Recursive derivation not working

[ahoy-jon]

probably the same as #401 (not sure)

While working on some examples with @guihardbastien, we can see with this code when the recursion fails: https://scastie.scala-lang.org/ahoy-jon/ijmFz87ESKO2vr6Syf3qRw/13

import language.experimental.macros, magnolia1._


trait Tc[T] 

trait TcObj[T] extends Tc[T]


object ShowDerivation {
  type Typeclass[T] = Tc[T]
  
  
  def join[T](ctx: CaseClass[Tc, T]): TcObj[T] = new TcObj[T] {}

  def split[T](ctx: SealedTrait[Tc, T]): TcObj[T] = new TcObj[T] {}
  

  def gen[T]: Tc[T] = macro Magnolia.gen[T]
  
  def genObj[T]: TcObj[T] = macro Magnolia.gen[T]
}


sealed trait A

case object B extends A

case class C(next:A) extends A


ShowDerivation.gen[B.type] //success

ShowDerivation.genObj[B.type] //success

ShowDerivation.gen[A] //success

//ShowDerivation.genObj[A] //failure

/*
type mismatch;
 found   : Playground.ShowDerivation.Typeclass[Playground.A]
    (which expands to)  Playground.Tc[Playground.A]
 required: Playground.TcObj[Playground.A]
*/


implicit val tca:Tc[A] = null

ShowDerivation.gen[C] //success

ShowDerivation.genObj[C] //success