path: root/src/compiler/scala/tools/nsc/ast/Trees.scala

/* NSC -- new Scala compiler
 * Copyright 2005-2011 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package ast

import scala.collection.mutable.ListBuffer
import scala.tools.nsc.symtab.SymbolTable
import scala.tools.nsc.symtab.Flags._
import scala.tools.nsc.util.{ FreshNameCreator, HashSet, SourceFile }

trait Trees extends reflect.generic.Trees { self: SymbolTable =>

  trait CompilationUnitTrait {
    var body: Tree
    val source: SourceFile
    def fresh : FreshNameCreator
    def freshTermName(prefix: String): TermName
    def freshTypeName(prefix: String): TypeName
  }

  type CompilationUnit <: CompilationUnitTrait

  protected def flagsIntoString(flags: Long, privateWithin: String): String = flagsToString(flags, privateWithin)

  // sub-components --------------------------------------------------

  lazy val treePrinter = newTreePrinter()

  object treeInfo extends {
    val trees: Trees.this.type = Trees.this
  } with TreeInfo

  val treeCopy = new LazyTreeCopier()

  implicit def treeWrapper(tree: Tree): TreeOps = new TreeOps(tree)

  class TreeOps(tree: Tree) {
    def isTerm: Boolean = tree match {
      case _: TermTree       => true
      case Bind(name, _)     => name.isTermName
      case Select(_, name)   => name.isTermName
      case Ident(name)       => name.isTermName
      case Annotated(_, arg) => arg.isTerm
      case DocDef(_, defn)   => defn.isTerm
      case _                 => false
    }

    def isType: Boolean = tree match {
      case _: TypTree        => true
      case Bind(name, _)     => name.isTypeName
      case Select(_, name)   => name.isTypeName
      case Ident(name)       => name.isTypeName
      case Annotated(_, arg) => arg.isType
      case DocDef(_, defn)   => defn.isType
      case _                 => false
    }

    def isErroneous = (tree.tpe ne null) && tree.tpe.isErroneous
    def isTyped     = (tree.tpe ne null) && !tree.tpe.isErroneous

    /** Apply `f' to each subtree */
    def foreach(f: Tree => Unit) { new ForeachTreeTraverser(f).traverse(tree) }

    /** If 'pf' is defined for a given subtree, call super.traverse(pf(tree)),
     *  otherwise super.traverse(tree).
     */
    def foreachPartial(pf: PartialFunction[Tree, Tree]) { new ForeachPartialTreeTraverser(pf).traverse(tree) }

    /** Find all subtrees matching predicate `p' */
    def filter(f: Tree => Boolean): List[Tree] = {
      val ft = new FilterTreeTraverser(f)
      ft.traverse(tree)
      ft.hits.toList
    }

    /** Returns optionally first tree (in a preorder traversal) which satisfies predicate `p',
     *  or None if none exists.
     */
    def find(p: Tree => Boolean): Option[Tree] = {
      val ft = new FindTreeTraverser(p)
      ft.traverse(tree)
      ft.result
    }

    def changeOwner(pairs: (Symbol, Symbol)*): Tree = {
      pairs.foldLeft(tree) { case (t, (oldOwner, newOwner)) =>
        new ChangeOwnerTraverser(oldOwner, newOwner) apply t
      }
    }

    /** Is there part of this tree which satisfies predicate `p'? */
    def exists(p: Tree => Boolean): Boolean = !find(p).isEmpty

    def equalsStructure(that : Tree) = equalsStructure0(that)(_ eq _)
    def equalsStructure0(that: Tree)(f: (Tree,Tree) => Boolean): Boolean =
      f(tree, that) || ((tree.productArity == that.productArity) && {
        def equals0(this0: Any, that0: Any): Boolean = (this0, that0) match {
          case (x: Tree, y: Tree)         => f(x, y) || (x equalsStructure0 y)(f)
          case (xs: List[_], ys: List[_]) => (xs corresponds ys)(equals0)
          case _                          => this0 == that0
        }
        def compareOriginals() = (tree, that) match {
          case (x: TypeTree, y: TypeTree) if x.original != null && y.original != null =>
            (x.original equalsStructure0 y.original)(f)
          case _                          =>
            true
        }

        (tree.productIterator zip that.productIterator forall { case (x, y) => equals0(x, y) }) && compareOriginals()
      })

    def shallowDuplicate: Tree = new ShallowDuplicator(tree) transform tree
    def shortClass: String = tree.getClass.getName split "[.$]" last
  }

  private[scala] override def duplicateTree(tree: Tree): Tree = duplicator transform tree

// ---- values and creators ---------------------------------------

  /** @param sym       the class symbol
   *  @return          the implementation template
   */
  def ClassDef(sym: Symbol, impl: Template): ClassDef =
    atPos(sym.pos) {
      ClassDef(Modifiers(sym.flags),
               sym.name.toTypeName,
               sym.typeParams map TypeDef,
               impl) setSymbol sym
    }

  /** Construct class definition with given class symbol, value parameters,
   *  supercall arguments and template body.
   *
   *  @param sym        the class symbol
   *  @param constrMods the modifiers for the class constructor, i.e. as in `class C private (...)'
   *  @param vparamss   the value parameters -- if they have symbols they
   *                    should be owned by `sym'
   *  @param argss      the supercall arguments
   *  @param body       the template statements without primary constructor
   *                    and value parameter fields.
   */
  def ClassDef(sym: Symbol, constrMods: Modifiers, vparamss: List[List[ValDef]], argss: List[List[Tree]], body: List[Tree], superPos: Position): ClassDef =
    ClassDef(sym,
      Template(sym.info.parents map TypeTree,
               if (sym.thisSym == sym || phase.erasedTypes) emptyValDef else ValDef(sym.thisSym),
               constrMods, vparamss, argss, body, superPos))

  /**
   *  @param sym       the class symbol
   *  @param impl      the implementation template
   */
  def ModuleDef(sym: Symbol, impl: Template): ModuleDef =
    atPos(sym.pos) {
      ModuleDef(Modifiers(sym.flags), sym.name, impl) setSymbol sym
    }

  def ValDef(sym: Symbol, rhs: Tree): ValDef =
    atPos(sym.pos) {
      ValDef(Modifiers(sym.flags), sym.name,
             TypeTree(sym.tpe) setPos sym.pos.focus,
             rhs) setSymbol sym
    }

  def ValDef(sym: Symbol): ValDef = ValDef(sym, EmptyTree)

  object emptyValDef extends ValDef(Modifiers(PRIVATE), nme.WILDCARD, TypeTree(NoType), EmptyTree) {
    override def isEmpty = true
    super.setPos(NoPosition)
    override def setPos(pos: Position) = { assert(false); this }
  }

  def DefDef(sym: Symbol, mods: Modifiers, vparamss: List[List[ValDef]], rhs: Tree): DefDef =
    atPos(sym.pos) {
      assert(sym != NoSymbol)
      DefDef(Modifiers(sym.flags),
             sym.name,
             sym.typeParams map TypeDef,
             vparamss,
             TypeTree(sym.tpe.finalResultType) setPos sym.pos.focus,
             rhs) setSymbol sym
    }

  def DefDef(sym: Symbol, vparamss: List[List[ValDef]], rhs: Tree): DefDef =
    DefDef(sym, Modifiers(sym.flags), vparamss, rhs)

  def DefDef(sym: Symbol, mods: Modifiers, rhs: Tree): DefDef =
    DefDef(sym, mods, sym.paramss map (_.map(ValDef)), rhs)

  def DefDef(sym: Symbol, rhs: Tree): DefDef =
    DefDef(sym, Modifiers(sym.flags), rhs)

  def DefDef(sym: Symbol, rhs: List[List[Symbol]] => Tree): DefDef = {
    DefDef(sym, rhs(sym.info.paramss))
  }

