path: root/src/compiler/scala/tools/nsc/typechecker/Typers.scala

/* NSC -- new scala compiler
 * Copyright 2005 LAMP/EPFL
 * @author  Martin Odersky
 */
// $Id$
//todo: rewrite or disllow new T where T is a mixin (currently: <init> not a member of T)
package scala.tools.nsc.typechecker

import symtab.Flags._
import util.HashSet
import scala.tools.nsc.util.Position
import scala.collection.mutable.{HashMap, ListBuffer}

/** Methods to create symbols and to enter them into scopes. */
trait Typers requires Analyzer {
  import global._
  import definitions._
  import posAssigner.atPos

  var appcnt = 0
  var idcnt = 0
  var selcnt = 0
  var implcnt = 0
  var impltime = 0l

  final val xviews = true

  private val transformed = new HashMap[Tree, Tree]

  private val superDefs = new HashMap[Symbol, ListBuffer[Tree]]

  def resetTyper: unit = {
    resetContexts
    transformed.clear
    superDefs  .clear
  }

  def newTyper(context: Context): Typer = new Typer(context)

  object UnTyper extends Traverser {
    override def traverse(tree: Tree) = {
      if (tree != EmptyTree) tree.tpe = null;
      if (tree.hasSymbol) tree.symbol = NoSymbol;
      super.traverse(tree)
    }
  }

  class Typer(context0: Context) {
    import context0.unit

    val infer = new Inferencer(context0) {
      override def isCoercible(tp: Type, pt: Type): boolean = (
        tp.isError || pt.isError ||
        context0.implicitsEnabled && // this condition prevents chains of views
        inferView(Position.NOPOS, tp, pt, false) != EmptyTree
      )
    }

    private def inferView(pos: int, from: Type, to: Type, reportAmbiguous: boolean): Tree = {
      if (settings.debug.value) log("infer view from "+from+" to "+to);//debug
      if (phase.erasedTypes) EmptyTree
      else from match {
        case MethodType(_, _) => EmptyTree
        case OverloadedType(_, _) => EmptyTree
        case PolyType(_, _) => EmptyTree
        case _ => inferImplicit(pos, functionType(List(from), to), true, reportAmbiguous)
      }
    }

    private def inferView(pos: int, from: Type, name: Name, tp: Type, reportAmbiguous: boolean): Tree = {
      val to = refinedType(List(WildcardType), NoSymbol)
      val psym = (if (name.isTypeName) to.symbol.newAbstractType(pos, name)
                  else to.symbol.newValue(pos, name)) setInfo tp
      to.decls.enter(psym)
      inferView(pos, from, to, reportAmbiguous)
    }

    import infer._

    private var namerCache: Namer = null
    def namer = {
      if (namerCache == null || namerCache.context != context) namerCache = new Namer(context)
      namerCache
    }

    private var context = context0

    /** Mode constants
     */
    val NOmode        = 0x000
    val EXPRmode      = 0x001;   // these 3 modes are mutually exclusive.
    val PATTERNmode   = 0x002
    val TYPEmode      = 0x004

    val SCCmode       = 0x008;   // orthogonal to above. When set we are
                                 // in the this or super constructor call of a constructor.

    val FUNmode       = 0x10;    // orthogonal to above. When set
                                 // we are looking for a method or constructor

    val POLYmode      = 0x020;   // orthogonal to above. When set
                                 // expression types can be polymorphic.

    val QUALmode      = 0x040;   // orthogonal to above. When set
                                 // expressions may be packages and
                                 // Java statics modules.

    val TAPPmode      = 0x080;   // Set for the function/type constructor part
                                 // of a type application. When set we do not
                                 // decompose PolyTypes.

    val SUPERCONSTRmode = 0x100; // Set for the `super' in a superclass constructor call
                                 // super.<init>

    val SNDTRYmode    = 0x200;   // indicates that an application is typed for the 2nd
                                 // time. In that case functions may no longer be
                                 // be coerced with implicit views.

