Robustness of pattern matching Trees with quasiquotes

Question

I have a macro and part of that macro consists of replacing every call to a certain method with something else. To accomplish this I use a Transformer and try to match every Tree that enters the transform method against a quasiquote. When I write it like below, it seems to work.

package mypackage

object myobject {
  implicit def mymethod[T](t: Option[T]): T = ???
}

object Macros {
  import scala.language.experimental.macros
  import scala.reflect.macros.blackbox.Context

  def myMacro(c: Context)(expr: c.Tree): c.Tree = {
    import c.universe._

    val transformer = new Transformer {
      private def doSomething(value: c.Tree): TermName = {
        ???
      }
      override def transform(tree: c.Tree) = tree match {
        case q"mypackage.myobject.mymethod[..$_]($value)" => 
          val result = doSomething(value)
          q"$result"
        case _ => super.transform(tree)
      }
    }
    val transformed = transformer.transform(expr)

    ???
  }
}

But I thought you should always use fully qualified names in macros or you could get into trouble. So I wrote it like q"_root_.mypackage.myobject.mymethod[..$_]($value)", but then it no longer matched and the calls to mymethod no longer got replaced.
I also looked at the suggestion in the scala docs to unquote symbols, but I couldn't get that to work either.

So my question is: will this code (with q"mypackage.myobject.mymethod[..$_]($value)") always replace all the calls to mymethod and never replace any other method calls? And if not, how can I make it more robust?

Answer 1

scala.reflect macros are non hygienic, so, theoretically, q"mypackage.myobject.mymethod[..$_]($value)" could be matched by someone else.

I'd suggest match that method with q"..$mods def $name[..$tparams](...$paramss): $tpeopt = $expr" (assuming that is definition, not declaration). You can add checks on name.

Another solution is to mark method with annotation, and remove it in macro phase.