[SWIFT4] Default values for ENUMs are using strings instead of the enum

Created by: grEvenX

Description

OpenAPI 3.0.0 has support for strings in enum format. The Swift4 generator maps these into enum in the Swift code which works fine. However if you provide a default value in the OpenAPI document, the values for the properties of enum types are set as strings instead of the enum which again causes the compiler to fail.

openapi-generator version

3.1.2

OpenAPI declaration file content or url

https://gist.github.com/grEvenX/76d508f2933456894492c38410b1ac49

Command line used for generation

docker run --rm -v $(pwd)/generated:/out openapitools/openapi-generator-cli:latest generate -i https://gist.githubusercontent.com/grEvenX/76d508f2933456894492c38410b1ac49/raw/6e3a93cc3bc219815769a21fdcad84628ab0af59/example.yaml -g swift4 -o /out/swift4

Steps to reproduce

Run the following docker command to generate a Swift4 client with the example YAML using enums and default values
Inspect the output of generated/swift4/OpenAPIClient/Classes/OpenAPIs/Models/NewPet.swift

Suggest a fix/enhancement

The generated model contains the line:

public enum Animal: String, Codable {
  case dog = "dog"
  case cat = "cat"
}
public var animal: Animal? = "cat"

The correct value that should be assigned to animal in this case is:

public var animal: Animal? = .cat