    val LHSmode       = 0x400;   // Set for the left-hand side of an assignment

    private val stickyModes: int  = EXPRmode | PATTERNmode | TYPEmode

    /** Report a type error.
     *  @param pos    The position where to report the error
     *  @param ex     The exception that caused the error */
    def reportTypeError(pos: int, ex: TypeError): unit = ex match {
      case CyclicReference(sym, info: TypeCompleter) =>
        context.unit.error(pos,
          info.tree match {
            case ValDef(_, _, tpt, _) if (tpt.tpe == null) =>
              "recursive "+sym+" needs type"
            case DefDef(_, _, _, _, tpt, _) if (tpt.tpe == null) =>
              (if (sym.owner.isClass && sym.owner.info.member(sym.name).hasFlag(OVERLOADED)) "overloaded "
               else "recursive ")+sym+" needs result type"
            case _ =>
              ex.getMessage()
          })
      case _ =>
        context.error(pos, ex.getMessage())
    }

    /** Check that tree is a stable expression.
     */
    def checkStable(tree: Tree): Tree =
      if (treeInfo.isPureExpr(tree)) tree
      else errorTree(tree, "stable identifier required, but "+tree+" found.")

    /** Check that type `tp' is not a subtype of itself.
     */
    def checkNonCyclic(pos: int, tp: Type): boolean = {
      def checkNotLocked(sym: Symbol): boolean = {
        sym.initialize
        if (sym hasFlag LOCKED) {
          error(pos, "cyclic aliasing or subtyping involving "+sym); false
        } else true
      }
      tp match {
        case TypeRef(pre, sym, args) =>
          (checkNotLocked(sym)) && (
            !sym.isAliasType && !sym.isAbstractType ||
            checkNonCyclic(pos, pre.memberInfo(sym).subst(sym.typeParams, args), sym)
          )
        case SingleType(pre, sym) =>
          checkNotLocked(sym)
        case st: SubType =>
          checkNonCyclic(pos, st.supertype)
        case ct: CompoundType =>
          var p = ct.parents
          while (!p.isEmpty && checkNonCyclic(pos, p.head)) p = p.tail
          p.isEmpty
        case _ =>
          true
      }
    }

    def checkNonCyclic(pos: int, tp: Type, lockedSym: Symbol): boolean = {
      lockedSym.setFlag(LOCKED)
      val result = checkNonCyclic(pos, tp)
      lockedSym.resetFlag(LOCKED)
      result
    }

    def checkNonCyclic(sym: Symbol): unit =
      if (!checkNonCyclic(sym.pos, sym.tpe)) sym.setInfo(ErrorType);

    def checkNonCyclic(defn: Tree, tpt: Tree): unit = {
      if (!checkNonCyclic(defn.pos, tpt.tpe, defn.symbol)) {
        tpt.tpe = ErrorType
        defn.symbol.setInfo(ErrorType)
      }
    }

    def checkParamsConvertible(pos: int, tpe: Type): unit = tpe match {
      case MethodType(formals, restpe) =>
        if (formals exists (.symbol.==(ByNameParamClass)))
          error(pos, "methods with `=>'-parameters cannot be converted to function values");
        if (formals exists (.symbol.==(RepeatedParamClass)))
          error(pos, "methods with `*'-parameters cannot be converted to function values");
        checkParamsConvertible(pos, restpe)
      case _ =>
    }

    /** Check that type of given tree does not contain local or private components
     */
    object checkNoEscaping extends TypeMap {
      private var owner: Symbol = _
      private var scope: Scope = _
      private var badSymbol: Symbol = _

      /** Check that type `tree' does not refer to private components unless itself is wrapped
       *  in something private (`owner' tells where the type occurs). */
      def privates[T <: Tree](owner: Symbol, tree: T): T = {
        check(owner, EmptyScope, tree)
      }

