Change in implicit resolution?

[BenFradet]

Hello 👋 ,

We're trying to upgrade a codebase from 0.2.2 to 0.2.3.

Our issues boil down to something like the following:

object Common:
  given Transformer.Fallible[Option, A, B] = ???

import Common.given
object Specialized:
  given Transformer.Fallible[Option, ADTA, ADTB] = _ match
    case V1A(v1) => v1.fallibleTo[V1B]
    // so on and so forth

This is failing with :

Couldn't build a transformation plan between A and scala.Option[B] @ V1.field

whereas it was working nicely with 0.2.2

Thank you,

[arainko]

Heyo! Thanks for submitting a report, could you provide the exact definitions of ADTA and ADTB and the fallible transformer definition in Common or provide a more complete minimization? I'd like to drill in on the exact cause of the problem

[BenFradet]

something like this:

import cats.syntax.apply.*
import io.github.arainko.ducktape.*

opaque type UnsignedLong = Long
extension (long: UnsignedLong) def value: Long = long
object UnsignedLong:
  def apply(l: Long): Either[String, UnsignedLong] =
    Either.cond(l >= 0, l, "Long was < 0, but must be >= 0")

final case class ClockL(epoch: Long, counter: Long)
final case class ClockUL(epoch: UnsignedLong, counter: UnsignedLong)

object Common:
  given Mode.FailFast.Option with {}
  given Transformer.Fallible[Option, Long, UnsignedLong] = l => UnsignedLong(l).toOption
  given Transformer.Fallible[Option, ClockL, ClockUL] = l =>
    (l.epoch.fallibleTo[UnsignedLong], l.counter.fallibleTo[UnsignedLong])
      .mapN(ClockUL.apply)

sealed trait A
final case class AA(w: AAWrapper) extends A
final case class AAWrapper(c: Option[ClockL])
sealed trait B
final case class BB(c: Option[ClockUL]) extends B

object Specialized:
  import Common.given
  given Transformer.Fallible[Option, A, B] =
    case AA(w) => w.fallibleTo[BB]

[arainko]

Thanks! I'll try to get to the bottom of it asap

[arainko]

Sorry, but I can't seem to reproduce the issue, my lightly edited minimization without the usage of cats seems to compile and work just fine:

class Issue187Suite extends DucktapeSuite {
  test("example works") {
    import Issue187Suite.*

    println(Issue187Suite.Specialized.t.transform(AA(AAWrapper(Some(ClockL(123, 123))))))
  }
}

object Issue187Suite {

  opaque type UnsignedLong = Long
  extension (long: UnsignedLong) def value: Long = long
  object UnsignedLong:
    def apply(l: Long): Either[String, UnsignedLong] =
      Either.cond(l >= 0, l, "Long was < 0, but must be >= 0")

  final case class ClockL(epoch: Long, counter: Long)
  final case class ClockUL(epoch: UnsignedLong, counter: UnsignedLong)

  object Common:
    given Mode.FailFast.Option with {}
    given Transformer.Fallible[Option, Long, UnsignedLong] = l => UnsignedLong(l).toOption
    given Transformer.Fallible[Option, ClockL, ClockUL] = l =>
      l.epoch.fallibleTo[UnsignedLong].zip(l.counter.fallibleTo[UnsignedLong]).map(ClockUL.apply)

  sealed trait A
  final case class AA(w: AAWrapper) extends A
  final case class AAWrapper(c: Option[ClockL])
  sealed trait B
  final case class BB(c: Option[ClockUL]) extends B

  object Specialized:
    import Common.given
    given t: Transformer.Fallible[Option, A, B] =
      case AA(w) => w.fallibleTo[BB]
}

the result is: Some(BB(Some(ClockUL(123,123))))

[arainko]

I think I managed to capture the culprit with a transformation like this:

given Transformer.Fallible[Option, Int, String] = a => Some(a.toString)

case class Source(int: Int)
case class Dest(int: Option[String])

Mode.FailFast.option.locally {
   Source(1).fallibleTo[Dest]
}

and it indeed does work in 0.2.2 but breaks in 0.2.3 - it's definitely due to how F-unwrapping takes precedence to the special-cased transformations on options.

[arainko]

I've published 0.2.3-16-ba40550-SNAPSHOT with the fix, it'd be extra-reassuring if you could test this release on your codebase before I pull the trigger on 0.2.4 ❤️

[necosta]

Hi @arainko , thank you very much for the fix. I published from local 0.2.3-15-ff6b08c-SNAPSHOT (branch origin/issue-187) and the issue we had on v0.2.3 no longer occurs in this branch.