know to what extent that they support being a oneOf.

[Mattias-Sehlstedt]

Within https://github.com/OpenAPITools/openapi-generator/pull/22610/changes we can also see that jaxrs-spec has not been modified, so the functionality added to data_class.mustache and associated will not affect jaxrs-spec since that library defines its own data_class.mustache which overrides the one defined in kotlin-server.

Edit: also raised by #22610 (comment).