  /** A TypeDef node which defines given `sym' with given tight hand side `rhs'. */
  def TypeDef(sym: Symbol, rhs: Tree): TypeDef =
    atPos(sym.pos) {
      TypeDef(Modifiers(sym.flags), sym.name.toTypeName, sym.typeParams map TypeDef, rhs) setSymbol sym
    }

  /** A TypeDef node which defines abstract type or type parameter for given `sym' */
  def TypeDef(sym: Symbol): TypeDef =
    TypeDef(sym, TypeBoundsTree(TypeTree(sym.info.bounds.lo), TypeTree(sym.info.bounds.hi)))

  def LabelDef(sym: Symbol, params: List[Symbol], rhs: Tree): LabelDef =
    atPos(sym.pos) {
      LabelDef(sym.name, params map Ident, rhs) setSymbol sym
    }

  /** Generates a template with constructor corresponding to
   *
   *  constrmods (vparams1_) ... (vparams_n) preSuper { presupers }
   *  extends superclass(args_1) ... (args_n) with mixins { self => body }
   *
   *  This gets translated to
   *
   *  extends superclass with mixins { self =>
   *    presupers' // presupers without rhs
   *    vparamss   // abstract fields corresponding to value parameters
   *    def <init>(vparamss) {
   *      presupers
   *      super.<init>(args)
   *    }
   *    body
   *  }
   */
  def Template(parents: List[Tree], self: ValDef, constrMods: Modifiers, vparamss: List[List[ValDef]], argss: List[List[Tree]], body: List[Tree], superPos: Position): Template = {
    /* Add constructor to template */

    // create parameters for <init> as synthetic trees.
    var vparamss1 =
      vparamss map (vps => vps.map { vd =>
        atPos(vd.pos.focus) {
          ValDef(
            Modifiers(vd.mods.flags & (IMPLICIT | DEFAULTPARAM | BYNAMEPARAM) | PARAM | PARAMACCESSOR) withAnnotations vd.mods.annotations,
            vd.name, vd.tpt.duplicate, vd.rhs.duplicate)
        }})
    val (edefs, rest) = body span treeInfo.isEarlyDef
    val (evdefs, etdefs) = edefs partition treeInfo.isEarlyValDef
    val (lvdefs, gvdefs) = evdefs map {
      case vdef @ ValDef(mods, name, tpt, rhs) =>
        val fld = treeCopy.ValDef(
          vdef.duplicate, mods, name,
          atPos(vdef.pos.focus) { TypeTree() setOriginal tpt setPos tpt.pos.focus }, // atPos in case
          EmptyTree)
        val local = treeCopy.ValDef(vdef, Modifiers(PRESUPER), name, tpt, rhs)
        (local, fld)
    } unzip

    val constrs = {
      if (constrMods hasFlag TRAIT) {
        if (body forall treeInfo.isInterfaceMember) List()
        else List(
          atPos(wrappingPos(superPos, lvdefs)) (
            DefDef(NoMods, nme.MIXIN_CONSTRUCTOR, List(), List(List()), TypeTree(), Block(lvdefs, Literal(())))))
      } else {
        // convert (implicit ... ) to ()(implicit ... ) if its the only parameter section
        if (vparamss1.isEmpty || !vparamss1.head.isEmpty && vparamss1.head.head.mods.isImplicit)
          vparamss1 = List() :: vparamss1;
        val superRef: Tree = atPos(superPos) {
          Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR)
        }
        val superCall = (superRef /: argss) (Apply)
        List(
          atPos(wrappingPos(superPos, lvdefs ::: argss.flatten)) (
            DefDef(constrMods, nme.CONSTRUCTOR, List(), vparamss1, TypeTree(), Block(lvdefs ::: List(superCall), Literal(())))))
      }
    }
    // println("typed template, gvdefs = "+gvdefs+", parents = "+parents+", constrs = "+constrs)
    constrs foreach (ensureNonOverlapping(_, parents ::: gvdefs))
    // vparamss2 are used as field definitions for the class. remove defaults
    val vparamss2 = vparamss map (vps => vps map { vd =>
      treeCopy.ValDef(vd, vd.mods &~ DEFAULTPARAM, vd.name, vd.tpt, EmptyTree)
    })
    Template(parents, self, gvdefs ::: vparamss2.flatten ::: constrs ::: etdefs ::: rest)
  }

  /** casedef shorthand */
  def CaseDef(pat: Tree, body: Tree): CaseDef = CaseDef(pat, EmptyTree, body)

  def Bind(sym: Symbol, body: Tree): Bind =
    Bind(sym.name, body) setSymbol sym


  /** Factory method for object creation `new tpt(args_1)...(args_n)`
   *  A `New(t, as)` is expanded to: `(new t).<init>(as)`
   */
  def New(tpt: Tree, argss: List[List[Tree]]): Tree = {
    assert(!argss.isEmpty)
    val superRef: Tree = Select(New(tpt), nme.CONSTRUCTOR)
    (superRef /: argss) (Apply)
  }

  def Apply(sym: Symbol, args: Tree*): Tree =
    Apply(Ident(sym), args.toList)

  def Super(sym: Symbol, mix: TypeName): Tree = Super(This(sym), mix)

  def This(sym: Symbol): Tree = This(sym.name.toTypeName) setSymbol sym

  def Select(qualifier: Tree, sym: Symbol): Select =
    Select(qualifier, sym.name) setSymbol sym

  def Ident(sym: Symbol): Ident =
    Ident(sym.name) setSymbol sym

  /** Block factory that flattens directly nested blocks.
   */
  def Block(stats: Tree*): Block = stats match {
    case Seq(b @ Block(_, _)) => b
    case Seq(stat) => Block(stats.toList, Literal(Constant(())))
    case Seq(_, rest @ _*) => Block(stats.init.toList, stats.last)
  }

