import scala.tools.partest._

trait BugBase [A, E] {
  val key: A
  var next: E = _
}

final class Bug[A, B](val key: A) extends BugBase[A, Bug[A, B]] {
  def foo = next
}

object Test extends SigTest {
  def main(args: Array[String]): Unit = {
    show[BugBase[_, _]]()
    show[Bug[_, _]]()    
  }
}