Macros: knownDirectSubclasses broken with nested type?

问题

I have a macro which enumerates the direct sub types of a sealed trait:

import scala.reflect.macros.Context
import language.experimental.macros

object Checker {
  def apply[A]: Unit = macro applyImpl[A]

  def applyImpl[A: c.WeakTypeTag](c: Context): c.Expr[Unit] = {
    val tpe = c.weakTypeOf[A].typeSymbol.asClass
    require (tpe.isSealed)
    tpe.typeSignature // SI-7046
    require (tpe.knownDirectSubclasses.nonEmpty)

    import c.universe._
    c.Expr[Unit](reify {} .tree)
  }
}

Then this works:

sealed trait A
case class A1(i: Int) extends A

object NotNested {
  val nada = Checker[A]
}

But this fails:

object Nested {
  sealed trait A
  case class A1(i: Int) extends A

  val nada = Checker[A]
}

[error] java.lang.IllegalArgumentException: requirement failed: 
        Did not find sub classes

I thought I ran into SI-7046, so I added the call to tpe.typeSignature, but that doesn't help apparently.

I need a work around for this using Scala 2.10.2. Somehow I must enforce some extra type trees to be initialised, I guess?

回答1:

A possible workaround is following (what do you think @EugeneBurmako).

val cls: ClassSymbol = sub.asClass

println(s"knownDirectSubclasses = ${cls.knownDirectSubclasses}")
// print "knownDirectSubclasses = Set()"

val subsub = cls.owner.typeSignature.decls.filter {
  case c: ClassSymbol =>
    cls != c && c.selfType.baseClasses.contains(cls)

  case _ => false
}

println(s"subsub = $subsub")
// print the actual sub classes

来源：https://stackoverflow.com/questions/17165932/macros-knowndirectsubclasses-broken-with-nested-type

标签

scala

macros

inner-classes