//> using options -Wunused:all 

trait MonadThrow[F[_]]
extension [T](value: T) def liftTo[F[_]](using MonadThrow[F]): F[T] = ???

trait Api[F[_]]:
  def setMaxAge(value: Int): F[Unit]
  def truncate(): F[Unit]

trait MetaStreamsSyntax:
  extension [F[_]](ms: Api[F])(using MonadThrow[F]) // warns: 
    def withMaxAge(): F[Unit] = 
      val lifted = 0.liftTo[F] // uses MonadThrow
      assert(lifted != null) // to enusre this val is used
      assert(ms != null) // to ensure ms is used
      ???
      
    def truncated(): F[Unit] = 
      ms.truncate() // required to trigger warning, does not warn if ms is not used

[warn] ./example.scala:11:38
[warn] unused implicit parameter
[warn]   extension [F[_]](ms: Api[F])(using MonadThrow[F])
[warn]