gistfile1.scala

sealed trait Base
case class D1(...) extends Base
case class D2(...) extedns Base

// Have defined all instances of EncodeJson & DecodeJson for D1 and D2

// works in 6.0.x but does not compile in 6.1-M5 since DecodeResult is now invariant
implicit val decode: DecodeJson[Base] = DecodeJson { c =>
  (c --\ "storeDelete").as[D1]  |||
  (c --\ "indexState").as[D2]   |||
  DecodeResult.fail(s"Unable to decode payload in [$c.asJson]", c.history)
}