Discriminator omitted when used in root level of composed schema

[spacether]

When using a discriminator in a composed schema model, the discriminator is omitted when the schema is parsed.

Given the following spec:

swagger: "2.0"
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"
  termsOfService: "http://swagger.io/terms/"
  contact:
    email: "[email protected]"
  license:
    name: "Apache 2.0"
    url: "http://www.apache.org/licenses/LICENSE-2.0.html"
host: "petstore.swagger.io"
basePath: "/v2"
tags:
- name: "pet"
  description: "Everything about your Pets"
  externalDocs:
    description: "Find out more"
    url: "http://swagger.io"
- name: "store"
  description: "Access to Petstore orders"
- name: "user"
  description: "Operations about user"
  externalDocs:
    description: "Find out more about our store"
    url: "http://swagger.io"
schemes:
- "https"
paths:
  /pet:
    post:
      tags:
      - "pet"
      summary: "Add a new pet to the store"
      description: ""
      operationId: "addPet"
      consumes:
      - "application/json"
      - "application/xml"
      produces:
      - "application/xml"
      - "application/json"
      parameters:
      - in: "body"
        name: "body"
        description: "Pet object that needs to be added to the store"
        required: true
        schema:
          $ref: "#/definitions/ParentPet"
      responses:
        405:
          description: "Invalid input"
definitions:
  GrandparentAnimal:
    type: object
    required:
    - pet_type
    properties:
      pet_type:
        type: string
  ParentPet:
    type: object
    allOf:
    - $ref: '#/definitions/GrandparentAnimal'
    discriminator: pet_type
  ChildCat:
    allOf:
    - $ref: '#/definitions/ParentPet'
    - type: object
      properties:
        name:
          type: string
  ChildDog:
    allOf:
    - $ref: '#/definitions/ParentPet'
    - type: object
      properties:
        bark:
          type: string
  ChildLizard:
    allOf:
    - $ref: '#/definitions/ParentPet'
    - type: object
      properties:
        lovesRocks:
          type: boolean
  Dog:
    allOf:
      - $ref: '#/definitions/Animal'
      - type: object
        properties:
          breed:
            type: string
  Cat:
    allOf:
      - $ref: '#/definitions/Animal'
      - type: object
        properties:
          declawed:
            type: boolean
  Animal:
    type: object
    discriminator: className
    required:
      - className
    properties:
      className:
        type: string
      color:
        type: string
        default: 'red'

For Animal we see the discriminator in the schema:

class ObjectSchema {
    class Schema {
        type: object
        format: null
        $ref: null
        description: null
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: [className]
        not: null
        properties: {className=class StringSchema {
            class Schema {
                type: string
                format: null
                $ref: null
                description: null
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: null
                minItems: null
                uniqueItems: null
                maxProperties: null
                minProperties: null
                required: null
                not: null
                properties: null
                additionalProperties: null
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
        }, color=class StringSchema {
            class Schema {
                type: string
                format: null
                $ref: null
                description: null
                title: null
                multipleOf: null
                maximum: null
                exclusiveMaximum: null
                minimum: null
                exclusiveMinimum: null
                maxLength: null
                minLength: null
                pattern: null
                maxItems: null
                minItems: null
                uniqueItems: null
                maxProperties: null
                minProperties: null
                required: null
                not: null
                properties: null
                additionalProperties: null
                nullable: null
                readOnly: null
                writeOnly: null
                example: null
                externalDocs: null
                deprecated: null
                discriminator: null
                xml: null
            }
        }}
        additionalProperties: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: null
        externalDocs: null
        deprecated: null
        discriminator: Discriminator{propertyName='className', mapping=null}
        xml: null
    }
}

But for ParentPet we do not see the discriminator set, even though it is included in our schema:

class ComposedSchema {
    class Schema {
        type: null
        format: null
        $ref: null
        description: null
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: null
        not: null
        properties: null
        additionalProperties: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: null
        externalDocs: null
        deprecated: null
        discriminator: null
        xml: null
    }
    allOf: [class Schema {
        type: null
        format: null
        $ref: #/components/schemas/GrandparentAnimal
        description: null
        title: null
        multipleOf: null
        maximum: null
        exclusiveMaximum: null
        minimum: null
        exclusiveMinimum: null
        maxLength: null
        minLength: null
        pattern: null
        maxItems: null
        minItems: null
        uniqueItems: null
        maxProperties: null
        minProperties: null
        required: null
        not: null
        properties: null
        additionalProperties: null
        nullable: null
        readOnly: null
        writeOnly: null
        example: null
        externalDocs: null
        deprecated: null
        discriminator: null
        xml: null
    }]
    anyOf: null
    oneOf: null
}

For composed schemas please include a discriminator if it is included in the schema.

[r-sreesaran]

The issue is with swagger 2.0 parser, where the parser fails to add the discriminator in ComposedModel.

[r-sreesaran]

The Composed Model class is missing discriminator field. Not sure as to why it was left out in the first place.