      /**  Check that type `tree' does not refer to entities defined in scope `scope'. */
      def locals[T <: Tree](scope: Scope, pt: Type, tree: T): T =
        if (isFullyDefined(pt)) tree setType pt else check(NoSymbol, scope, tree)

      def check[T <: Tree](owner: Symbol, scope: Scope, tree: T): T = {
        this.owner = owner
        this.scope = scope
        badSymbol = NoSymbol
        assert(tree.tpe != null, tree);//debug
        apply(tree.tpe)
        if (badSymbol == NoSymbol) tree
        else {
          if (!badSymbol.isErroneous)
            error(tree.pos,
                  (if (badSymbol.hasFlag(PRIVATE)) "private " else "") + badSymbol +
                  " escapes its defining scope as part of type "+tree.tpe)
          setError(tree)
        }
      }

      override def apply(t: Type): Type = {
        def checkNoEscape(sym: Symbol): unit = {
          if (sym.hasFlag(PRIVATE)) {
            var o = owner
            while (o != NoSymbol && o != sym.owner && !o.isLocal && !o.hasFlag(PRIVATE))
              o = o.owner
            if (o == sym.owner) badSymbol = sym
          } else if (sym.owner.isTerm) {
            val e = scope.lookupEntry(sym.name)
            if (e != null && e.sym == sym && e.owner == scope && !e.sym.isTypeParameterOrSkolem)
              badSymbol = e.sym
          }
        }
        if (badSymbol == NoSymbol)
          t match {
            case TypeRef(_, sym, _) => checkNoEscape(sym)
            case SingleType(_, sym) => checkNoEscape(sym)
            case _ =>
          }
        mapOver(t)
      }
    }

    def reenterValueParams(vparamss: List[List[ValDef]]): unit =
      for (val vparams <- vparamss; val vparam <- vparams) context.scope enter vparam.symbol

    def reenterTypeParams(tparams: List[AbsTypeDef]): List[Symbol] =
      for (val tparam <- tparams) yield {
        context.scope enter tparam.symbol;
        tparam.symbol.deSkolemize
      }

    /** The qualifying class of a this or super with prefix `qual' */
    def qualifyingClassContext(tree: Tree, qual: Name): Context = {
      if (qual.isEmpty) {
        if (context.enclClass.owner.isPackageClass)
          error(tree.pos, ""+tree+" can be used only in a class, object, or template")
        context.enclClass
      } else {
        var c = context.enclClass
        while (c != NoContext && c.owner.name != qual) c = c.outer.enclClass
        if (c == NoContext) error(tree.pos, ""+qual+" is not an enclosing class")
        c
      }
    }

    /** Post-process an identifier or selection node, performing the following:
     *  (1) Check that non-function pattern expressions are stable
     *  (2) Check that packages and static modules are not used as values
     *  (3) Turn tree type into stable type if possible and required by context. */
    private def stabilize(tree: Tree, pre: Type, mode: int, pt: Type): Tree = {
      if (tree.symbol.hasFlag(OVERLOADED) && (mode & FUNmode) == 0)
        inferExprAlternative(tree, pt)
      val sym = tree.symbol
      if (tree.tpe.isError) tree
      else if ((mode & (PATTERNmode | FUNmode)) == PATTERNmode && tree.isTerm) { // (1)
        checkStable(tree)
      } else if ((mode & (EXPRmode | QUALmode)) == EXPRmode && !sym.isValue) { // (2)
        errorTree(tree, ""+sym+" is not a value")
      } else if (sym.isStable && pre.isStable && tree.tpe.symbol != ByNameParamClass &&
                 (pt.isStable || (mode & QUALmode) != 0 && !sym.isConstant ||
                  sym.isModule && !sym.isMethod)) {
        tree.setType(singleType(pre, sym))
      } else tree
    }

    def stabilizeFun(tree: Tree, mode: int, pt: Type): Tree = {
      val sym = tree.symbol
      val pre = tree match {
        case Select(qual, _) => qual.tpe
        case _ => NoPrefix
      }
      if (tree.tpe.isInstanceOf[MethodType] && pre.isStable &&
          (pt.isStable || (mode & QUALmode) != 0 && !sym.isConstant || sym.isModule)) {
        assert(sym.tpe.paramTypes.isEmpty);
        tree.setType(MethodType(List(), singleType(pre, sym)))
      } else tree
    }

