Auto derivation of Circe codecs for shapeless Newtypes and TaggedTypes

circe.scala

import io.circe.{Decoder, Encoder}

trait Implicits {
  /** Derive circe codecs for newtypes and tagged types. */
  implicit def coercibleEncoder[R, N](implicit ev: Coercible[Encoder[R], Encoder[N]], R: Encoder[R]): Encoder[N] = ev(R)
  implicit def coercibleDecoder[R, N](implicit ev: Coercible[Decoder[R], Decoder[N]], R: Decoder[R]): Decoder[N] = ev(R)
}

Coercible.scala

import shapeless.newtype.Newtype

/** Coercion to derive [[shapeless.newtype.Newtype]] and [[shapeless.tag.Tagged]] type classes */
trait Coercible[A, B] {
  def apply(a: A): B = a.asInstanceOf[B]
}

object Coercible {
  implicit def newTypeToCoercible[R: * => O, O]: Coercible[R, Newtype[R, O]] = new Coercible[R, Newtype[R, O]] { }
  implicit def newTypeToCoercibleK[F[_], R: Coercible[*, Newtype[R, O]]: * => O, O]: Coercible[F[R], F[Newtype[R, O]]] = new Coercible[F[R], F[Newtype[R, O]]] { }

  implicit def taggedTpeToCoercible[T, U]: Coercible[T, T @@ U] = new Coercible[T, T @@ U] { }
  implicit def taggedTypeToCoercibleK[F[_], T: Coercible[*, T @@ U], U]: Coercible[F[T], F[T @@ U]] = new Coercible[F[T], F[T @@ U]] { }
}

derivation.scala

package object derivation {
  // to workaround https://github.com/scala/bug/issues/8740
  type @@[+T, U] <: shapeless.tag.@@[T, U]

  // required to use shapeless.tag
  implicit def coerce[T, U](t: shapeless.tag.@@[T, U]): T @@ U = t.asInstanceOf[T @@ U]

  // alias in order not to cause extra coercion call above
  def stag[T, U](value: T): T @@ U = shapeless.tag[U][T](value)
}