Embedded collection of Enumeration values causes errors in serialization of collection of objects

I have observed weird behavior of serialization of objects with collection of Enumeration values (for example case class User(roles: Seq[Roles.Value])) . Serialization of collection of this objects (for example Seq[User]) produces JSON Object with double-colon attribute: {"::":[obj1, obj2, ...]}, when correct output should be JSON Array: [obj1, obj2, ...].

This error does not occur when instead of Enumeration values we have other objects (even with custom Encoders).

Workaround: Implement your own Encoder for collection of Enumeration values.

Minimal example:

import io.circe._
import io.circe.syntax._
import io.circe.generic.auto._

object Roles extends Enumeration {
  val Admin, Guest = Value
}

implicit object RoleEncoder extends Encoder[Roles.Value] {
  override def apply(r: Roles.Value): Json = r.toString.asJson
}

case class User(roles: Seq[Roles.Value])

val u = User(Seq(Roles.Admin))

Seq(u).asJson.noSpaces
// ERROR: res0: String = {"::":[{"roles":["Admin"]}]}

implicit object RolesSeqEncoder extends Encoder[Seq[Roles.Value]] {
  override def apply(rs: Seq[Roles.Value]): Json = rs.map(_.asJson).asJson
}

Seq(u).asJson.noSpaces
// OK: res1: String = [{"roles":["Admin"]}]

[travisbrown]

@dzikowski I’ve got an enumeration-less minimization:

import io.circe._
import io.circe.syntax._
import io.circe.generic.auto._

object X { case class Foo(i: Int) }

implicit val encodeFoo: Encoder[X.Foo] = Encoder[Int].contramap(_.i)

case class Foos(values: Seq[X.Foo])

List(Foos(List(X.Foo(1)))).asJson.noSpaces
// res0: String = {"::":[{"xs":[1]}]}

And I’ve tracked down the problem, although I don’t have a solution yet (short of adding a Shapeless dependency to core so we can use Lazy in the default Seq encoder, which unfortunately isn’t really an option).

Thanks for reporting this! It’s definitely a big problem, in an area where I thought we’d worked out all the corner cases. I’ll do my best to get a fix in today.

[travisbrown]

Confirmed that this is resolved in all current Scala version on master.