[elm-client] Recursive type aliases

Created by: andys8

A recursive data structure will lead to elm code, which is not being parsed. The main issue and how to workaround is described here: https://github.com/elm/compiler/blob/0.18.0/hints/recursive-alias.md

    "tags": {
      "type": "object",
      "properties": {
        "id": {
          "type": "string",
          "format": "uuid",
        },
        "children": {
          "type": "array",
          "items": { "$ref": "#/definitions/tags" }
        }
      }
    }

Will generate this:

type alias Tags =
    { id : UUID
    , children : List Tags
    }


tagsDecoder : Decoder Tags
tagsDecoder =
    decode Tags
        |> required "id" uUIDDecoder
        |> required "children" (Decode.list tagsDecoder)


tagsEncoder : Tags -> Encode.Value
tagsEncoder model =
    Encode.object
        [ ( "id", uUIDEncoder model.id )
        , ( "children", (Encode.list << List.map tagsEncoder) model.children )
        ]

But should be something like this, where Decode.lazy is used and a type definition for the recursive list:

type alias Tags =
    { id : UUID
    , children : Children
    }


type Children
    = Children (List Tags)


childrenToTags : Children -> List Tags
childrenToTags (Children tags) =
    tags


tagsDecoder : Decoder Tags
tagsDecoder =
    decode Tags
        |> required "id" uUIDDecoder
        |> required "children"
            (Decode.map Children (Decode.list (Decode.lazy (\_ -> tagsDecoder))))


tagsEncoder : Tags -> Encode.Value
tagsEncoder model =
    Encode.object
        [ ( "id", uUIDEncoder model.id )
        , ( "children", (Encode.list << List.map tagsEncoder) (childrenToTags model.children) )
        ]

OpenAPI spec version: 0.4.0 Generator version 3.0.1