Erreur chelou de play-json qui ne trouve pas un formateur pourtant existant.

NonEmptyListMaxSizeJsonFmt.scala

import domain.common.collection.{NonEmptyListMaxSizeExceeded, NonEmptyListMaxSizeNewType}
import domain.common.collection.NonEmptyListMaxSizeNewType.NEL_MaxSize_2
import play.api.libs.json._

object NonEmptyListMaxSizeJsonFmt {
	import NonEmptyListJsonFmt.nonEmptyListJsonFmt

	implicit def nonemptyListMaxSize_2_JsonFmt[A](implicit fmt: Format[A]) = new Format[NEL_MaxSize_2.List_[A]] {
		override def writes(o: NonEmptyListMaxSizeNewType.NEL_MaxSize_2.List_[A]): JsValue = nonEmptyListJsonFmt[A].writes(NEL_MaxSize_2.rawValue(o))

		override def reads(json: JsValue): JsResult[NonEmptyListMaxSizeNewType.NEL_MaxSize_2.List_[A]] = nonEmptyListJsonFmt[A].reads(json).flatMap { nel =>
			NEL_MaxSize_2.apply(nel).fold(
				error => error match {
					case NonEmptyListMaxSizeExceeded(maxSize, size) => JsError(s"list has size of $size that exceed the fixed max size of $maxSize")
				},
				nel => JsSuccess(nel)
			)

		}
	}
	
    case class Toto(s: String)
    case class Titi(t: NEL_MaxSize_2.List_[Toto])

implicit val toto = Json.format[Toto]
implicit val titi = Json.format[Titi]

/**
	No instance of play.api.libs.json.Format is available for domain.common.collection.NonEmptyListMaxSizeBuilder.NonEmptyListMaxSizeImpl[service.binding.json.NonEmptyListMaxSizeJsonFmt.Toto] in the implicit scope (Hint: if declared in the same file, make sure it's declared before)
[error] 	implicit val titi = Json.format[Titi]

Et j'ai ce message d'erreur.

*/
}

NonEmptyListMaxSizeNewType.scala

import scalaz.Scalaz.ToEitherOps
import scalaz.{NonEmptyList, \/}
import service.utils.collection.NEL

object NonEmptyListMaxSizeNewType {
	object NEL_MaxSize_2 extends NonEmptyListMaxSizeBuilder(2) {
		//override def maxSize: Int = 2
	}
}

sealed trait NonEmptyListMaxSizeError
case class NonEmptyListMaxSizeExceeded(maxSize: Int, size: Int) extends NonEmptyListMaxSizeError

class NonEmptyListMaxSizeBuilder(maxSize: Int) {
	private[NonEmptyListMaxSizeBuilder] case class NEL_Impl[+A](h: A, t: List[A])
	case class NonEmptyListMaxSizeImpl[+A](rawValue: NEL_Impl[A])
	type List_[+A] = NonEmptyListMaxSizeImpl[A]

	def apply[A](rawValue: NonEmptyList[A]): NonEmptyListMaxSizeError \/ List_[A] = {
		if(rawValue.size <= maxSize) buildType(rawValue).right
		else NonEmptyListMaxSizeExceeded(maxSize, rawValue.size).left
	}


	private def buildType[A](nel: NonEmptyList[A]) = NonEmptyListMaxSizeImpl(NEL_Impl(nel.head, nel.tail.toList))

	...
}