  /** A synthetic term holding an arbitrary type.  Not to be confused with
    * with TypTree, the trait for trees that are only used for type trees.
    * TypeTree's are inserted in several places, but most notably in
    * <code>RefCheck</code>, where the arbitrary type trees are all replaced by
    * TypeTree's. */
  case class TypeTree() extends AbsTypeTree {
    private var orig: Tree = null
    private[Trees] var wasEmpty: Boolean = false

    def original: Tree = orig
    def setOriginal(tree: Tree): this.type = {
      def followOriginal(t: Tree): Tree = t match {
        case tt: TypeTree => followOriginal(tt.original)
        case t => t
      }

      orig = followOriginal(tree); setPos(tree.pos);
      this
    }

    override def defineType(tp: Type): this.type = {
      wasEmpty = isEmpty
      setType(tp)
    }
  }

  object TypeTree extends TypeTreeExtractor

  def TypeTree(tp: Type): TypeTree = TypeTree() setType tp

  /** Documented definition, eliminated by analyzer */
  case class DocDef(comment: DocComment, definition: Tree)
       extends Tree {
    override def symbol: Symbol = definition.symbol
    override def symbol_=(sym: Symbol) { definition.symbol = sym }
    // sean: seems to be important to the IDE
    override def isDef = definition.isDef
  }

  /** Either an assignment or a named argument. Only appears in argument lists,
   *  eliminated by typecheck (doTypedApply)
   */
  case class AssignOrNamedArg(lhs: Tree, rhs: Tree)
       extends TermTree

  case class Parens(args: List[Tree]) extends Tree // only used during parsing

  /** emitted by typer, eliminated by refchecks */
  case class TypeTreeWithDeferredRefCheck()(val check: () => TypeTree) extends AbsTypeTree

// ----- subconstructors --------------------------------------------

  class ApplyToImplicitArgs(fun: Tree, args: List[Tree]) extends Apply(fun, args)

  class ApplyImplicitView(fun: Tree, args: List[Tree]) extends Apply(fun, args)

// ----- auxiliary objects and methods ------------------------------

  abstract class TreeCopier {
    def ClassDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], impl: Template): ClassDef
    def PackageDef(tree: Tree, pid: RefTree, stats: List[Tree]): PackageDef
    def ModuleDef(tree: Tree, mods: Modifiers, name: Name, impl: Template): ModuleDef
    def ValDef(tree: Tree, mods: Modifiers, name: Name, tpt: Tree, rhs: Tree): ValDef
    def DefDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], vparamss: List[List[ValDef]], tpt: Tree, rhs: Tree): DefDef
    def TypeDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], rhs: Tree): TypeDef
    def LabelDef(tree: Tree, name: Name, params: List[Ident], rhs: Tree): LabelDef
    def Import(tree: Tree, expr: Tree, selectors: List[ImportSelector]): Import
    def DocDef(tree: Tree, comment: DocComment, definition: Tree): DocDef
    def Template(tree: Tree, parents: List[Tree], self: ValDef, body: List[Tree]): Template
    def Block(tree: Tree, stats: List[Tree], expr: Tree): Block
    def CaseDef(tree: Tree, pat: Tree, guard: Tree, body: Tree): CaseDef
    def Alternative(tree: Tree, trees: List[Tree]): Alternative
    def Star(tree: Tree, elem: Tree): Star
    def Bind(tree: Tree, name: Name, body: Tree): Bind
    def UnApply(tree: Tree, fun: Tree, args: List[Tree]): UnApply
    def ArrayValue(tree: Tree, elemtpt: Tree, trees: List[Tree]): ArrayValue
    def Function(tree: Tree, vparams: List[ValDef], body: Tree): Function
    def Assign(tree: Tree, lhs: Tree, rhs: Tree): Assign
    def AssignOrNamedArg(tree: Tree, lhs: Tree, rhs: Tree): AssignOrNamedArg
    def If(tree: Tree, cond: Tree, thenp: Tree, elsep: Tree): If
    def Match(tree: Tree, selector: Tree, cases: List[CaseDef]): Match
    def Return(tree: Tree, expr: Tree): Return
    def Try(tree: Tree, block: Tree, catches: List[CaseDef], finalizer: Tree): Try
    def Throw(tree: Tree, expr: Tree): Throw
    def New(tree: Tree, tpt: Tree): New
    def Typed(tree: Tree, expr: Tree, tpt: Tree): Typed
    def TypeApply(tree: Tree, fun: Tree, args: List[Tree]): TypeApply
    def Apply(tree: Tree, fun: Tree, args: List[Tree]): Apply
    def ApplyDynamic(tree: Tree, qual: Tree, args: List[Tree]): ApplyDynamic
    def Super(tree: Tree, qual: Tree, mix: TypeName): Super
    def This(tree: Tree, qual: Name): This
    def Select(tree: Tree, qualifier: Tree, selector: Name): Select
    def Ident(tree: Tree, name: Name): Ident
    def Literal(tree: Tree, value: Constant): Literal
    def TypeTree(tree: Tree): TypeTree
    def TypeTreeWithDeferredRefCheck(tree: Tree): TypeTreeWithDeferredRefCheck
    def Annotated(tree: Tree, annot: Tree, arg: Tree): Annotated
    def SingletonTypeTree(tree: Tree, ref: Tree): SingletonTypeTree
    def SelectFromTypeTree(tree: Tree, qualifier: Tree, selector: Name): SelectFromTypeTree
    def CompoundTypeTree(tree: Tree, templ: Template): CompoundTypeTree
    def AppliedTypeTree(tree: Tree, tpt: Tree, args: List[Tree]): AppliedTypeTree
    def TypeBoundsTree(tree: Tree, lo: Tree, hi: Tree): TypeBoundsTree
    def ExistentialTypeTree(tree: Tree, tpt: Tree, whereClauses: List[Tree]): ExistentialTypeTree
    def SelectFromArray(tree: Tree, qualifier: Tree, selector: Name, erasure: Type): SelectFromArray
  }

