0.2.0 macro expansion creates unused ZLayer.requires[Any] val, which triggers scalac warnings

Thanks @kitlangton for back-porting layer memoization, it’s a life-saver!

It did create a new issue: there is now a val layer$macro$1 = ZLayer.requires[Any]; val generated, which will trigger scalac warnings since it’s unused. Here’s a reproducer:

Given this scalac options in build.sbt:

scalacOptions := Seq(
  "-Wunused:_", // Warn unused
  "-Wmacros:after", // Warn after macro expansions, a must for Scala 2.13.5+, else there are tons of false positive warnings due to typeclass derivation for most Scala libraries out there
  "-Wconf:any:wv"
)

And this app:

import zio.{Has, ZLayer}
import zio.magic._

object ZioMagicUnusedWarnings {
  def main(args: Array[String]): Unit = {
    val layer = ZLayer.fromMagic[Has[Double]](
      ZLayer.requires[Has[Int]].map(v => Has(v.get.toDouble)),
      ZLayer.succeed(123)
    )

    println(layer)
  }
}

The macro will expand into:

val layer$macro$1 = ZLayer.requires[Any];
val layer$macro$2 = zio.ZLayer.requires[zio.Has[Int]].map[zio.Has[Double]](((v: zio.Has[Int]) =>
  zio.Has.apply[Double](zio.this.Has.HasSyntax[zio.Has[Int]](v).get[Int](
    scala.this.<:<.refl[zio.Has[Int]],
    (izumi.reflect.Tag.apply[Int](
      classOf[scala.Int],
      izumi.reflect.macrortti.LightTypeTag.parse[Nothing](
        (1454689320: Int),
        ("\u0004\u0000\u0001\tscala.Int\u0001\u0001": String),
        ("\u0000\u0001\u0004\u0000\u0001\tscala.Int\u0001\u0001\u0001\u0004\u0000\u0001\fscala.AnyVal\u0001\u0001\u0001\u0000\u0001\u0090\u0002\u0001\u0001\u0001\u0000\u0001\u0090\u0003\u0001\u0001": String),
        (1: Int)
      )
    ): izumi.reflect.Tag[Int])
  ).toDouble)((izumi.reflect.Tag.apply[Double](
    classOf[scala.Double],
    izumi.reflect.macrortti.LightTypeTag.parse[Nothing](
      (1618223923: Int),
      ("\u0004\u0000\u0001\fscala.Double\u0001\u0001": String),
      ("\u0000\u0001\u0004\u0000\u0001\fscala.Double\u0001\u0001\u0001\u0004\u0000\u0001\fscala.AnyVal\u0001\u0001\u0001\u0000\u0001\u0090\u0002\u0001\u0001\u0001\u0000\u0001\u0090\u0003\u0001\u0001": String),
      (1: Int)
    )
  ): izumi.reflect.Tag[Double])))
);
val layer$macro$3 = zio.ZLayer.succeed[Int](123)((izumi.reflect.Tag.apply[Int](
  classOf[scala.Int],
  izumi.reflect.macrortti.LightTypeTag.parse[Nothing](
    (1454689320: Int),
    ("\u0004\u0000\u0001\tscala.Int\u0001\u0001": String),
    ("\u0000\u0001\u0004\u0000\u0001\tscala.Int\u0001\u0001\u0001\u0004\u0000\u0001\fscala.AnyVal\u0001\u0001\u0001\u0000\u0001\u0090\u0002\u0001\u0001\u0001\u0000\u0001\u0090\u0003\u0001\u0001": String),
    (1: Int)
  )
): izumi.reflect.Tag[Int]));
layer$macro$3.$greater$greater$greater(layer$macro$2)

Looks like Any should just be ignored when decomposing the Env type.

[nktpro]

0.2.2 did it! I don’t see any more of those so will close this now.

[nktpro]

@kitlangton Oh I just added "-Ymacro-debug-lite" to scalacOptions, scary output for sure 😃)

Also hopefully this PR will catch all of those in the future https://github.com/kitlangton/zio-magic/pull/48