Could not find implicit value for nested parameter of same case class type (recursive reference)

[vidalgp]

Cheers folks,

I am migrating the code base from scala 2.13.10 to 2.13.12 and I'm having troubles with the following issue:

Given the case class:

case class MyAttribute(
    name: MyAttribute.AttributeName,
    values: Map[MyAttribute.AttributeValue, Seq[MyAttribute]]
) {
  val rootValues: Set[MyAttribute.AttributeValue] = values.keySet
}
object MyAttribute {
  type AttributeValue = String
  type AttributeName  = String
}

In Scala 2.13.10 i was able to let the compile figure out the type of an implicit val and everything worked as expected:

implicit val MyAttributePickler  = generatePickler[MyAttribute] ✅

Now with Scala 2.13.12 the compiler will throw an error:

"Implicit definition should have explicit type ..."

Then when we do define explicitly this type:

implicit val MyAttributePickler: Pickler[MyAttribute]  = generatePickler[MyAttribute] ❌

We get the error:

"could not find implicit value for parameter p: boopickle.Pickler[Map[MyAttribute.AttributeValue,Seq[MyAttribute]]]"

which I believe is because the class is referenced in itself. Is there a workaround for this?

Thanks in advanced for your input

---

EDIT:

As a workaround i found that manually defining the Pickler does the job.

  new Pickler[MyAttribute] {
    override def pickle(obj: MyAttribute)(implicit state: PickleState): Unit = {
      // Serialize the name and values fields manually
      state.pickle(obj.name)
      state.pickle(obj.values)
    }
    override def unpickle(implicit state: UnpickleState): MyAttribute = {
      // Deserialize the name and values fields manually
      val name   = state.unpickle[MyAttribute.AttributeName]
      val values = state.unpickle[Map[MyAttribute.AttributeValue, Seq[MyAttribute]]]
      MyAttribute(name, values)
    }
  }

Maybe this could be improved in a future version, but I will close the issue as the workaround is rather simple.