[BUG][JAVA][SPRING] Invalid allOf generation for RestAssured library

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

Yaml files containing the allOf keywords don't work well with the rest-assured library. I'm getting a list of objects instead of a list of something reasonable, so I don't have direct access to its field.

openapi-generator version

I tested with the latest beta release (v5.0.0-beta2) and latest stable release

OpenAPI declaration file content or url

openapi: 3.0.2
info:
  title: ''
  description: ''
  version: 0.1.0
servers:
  - url: /v1/bar
paths:
  /foo:
    get:
      description: ''
      responses:
        '200':
          description: ''
          content:
            application/json:
              schema:
                type: object
                properties:
                  foo:
                    description: ''
                    type: array
                    items:
                      allOf:
                        - type: object
                          properties:
                            first_id:
                              type: number
                              format: int64
                        - type: object
                          properties:
                            second_id:
                              type: number
                              format: int64

Generation Details

java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g java -i example.yaml -o /var/tmp/restassured --library rest-assured

Steps to reproduce, actual/expected output

• Generate classes
• Look inside InlineResponse200 class. Foo field is a list of Objects, not list of special generated POJOs

Related issues/PRs

Suggest a fix

It could be fixed by merging properties of each object into single object, but it requires time and this is manual operation

Start by running the command from the issue with the provided example.yaml and inspect the generated InlineResponse200 class. Trace how the Java rest-assured generator handles array items using allOf. Done means the foo field is generated as a typed list with access to first_id and second_id, with a regression test covering the specification.