[Swift] Convert default value of enum with not string type to string

[tasuwo]

Fixes #4480

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[tasuwo]

With enum, name of default value should be converted as enum var name.

In current master version generator, if you use following declaration...

openapi: 3.0.0
info:
  description: ''
  version: 1.0.0
  title: ''
paths:
  /items:
    post:
      description: ''
      operationId: addItem
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/NewItem'
      responses:
        '405':
          description: Invalid input
components:
  schemas:
    NewItem:
      properties:
        size:
          type: string
          enum:
          - VALUE1
          - VALUE2
          - VALUE3
          default: VALUE2

... following code will be generated.

import Foundation

public struct NewItem: Codable {

    public enum Size: String, Codable {
        case value1 = "VALUE1"
        case value2 = "VALUE2"
        case value3 = "VALUE3"
    }
    public var size: Size? = .VALUE2

    public init(size: Size?) {
        self.size = size
    }

}

This code fails to compile.

This is because, enum var name is camelized at following.

https://github.com/OpenAPITools/openapi-generator/pull/4481/files#diff-01cf6e8770037e6a2a690476f2310d57R776-R781

So name of default value for enum should be converted as enum var name by toEnumVarName, even if the type is string.

After apply this PR's fix, code will be generated as follows.

import Foundation

public struct NewItem: Codable {

    public enum Size: String, Codable {
        case value1 = "VALUE1"
        case value2 = "VALUE2"
        case value3 = "VALUE3"
    }
    public var size: Size? = .value2

    public init(size: Size?) {
        self.size = size
    }

}

[d-date]

@tasuwo Thanks to raise PR. Please run script under ./bin/petstore-swift4-all.sh and run build on each Xcode project and compile should be passed.

[wing328]

Sync'd master and updates samples. Tests passed via https://app.bitrise.io/build/8d5397847f3ed3b8 (bitrise.io CI)

[tasuwo]

@wing328
Thank you for updating samples and merging PR 🙇

[wing328]

@tasuwo thanks for the PR, which has been included in the v4.2.2 release: https://twitter.com/oas_generator/status/1201432648544972800