    /** Perform the following adaptations of expression, pattern or type `tree' wrt to
     *  given mode `mode' and given prototype `pt':
     *  (0) Convert expressions with constant types to literals
     *  (1) Resolve overloading, unless mode contains FUNmode
     *  (2) Apply parameterless functions
     *  (3) Apply polymorphic types to fresh instances of their type parameters and
     *      store these instances in context.undetparams,
     *      unless followed by explicit type application.
     *  (4) Do the following to unapplied methods used as values:
     *  (4.1) If the method has only implicit parameters pass implicit arguments
     *  (4.2) otherwise, if `pt' is a function type and method is not a constructor,
     *        convert to function by eta-expansion,
     *  (4.3) otherwise, if the method is nullary with a result type compatible to `pt'
     *        and it is not a constructor, apply it to ()
     *  otherwise issue an error
     *  (5) Convert a class type that serves as a constructor in a pattern as follows:
     *  (5.1) If this type refers to a case class, set tree's type to the unique
     *        instance of its primary constructor that is a subtype of the expected type.
     *  (5.2) Otherwise, if this type is a subtype of scala.Seq[A], set trees' type
     *        to a method type from a repeated parameter sequence type A* to the expected type.
     *  (6) Convert all other types to TypeTree nodes.
     *  (7) When in TYPEmode nut not FUNmode, check that types are fully parameterized
     *  (8) When in both EXPRmode and FUNmode, add apply method calls to values of object type.
     *  (9) If there are undetermined type variables and not POLYmode, infer expression instance
     *  Then, if tree's type is not a subtype of expected type, try the following adaptations:
     *  (10) If the expected type is byte, short or char, and the expression
     *      is an integer fitting in the range of that type, convert it to that type.
     *  (11) Widen numeric literals to their expected type, if necessary
     *  (12) When in mode EXPRmode, convert E to { E; () } if expected type is Scala.unit.
     *  (13) When in mode EXPRmode, apply a view
     *  If all this fails, error
     */
//    def adapt(tree: Tree, mode: int, pt: Type): Tree = {
    protected def adapt(tree: Tree, mode: int, pt: Type): Tree = tree.tpe match {
      case ct @ ConstantType(value) if ((mode & TYPEmode) == 0 && (ct <:< pt)) => // (0)
        copy.Literal(tree, value)
      case OverloadedType(pre, alts) if ((mode & FUNmode) == 0) => // (1)
        inferExprAlternative(tree, pt);
        adapt(tree, mode, pt)
      case PolyType(List(), restpe) => // (2)
        adapt(tree setType restpe, mode, pt)
      case TypeRef(_, sym, List(arg))
      if ((mode & EXPRmode) != 0 && sym == ByNameParamClass) => // (2)
        adapt(tree setType arg, mode, pt)
      case PolyType(tparams, restpe) if ((mode & TAPPmode) == 0) => // (3)
        val tparams1 = cloneSymbols(tparams)
        val tree1 = if (tree.isType) tree
                    else TypeApply(tree, tparams1 map (tparam =>
                      TypeTree(tparam.tpe) setOriginal tree /* setPos tree.pos */)) setPos tree.pos
        context.undetparams = context.undetparams ::: tparams1
        adapt(tree1 setType restpe.substSym(tparams, tparams1), mode, pt)
      case mt: ImplicitMethodType if ((mode & (EXPRmode | FUNmode | LHSmode)) == EXPRmode) => // (4.1)
        val tree1 =
          if (!context.undetparams.isEmpty & (mode & POLYmode) == 0) { // (9)
            val tparams = context.undetparams
            context.undetparams = List()
            inferExprInstance(tree, tparams, pt)
            adapt(tree, mode, pt)
          } else tree
        typed(applyImplicitArgs(tree1), mode, pt)
      case mt: MethodType
      if (((mode & (EXPRmode | FUNmode | LHSmode)) == EXPRmode) &&
          (context.undetparams.isEmpty || (mode & POLYmode) != 0)) =>
        if (!tree.symbol.isConstructor && pt != WildcardType && isCompatible(mt, pt) &&
            (pt <:< functionType(mt.paramTypes map (t => WildcardType), WildcardType))) { // (4.2)
          if (settings.debug.value) log("eta-expanding "+tree+":"+tree.tpe+" to "+pt)
          checkParamsConvertible(tree.pos, tree.tpe);
          typed(etaExpand(tree), mode, pt)
        } else if (!tree.symbol.isConstructor && mt.paramTypes.isEmpty) { // (4.3)
          adapt(typed(Apply(tree, List()) setPos tree.pos), mode, pt)
        } else if (context.implicitsEnabled) {
          if (settings.migrate.value && !tree.symbol.isConstructor && isCompatible(mt, pt))
            errorTree(tree, migrateMsg + " method can be converted to function only if an expected function type is given");
          else
