Wrapped Option type results in Json decoding failure missing required field

[kamilkloch]

(Scala 2)

type WsTag = WsTag.Type

object WsTag extends NewtypeWrapped[Option[Long]] with DerivedCirceCodec

case class A(wsTag: WsTag, i: Int)

implicit val decoder: Decoder[A] = io.circe.generic.semiauto.deriveDecoder
println(io.circe.parser.parse("""{"i" : 1}""").value.as[A])

results in

Left(DecodingFailure at .wsTag: Missing required field)

Replacing WsTag with the underlying type Option[Long] in A gets rid of the error:

case class A(wsTag: Option[Long], i: Int)

println(io.circe.parser.parse("""{"i" : 1}""").value.as[A])

> Right(A(None,1))

[kamilkloch]

Update: defining Decoder manually as follows:

implicit val decoder: Decoder[WsTag] = implicitly[Decoder[Option[Long]]].map(unsafeCoerce)

solves the issue. It looks that the special handling of Option by the decoder may be lost in

trait DerivedCirceDecoder {
  implicit def jsonDecoder[T, S](implicit 
    builder: HasBuilder.Aux[T, S],
    dec: Decoder[S],
  ): Decoder[T] = {
    jsonDecode(_)
  }
}