[BUG] [Kotlin-Spring] Generate interface extension for Kotlin-Spring, but it still generates fields in the sub-interface that already exist in the base interface.

Description

The language I'm using is Kotlin. I've defined two template YMLs for two interfaces, where one interface extends the other. When OpenAPI Generator processes these, it defaults to generating fields in the sub-interface that already exist in the base interface, and it does so without the 'override' keyword.

However, in Kotlin, if an interface extends a base interface, the fields from the base interface cannot be defined again in the sub-interface. Therefore, I believe OpenAPI Generator should not generate these redundant fields for my sub-interface.

openapi-generator version

7.9.0

OpenAPI declaration file content or url

As the YMLs in the following, the interface CommonSearchRequest extends BaseCommonSearchRequest by using
discriminator, allOf and ref.

1. base-common-search-request.yml:

type: object
discriminator:
  propertyName: requestType
required:
  - requestType
  - pagination
properties:
  requestType:
    type: string
  pagination:
    $ref: './request/providers/pagination.yml'

2. common-search-request.yml

type: object
discriminator:
  propertyName: requestType
required:
  - checkInDate
  - checkOutDate
allOf:
  - $ref: 'base-common-search-request.yml'
  - type: object
    properties:
      checkInDate:
        type: string
        format: date
        example: 2024-10-19
      checkOutDate:
        type: string
        format: date
        example: 2024-10-20

3. pagination.yml

type: object
required:
  - offset
properties:
  offset:
    type: integer
    minimum: 0
    example: 0
  limit:
    type: integer
    minimum: 1
    example: 30

Generation Details

I used general commands for OpenAPI Generator and here are two Kotlin interfaces generated.

1. BaseCommonSearchRequest:

interface BaseCommonSearchRequest {
        val requestType: kotlin.String
        val pagination: Pagination
}

2. CommonSearchRequest:

interface CommonSearchRequest: BaseCommonSearchRequest {
        val checkInDate: java.time.LocalDate
        val checkOutDate: java.time.LocalDate
        val requestType: kotlin.String
        val pagination: Pagination
}

Expectation
For my Kotlin example, I expect CommonSearchRequest to only declare property checkInDate and checkOutDate, given that the fields requestType and pagination are inherited from the base interface and therefore should not be redefined in the sub-interface.

Due to this behavior, the compiler will show errors, and require you to manually add an override to these two properties.

Related issues/PRs

N/A

Suggest a fix

N/A

Reproduce the Kotlin-Spring generation with the supplied base-common-search-request.yml, common-search-request.yml, and pagination.yml files, then trace how allOf and discriminator properties are collected. Add a regression test for the generated interfaces; done means inherited requestType and pagination are not redeclared in CommonSearchRequest and the generated Kotlin compiles.