[BUG] [Java] [okhttp-gson] enum values are not validated in some cases

[ctreatma]

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

We are using the Java generator with okhttp-gson. We have noticed that enum values are not validated consistently by the generated models.

With the example schema below, we have observed that the code generated by okhttp-gson generator works as follows when deserializing an object that matches the FooThing schema (i.e., it has a kind property with value foo):

• FooThing deserializes the object without an error (correct)
• BarThing throws an error that the object isn't valid according to the schema (correct)
• Thing model doesn't validate the enum values, throws an error that the object matches both FooThing and BarThing (incorrect)
• Container model, which only allows a BarThing, doesn't validate the enum value and does not throw a validation error (incorrect)

openapi-generator version

v7.0.0

OpenAPI declaration file content or url

components:
  schemas:
    Thing:
      type: object
      oneOf:
        - $ref: '#/components/schemas/FooThing'
        - $ref: '#/components/schemas/BarThing'
    FooThing:
      type: object
      properties:
        kind:
          type: string
          enum:
          - foo
    BarThing:
      type: object
      properties:
        kind:
          type: string
          enum:
          - bar
    Container:
      type: object
      properties:
        thing:
          $ref: '#/components/schemas/BarThing'

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Generate validateJsonElement functions when using the Java okhttp-gson generator