Get instances of a typeclass `TC[_]` for all cases of a Coproduct [shapeless]

Ex.scala

import shapeless._

@annotation.implicitNotFound("Make sure all cases of ${C} have an instance of ${TC}")
trait CopTCs[C <: Coproduct, TC[_]] {
  type Out <: HList
  def result: Out
}
object CopTCs {
  type Aux[C <: Coproduct, TC[_], O <: HList] = CopTCs[C, TC] { type Out = O }
  def apply[C <: Coproduct, TC[_]](implicit ev: CopTCs[C, TC]) = ev

  implicit def cnil[TC[_]]: CopTCs.Aux[CNil, TC, HNil]  = new CopTCs[CNil, TC] {
    type Out = HNil
    def result = HNil
  }

  implicit def ccons[TC[_], L, R <: Coproduct, O <: HList](implicit ev: TC[L], rest: CopTCs.Aux[R, TC, O]): CopTCs.Aux[L :+: R, TC, TC[L] :: O] = new CopTCs[L :+: R, TC] {
    type Out = TC[L] :: O
    def result = ev :: rest.result
  }
}

object Ex {
  import cats._, implicits._

  type Monoids = Int :+: String :+: CNil
  type Nope
  type NotMonoids = Nope :+: Monoids

  def instances = CopTCs[Monoids, Monoid].result
  // res0: CopTCs[Ex.Monoids,cats.Monoid]#Out = cats.kernel.instances.IntGroup@69aba755 :: cats.kernel.instances.StringMonoid@981dd7c :: HNil

  def compilationError = CopTCs[NotMonoids, Monoid].result
//    Make sure all cases of Ex.NotMonoids have an instance of cats.Monoid
// [error]   def compilationError = CopTCs[NotMonoids, Monoid].result

}