            errorTree(tree, "missing arguments for "+tree.symbol+tree.symbol.locationString+
                      (if (tree.symbol.isConstructor) ""
                       else ";\nprefix this method with `&' if you want to treat it as a partially applied function"))
        } else {
          setError(tree)
        }
      case _ =>
        if (tree.isType) {
          val clazz = tree.tpe.symbol
          if ((mode & PATTERNmode) != 0) { // (5)
            if (tree.tpe.isInstanceOf[MethodType]) {
              tree // everything done already
            } else {
              clazz.initialize
              if (clazz.hasFlag(CASE)) {   // (5.1)
                val tree1 = TypeTree(clazz.primaryConstructor.tpe.asSeenFrom(tree.tpe.prefix, clazz.owner)) setOriginal tree
                try {
                  inferConstructorInstance(tree1, clazz.typeParams, pt)
                } catch {
                  case npe : NullPointerException =>
                    logError("CONTEXT: " + context . unit . source .dbg(tree.pos), npe);
                    throw npe;
                  case fe : FatalError =>
                    logError("CONTEXT: " + context . unit . source .dbg(tree.pos), fe);
                    throw fe;
                  case t : Throwable =>
                    logError("CONTEXT: " + context . unit . source .dbg(tree.pos), t);
                    throw t;
                }
                tree1
              } else if (clazz.isSubClass(SeqClass)) { // (5.2)
                pt.baseType(clazz).baseType(SeqClass) match {
                  case TypeRef(pre, seqClass, args) =>
                    tree.setType(MethodType(List(typeRef(pre, RepeatedParamClass, args)), pt))
                  case NoType =>
                    errorTree(tree, "expected pattern type "+pt +
                              " does not conform to sequence "+clazz)
                  case ErrorType =>
                    setError(tree)
                }
              } else {
                errorTree(tree, ""+clazz+" is neither a case class nor a sequence class")
              }
            }
          } else if ((mode & FUNmode) != 0) {
            tree
          } else if (tree.hasSymbol && !tree.symbol.typeParams.isEmpty) { // (7)
            errorTree(tree, ""+clazz+" takes type parameters")
          } else tree match { // (6)
            case TypeTree() => tree
            case _ => TypeTree(tree.tpe) setOriginal(tree)
          }
        } else if ((mode & (EXPRmode | FUNmode)) == (EXPRmode | FUNmode) &&
                   !tree.tpe.isInstanceOf[MethodType] && !tree.tpe.isInstanceOf[OverloadedType] &&
                   ((mode & TAPPmode) == 0 || tree.tpe.typeParams.isEmpty) &&
                   adaptToName(tree, nme.apply).tpe.nonLocalMember(nme.apply)
                     .filter(m => m.tpe.paramSectionCount > 0) != NoSymbol) { // (8)
          typed(atPos(tree.pos)(Select(adaptToName(tree, nme.apply), nme.apply)), mode, pt)
        } else if (!context.undetparams.isEmpty & (mode & POLYmode) == 0) { // (9)
            val tparams = context.undetparams
            context.undetparams = List()
            inferExprInstance(tree, tparams, pt)
            adapt(tree, mode, pt)
        } else if (tree.tpe <:< pt) {
          tree
        } else {
          val tree1 = constfold(tree, pt); // (10) (11)
          if (tree1.tpe <:< pt) adapt(tree1, mode, pt)
          else {
            if ((mode & (EXPRmode | FUNmode)) == EXPRmode) {
              pt match {
                case TypeRef(_, sym, _) =>
                  // note: was if (pt.symbol == UnitClass) but this leads to a potentially
                  // infinite expansion if pt is constant type ()
                  if (sym == UnitClass && tree.tpe <:< AnyClass.tpe) // (12)
                    return typed(atPos(tree.pos)(Block(List(tree), Literal(()))), mode, pt)
                case _ =>
              }
              if (context.implicitsEnabled && !tree.tpe.isError && !pt.isError) {
                // (13); the condition prevents chains of views
                if (settings.debug.value) log("inferring view from "+tree.tpe+" to "+pt)
                val coercion = inferView(tree.pos, tree.tpe, pt, true)
                if (coercion != EmptyTree) {
                  if (settings.debug.value) log("inferred view from "+tree.tpe+" to "+pt+" = "+coercion+":"+coercion.tpe)
                  return typed(Apply(coercion, List(tree)) setPos tree.pos, mode, pt)
                }
              }
            }
            if (settings.debug.value) log("error tree = "+tree)
            typeErrorTree(tree, tree.tpe, pt)
          }
        }
    }
//      System.out.println("adapt "+tree+":"+tree.tpe+", mode = "+mode+", pt = "+pt)
//      adapt(tree, mode, pt)
//    }

