splain 0.4.1 on scala 2.13... breaks by-name implicits ?

[chwthewke]

Hello,

I'm somewhat confused, but I think I have a weird one here.

Apparently, using splain breaks the new in Scala 2.13 "by-name implicits", such as used for generic derivation in Typelevel Kittens (https://github.com/typelevel/kittens)

A short example such as:

import cats.Show
import cats.derived.semi
import cats.instances.string._

case class Inner( x: Option[Int] )

object Inner {
  implicit val innerShow: Show[Inner] =
    Show.show( _.x.fold( "*" )( _.toString ) )
}

case class Outer( name: String, inner: Inner )

object Outer {
  implicit val outerShow: Show[Outer] = semi.show[Outer]
}

compiles fine without splain but fails with splain. The failing output is:

[error] !I ev: MkShow[Outer]
[error] Lazy.instance invalid because
[error] !I ev: <byname>[MkShow[Outer]]
[error]     implicit val outerShow: Show[Outer] = semi.show[Outer]

which seems to point towards a by-name implicit in kittens (which should indeed occur somewhere in the expected derivation).

Should it be useful, I've put a minimal-ish reproduction at https://github.com/chwthewke/splain-by-name (not so minimal because it starts from my usual template sadly, but I took care to disable anything that could interfere so it should reproduce nicely). The project has two modules with the same source, one with splain active, the other without. It targets scala 2.13.1 but from other testing I think 2.13.0 is similarly affected.

Thank you

[tek]

thanks! will take a look

[tek]

here we go. damn default arguments! :imp: :smile: I did quite a bit of (unrelated) restructuring, so there might be unintended side effects. If something is weird, please report!

[chwthewke]

Whoa that was fast! Many thanks!