[Go][Client] Multipart array elements gets rendered as struct.String()

Created by: Miroku87

Description

When generating a Go client that has a 'requestBody' of the 'multipart/form-data' type, properties which are arrays of objects gets rendered in the HTTP request body as plain struct.String() values and not with JSON formatted text. This happens only when the content of the requestBody is stated under the paths: property of the YAML. If the contents are state inside components/requestBodies the issue does not occur (a different issue occurs but I will make a different issue about that #3045 ).

In the case a property of the form-data contains an object this object will become an interface and this interface will have to be rendered as a string to be inserted in the localVarFormParams struct, so the parameterToString function will be used. Nothing unusual here. The unusual thing is that, when calling the parameterToString function, the collectionFormat parameter is set to csv causing the program to render the object as if printing it with fmt.Printf('%v',userpayload).

openapi-generator version

4.0.1-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.0
servers:
- url: http://petstore.swagger.io/v2
info:
  description: 'This is a sample server Petstore server.  You can find out more about
    Swagger at [http://swagger.io](http://swagger.io) or on [irc.freenode.net, #swagger](http://swagger.io/irc/).  For
    this sample, you can use the api key `special-key` to test the authorization filters.'
  version: 1.0.0
  title: Swagger Petstore
paths:
  "/user/createWithArray":
    post:
      tags:
      - user
      summary: Creates list of users with given input array
      description: ''
      operationId: createUsersWithArrayInput
      responses:
        default:
          description: successful operation
      requestBody:
        content:
          multipart/form-data:
            schema:
              "$ref": "#/components/schemas/UserPayload"
  
components:
  schemas:
    User:
      type: object
      properties:
        email:
          type: string
        password:
          type: string
      xml:
        name: User
        
    UserPayload:
      type: object
      properties:
        foo:
          type: string
        bar:
          type: array
          items:
            "$ref": "#/components/schemas/User"

Command line used for generation

I'm using the docker generator:

sudo docker run --rm -v \
    ${PWD}:/local \
    openapitools/openapi-generator-cli generate \
    --package-name foo \
    -i /local/openapi.yaml \
    -g go \
    -o /local

Steps to reproduce

Use the above command to generate a client passing the above YAML as input.

Related issues/PRs

#2964 (closed) #3045

Suggest a fix/enhancement

Instead of passing "csv" as a collectionFormat parameter to the parameterToString function the normal thing to do would be to print the object as a JSON string (which the parameterToString does not yet support as said in this issue: #2964 (closed) )

I think the line in the template is this one: https://github.com/OpenAPITools/openapi-generator/blob/e5a0d183744c3a7d331b77af4d451ff36cc3da16/modules/openapi-generator/src/main/resources/go/api.mustache#L140