    def adaptToMember(qual: Tree, name: Name, tp: Type): Tree = {
      val qtpe = qual.tpe.widen;
      if (qual.isTerm && (qual.symbol == null || qual.symbol.isValue) &&
          !phase.erasedTypes && !qtpe.isError && !tp.isError &&
          qtpe.symbol != AllRefClass && qtpe.symbol != AllClass && qtpe != WildcardType) {
        val coercion = inferView(qual.pos, qtpe, name, tp, true)
        if (coercion != EmptyTree)
          typedQualifier(atPos(qual.pos)(Apply(coercion, List(qual))))
        else qual
      } else qual
    }

    def adaptToName(qual: Tree, name: Name) =
      if (qual.tpe.nonLocalMember(name) != NoSymbol) qual
      else adaptToMember(qual, name, WildcardType)

    private def completeParentType(tpt: Tree, tparams: List[Symbol], enclTparams: List[Symbol], vparamss: List[List[ValDef]], superargs: List[Tree]): Type = {
      enclTparams foreach context.scope.enter
      namer.enterValueParams(context.owner, vparamss)
      val newTree = New(tpt)
        .setType(PolyType(tparams, appliedType(tpt.tpe, tparams map (.tpe))))
      val tree = typed(atPos(tpt.pos)(Apply(Select(newTree, nme.CONSTRUCTOR), superargs)))
      if (settings.debug.value) log("superconstr "+tree+" co = "+context.owner);//debug
      tree.tpe
    }

