[R] Enum R6Class Support, closes #3367

Created by: LiNk-NY

Hi all,

We've (@mtmorgan, @dvantwisk) provided an R6 class based on guidelines in issue #3367 (closed).

This PR includes:

• modelEnum.mustache
• changes to methods within R6Class: fromJSONString, fromJSON, etc.
• removal of stray commas: function(, ...) to function(...)
• use of httr::content(resp) instead of apiResponse$content
• updates to the petstore API by running ./bin/r-petstore.sh

Diff of the changes: https://github.com/OpenAPITools/openapi-generator/compare/master...LiNk-NY:enum

Example implementation from the HCAMatrix Service:

    v1_ComparisonFilterOperator:
      description: 'Comparison operators allowed in matrix filters.'
      type: string
      enum:
        - '='
        - '!='
        - '>'
        - '<'
        - '>='
        - '<='
        - 'in'

# HCA Matrix Service
#
# Human Cell Atlas Matrix Service API
#
# The version of the OpenAPI document: 1.0.0
# 
# Generated by: https://openapi-generator.tech

#' @docType class
#' @title V1ComparisonFilterOperator
#'
#' @description V1ComparisonFilterOperator Class
#'
#' @format An \code{R6Class} generator object
#'
#' @importFrom R6 R6Class
#' @importFrom jsonlite fromJSON toJSON
# add to utils.R
.parse_v1_ComparisonFilterOperator <- function(vals) {
    res <- gsub("^\\[|\\]$", "",
        "[=, !=, >, <, >=, <=, in]"
    )
    unlist(strsplit(res, ", "))
}

#' @export
V1ComparisonFilterOperator <- R6::R6Class(
    "V1ComparisonFilterOperator",
    public = list(
        initialize = function(...) {
            local.optional.var <- list(...)
            val <- unlist(local.optional.var)
            enumvec <- .parse_v1_ComparisonFilterOperator()

            stopifnot(length(val) == 1L)

            if (!val %in% enumvec)
                stop("Use one of the valid values: ",
                    paste0(enumvec, collapse = ", "))
            private$value <- val
        },
        toJSON = function() {
            jsonlite::toJSON(private$value, auto_unbox = TRUE)
        },
        fromJSON = function(V1ComparisonFilterOperatorJson) {
            private$value <- jsonlite::fromJSON(V1ComparisonFilterOperatorJson,
                simplifyVector = FALSE)
            self
        },
        toJSONString = function() {
            as.character(jsonlite::toJSON(private$value,
                auto_unbox = TRUE))
        },
        fromJSONString = function(V1ComparisonFilterOperatorJson) {
            private$value <- jsonlite::fromJSON(V1ComparisonFilterOperatorJson,
                simplifyVector = FALSE)
            self
        }
    ),
    private = list(
        value = NULL
    )
)

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

Best regards, Marcel

cc @Leo-Rutschmann @wing328 @ramnov

To close #3367 (closed)