Support for cats 0.8.0

[nmeln]

Xor is gone in cats 0.8.0.
typelevel/cats#1310

AFAIK kantan.csv-cats uses Xor, so migration to Either is needed.

[nrinaudo]

Yes, you're absolutely correct. I'm actually working on that as we speak, but it forces other issues to the front: I need to upgrade to more recent versions of scalacheck and discipline, which break a lot of things.

But yes, that's what's driving the next release and it's at the top of the list of priorities.

[ScalaWilliam]

Managed to reduce to:

import org.scalacheck._
import org.scalacheck.derive._
import org.scalatest.FunSuite
import org.scalatest.prop.GeneratorDrivenPropertyChecks

class Testor extends FunSuite with GeneratorDrivenPropertyChecks
  with DerivedInstances
{
  sealed trait Or[+A, +B] extends Product with Serializable

  case class Left[A](a: A) extends Or[A, Nothing]

  case class Right[B](b: B) extends Or[Nothing, B]

  type T = Unit ⇒ Float Or Boolean

  test("Rep again") {
    var good: Int = 0
    var bad: Int = 0
    var caught: Throwable = null
    val frall = Prop.forAll({
      (a: T) =>
        try {
          a(())
          good = good + 1
        }
        catch {
          case e: Throwable =>
            bad = bad + 1
            caught = e
        }
        Prop(true)
    })
    frall.main(Array.empty)
    info(s"Good = ${good}, Bad = ${bad}")
    throw caught
  }
}

[info] - Rep again *** FAILED ***
[info]   org.scalacheck.Gen$RetrievalError: couldn't generate value
[info]   at org.scalacheck.Gen.loop$1(Gen.scala:57)
[info]   at org.scalacheck.Gen.doPureApply(Gen.scala:58)
[info]   at org.scalacheck.Gen.pureApply(Gen.scala:72)
[info]   at org.scalacheck.GenArities$$anonfun$function1$1$$anonfun$1.apply(GenArities.scala:15)
[info]   at Testor$$anonfun$1$$anonfun$2.apply(Testor.scala:22)
[info]   at Testor$$anonfun$1$$anonfun$2.apply(Testor.scala:20)
[info]   at scala.Function1$$anonfun$andThen$1.apply(Function1.scala:52)
[info]   at org.scalacheck.Prop$$anonfun$forAllShrink$1$$anonfun$3.apply(Prop.scala:712)
[info]   at org.scalacheck.Prop$$anonfun$forAllShrink$1$$anonfun$3.apply(Prop.scala:712)
[info]   at org.scalacheck.Prop$.secure(Prop.scala:456)
[info]   ...
[info]   + Good = 99, Bad = 1 

[ScalaWilliam]

Changing to:

sealed trait Or[+A, +B] extends Product with Serializable
case class Left[A, B](a: A) extends Or[A, B]
case class Right[A, B](b: B) extends Or[A, B]

Fixes this for some reason. Do you necessarily needs the Nothing's?
Why not just use Scala's Either?

[ScalaWilliam]

Just looking at the cats, they moved it all to Scala's Either.
If vanilla Either is not working between both versions -- you can have multiple sources per Scala version, and create a type alias for your Or.

[nrinaudo]

Thanks a lot for the test cases, I need to look into them as soon as possible.

As or cats having moved to Either, that's not the point of this test. Its purpose is to use shapeless to derive automatic encoder and decoder instances for a "complex" ADT. Or is only ever used in this test.

[ScalaWilliam]

Good news. Reduced the test case further.

import org.scalacheck._
import org.scalacheck.derive._
import org.scalacheck.rng.Seed
import org.scalatest.FunSuite
import org.scalatest.prop.GeneratorDrivenPropertyChecks

class Testor extends FunSuite with GeneratorDrivenPropertyChecks
  with DerivedInstances {

  sealed trait Or[+A, +B]

  final case class Right[B](b: B) extends Or[Nothing, B]

  type T = Unit ⇒ Float Or Boolean

  test("Better test case") {
    val arb = implicitly[Arbitrary[T]].arbitrary
    arb.doPureApply(Gen.Parameters.default.withSize(0), seed = Seed.random(), retries = 0)
      .retrieve.get.apply(())
  }

}

Output:

[info] - Better test case *** FAILED ***
[info]   org.scalacheck.Gen$RetrievalError: couldn't generate value
[info]   at org.scalacheck.Gen.loop$1(Gen.scala:57)
[info]   at org.scalacheck.Gen.doPureApply(Gen.scala:58)
[info]   at org.scalacheck.Gen.pureApply(Gen.scala:72)
[info]   at org.scalacheck.GenArities$$anonfun$function1$1$$anonfun$1.apply(GenArities.scala:15)
[info]   at Testor$$anonfun$1.apply(Testor.scala:19)
[info]   at Testor$$anonfun$1.apply(Testor.scala:16)
[info]   at org.scalatest.OutcomeOf$class.outcomeOf(OutcomeOf.scala:85)
[info]   at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
[info]   at org.scalatest.Transformer.apply(Transformer.scala:22)
[info]   at org.scalatest.Transformer.apply(Transformer.scala:20)
[info]   ...

build.sbt for anyone:

resolvers += Resolver.sonatypeRepo("releases")

libraryDependencies += "com.github.alexarchambault" %% "scalacheck-shapeless_1.13" % "1.1.3"
libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.0" % "test"
scalaVersion := "2.11.8"

When generation size is 0 then Gen.fail is used. I'm not sure what is the purpose of this is so far. Here's the specific line of code.

https://github.com/alexarchambault/scalacheck-shapeless/blob/master/core/shared/src/main/scala/org/scalacheck/derive/MkArbitrary.scala#L120

So:

• Either ScalaCheck is wrongly calling generation size 0
• Or MkArbitrary uses Gen.fail incorrectly.

[ScalaWilliam]

Maybe @alexarchambault has something to say?

[alexarchambault]

@nrinaudo @ScalaWilliam Yep, this: http://stackoverflow.com/questions/40390846/deriving-arbitrary-function-instances-using-shapeless-scalacheck/40412807#40412807 :-)

[ScalaWilliam]

@nrinaudo that should be a sufficient solution

[nrinaudo]

It would be, but it doesn't actually work - yet. I might be doing something wrong. Or, alternatively, if @alexarchambault intends to fix that at the scalacheck-shapeless level, I've no issue with disabling these tests and re-enabling them when a fix a available.

[nrinaudo]

0.1.16-SNAPSHOT is being published as I type this and has support for cats 0.8.0.

[nrinaudo]

Note that I'm waiting on #58 before releasing 0.1.16. It's just a matter of time - I'm still waiting for a typelevel cats 2.12.0 build, which I believe is ready and just needs to be published.

[ScalaWilliam]

What resolver should I use? Doesn't work for me.

[nrinaudo]

@ScalaWilliam ah, yes, not everyone has sonatype-snapshots enabled by default :)

This is what you need:

scalaVersion := "2.11.8"

resolvers := Seq(Resolver.sonatypeRepo("snapshots"))

libraryDependencies += "com.nrinaudo" %% "kantan.csv" % "0.1.16-SNAPSHOT"