[Elixir] Bug in 2.3.1. Generating multi-part body instead of direct JSON content

Description

The generated Elixir code from a Swagger definition seems to be wrong, but I'm not sure.

I try to generate an Elixir SDK for the Azure Resource Management API. I wrote a generator app, which uses uses swagger-codegen-cli-2.3.1.jar to generate Elixir code.

The swagger spec document says "in": "body", and the API expects JSON structure directly in the body, but the Elixir code generates a multi-part body.

      "put": {
        "operationId": "Deployments_CreateOrUpdate",
        "summary": "Deploys resources to a resource group.",
        "parameters": [
          ...
          {
            "name": "parameters",
            "in": "body",
            "required": true,
            "schema": { "$ref": "#/definitions/Deployment" },
            "description": "Additional parameters supplied to the operation."
          },

The Elixir swagger generator creates this code

  @spec deployments_create_or_update(Tesla.Env.client, String.t, String.t, Microsoft.Azure.Management.Resources.Model.Deployment.t, String.t, String.t, keyword()) :: {:ok, Microsoft.Azure.Management.Resources.Model.DeploymentExtended.t} | {:error, Tesla.Env.t}
  def deployments_create_or_update(connection, resource_group_name, deployment_name, parameters, api_version, subscription_id, _opts \\ []) do
    %{}
    |> method(:put)
    |> url("/subscriptions/#{subscription_id}/resourcegroups/#{resource_group_name}/providers/Microsoft.Resources/deployments/#{deployment_name}")
    |> add_param(:body, :"parameters", parameters)
    |> add_param(:query, :"api-version", api_version)

The parameter JSON is added as |> add_param(:body, :"parameters", parameters), which results in

 body: %Tesla.Multipart{
    boundary: "6R3XOsKKCMYMatbOce3P7yRHKD6Zmm",
    content_type_params: [],
    parts: [
      %Tesla.Multipart.Part{
        dispositions: [name: :parameters],
        headers: ["Content-Type": "application/json"],
        body: "{\"properties\":{\"template\":{\"a\":\"b\"},\"parameters\":{\"a\":\"b\"},\"mode\":\"Incremental\"}}"
      }
    ]
  },

instead of

  body: %{
    properties: %{ 
        parameters: %{a: "b"}, 
        template: %{a: "b"}, 
        mode: "Incremental" 
    }
  },

Shouldn't the generated SDK code be add_param(:body, :body, parameters) instead of add_param(:body, :"parameters", parameters)?

When I check the Swagger 2 Spec, it says that in: body means that the payload is directly in the body, not in a Multi-part message.

Swagger-codegen version

I am using version 2.3.1

Swagger declaration file content or url

The Swagger definition is https://github.com/Azure/azure-rest-api-specs/blob/master/specification/resources/resource-manager/Microsoft.Resources/stable/2018-02-01/resources.json#L155-L162

      "put": {
        "operationId": "Deployments_CreateOrUpdate",
        "summary": "Deploys resources to a resource group.",
        "parameters": [
          ...
          {
            "name": "parameters",
            "in": "body",
            "required": true,
            "schema": { "$ref": "#/definitions/Deployment" },
            "description": "Additional parameters supplied to the operation."
          },

Command line used for generation

#!/bin/bash

curl -O http://central.maven.org/maven2/io/swagger/swagger-codegen-cli/2.3.1/swagger-codegen-cli-2.3.1.jar

cat > Microsoft.Azure.Management.Resources.json <<-EOF
    { 
        "packageName": "azure", 
        "invokerPackage": "Microsoft.Azure.Management.Resources" 
    }
EOF

java \
   -jar swagger-codegen-cli-2.3.1.jar \
   generate \
   -l elixir \
   -i https://raw.githubusercontent.com/Azure/azure-rest-api-specs/master/specification/resources/resource-manager/Microsoft.Resources/stable/2018-02-01/resources.json \
   -o clients/Microsoft.Azure.Management \
   -c ./Microsoft.Azure.Management.Resources.json

sed -n 91,100p clients/Microsoft.Azure.Management/lib/microsoft/azure/management/resources/api/deployments.ex

Consumer-side fix

When I replace all occurrences of add_param(:body, :"whatever-here", parameters) in the .ex-files, my SDK works.

#!/bin/bash
find . -type f -name "*.ex" -exec \
   sed -i'' -e 's/add_param(:body, :"[^"]*", /add_param(:body, :body, /g' {} +

/cc @niku

Run the posted swagger-codegen 2.3.1 command with the linked Azure definition and inspect the generated deployments.ex file. Trace how the Elixir generator handles the Swagger in: body parameter; done means the generated call sends the parameter as the direct JSON body rather than a Tesla.Multipart body.