  class StrictTreeCopier extends TreeCopier {
    def ClassDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], impl: Template) =
      new ClassDef(mods, name.toTypeName, tparams, impl).copyAttrs(tree)
    def PackageDef(tree: Tree, pid: RefTree, stats: List[Tree]) =
      new PackageDef(pid, stats).copyAttrs(tree)
    def ModuleDef(tree: Tree, mods: Modifiers, name: Name, impl: Template) =
      new ModuleDef(mods, name, impl).copyAttrs(tree)
    def ValDef(tree: Tree, mods: Modifiers, name: Name, tpt: Tree, rhs: Tree) =
      new ValDef(mods, name, tpt, rhs).copyAttrs(tree)
    def DefDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], vparamss: List[List[ValDef]], tpt: Tree, rhs: Tree) =
      new DefDef(mods, name, tparams, vparamss, tpt, rhs).copyAttrs(tree)
    def TypeDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], rhs: Tree) =
      new TypeDef(mods, name.toTypeName, tparams, rhs).copyAttrs(tree)
    def LabelDef(tree: Tree, name: Name, params: List[Ident], rhs: Tree) =
      new LabelDef(name, params, rhs).copyAttrs(tree)
    def Import(tree: Tree, expr: Tree, selectors: List[ImportSelector]) =
      new Import(expr, selectors).copyAttrs(tree)
    def DocDef(tree: Tree, comment: DocComment, definition: Tree) =
      new DocDef(comment, definition).copyAttrs(tree)
    def Template(tree: Tree, parents: List[Tree], self: ValDef, body: List[Tree]) =
      new Template(parents, self, body).copyAttrs(tree)
    def Block(tree: Tree, stats: List[Tree], expr: Tree) =
      new Block(stats, expr).copyAttrs(tree)
    def CaseDef(tree: Tree, pat: Tree, guard: Tree, body: Tree) =
      new CaseDef(pat, guard, body).copyAttrs(tree)
    def Alternative(tree: Tree, trees: List[Tree]) =
      new Alternative(trees).copyAttrs(tree)
    def Star(tree: Tree, elem: Tree) =
      new Star(elem).copyAttrs(tree)
    def Bind(tree: Tree, name: Name, body: Tree) =
      new Bind(name, body).copyAttrs(tree)
    def UnApply(tree: Tree, fun: Tree, args: List[Tree]) =
      new UnApply(fun, args).copyAttrs(tree)
    def ArrayValue(tree: Tree, elemtpt: Tree, trees: List[Tree]) =
      new ArrayValue(elemtpt, trees).copyAttrs(tree)
    def Function(tree: Tree, vparams: List[ValDef], body: Tree) =
      new Function(vparams, body).copyAttrs(tree)
    def Assign(tree: Tree, lhs: Tree, rhs: Tree) =
      new Assign(lhs, rhs).copyAttrs(tree)
    def AssignOrNamedArg(tree: Tree, lhs: Tree, rhs: Tree) =
      new AssignOrNamedArg(lhs, rhs).copyAttrs(tree)
    def If(tree: Tree, cond: Tree, thenp: Tree, elsep: Tree) =
      new If(cond, thenp, elsep).copyAttrs(tree)
    def Match(tree: Tree, selector: Tree, cases: List[CaseDef]) =
      new Match(selector, cases).copyAttrs(tree)
    def Return(tree: Tree, expr: Tree) =
      new Return(expr).copyAttrs(tree)
    def Try(tree: Tree, block: Tree, catches: List[CaseDef], finalizer: Tree) =
      new Try(block, catches, finalizer).copyAttrs(tree)
    def Throw(tree: Tree, expr: Tree) =
      new Throw(expr).copyAttrs(tree)
    def New(tree: Tree, tpt: Tree) =
      new New(tpt).copyAttrs(tree)
    def Typed(tree: Tree, expr: Tree, tpt: Tree) =
      new Typed(expr, tpt).copyAttrs(tree)
    def TypeApply(tree: Tree, fun: Tree, args: List[Tree]) =
      new TypeApply(fun, args).copyAttrs(tree)
    def Apply(tree: Tree, fun: Tree, args: List[Tree]) =
      (tree match {
        case _: ApplyToImplicitArgs => new ApplyToImplicitArgs(fun, args)
        case _: ApplyImplicitView => new ApplyImplicitView(fun, args)
        case _ => new Apply(fun, args)
      }).copyAttrs(tree)
    def ApplyDynamic(tree: Tree, qual: Tree, args: List[Tree]) =
      new ApplyDynamic(qual, args).copyAttrs(tree)
    def Super(tree: Tree, qual: Tree, mix: TypeName) =
      new Super(qual, mix).copyAttrs(tree)
    def This(tree: Tree, qual: Name) =
      new This(qual.toTypeName).copyAttrs(tree)
    def Select(tree: Tree, qualifier: Tree, selector: Name) =
      new Select(qualifier, selector).copyAttrs(tree)
    def Ident(tree: Tree, name: Name) =
      new Ident(name).copyAttrs(tree)
    def Literal(tree: Tree, value: Constant) =
      new Literal(value).copyAttrs(tree)
    def TypeTree(tree: Tree) =
      new TypeTree().copyAttrs(tree)
    def TypeTreeWithDeferredRefCheck(tree: Tree) = tree match {
      case dc@TypeTreeWithDeferredRefCheck() => new TypeTreeWithDeferredRefCheck()(dc.check).copyAttrs(tree)
    }
    def Annotated(tree: Tree, annot: Tree, arg: Tree) =
      new Annotated(annot, arg).copyAttrs(tree)
    def SingletonTypeTree(tree: Tree, ref: Tree) =
      new SingletonTypeTree(ref).copyAttrs(tree)
    def SelectFromTypeTree(tree: Tree, qualifier: Tree, selector: Name) =
      new SelectFromTypeTree(qualifier, selector.toTypeName).copyAttrs(tree)
    def CompoundTypeTree(tree: Tree, templ: Template) =
      new CompoundTypeTree(templ).copyAttrs(tree)
    def AppliedTypeTree(tree: Tree, tpt: Tree, args: List[Tree]) =
      new AppliedTypeTree(tpt, args).copyAttrs(tree)
    def TypeBoundsTree(tree: Tree, lo: Tree, hi: Tree) =
      new TypeBoundsTree(lo, hi).copyAttrs(tree)
    def ExistentialTypeTree(tree: Tree, tpt: Tree, whereClauses: List[Tree]) =
      new ExistentialTypeTree(tpt, whereClauses).copyAttrs(tree)
    def SelectFromArray(tree: Tree, qualifier: Tree, selector: Name, erasure: Type) =
      new SelectFromArray(qualifier, selector, erasure).copyAttrs(tree)
  }

