Mill build file with shared Cross project

build.sc

import mill._
import mill.api.Loose
import mill.define.Target
import mill.scalajslib._
import mill.scalalib._
import mill.scalalib.api.CompilationResult

trait BaseModule extends ScalaModule {
  def scalaVersion = T("3.0.0-RC3")
  def scalaJSVersion = T("1.5.1")
  //def scalaNativeVersion = T()
}

trait BaseCrossModule extends BaseModule {
  override def millSourcePath = super.millSourcePath / os.up
}

trait CrossModule extends Module { outer =>
  def moduleDeps: Seq[CrossModule] = Seq.empty
  object jvm extends BaseCrossModule with ScalaModule {
    override def moduleDeps
      = super.moduleDeps ++ outer.moduleDeps.map(_.jvm)
  }
  object js extends BaseCrossModule with ScalaJSModule {
    override def moduleDeps
      = super.moduleDeps ++ outer.moduleDeps.map(_.js)
  }
//  object native extends BaseCrossModule with ScalaNativeModule {
//    def moduleDeps = super.moduleDeps ++ outer.moduleDeps.map(_.native)
//  }
}

//noinspection ScalaFileName
object concur extends Module {

  object core extends CrossModule {

    def ivyDeps: Target[Loose.Agg[Dep]] = Agg(
      ivy"dev.zio::zio::1.0.7"
    )

  }

  object frontend extends BaseModule with ScalaJSModule {

    override def moduleDeps = super.moduleDeps ++ Seq(core.jvm)

    override def ivyDeps: Target[Loose.Agg[Dep]] = T {
      super.ivyDeps() ++ Agg(
        ivy"org.scala-js::scalajs-dom::1.1.0".withDottyCompat(scalaVersion())
      )
    }

  }

  object backend extends BaseModule {

    override def moduleDeps = super.moduleDeps ++ Seq(core.jvm)

    override def ivyDeps: Target[Loose.Agg[Dep]] = T {
      super.ivyDeps() ++ Agg(
        ivy"com.lihaoyi::scalatags:0.9.4".withDottyCompat(scalaVersion()),
        ivy"io.d11::zhttp:1.0.0.0-RC15+10-355fc872-SNAPSHOT"
      )
    }

    override def compile: T[CompilationResult] = T {
      frontend.fastOpt.apply()
      super.compile.apply()
    }

  }

}