[BUG] substantive difference between yaml and json generator generation

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?

Description

Our openapi spec generation bundling has substantive difference between json and yaml output. We would like to use yaml bundle, but it drops an example (and many other examples).

openapi-generator version

I've tried with:

openapi-generator-cli:v4.3.1
openapi-generator-cli:v5.0.0
openapi-generator-cli:v5.1.0
openapi-generator-cli:latest

OpenAPI declaration file content or url

Path spec

paths:
  /enroll:
    post:
      operationId: enrollCustomer
      summary: Enroll Customer
      tags: [ Enroll ]
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateEnrollment'

CreateEnrollment

    CreateEnrollment:
      description: Describes an example.
      type: object
      additionalProperties: false
      properties:
        customer:
          $ref: './customers.yml#/components/schemas/Customer'
        account:
          $ref: './customers.yml#/components/schemas/Account'
        statementDeliveryOptions:
          $ref: './statements.yml#/components/schemas/CreateCustomerPreferences'
      required:
        - customer
        - account
        - statementDeliveryOptions

Customer

    Customer:
      oneOf: # whichever option is listed first is the one for which example JSON will be displayed in the swagger editor
        - $ref: '#/components/schemas/CorporationAsCustomer'
        - $ref: '#/components/schemas/SoleProprietorAsCustomer'
        - $ref: '#/components/schemas/IndividualAsCustomer'
      discriminator:
        propertyName: type
        mapping:
          individual: '#/components/schemas/IndividualAsCustomer'
          sole-proprietor: '#/components/schemas/SoleProprietorAsCustomer'
          corporation: '#/components/schemas/CorporationAsCustomer'
          non-profit: '#/components/schemas/CorporationAsCustomer'
          partnership: '#/components/schemas/CorporationAsCustomer'
          llc: '#/components/schemas/CorporationAsCustomer'

Generation Details

for json bundle

	rm -rf ./bundle
	mkdir -p ./bundle
	docker run --rm \
                -u $(USERID):$(GROUPID) \
		-v ${PWD}:/local openapitools/openapi-generator-cli:v5.0.0 generate  \
                --input-spec /local/openapi/openapi.yaml \
                --output /local/bundle \
                --generator-name openapi

for yaml bundle

	rm -rf ./bundle
	mkdir -p ./bundle
	docker run --rm \
                -u $(USERID):$(GROUPID) \
		-v ${PWD}:/local openapitools/openapi-generator-cli:v5.0.0 generate  \
                --input-spec /local/openapi/openapi.yaml \
                --output /local/bundle \
                --generator-name openapi-yaml

Steps to reproduce

Run each of the above commands for generating both a json and yaml bundle.
Comparing the /enroll endpoint is different, most concerning is the dropped example in the yaml output.

json output:

      "CreateEnrollment" : {
        "additionalProperties" : false,
        "description" : "Describes an example.",
        "properties" : {
          "customer" : {
            "$ref" : "#/components/schemas/Customer"
          },
          "account" : {
            "$ref" : "#/components/schemas/Account"
          },
          "statementDeliveryOptions" : {
            "$ref" : "#/components/schemas/CreateCustomerPreferences"
          }
        },
        "required" : [ "account", "customer", "statementDeliveryOptions" ],
        "type" : "object"
      },

yaml output:

    CreateEnrollment:
      additionalProperties: false
      description: Describes an example.
      example:
        statementDeliveryOptions:
          mail: false
        account:
          accountID: e1b1544a
          routingNumber: "051504597"
          institution:
            routingNumber: "123456780"
            phoneNumber: "5551112222"
            address:
              zip: "43724"
              address2: ""
              city: CALDWELL
              address1: 430 NORTH ST
              state: OH
            name: First Bank
          archivedAt: 2020-12-03T03:09:49.381Z
          holderName: My Company,llc or Wade Arnold
          customerID: e1b1544a
          accountNumber: "0001027028"
          type: checking
          maskedAccountNumber: "0001027028"
          status: validated
      properties:
        customer:
          $ref: '#/components/schemas/Customer'
        account:
          $ref: '#/components/schemas/Account'
        statementDeliveryOptions:
          $ref: '#/components/schemas/CreateCustomerPreferences'
      required:
      - account
      - customer
      - statementDeliveryOptions
      type: object

Notice the example for customer is dropped in the yaml. I expect the customer example to be present.

I recognize this is a partial and will not be 100% to reproduce. I could demo the issue, or get on a call to demonstrate. I can't provide the repo as our code models are tied in. I could provide more (all) complete spec files if that would be helpful.

Related issues/PRs

I found some adjacent PR's but nothing that is the same.

Suggest a fix

I suspect this has to do with using $ref for complex structures which themselves have oneOf with discriminator.

Start with the supplied OpenAPI fragments and run the two openapi-generator-cli commands using the openapi and openapi-yaml generators. Compare the generated JSON and YAML bundles, focusing on the customer example under CreateEnrollment; done means the YAML output preserves the example consistently with the JSON output.