  class LazyTreeCopier(treeCopy: TreeCopier) extends TreeCopier {
    def this() = this(new StrictTreeCopier)
    def ClassDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], impl: Template) = tree match {
      case t @ ClassDef(mods0, name0, tparams0, impl0)
      if (mods0 == mods) && (name0 == name) && (tparams0 == tparams) && (impl0 == impl) => t
      case _ => treeCopy.ClassDef(tree, mods, name, tparams, impl)
    }
    def PackageDef(tree: Tree, pid: RefTree, stats: List[Tree]) = tree match {
      case t @ PackageDef(pid0, stats0)
      if (pid0 == pid) && (stats0 == stats) => t
      case _ => treeCopy.PackageDef(tree, pid, stats)
    }
    def ModuleDef(tree: Tree, mods: Modifiers, name: Name, impl: Template) = tree match {
      case t @ ModuleDef(mods0, name0, impl0)
      if (mods0 == mods) && (name0 == name) && (impl0 == impl) => t
      case _ => treeCopy.ModuleDef(tree, mods, name, impl)
    }
    def ValDef(tree: Tree, mods: Modifiers, name: Name, tpt: Tree, rhs: Tree) = tree match {
      case t @ ValDef(mods0, name0, tpt0, rhs0)
      if (mods0 == mods) && (name0 == name) && (tpt0 == tpt) && (rhs0 == rhs) => t
      case _ => treeCopy.ValDef(tree, mods, name, tpt, rhs)
    }
    def DefDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], vparamss: List[List[ValDef]], tpt: Tree, rhs: Tree) = tree match {
      case t @ DefDef(mods0, name0, tparams0, vparamss0, tpt0, rhs0)
      if (mods0 == mods) && (name0 == name) && (tparams0 == tparams) &&
         (vparamss0 == vparamss) && (tpt0 == tpt) && (rhs == rhs0) => t
      case _ => treeCopy.DefDef(tree, mods, name, tparams, vparamss, tpt, rhs)
    }
    def TypeDef(tree: Tree, mods: Modifiers, name: Name, tparams: List[TypeDef], rhs: Tree) = tree match {
      case t @ TypeDef(mods0, name0, tparams0, rhs0)
      if (mods0 == mods) && (name0 == name) && (tparams0 == tparams) && (rhs0 == rhs) => t
      case _ => treeCopy.TypeDef(tree, mods, name, tparams, rhs)
    }
    def LabelDef(tree: Tree, name: Name, params: List[Ident], rhs: Tree) = tree match {
      case t @ LabelDef(name0, params0, rhs0)
      if (name0 == name) && (params0 == params) && (rhs0 == rhs) => t
      case _ => treeCopy.LabelDef(tree, name, params, rhs)
    }
    def Import(tree: Tree, expr: Tree, selectors: List[ImportSelector]) = tree match {
      case t @ Import(expr0, selectors0)
      if (expr0 == expr) && (selectors0 == selectors) => t
      case _ => treeCopy.Import(tree, expr, selectors)
    }
    def DocDef(tree: Tree, comment: DocComment, definition: Tree) = tree match {
      case t @ DocDef(comment0, definition0)
      if (comment0 == comment) && (definition0 == definition) => t
      case _ => treeCopy.DocDef(tree, comment, definition)
    }
    def Template(tree: Tree, parents: List[Tree], self: ValDef, body: List[Tree]) = tree match {
      case t @ Template(parents0, self0, body0)
      if (parents0 == parents) && (self0 == self) && (body0 == body) => t
      case _ => treeCopy.Template(tree, parents, self, body)
    }
    def Block(tree: Tree, stats: List[Tree], expr: Tree) = tree match {
      case t @ Block(stats0, expr0)
      if ((stats0 == stats) && (expr0 == expr)) => t
      case _ => treeCopy.Block(tree, stats, expr)
    }
    def CaseDef(tree: Tree, pat: Tree, guard: Tree, body: Tree) = tree match {
      case t @ CaseDef(pat0, guard0, body0)
      if (pat0 == pat) && (guard0 == guard) && (body0 == body) => t
      case _ => treeCopy.CaseDef(tree, pat, guard, body)
    }
    def Alternative(tree: Tree, trees: List[Tree]) = tree match {
      case t @ Alternative(trees0)
      if trees0 == trees => t
      case _ => treeCopy.Alternative(tree, trees)
    }
    def Star(tree: Tree, elem: Tree) = tree match {
      case t @ Star(elem0)
      if elem0 == elem => t
      case _ => treeCopy.Star(tree, elem)
    }
    def Bind(tree: Tree, name: Name, body: Tree) = tree match {
      case t @ Bind(name0, body0)
      if (name0 == name) && (body0 == body) => t
      case _ => treeCopy.Bind(tree, name, body)
    }
    def UnApply(tree: Tree, fun: Tree, args: List[Tree]) = tree match {
      case t @ UnApply(fun0, args0)
      if (fun0 == fun) && (args0 == args) => t
      case _ => treeCopy.UnApply(tree, fun, args)
    }
    def ArrayValue(tree: Tree, elemtpt: Tree, trees: List[Tree]) = tree match {
      case t @ ArrayValue(elemtpt0, trees0)
      if (elemtpt0 == elemtpt) && (trees0 == trees) => t
      case _ => treeCopy.ArrayValue(tree, elemtpt, trees)
    }
    def Function(tree: Tree, vparams: List[ValDef], body: Tree) = tree match {
      case t @ Function(vparams0, body0)
      if (vparams0 == vparams) && (body0 == body) => t
      case _ => treeCopy.Function(tree, vparams, body)
    }
    def Assign(tree: Tree, lhs: Tree, rhs: Tree) = tree match {
      case t @ Assign(lhs0, rhs0)
      if (lhs0 == lhs) && (rhs0 == rhs) => t
      case _ => treeCopy.Assign(tree, lhs, rhs)
    }
    def AssignOrNamedArg(tree: Tree, lhs: Tree, rhs: Tree) = tree match {
      case t @ AssignOrNamedArg(lhs0, rhs0)
      if (lhs0 == lhs) && (rhs0 == rhs) => t
      case _ => treeCopy.AssignOrNamedArg(tree, lhs, rhs)
    }
    def If(tree: Tree, cond: Tree, thenp: Tree, elsep: Tree) = tree match {
      case t @ If(cond0, thenp0, elsep0)
      if (cond0 == cond) && (thenp0 == thenp) && (elsep0 == elsep) => t
      case _ => treeCopy.If(tree, cond, thenp, elsep)
    }
    def Match(tree: Tree, selector: Tree, cases: List[CaseDef]) =  tree match {
      case t @ Match(selector0, cases0)
      if (selector0 == selector) && (cases0 == cases) => t
      case _ => treeCopy.Match(tree, selector, cases)
    }
    def Return(tree: Tree, expr: Tree) = tree match {
      case t @ Return(expr0)
      if expr0 == expr => t
      case _ => treeCopy.Return(tree, expr)
    }
    def Try(tree: Tree, block: Tree, catches: List[CaseDef], finalizer: Tree) = tree match {
      case t @ Try(block0, catches0, finalizer0)
      if (block0 == block) && (catches0 == catches) && (finalizer0 == finalizer) => t
      case _ => treeCopy.Try(tree, block, catches, finalizer)
    }
    def Throw(tree: Tree, expr: Tree) = tree match {
      case t @ Throw(expr0)
      if expr0 == expr => t
      case _ => treeCopy.Throw(tree, expr)
    }
    def New(tree: Tree, tpt: Tree) = tree match {
      case t @ New(tpt0)
      if tpt0 == tpt => t
      case _ => treeCopy.New(tree, tpt)
    }
    def Typed(tree: Tree, expr: Tree, tpt: Tree) = tree match {
      case t @ Typed(expr0, tpt0)
      if (expr0 == expr) && (tpt0 == tpt) => t
      case _ => treeCopy.Typed(tree, expr, tpt)
    }
    def TypeApply(tree: Tree, fun: Tree, args: List[Tree]) = tree match {
      case t @ TypeApply(fun0, args0)
      if (fun0 == fun) && (args0 == args) => t
      case _ => treeCopy.TypeApply(tree, fun, args)
    }
    def Apply(tree: Tree, fun: Tree, args: List[Tree]) = tree match {
      case t @ Apply(fun0, args0)
      if (fun0 == fun) && (args0 == args) => t
      case _ => treeCopy.Apply(tree, fun, args)
    }
    def ApplyDynamic(tree: Tree, qual: Tree, args: List[Tree]) = tree match {
      case t @ ApplyDynamic(qual0, args0)
      if (qual0 == qual) && (args0 == args) => t
      case _ => treeCopy.ApplyDynamic(tree, qual, args)
    }
    def Super(tree: Tree, qual: Tree, mix: TypeName) = tree match {
      case t @ Super(qual0, mix0)
      if (qual0 == qual) && (mix0 == mix) => t
      case _ => treeCopy.Super(tree, qual, mix)
    }
    def This(tree: Tree, qual: Name) = tree match {
      case t @ This(qual0)
      if qual0 == qual => t
      case _ => treeCopy.This(tree, qual)
    }
    def Select(tree: Tree, qualifier: Tree, selector: Name) = tree match {
      case t @ Select(qualifier0, selector0)
      if (qualifier0 == qualifier) && (selector0 == selector) => t
      case _ => treeCopy.Select(tree, qualifier, selector)
    }
    def Ident(tree: Tree, name: Name) = tree match {
      case t @ Ident(name0)
      if name0 == name => t
      case _ => treeCopy.Ident(tree, name)
    }
    def Literal(tree: Tree, value: Constant) = tree match {
      case t @ Literal(value0)
      if value0 == value => t
      case _ => treeCopy.Literal(tree, value)
    }
    def TypeTree(tree: Tree) = tree match {
      case t @ TypeTree() => t
      case _ => treeCopy.TypeTree(tree)
    }
    def TypeTreeWithDeferredRefCheck(tree: Tree) = tree match {
      case t @ TypeTreeWithDeferredRefCheck() => t
      case _ => treeCopy.TypeTreeWithDeferredRefCheck(tree)
    }
    def Annotated(tree: Tree, annot: Tree, arg: Tree) = tree match {
      case t @ Annotated(annot0, arg0)
      if (annot0==annot) => t
      case _ => treeCopy.Annotated(tree, annot, arg)
    }
    def SingletonTypeTree(tree: Tree, ref: Tree) = tree match {
      case t @ SingletonTypeTree(ref0)
      if ref0 == ref => t
      case _ => treeCopy.SingletonTypeTree(tree, ref)
    }
    def SelectFromTypeTree(tree: Tree, qualifier: Tree, selector: Name) = tree match {
      case t @ SelectFromTypeTree(qualifier0, selector0)
      if (qualifier0 == qualifier) && (selector0 == selector) => t
      case _ => treeCopy.SelectFromTypeTree(tree, qualifier, selector)
    }
    def CompoundTypeTree(tree: Tree, templ: Template) = tree match {
      case t @ CompoundTypeTree(templ0)
      if templ0 == templ => t
      case _ => treeCopy.CompoundTypeTree(tree, templ)
    }
    def AppliedTypeTree(tree: Tree, tpt: Tree, args: List[Tree]) = tree match {
      case t @ AppliedTypeTree(tpt0, args0)
      if (tpt0 == tpt) && (args0 == args) => t
      case _ => treeCopy.AppliedTypeTree(tree, tpt, args)
    }
    def TypeBoundsTree(tree: Tree, lo: Tree, hi: Tree) = tree match {
      case t @ TypeBoundsTree(lo0, hi0)
      if (lo0 == lo) && (hi0 == hi) => t
      case _ => treeCopy.TypeBoundsTree(tree, lo, hi)
    }
    def ExistentialTypeTree(tree: Tree, tpt: Tree, whereClauses: List[Tree]) = tree match {
      case t @ ExistentialTypeTree(tpt0, whereClauses0)
      if (tpt0 == tpt) && (whereClauses0 == whereClauses) => t
      case _ => treeCopy.ExistentialTypeTree(tree, tpt, whereClauses)
    }
    def SelectFromArray(tree: Tree, qualifier: Tree, selector: Name, erasure: Type) = tree match {
      case t @ SelectFromArray(qualifier0, selector0, _)
      if (qualifier0 == qualifier) && (selector0 == selector) => t
      case _ => treeCopy.SelectFromArray(tree, qualifier, selector, erasure)
    }
  }

