[Swift4] Generating empty class/struct when type is string

Description

The following Swagger 2.0 code (full file here: https://raw.githubusercontent.com/OpenBankingUK/read-write-api-specs/v3.1.0/dist/account-info-swagger.json ):

  "definitions": {
    "AccountId": {
      "description": "A unique and immutable identifier used to identify the account resource. This identifier has no meaning to the account owner.",
      "type": "string",
      "minLength": 1,
      "maxLength": 40
    },

produces the following non-String empty Swift class instead of a string:

import Foundation


/** A unique and immutable identifier used to identify the account resource. This identifier has no meaning to the account owner. */

open class AccountId: Codable {



    

    // Encodable protocol methods

    public func encode(to encoder: Encoder) throws {

        var container = encoder.container(keyedBy: String.self)

    }

    // Decodable protocol methods

    public required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: String.self)

    }
}

This in turn causes issues with JSON decoding etc via Codable.

There are multiple string definitions in the same Swagger file that show the same issue.

Swagger-codegen version

Ran via https://generator.swagger.io/api/gen/clients/swift4 on 19 Dec 2018 (see next section).

Steps to reproduce

curl -X POST -H "content-type:application/json" -d '{"swaggerUrl":"https://raw.githubusercontent.com/OpenBankingUK/read-write-api-specs/v3.1.0/dist/account-info-swagger.json"}' https://generator.swagger.io/api/gen/clients/swift4

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/issues/7707

Reproduce the problem with the provided Swagger URL and the generator.swagger.io Swift4 endpoint. Trace how string definitions such as AccountId are mapped into generated Swift models; done means those definitions generate usable String types rather than empty Codable classes, with JSON decoding working as expected.