[BUG] openapi-yaml generator does not handle requestBody references correctly

Description

I use the OpenAPI generator to merge a set of OpenAPI yaml files into one single file. That is done within a Maven build using the openapi-generator-maven-plugin.

After executing the generator the requestBody parts in the resulting yaml file have duplicated content. One version of the content is referenced correctly using the $ref keyword. The duplicated content is directly printed inline after the line starting with the $ref keyword.

As an effect the Swagger UI (tested with editor.swagger.io) does not show the requestBody data (neither examples nor schema).

openapi-generator version

I use the openapi-generator-maven-plugin version 4.2.1. It uses the openapi-generator 4.2.1 as a dependency. The problem can be reproduced with all available 4.x.x versions.

OpenAPI declaration file content or url

There are three files in the src/main/resources folder:

openapi.yaml:

openapi: 3.0.2

info:
  version: 9.9.9
  title: requestBody bug report

servers:
  - url: http://localhost:8080

tags:
  - name: Bugreport

paths:
  /test:
    post:
      tags: 
        - Bugreport
      operationId: POST_Test
      requestBody:
        description: Example Request
        content:
          application/json:
            schema:
              type: object
              required: [
                foo
              ]
              properties:
                foo:
                  $ref: ./content.yaml
      responses:
        201:
          description: Example Response
          content:
            application/json:
              schema:
                type: object
                required: [
                  bar
                ]
                properties:
                  bar:
                    $ref: ./content.yaml
          headers:
            Location:
              description: Created Resource
              schema:
                type: string
                example: http://localhost:8080/test/999

content.yaml:

type: object
required: [
  baz
]
properties:
  baz:
    $ref: ./baz.yaml

baz.yaml:

type: string
example: baz

And in the root there is a Maven pom.xml file:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <build>
        <plugins>
            <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>4.2.1</version>
                <executions>
                    <execution>
                        <id>merge-openapi-yaml</id>
                        <phase>generate-resources</phase>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/src/main/resources/openapi.yaml</inputSpec>
                            <generatorName>openapi-yaml</generatorName>
                            <configOptions>
                                <outputFile>openapi.yaml</outputFile>
                            </configOptions>
                            <output>${project.build.directory}</output>
                            <skipValidateSpec>false</skipValidateSpec>
                            <strictSpec>true</strictSpec>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Command line used for generation

Run mvn clean install.

Steps to reproduce

After running the generation there is an openapi.yaml file being created in the target folder. It looks like:

openapi: 3.0.2
info:
  title: requestBody bug report
  version: 9.9.9
servers:
- url: http://localhost:8080
tags:
- name: Bugreport
paths:
  /test:
    post:
      operationId: POST_Test
      requestBody:
        $ref: '#/components/requestBodies/inline_object'
        content:
          application/json:
            schema:
              properties:
                foo:
                  $ref: '#/components/schemas/content'
              required:
              - foo
              type: object
        description: Example Request
      responses:
        201:
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/inline_response_201'
          description: Example Response
          headers:
            Location:
              description: Created Resource
              explode: false
              schema:
                example: http://localhost:8080/test/999
                type: string
              style: simple
      tags:
      - Bugreport
components:
  requestBodies:
    inline_object:
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/inline_object'
  schemas:
    content:
      example:
        baz: baz
      properties:
        baz:
          example: baz
          type: string
      required:
      - baz
      type: object
    baz:
      example: baz
      type: string
    inline_object:
      properties:
        foo:
          $ref: '#/components/schemas/content'
      required:
      - foo
      type: object
    inline_response_201:
      example:
        bar:
          baz: baz
      properties:
        bar:
          $ref: '#/components/schemas/content'
      required:
      - bar

This results into a buggy Swagger UI representation due to the duplicated content:

The response part looks ok and I would expect to have the request part looking alike:

I would expect the yaml to be generated as follows:

openapi: 3.0.2
info:
  title: requestBody bug report
  version: 9.9.9
servers:
- url: http://localhost:8080
tags:
- name: Bugreport
paths:
  /test:
    post:
      operationId: POST_Test
      requestBody:
        $ref: '#/components/requestBodies/inline_object'
      responses:
        201:
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/inline_response_201'
          description: Example Response
          headers:
            Location:
              description: Created Resource
              explode: false
              schema:
                example: http://localhost:8080/test/999
                type: string
              style: simple
      tags:
      - Bugreport
components:
  requestBodies:
    inline_object:
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/inline_object'
  schemas:
    content:
      example:
        baz: baz
      properties:
        baz:
          example: baz
          type: string
      required:
      - baz
      type: object
    baz:
      example: baz
      type: string
    inline_object:
      properties:
        foo:
          $ref: '#/components/schemas/content'
      required:
      - foo
      type: object
    inline_response_201:
      example:
        bar:
          baz: baz
      properties:
        bar:
          $ref: '#/components/schemas/content'
      required:
      - bar

This would result into a proper Swagger UI representation:

Run mvn clean install with the provided pom.xml and the openapi.yaml, content.yaml, and baz.yaml files, then inspect target/openapi.yaml. Start at the openapi-yaml generator and compare the generated requestBody with the expected output: the requestBody should contain only its $ref, without duplicated inline content, while the response remains unchanged.