Inconsistent encoding/decoding of nested sum types

[matil019]

As of 0.14.5, derived encoder and decoder of a nested sum type are inconsistent. The Decoder can't decode a JSON encoded by the Encoder.

Minimal example:

import io.circe.Decoder
import io.circe.Encoder
import io.circe.generic.semiauto.deriveDecoder
import io.circe.generic.semiauto.deriveEncoder
import io.circe.parser.decode
import io.circe.syntax._

sealed trait Top

object Top {
  sealed trait Middle extends Top

  object Middle {
    case object Bottom extends Middle
  }

  implicit val decodeTop: Decoder[Top] = deriveDecoder
  implicit val encodeTop: Encoder[Top] = deriveEncoder
}

object Main {
  def main(args: Array[String]): Unit = {
    val s = (Top.Middle.Bottom: Top).asJson.noSpaces
    println(s)
    println(decode[Top](s))
  }
}

Expected output (scala:3.2.2, circe:0.14.3)

{"Middle":{"Bottom":{}}}
Right(Bottom)

Actual output (scala:3.2.2, circe:0.14.5)

{"Middle":{"Bottom":{}}}
Left(DecodingFailure at .Middle: type Top has no class/object/case named 'Middle'.)

^ In this case, the decoder can decode {"Bottom":{}} to Bottom.

---

It turned out that both of the above are also inconsistent with scala 2.13 build of circe:

Output (scala:2.13.0, circe:0.14.3/0.14.5)

{"Bottom":{}}
Right(Bottom)

So I'm not sure which encoding is correct.

[Darren Gibson]

I would expect the Scala 2 output, not the Scala 3 output.

[Martin Hansen]

Seems like this relates to / was introduced by #2098 (I didn't look into the code changes (yet), but did test before / after that commit).

[Martin Hansen]

Found a fix for the inconsistency.

(I do agree that the encoded json should be the same as for Scala 2, but fixing that is beyond what I'm currently able to contribute.)

[Martin Hansen]

(I do agree that the encoded json should be the same as for Scala 2, but fixing that is beyond what I'm currently able to contribute.)

Nevermind - found a better way to fix the inconsistency that also fixes the encoding to {"Bottom":{}}.