[BUG][Kotlin] Data class is not generated anymore

[joellportier]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Our spec used to generated data classes, but now it generates classes without the data keyword. This happens when I have a component that has a allOf with a $ref to a supertype and no extra properties. When I have a component that has a allOf with a $ref to a supertype and an extra property it does generate a data class.

openapi-generator version

Broken in 7.9.0, it did work in 7.8.0

OpenAPI declaration file content or url

components:
  schemas:
    AssetType:
      type: string
      enum:
        - ASSET_A
        - ASSET_B
    BaseAsset:
      type: object
      required:
        - assetId
        - assetType
      properties:
        assetId:
          type: string
          format: uuid
        assetType:
          $ref: '#/components/schemas/AssetType'
      discriminator:
        propertyName: assetType
        mapping:
          ASSET_A: '#/components/schemas/AssetWithoutDataClass'
          ASSET_B: '#/components/schemas/AssetWithDataClass'
    AssetWithoutDataClass:
      allOf:
        - $ref: '#/components/schemas/BaseAsset'
        - type: object          
    AssetWithDataClass:
      allOf:
        - $ref: '#/components/schemas/BaseAsset'
        - type: object
          required:
            - number
          properties:
            number:
              type: string
              example: 'CK1924'

AssetWithDataClass now generates a data class. AssetWithoutDataClass does not generate a data class anymore, but it did in 7.8.0.

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

[Daredevil9999]

This seems to be originating from #19526 . The variable hasVars is true only when the generated class has properties and does not consider the base class properties.

[wing328]

@jaqxues can you please have a look at this issue when you've time?

[renatosilvarosa]

I have the same issue when updating to 7.9.0. Before, the generator created data classes implementing an interface, but now it outputs simple classes. This causes problems, e.g. in tests, that were using the default field-based equals method to compare instances, which are now compared by identity and make the assertions fail.

[jaqxues]

I am not that deep into the OpenAPI spec and the generator. I can look at it again, but for now I think replacing the hasVars variable from #19526 with a check if the allVars is empty would solve the issue. I do not have enough experience with both to come up with edge cases for now.