[Swift3] Request body cannot be an array, only a dictionary

Description

The request body cannot be an array of dictionaries, or in fact an array of any object, it can only be a dictionary (which can be a dictionary containing other dictionaries as values).
The issue comes from the Alamofire implementation that the request body is converted from the query parameters and the query parameters have to be a dictionary and cannot be an array.

Swagger-codegen version

2.2.2

Swagger declaration file content or url

/path/{to}/file:
    post:
      tags:
        - tag1
      operationId: something
      summary: summary
      description: 
        description
      parameters:
        - $ref: '#/parameters/param1'
        - $ref: '#/parameters/param2'
        - $ref: '#/parameters/param3'
        - name: postBody
          description: data to be posted in the body
          in: body
          required: true
          schema:
            type: array
            items:
              $ref: '#/definitions/Item1'
      responses:
        '201':
          description: Created
          schema:
            $ref: '#/definitions/Reply'

        '400':
          description: Bad request
          schema:
            $ref: '#/definitions/_Messages'
        default:
          description: Unexpected error
          schema:
            $ref: '#/definitions/_Messages'
      security:
        - basicAuth: []

Command line used for generation

swagger-codegen generate -i /path/spec.yaml -l swift3

Steps to reproduce

Generate a Swift3 client side code from a swagger spec that contains type: array in its schema for an object that is in:body.

Related issues

https://github.com/swagger-api/swagger-codegen/issues/2483
https://github.com/swagger-api/swagger-codegen/pull/4490

Suggest a Fix

The Swift file API.swift generated by swagger-codegen has the following method:

open class RequestBuilder<T> {
    var credential: URLCredential?
    var headers: [String:String]
    let parameters: [String:Any]?
    let isBody: Bool
    let method: String
    let URLString: String
    
    /// Optional block to obtain a reference to the request's progress instance when available.
    public var onProgressReady: ((Progress) -> ())?

    required public init(method: String, URLString: String, parameters: [String:Any]?, isBody: Bool, headers: [String:String] = [:]) {
        self.method = method
        self.URLString = URLString
        self.parameters = parameters
        self.isBody = isBody
        self.headers = headers
        
        addHeaders(SwaggerClientAPI.customHeaders)
    }
    
    open func addHeaders(_ aHeaders:[String:String]) {
        for (header, value) in aHeaders {
            headers[header] = value
        }
    }
    
    open func execute(_ completion: @escaping (_ response: Response<T>?, _ error: Error?) -> Void) { }

    public func addHeader(name: String, value: String) -> Self {
        if !value.isEmpty {
            headers[name] = value
        }
        return self
    }
    
    open func addCredential() -> Self {
        self.credential = SwaggerClientAPI.credential
        return self
    }
}

The problem comes from the fact that there is no body input parameter for the initialiser, only the isBody Bool, which makes it impossible to have a query parameter and a request body of different types. This is an issue, since quite a few APIs expect an array of values as the body of the request, which is not possible with the current implementation.

Start with the generated Swift3 API.swift and its RequestBuilder initializer, then reproduce the issue using the provided Swagger declaration and swift3 generation command. Trace how body and query parameters are represented and run the generated client against a request whose body schema is an array. Done means Swift3 clients can send array request bodies while retaining separate query parameters.