When I try to add a macro annotation to my case class:
@macid case class CC[A: T](val x: A)
I get the error:
private[this] not allowed for case class parameters
@macid
is just the identity function, defined as a whitebox StaticAnnotation:
import scala.language.experimental.macros
import scala.reflect.macros.whitebox.Context
import scala.annotation.StaticAnnotation
class macid extends StaticAnnotation {
def macroTransform(annottees: Any*): Any = macro macidMacro.impl
}
object macidMacro {
def impl(c: Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
new Macros[c.type](c).macidMacroImpl(annottees.toList)
}
}
class Macros[C <: Context](val c: C) {
import c.universe._
def macidMacroImpl(annottees: List[c.Expr[Any]]): c.Expr[Any] =
annottees(0)
}
The unannotated code works:
case class CC[A: T](val x: A)
It works if I remove the context bound:
@macid case class CC[A](val x: A)
What's happening is the context bound is desugared into a private parameter. The following desugared code gets the same error:
@macid case class CC[A](val x: A)(implicit aIsT: T[A])
To get working code I make the implicit parameter public with val
:
@macid case class CC[A](val x: A)(implicit val aIsT: T[A])
So my questions are: What's the right way for a macro annotation to support context bounds? Why does the compiler perform a no-private-parameters-of-case-classes check for code that's generated by a macro annotation, but doesn't perform the check for ordinary code?
Scala versions 2.11.7 and 2.12.0-M3 both report the error. All the above code examples compile and run as expected in 2.11.3.