Scala 3 - Arbitrary typeclass derivation

ArbitraryDeriving.scala

package me.panavtec.scalacheck

import org.scalacheck.Arbitrary
import org.scalacheck.Gen

import scala.compiletime.{erasedValue, summonInline}
import scala.deriving.*

object ArbitraryDeriving:

  inline def summonAll[T <: Tuple]: List[Arbitrary[?]] =
    inline erasedValue[T] match
      case _: EmptyTuple => Nil
      case _: (t *: ts)  => summonInline[Arbitrary[t]] :: summonAll[ts]

  inline given derived[T](using m: Mirror.Of[T]): Arbitrary[T] =
    val elemInstances = summonAll[m.MirroredElemTypes]
    inline m match
      case s: Mirror.SumOf[T]     => deriveSum(s, elemInstances)
      case p: Mirror.ProductOf[T] => deriveProduct(p, elemInstances)

  def deriveSum[T](s: Mirror.SumOf[T], elems: List[Arbitrary[?]]): Arbitrary[T] =
    Arbitrary(
      Gen
        .chooseNum(0, elems.size - 1)
        .flatMap(elems(_).arbitrary.asInstanceOf[Gen[T]])
    )

  def deriveProduct[T](p: Mirror.ProductOf[T], elems: List[Arbitrary[?]]): Arbitrary[T] =
    Arbitrary(
      elems
        .foldRight[Gen[Tuple]](Gen.const(EmptyTuple)) { (arb: Arbitrary[?], acc: Gen[Tuple]) =>
          arb.arbitrary.flatMap { gen => acc.map(gen *: _) }
        }
        .map(p.fromProduct(_))
    )

Examples.scala

final case class SomeProduct(
    id: String,
    name: String,
    color: Color
)

enum Color:
  case Red
  case Blue
  
object SomeProduct:
  val f: SomeProduct = summon[Arbitrary[SomeProduct]].sample.get
  
  given Arbitrary[Red.type] = ArbitraryDeriving.derived
  given Arbitrary[Blue.type] = ArbitraryDeriving.derived
  given Arbitrary[Color] = ArbitraryDeriving.derived
  given Arbitrary[SomeProduct] = ArbitraryDeriving.derived