  abstract class Transformer {
    val treeCopy: TreeCopier = new LazyTreeCopier
    protected var currentOwner: Symbol = definitions.RootClass
    protected def currentMethod = currentOwner.enclMethod
    protected def currentClass = currentOwner.enclClass
    protected def currentPackage = currentOwner.toplevelClass.owner
    def transform(tree: Tree): Tree = tree match {
      case EmptyTree =>
        tree
      case PackageDef(pid, stats) =>
        treeCopy.PackageDef(
          tree, transform(pid).asInstanceOf[RefTree],
          atOwner(tree.symbol.moduleClass) {
            transformStats(stats, currentOwner)
          }
        )
      case ClassDef(mods, name, tparams, impl) =>
        atOwner(tree.symbol) {
          treeCopy.ClassDef(tree, transformModifiers(mods), name,
                            transformTypeDefs(tparams), transformTemplate(impl))
        }
      case ModuleDef(mods, name, impl) =>
        atOwner(tree.symbol.moduleClass) {
          treeCopy.ModuleDef(tree, transformModifiers(mods),
                             name, transformTemplate(impl))
        }
      case ValDef(mods, name, tpt, rhs) =>
        atOwner(tree.symbol) {
          treeCopy.ValDef(tree, transformModifiers(mods),
                          name, transform(tpt), transform(rhs))
        }
      case DefDef(mods, name, tparams, vparamss, tpt, rhs) =>
        atOwner(tree.symbol) {
          treeCopy.DefDef(tree, transformModifiers(mods), name,
                          transformTypeDefs(tparams), transformValDefss(vparamss),
                          transform(tpt), transform(rhs))
        }
      case TypeDef(mods, name, tparams, rhs) =>
        atOwner(tree.symbol) {
          treeCopy.TypeDef(tree, transformModifiers(mods), name,
                           transformTypeDefs(tparams), transform(rhs))
        }
      case LabelDef(name, params, rhs) =>
        treeCopy.LabelDef(tree, name, transformIdents(params), transform(rhs)) //bq: Martin, once, atOwner(...) works, also change `LamdaLifter.proxy'
      case Import(expr, selectors) =>
        treeCopy.Import(tree, transform(expr), selectors)
      case DocDef(comment, definition) =>
        treeCopy.DocDef(tree, comment, transform(definition))
      case Template(parents, self, body) =>
        treeCopy.Template(tree, transformTrees(parents), transformValDef(self), transformStats(body, tree.symbol))
      case Block(stats, expr) =>
        treeCopy.Block(tree, transformStats(stats, currentOwner), transform(expr))
      case CaseDef(pat, guard, body) =>
        treeCopy.CaseDef(tree, transform(pat), transform(guard), transform(body))
      case Alternative(trees) =>
        treeCopy.Alternative(tree, transformTrees(trees))
      case Star(elem) =>
        treeCopy.Star(tree, transform(elem))
      case Bind(name, body) =>
        treeCopy.Bind(tree, name, transform(body))
      case UnApply(fun, args) =>
        treeCopy.UnApply(tree, fun, transformTrees(args)) // bq: see test/.../unapplyContexts2.scala
      case ArrayValue(elemtpt, trees) =>
        treeCopy.ArrayValue(tree, transform(elemtpt), transformTrees(trees))
      case Function(vparams, body) =>
        atOwner(tree.symbol) {
          treeCopy.Function(tree, transformValDefs(vparams), transform(body))
        }
      case Assign(lhs, rhs) =>
        treeCopy.Assign(tree, transform(lhs), transform(rhs))
      case AssignOrNamedArg(lhs, rhs) =>
        treeCopy.AssignOrNamedArg(tree, transform(lhs), transform(rhs))
      case If(cond, thenp, elsep) =>
        treeCopy.If(tree, transform(cond), transform(thenp), transform(elsep))
      case Match(selector, cases) =>
        treeCopy.Match(tree, transform(selector), transformCaseDefs(cases))
      case Return(expr) =>
        treeCopy.Return(tree, transform(expr))
      case Try(block, catches, finalizer) =>
        treeCopy.Try(tree, transform(block), transformCaseDefs(catches), transform(finalizer))
      case Throw(expr) =>
        treeCopy.Throw(tree, transform(expr))
      case New(tpt) =>
        treeCopy.New(tree, transform(tpt))
      case Typed(expr, tpt) =>
        treeCopy.Typed(tree, transform(expr), transform(tpt))
      case TypeApply(fun, args) =>
        treeCopy.TypeApply(tree, transform(fun), transformTrees(args))
      case Apply(fun, args) =>
        treeCopy.Apply(tree, transform(fun), transformTrees(args))
      case ApplyDynamic(qual, args) =>
        treeCopy.ApplyDynamic(tree, transform(qual), transformTrees(args))
      case Super(qual, mix) =>
        treeCopy.Super(tree, transform(qual), mix)
      case This(qual) =>
        treeCopy.This(tree, qual)
      case Select(qualifier, selector) =>
        treeCopy.Select(tree, transform(qualifier), selector)
      case Ident(name) =>
        treeCopy.Ident(tree, name)
      case Literal(value) =>
        treeCopy.Literal(tree, value)
      case TypeTree() =>
        treeCopy.TypeTree(tree)
      case TypeTreeWithDeferredRefCheck() =>
        treeCopy.TypeTreeWithDeferredRefCheck(tree)
      case Annotated(annot, arg) =>
        treeCopy.Annotated(tree, transform(annot), transform(arg))
      case SingletonTypeTree(ref) =>
        treeCopy.SingletonTypeTree(tree, transform(ref))
      case SelectFromTypeTree(qualifier, selector) =>
        treeCopy.SelectFromTypeTree(tree, transform(qualifier), selector)
      case CompoundTypeTree(templ) =>
        treeCopy.CompoundTypeTree(tree, transformTemplate(templ))
      case AppliedTypeTree(tpt, args) =>
        treeCopy.AppliedTypeTree(tree, transform(tpt), transformTrees(args))
      case TypeBoundsTree(lo, hi) =>
        treeCopy.TypeBoundsTree(tree, transform(lo), transform(hi))
      case ExistentialTypeTree(tpt, whereClauses) =>
        treeCopy.ExistentialTypeTree(tree, transform(tpt), transformTrees(whereClauses))
      case SelectFromArray(qualifier, selector, erasure) =>
        treeCopy.SelectFromArray(tree, transform(qualifier), selector, erasure)
    }

