[BUG] all languages: not handling array parameters

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

I'm using the swift4 generator, with a Swagger 2 spec, and an array parameter with collectionFormat=csv. The parameter looks like:

          {
            "name": "categories",
            "in": "path",
            "required": true,
            "type": "array",
            "items": {
              "type": "string"
            },
            "collectionFormat": "csv"
          }

It generates code that (correctly) expects an array of strings:

open class func usersGet(categories: [String], completion: @escaping ((_ data: [User]?,_ error: Error?) -> Void)) {

But if I pass an array to it:

DefaultAPI.usersGet(categories: ["sample"] )

it URL-encodes the array literal, rather than using comma-separated values as specified in collectionFormat:

GET /users/%5B%22sample%22%5D

I'm curious if this will be an issue with all generator types.

openapi-generator version

4.0.0-SNAPSHOT

OpenAPI declaration file content or url

https://gist.github.com/jacobweber/2a8b3145952464997545d212772a1b96

Command line used for generation

java -jar /path/to/openapi-generator-cli.jar generate -i /path/to/spec.json -g swift4 -o /path/to/output

Steps to reproduce

See above

Related issues/PRs

None

Suggest a fix

This is not Swift, but swagger-codegen had a fix for one Java client here, and a PR for another one here.

Start with the supplied Swagger 2 declaration and the generated Swift4 client from the documented generation command. Reproduce the path request using the categories array and compare its URL encoding with the declared collectionFormat=csv behavior. Done means the generated request uses comma-separated array values rather than encoding the array literal.