[Scala 3] - Wildcard derivation import not working

[gvolpe]

Super simple reproduction:

import cats.Show
// import cats.derived.semiauto.{ derived, product } // this works
// import cats.derived.semiauto.{ given, * } // this works (as per the 3rd comment)
import cats.derived.semiauto.* // does not work

enum TradeAction derives Show:
  case Ask, Bid

It fails with the following error:

no implicit argument of type cats.Show[(Playground.TradeAction.Ask : Playground.TradeAction)] was found

The following import might fix the problem:

  import cats.derived.semiauto.product

https://scastie.scala-lang.org/0q4XaUbJTqibfe78MuyzAA

---

Not sure whether this has already been discussed or not but I figured it might be better to keep track of it right here.

[gvolpe]

Another example that adds Eq:

import cats.{ Eq, Show }
// import cats.derived.semiauto.{ derived, product, productOrder } // this works
import cats.derived.semiauto.* // does not work

enum ForecastTag derives Eq, Show:
  case Long, Short

Fails with the following error:

no implicit argument of type cats.kernel.Eq[(Playground.ForecastTag.Long : Playground.ForecastTag)] was found

The following import might fix the problem:

  import cats.derived.semiauto.productEq

no implicit argument of type cats.Show[(Playground.ForecastTag.Long : Playground.ForecastTag)] was found

https://scastie.scala-lang.org/HGVuAPc3TlmfGyirNlYVxw

[gvolpe]

There are a few other (probably related) issues with sealed trait as well, if it's useful, I can try to produce a minimal reproducible example of this: https://github.com/gvolpe/trading/blob/main/modules/domain/src/main/scala/trading/commands/ForecastCommand.scala#L8

[gvolpe]

Ok, the first one is simply fixed with this import

import cats.derived.semiauto.{ given, * }

The second and the latter still do not work, though.

[gvolpe]

Hmmm this for some reason does not compile locally:

import cats.{ Eq, Show }
import cats.derived.semiauto.{ given, * } 
import cats.syntax.all.*

enum TradingStatus derives Eq, Show:
  case On, Off

object TradingStatus:
  def from(str: String): Option[TradingStatus] =
    Either.catchNonFatal(valueOf(str)).toOption

Fails with this error:

[error] -- Error: /home/gvolpe/workspace/trading/modules/domain/src/main/scala/trading/domain/TradingStatus.scala:8:27
[error] 8 |enum TradingStatus derives Eq, Show:
[error]   |                           ^
[error]   |ambiguous implicit arguments: both given instance productOrder in trait OrderDerivation and given instance productHash in trait HashDerivation match type cats.kernel.Eq[(trading.domain.TradingStatus.On : trading.domain.TradingStatus)]
[error]   | This location contains code that was inlined from deriving.scala:35
[error]   | This location contains code that was inlined from deriving.scala:30
[error]   | This location contains code that was inlined from erased.scala:301
[error]   | This location contains code that was inlined from kinds.scala:149
[error]   | This location contains code that was inlined from eq.scala:24
[error] one error found
[error] one error found
[error] (domain / Compile / compileIncremental) Compilation failed

But it compiles just fine on Scastie: https://scastie.scala-lang.org/7Eqo9m1hRNCdhX55GTTBdw

I need to dig in more into this.

[joroKr21]

Kittens for Scala 3 is not ready yet - I think some functionality is missing / implemented inconsistently in the released version.

But we are blocked by a Scala compiler issue: scala/scala3#13406
On the other hand we need a newer version that contains this fix: scala/scala3#14003

[gvolpe]

Thanks for the quick reply, @joroKr21 !

I understand it's not ready yet. Are you keeping track of the issues / limitations somewhere else? If not, it's probably a good idea to have them on this repo, no?

[joroKr21]

I understand it's not ready yet. Are you keeping track of the issues / limitations somewhere else? If not, it's probably a good idea to have them on this repo, no?

Yeah, I'm just not sure if this is a limitation that applies in general or we just need to get unblocked by fixing that Scala bug and release 😄

[gvolpe]

Got you! Ok, if you don't mind, I'll leave this issue open but will refrain from opening new ones. I was aware of these issues for a while but I thought I should raise it here now that the project where I use Kittens is public 😄

[TimWSpence]

Thanks @gvolpe! It's great to have feedback on what else we might need to fix once we're unblocked upstream 😅

[joroKr21]

Let's just go for it and release what we can - even if it's not working perfectly at least people can use it.
#427 is the first step. We still have a around half the type classes to port.

[gvolpe]

That is awesome, thanks @joroKr21 🤩