    def transformTrees(trees: List[Tree]): List[Tree] =
        trees mapConserve (transform(_))
    def transformTemplate(tree: Template): Template =
      transform(tree: Tree).asInstanceOf[Template]
    def transformTypeDefs(trees: List[TypeDef]): List[TypeDef] =
      trees mapConserve (tree => transform(tree).asInstanceOf[TypeDef])
    def transformValDef(tree: ValDef): ValDef =
      if (tree.isEmpty) tree else transform(tree).asInstanceOf[ValDef]
    def transformValDefs(trees: List[ValDef]): List[ValDef] =
      trees mapConserve (transformValDef(_))
    def transformValDefss(treess: List[List[ValDef]]): List[List[ValDef]] =
      treess mapConserve (transformValDefs(_))
    def transformCaseDefs(trees: List[CaseDef]): List[CaseDef] =
      trees mapConserve (tree => transform(tree).asInstanceOf[CaseDef])
    def transformIdents(trees: List[Ident]): List[Ident] =
      trees mapConserve (tree => transform(tree).asInstanceOf[Ident])
    def transformStats(stats: List[Tree], exprOwner: Symbol): List[Tree] =
      stats mapConserve (stat =>
        if (exprOwner != currentOwner && stat.isTerm) atOwner(exprOwner)(transform(stat))
        else transform(stat)) filter (EmptyTree !=)
    def transformUnit(unit: CompilationUnit) { unit.body = transform(unit.body) }
    def transformModifiers(mods: Modifiers): Modifiers =
      Modifiers(mods.flags, mods.privateWithin, transformTrees(mods.annotations), mods.positions)

    def atOwner[A](owner: Symbol)(trans: => A): A = {
      val prevOwner = currentOwner
      currentOwner = owner
      val result = trans
      currentOwner = prevOwner
      result
    }
  }

  class Traverser extends super.Traverser {
    /** Compiler specific tree types are handled here: the remainder are in
     *  the library's abstract tree traverser.
     */
    override def traverse(tree: Tree): Unit = tree match {
      case AssignOrNamedArg(lhs, rhs) =>
        traverse(lhs); traverse(rhs)
      case DocDef(comment, definition) =>
        traverse(definition)
      case Parens(ts) =>
        traverseTrees(ts)
      case TypeTreeWithDeferredRefCheck() => // TODO: should we traverse the wrapped tree?
      // (and rewrap the result? how to update the deferred check? would need to store wrapped tree instead of returning it from check)
      case Super(qual, _) =>
        traverse(qual)  // !!! remove when Super is done
      case _ => super.traverse(tree)
    }

    /** The abstract traverser is not aware of Tree.isTerm, so we override this one.
     */
    override def traverseStats(stats: List[Tree], exprOwner: Symbol) {
      stats foreach (stat =>
        if (exprOwner != currentOwner && stat.isTerm) atOwner(exprOwner)(traverse(stat))
        else traverse(stat)
      )
    }

    /** Leave apply available in the generic traverser to do something else.
     */
    def apply[T <: Tree](tree: T): T = { traverse(tree); tree }
  }

  private lazy val duplicator = new Transformer {
    override val treeCopy = new StrictTreeCopier
    override def transform(t: Tree) = {
      val t1 = super.transform(t)
      if ((t1 ne t) && t1.pos.isRange) t1 setPos t.pos.focus
      t1
    }
  }

  private class ShallowDuplicator(orig: Tree) extends Transformer {
    override val treeCopy = new StrictTreeCopier
    override def transform(tree: Tree) =
      if (tree eq orig) super.transform(tree)
      else tree
  }

  class TreeSubstituter(from: List[Symbol], to: List[Tree]) extends Transformer {
    override def transform(tree: Tree): Tree = tree match {
      case Ident(_) =>
        def subst(from: List[Symbol], to: List[Tree]): Tree =
          if (from.isEmpty) tree
          else if (tree.symbol == from.head) to.head
          else subst(from.tail, to.tail);
        subst(from, to)
      case _ =>
        super.transform(tree)
    }
  }

