[BUG][JAVA] Fluent setters from inherited from parent return parents type

[leonard84]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [x] Have you tested with the latest master to confirm the issue still exists?
• [x] Have you searched for related issues/PRs?
• [x] What's the actual output vs expected output?
• [ ] [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When using inheritance via allOf the setters always return the type they are declared on, so using setters declared on the parent type will return Parent instead of Child.

openapi-generator version

6.4.0

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: test
  description: >-
    test schema
  version: 1.0.0
servers:
  - url: 'http://test.com'
    description: stage
paths:
  /demo:
    get:
      summary: placeholder summary
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Child'
components:
  schemas:
    Parent:
      type: object
      properties:
        name:
          type: string
    Child:
      x-all-of-name: Child
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object
          properties:
            childProperty:
              type: string

Generation Details

https://github.com/gradle/gradle-enterprise-api-samples/blob/5b9a67556042413337860c47532512046f8765a0/build.gradle.kts#L35-L57

Steps to reproduce

Checkout the demo at https://github.com/gradle/gradle-enterprise-api-samples/tree/openapi-generator-issue_inheritance and run build

Will fail with:

error: incompatible types: demo.api.model.Parent cannot be converted to demo.api.model.Child
        Child child = new Child().name("bar");
                                      ^

Related issues/PRs

Suggest a fix

The straight forward solution would be to @Override all inherited fluent setters on the child types, so that they return the correct type.

So on Child add this method

  @Override
  public Child name(String name) {    
    this.name = name;
    return this;
  }

[borsch]

@leonard84 if you using lombok in your project you can fix this by adding @lombok.SuperBuilder to additionalModelTypeAnnotations

[leonard84]

@borsch thanks for the hint, but we don't use lombok.