Comparing Chunk to Seq causes ClassCastException

[andrzejressel]

Scala 3 (2.13 does not compile with found Seq, require Chunk error)
Both 2.0 and 2.1-RC

https://scastie.scala-lang.org/7CX9Y9D3QYq0v4TNcsIDmw

object Suite extends ZIOSpecDefault {
  override def spec = suite("suite") {
    test("test") {
     assertTrue(Chunk(1, 2, 3) == Seq(1, 2, 3, 4));
    }
  }
}

  - suite�[2m / test
    ✗ ERROR: java.lang.ClassCastException: class scala.collection.immutable.$colon$colon cannot be cast to class zio.Chunk (scala.collection.immutable.$colon$colon is in unnamed module of loader sbt.internal.ScalaLibraryClassLoader @5ad07354; zio.Chunk is in unnamed module of loader sbt.internal.ReverseLookupClassLoader @3094bb)
      zio.test.diff.DiffInstances.mkSeqDiff$$anonfun$1(Diff.scala:113)
      zio.test.internal.SmartAssertions$.equalTo$$anonfun$1(SmartAssertions.scala:291)
    Chunk(1, 2, 3) == Seq(1, 2, 3, 4)
    �[2m(1, 2, 3) = Chunk(1, 2, 3)
    �[2mChunk = zio.Chunk$@3f018ce
    at /tmp/scastie5353637521019907974/src/main/scala/main.scala:10 

[andrzejressel]

I believe it's caused by

      case Unseal(MethodCall(lhs, "==", tpes, Some(List(rhs)))) =>
        val span = getSpan(rhs)
        lhs.tpe.widen.asType match {
          case '[l] =>
            Expr.summon[OptionalImplicit[Diff[l]]] match {
              case Some(optDiff) =>
                '{${transform(lhs.asExpr)} >>> SmartAssertions.equalTo(${rhs.asExpr})($optDiff.asInstanceOf[OptionalImplicit[Diff[Any]]]).span($span)}.asExprOf[TestArrow[Any, A]]
              case _ => throw new Error("OptionalImplicit should be always available")
            }
        }

lhs should be first common class (GCD of class I guess)

[jdegoes]

/bounty $50

[algora-pbc]

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Attempt	Started (GMT+0)	Solution
🟢 @kyri-petrou		#8848

[andrzejressel]

I was wrong with my initial checks - Chunk and Seq are related. It just required proper mapping logic like in Scala 2.13

[joroKr21]

lhs should be first common class (GCD of class I guess)

LUB and GLB are not exposed in Scala 3 macros. You could make Diff[-A] contravariant and use A | B.

[andrzejressel]

I was writing that before i knew how Scala 2 macro work - it should propably work like it. So one class has to be subtype of another.

[joroKr21]

I was writing that before i knew how Scala 2 macro work - it should propably work like it.

Not sure what you mean. This is Scala 3.

So one class has to be subtype of another.

Nope, LUB doesn't require one class to be subtype of the other.

[andrzejressel]

I meant that assertTrue in Scala 2 does not allow unrelated classes for any comparison. Scala 3 should propably have the same behaviour.

[andrzejressel]

S3 unfortunately does allow it and it generate pretty ugly comparisons - I think I would prefer for it to be reported during compilation.

[joroKr21]

They are related though, Chunk extends Seq

[andrzejressel]

Yes, this specific issue is about directly related classes (which I didn't know at the beginning) and I want to focus on that.

The issue with non directly related classes is that they are all ultimately related anyway thought Any (which have diff instance). And I like Scala 2 behavior of not allowing comparisons of non directly related classes.

[andrzejressel]

Maybe it just my thing - but when I'm comparing A to option A or Seq A, I'd rather have compile error than downcast to Any.