lazytrace.scala

package localhost

import scala.tools.nsc
import nsc.Global
import nsc.plugins.Plugin
import nsc.plugins.PluginComponent
import nsc.transform.Transform

class LazyTracePlugin(val global: Global) extends Plugin {
  import global._
  import definitions._

  val name = "lazy-trace"
  val description = "print stack trace in creating lazy value"
  val components = List[PluginComponent](LazyTraceComponent)

  def mkTraceTree =
    Apply( // sym=<none>, tpe=null
      Select( // sym=<none>, sym.tpe=<notype>, tpe=null
	Select( // sym=<none>, sym.tpe=<notype>, tpe=null
	  Select( // sym=<none>, sym.tpe=<notype>, tpe=null
            Ident("Thread"), // sym=<none>, sym.tpe=<notype>, tpe=null,
            "currentThread"),
	  "getStackTrace"),
	"foreach"),
      List( // 1 arguments(s)
	Ident("println") // sym=<none>, sym.tpe=<notype>, tpe=null
      )
    )

  private object LazyTraceComponent extends PluginComponent with Transform{

    val global: LazyTracePlugin.this.global.type = LazyTracePlugin.this.global
    val runsAfter = List[String]("parser")
    val phaseName = LazyTracePlugin.this.name

    def newTransformer(unit: global.CompilationUnit) = LazyTraceTransformer

    object LazyTraceTransformer extends global.Transformer {
      override def transform(tree: global.Tree) = {
        tree match {
	  case ValDef(mods, name, tpe, rhs) if mods.isLazy=>
	    ValDef(mods, name, tpe, Block(mkTraceTree,rhs))
	  case t => super.transform(t)
	}
      }
    }
  }
}