[BUG] Java and javascript generators don't create suitable polymorphic types

Created by: ccpulse

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

See https://stackoverflow.com/questions/63411617/how-can-i-generate-an-openapi-definition-which-supports-a-polymorphic-request-bo for a full description, but essentially: polymorphism just seems to not be functional in the way I'd expect for request bodies. Given a base type and two extensions of that type, I should be able to define an endpoint which accepts either of the extension types and have the generated code infer that they have a common supertype, and use that as the acceptable type parameter in generated code

Is what I'm trying to do just not supported by the spec? Or is it a problem with the generators themselves?

openapi-generator version

4.2.3

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: OpenAPI definition
  version: v0
servers:
  - url: 'http://localhost:8080'
    description: Generated server url
paths:
  /widgets:
    post:
      tags:
        - widget-controller
      operationId: createWidgets
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/WidgetGroup'
        required: true
      responses:
        '200':
          description: OK
components:
  schemas:
    BarWidget:
      type: object
      allOf:
        - $ref: '#/components/schemas/Widget'
        - type: object
          properties:
            bar:
              type: string
    FooWidget:
      type: object
      allOf:
        - $ref: '#/components/schemas/Widget'
        - type: object
          properties:
            foo:
              type: string
    Widget:
      required:
        - type
      type: object
      properties:
        type:
          type: string
      discriminator:
        propertyName: type
    WidgetGroup:
      type: object
      properties:
        widgets:
          type: array
          items:
            oneOf:
              - $ref: '#/components/schemas/BarWidget'
              - $ref: '#/components/schemas/FooWidget'

Generation Details

The above spec was generated by writing the Java server code first and is the output from springdoc. Have then attempted to generate server stubs and JS client libs using the maven plugin.