Debug derivation stack overflows due to contravariance (scala 2)

[nafg]

Take this code for instance:

  sealed trait TasksServiceConfig
  object TasksServiceConfig {
    case class GoogleCloudTasks(projectId: String, queueLocation: String, queueName: String) extends TasksServiceConfig
    case object Disabled                                                                     extends TasksServiceConfig

    implicit val debugTasksServiceConfig: Debug[TasksServiceConfig] = {
      @unused implicit val debugGoogleCloudTasks = DeriveDebug.derived[GoogleCloudTasks]
      @unused implicit val debugDisabled         = DeriveDebug.derived[Disabled.type]
      DeriveDebug.derived[TasksServiceConfig]
    }

    val layer = ZLayer.fromFunction((_: AppConfig).tasksService)
  }

Or I could omit the leaf implicits, or I could write it more explicitly as

Debug.make {
  case google: GoogleCloudTasks => google.debug
  case Disabled => Disabled.debug
}

Because Debug is contravariant, debugTasksServiceConfig is the implicit selected for a Debug[GoogleCloudTasks], leading to infinite recursion.