Trait expansion macro

Macros.scala

object helloMacro {
  def impl(c: Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
    import c.universe._
    import Flag._
    val result = {
      annottees.map(_.tree).toList match {
        case q"trait $name extends ..$parents { ..$body }" :: Nil =>
          q"""
            trait $name extends ..$parents {
              def hello = "hello"
              ..$body
            }
          """
      }
    }
    c.Expr[Any](result)
  }
}

class hello extends StaticAnnotation {
  def macroTransform(annottees: Any*) = macro helloMacro.impl
}