[BUG] [kotlin-server] Does not create type mapping for oneOf (jaxrs-spec)

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

https://github.com/OpenAPITools/openapi-generator/pull/22610

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

Thank you :)

Start with the kotlin-server generator using the jaxrs-spec library and Jackson, reproducing the supplied OpenAPI 3.1 oneOf/discriminator specification on version 7.24.0. Compare the generated ClassA, ClassB, and ServiceTOAllOfServiceDetails output with the expected @JsonTypeInfo and @JsonSubTypes annotations; done means serviceDetails JSON parses correctly. Check related pull request 22610 before starting.