  class TreeTypeSubstituter(val from: List[Symbol], val to: List[Type]) extends Traverser {
    val typeSubst = new SubstTypeMap(from, to)
    def fromContains = typeSubst.fromContains

    override def traverse(tree: Tree) {
      if (tree.tpe ne null) tree.tpe = typeSubst(tree.tpe)
      if (tree.isDef) {
        val sym = tree.symbol
        val info1 = typeSubst(sym.info)
        if (info1 ne sym.info) sym.setInfo(info1)
      }
      super.traverse(tree)
    }
    override def apply[T <: Tree](tree: T): T = super.apply(tree.duplicate)
    override def toString() = "TreeTypeSubstituter("+from+","+to+")"
  }

  lazy val EmptyTreeTypeSubstituter = new TreeTypeSubstituter(List(), List())

  class TreeSymSubstTraverser(val from: List[Symbol], val to: List[Symbol]) extends Traverser {
    val subst = new SubstSymMap(from, to)
    override def traverse(tree: Tree) {
      if (tree.tpe ne null) tree.tpe = subst(tree.tpe)
      if (tree.isDef) {
        val sym = tree.symbol
        val info1 = subst(sym.info)
        if (info1 ne sym.info) sym.setInfo(info1)
      }
      super.traverse(tree)
    }
    override def apply[T <: Tree](tree: T): T = super.apply(tree.duplicate)
    override def toString() = "TreeSymSubstTraverser("+from+","+to+")"
  }

  /** Substitute symbols in 'from' with symbols in 'to'. Returns a new
   *  tree using the new symbols and whose Ident and Select nodes are
   *  name-consistent with the new symbols.
   */
  class TreeSymSubstituter(from: List[Symbol], to: List[Symbol]) extends Transformer {
    val symSubst = new SubstSymMap(from, to)
    override def transform(tree: Tree): Tree = {
      def subst(from: List[Symbol], to: List[Symbol]) {
        if (!from.isEmpty)
          if (tree.symbol == from.head) tree setSymbol to.head
          else subst(from.tail, to.tail)
      }

      if (tree.tpe ne null) tree.tpe = symSubst(tree.tpe)
      if (tree.hasSymbol) {
        subst(from, to)
        tree match {
          case Ident(name0) if tree.symbol != NoSymbol =>
            treeCopy.Ident(tree, tree.symbol.name)
          case Select(qual, name0) =>
            treeCopy.Select(tree, transform(qual), tree.symbol.name)
          case _ =>
            super.transform(tree)
        }
      } else
        super.transform(tree)
    }
    def apply[T <: Tree](tree: T): T = transform(tree).asInstanceOf[T]
    override def toString() = "TreeSymSubstituter("+from+","+to+")"
  }

  class ChangeOwnerTraverser(val oldowner: Symbol, val newowner: Symbol) extends Traverser {
    def changeOwner(tree: Tree) = {
      if ((tree.isDef || tree.isInstanceOf[Function]) &&
          tree.symbol != NoSymbol && tree.symbol.owner == oldowner)
        tree.symbol.owner = newowner
    }
    override def traverse(tree: Tree) {
      changeOwner(tree)
      super.traverse(tree)
    }
  }

  object posAssigner extends Traverser {
    var pos: Position = _
    override def traverse(t: Tree) {
      if (t != EmptyTree && t.pos == NoPosition) {
        t.setPos(pos)
        super.traverse(t)
      }
    }
  }

  def atPos[T <: Tree](pos: Position)(tree: T): T = {
    posAssigner.pos = pos
    posAssigner.traverse(tree)
    tree
  }

  class ForeachPartialTreeTraverser(pf: PartialFunction[Tree, Tree]) extends Traverser {
    override def traverse(tree: Tree) {
      val t = if (pf isDefinedAt tree) pf(tree) else tree
      super.traverse(t)
    }
  }

  class ForeachTreeTraverser(f: Tree => Unit) extends Traverser {
    override def traverse(t: Tree) {
      f(t)
      super.traverse(t)
    }
  }

  class FilterTreeTraverser(p: Tree => Boolean) extends Traverser {
    val hits = new ListBuffer[Tree]
    override def traverse(t: Tree) {
      if (p(t)) hits += t
      super.traverse(t)
    }
  }

  class FindTreeTraverser(p: Tree => Boolean) extends Traverser {
    var result: Option[Tree] = None
    override def traverse(t: Tree) {
      if (result.isEmpty) {
        if (p(t)) result = Some(t)
        super.traverse(t)
      }
    }
  }

  object resetPos extends Traverser {
    override def traverse(t: Tree) {
      if (t != EmptyTree) t.setPos(NoPosition)
      super.traverse(t)
    }
  }


  /** resets symbol and tpe fields in a tree, @see ResetAttrsTraverse
   */
  def resetAllAttrs[A<:Tree](x:A): A = { new ResetAttrsTraverser().traverse(x); x }
  def resetLocalAttrs[A<:Tree](x:A): A = { new ResetLocalAttrsTraverser().traverse(x); x }

  /** A traverser which resets symbol and tpe fields of all nodes in a given tree
   *  except for (1) TypeTree nodes, whose <code>.tpe</code> field is kept, and
   *  (2) This(pkg) nodes, where pkg refers to a package symbol -- their attributes are kept, and
   *  (3) if a <code>.symbol</code> field refers to a symbol which is defined
   *  outside the tree, it is also kept.
   *
   *  (2) is necessary because some This(pkg) are generated where pkg is not
   *  an enclosing package.n In that case, resetting the symbol would cause the
   *  next type checking run to fail. See #3152.
   *
   *  (bq:) This traverser has mutable state and should be discarded after use
   */
  private class ResetAttrsTraverser extends Traverser {
    protected def isLocal(sym: Symbol): Boolean = true
    protected def resetDef(tree: Tree) {
      tree.symbol = NoSymbol
    }
    override def traverse(tree: Tree): Unit = {
      tree match {
        case _: DefTree | Function(_, _) | Template(_, _, _) =>
          resetDef(tree)
          tree.tpe = null
        case tpt: TypeTree =>
          if (tpt.wasEmpty) tree.tpe = null
        case This(_) if tree.symbol != null && tree.symbol.isPackageClass =>
          ;
        case EmptyTree =>
          ;
        case _ =>
          if (tree.hasSymbol && isLocal(tree.symbol)) tree.symbol = NoSymbol
          tree.tpe = null
      }
      super.traverse(tree)
    }
  }

  private class ResetLocalAttrsTraverser extends ResetAttrsTraverser {
    private val erasedSyms = HashSet[Symbol](8)
    override protected def isLocal(sym: Symbol) = erasedSyms(sym)
    override protected def resetDef(tree: Tree) {
      erasedSyms addEntry tree.symbol
      super.resetDef(tree)
    }
    override def traverse(tree: Tree): Unit = tree match {
      case Template(parents, self, body) =>
        for (stat <- body)
          if (stat.isDef) erasedSyms.addEntry(stat.symbol)
        super.traverse(tree)
      case _ =>
        super.traverse(tree)
    }
  }
}