gistfile1.txt

14:58 ~/Projects/211x/sandbox (2.11.x)$ cat Macros.scala
import scala.reflect.macros.whitebox._
import scala.language.experimental.macros

object Macros {
  def macroImpl[T: c.WeakTypeTag](c: Context) = {
    import c.universe._
    val tpe = weakTypeTag[T].tpe
    implicit class RichType(tpe: Type) {
      def pre: Type = tpe match {
        case SingleType(pre, _) => pre
        case TypeRef(pre, _, _) => pre // this doesn't dealias!
        case PolyType(_, underlying) => underlying.pre
        case ExistentialType(_, underlying) => underlying.pre
        case AnnotatedType(_, underlying) => underlying.pre
        case _ => c.abort(c.enclosingPosition, s"unexpected type $tpe: ${showRaw(tpe)}")
      }
    }
    val companionRef = c.internal.gen.mkAttributedRef(tpe.pre, tpe.typeSymbol.companion)
    q"$companionRef"
  }

  def myMacro[T]: Any = macro macroImpl[T]
}

14:58 ~/Projects/211x/sandbox (2.11.x)$ cat Test.scala
trait Trt3{
  case class Cls(i: Int)
}
trait Trt2{
  object Obj2 extends Trt3
}
trait Trt1{
  object Obj1 extends Trt2
}
object Obj extends Trt1

object Test extends App {
  println(Macros.myMacro[Obj.Obj1.Obj2.Cls])
}

14:58 ~/Projects/211x/sandbox (2.11.x)$ scalac Macros.scala && scalac Test.scala && scala Test
Cls

14:59 ~/Projects/211x/sandbox (2.11.x)$

In 2.10

// ==> sandbox/Macro.scala <==
import scala.reflect.macros.Context
import scala.language.experimental.macros

object Macros {
  def macroImpl[T: c.WeakTypeTag](c: Context): c.Expr[Any] = {
    import c.universe._
    val tpe = weakTypeTag[T].tpe
    val symTab = c.universe.asInstanceOf[reflect.internal.SymbolTable]
    val pre = tpe.asInstanceOf[symTab.Type].prefix.asInstanceOf[Type]
    val companionRef = c.universe.treeBuild.mkAttributedRef(pre, tpe.typeSymbol.companionSymbol)
    c.Expr(companionRef)
  }

  def myMacro[T]: Any = macro macroImpl[T]
}

// ==> sandbox/Test.scala <==
trait Trt3{
  case class Cls(i: Int)
}
trait Trt2{
  object Obj2 extends Trt3
}
trait Trt1{
  object Obj1 extends Trt2
}
object Obj extends Trt1

object Test extends App {
  println(Macros.myMacro[Obj.Obj1.Obj2.Cls])

  class C {
    class D
    object D
  }
  val c = new C
  println(Macros.myMacro[c.D])
}

% (export V=v2.10.4; scalac-hash $V sandbox/Macro.scala && scalac-hash $V sandbox/Test.scala && scala-hash $V Test)
Cls
Test$C$D$@b4c966a

Note: the switch to downcasting to access Type#prefix, rather than the copy/pasted impl above isn't necessary.

Testing with prefixes like c above (which is not a "static" prefix) is important for this sort of thing.