/*
    def completeParentType(tpt: Tree, templ: Template): Tree =
      if (tpt.hasSymbol) {
        val tparams = tpt.symbol.typeParams
        if (!tparams.isEmpty) {
          val constr @ DefDef(_, _, _, vparamss, _, rhs) = treeInfo.firstConstructor(templ.body)
          val Apply(_, superargs) = treeInfo.superCall(rhs, tpt.symbol.name)
          val outercontext = context.outer
          TypeTree(
            newTyper(outercontext.makeNewScope(constr, outercontext.owner))
              .completeParentType(
                tpt,
                tparams,
                context.owner.unsafeTypeParams,
                vparamss map (.map(.duplicate.asInstanceOf[ValDef])),
                superargs map (.duplicate))) setPos tpt.pos
        } else tpt
      } else tpt
*/
    def parentTypes(templ: Template): List[Tree] = try {
      if (templ.parents.isEmpty) List()
      else {
        var supertpt = typedTypeConstructor(templ.parents.head)
        var mixins = templ.parents.tail map typedType
        // If first parent is a trait, make it first mixin and add its superclass as first parent
        while (supertpt.tpe.symbol != null && supertpt.tpe.symbol.initialize.isTrait) {
          mixins = typedType(supertpt) :: mixins
          supertpt = TypeTree(supertpt.tpe.parents.head) setOriginal supertpt /* setPos supertpt.pos */
        }
        if (supertpt.hasSymbol) {
          val tparams = supertpt.symbol.typeParams
          if (!tparams.isEmpty) {
            val constr @ DefDef(_, _, _, vparamss, _, Apply(_, superargs)) =
              treeInfo.firstConstructor(templ.body)
            val outercontext = context.outer
            supertpt = TypeTree(
              newTyper(outercontext.makeNewScope(constr, outercontext.owner))
                .completeParentType(
                  supertpt,
                  tparams,
                  context.owner.unsafeTypeParams,
                  vparamss map (.map(.duplicate.asInstanceOf[ValDef])),
                  superargs map (.duplicate))) setOriginal supertpt /* setPos supertpt.pos */
          }
        }
        //System.out.println("parents("+context.owner+") = "+supertpt :: mixins);//DEBUG
        List.mapConserve(supertpt :: mixins)(tpt => checkNoEscaping.privates(context.owner, tpt))
      }
    } catch {
      case ex: TypeError =>
        reportTypeError(templ.pos, ex)
        List(TypeTree(AnyRefClass.tpe))
    }

    /** Check that
     *  - all parents are class types,
     *  - first parent cluss is not a mixin; following classes are mixins,
     *  - final classes are not inherited,
     *  - sealed classes are only inherited by classes which are
     *    nested within definition of base class, or that occur within same
     *    statement sequence,
     *  - self-type of current class is a subtype of self-type of each parent class.
     *  - no two parents define same symbol.
     */
    def validateParentClasses(parents: List[Tree], selfType: Type): unit = {

      def validateParentClass(parent: Tree, superclazz: Symbol): unit = {
        if (!parent.tpe.isError) {
          val psym = parent.tpe.symbol.initialize
          if (!psym.isClass)
            error(parent.pos, "class type expected")
          else if (psym != superclazz)
            if (psym.isTrait) {
              val ps = psym.info.parents
              if (!ps.isEmpty && !superclazz.isSubClass(ps.head.symbol))
                error(parent.pos, "illegal inheritance; super"+superclazz+
                      "\n is not a subclass of the super"+ps.head.symbol+
                      "\n of the mixin " + psym);
            } else if (settings.migrate.value) {
              error(parent.pos, migrateMsg+psym+" needs to be a declared as a trait")
            }else {
              error(parent.pos, ""+psym+" needs to be a trait be mixed in")
            }
          else if (psym.hasFlag(FINAL))
            error(parent.pos, "illegal inheritance from final class")
          else if (!phase.erasedTypes && psym.isSealed &&
                   context.unit.source.file != psym.sourceFile)
            error(parent.pos, "illegal inheritance from sealed "+psym)
          if (!(selfType <:< parent.tpe.typeOfThis) && !phase.erasedTypes) {
            //System.out.println(context.owner);//DEBUG
            //System.out.println(context.owner.unsafeTypeParams);//DEBUG
            //System.out.println(List.fromArray(context.owner.info.closure));//DEBUG
            error(parent.pos, "illegal inheritance;\n self-type "+
                  selfType+" does not conform to "+parent +
                  "'s selftype "+parent.tpe.typeOfThis)
            if (settings.explaintypes.value) explainTypes(selfType, parent.tpe.typeOfThis)
          }
          if (parents exists (p => p != parent && p.tpe.symbol == psym && !psym.isError))
            error(parent.pos, ""+psym+" is inherited twice")
        }
      }

      if (!parents.head.tpe.isError)
        for (val p <- parents) validateParentClass(p, parents.head.tpe.symbol)
    }

    def typedClassDef(cdef: ClassDef): Tree = {
      val clazz = cdef.symbol
      reenterTypeParams(cdef.tparams)
      val tparams1 = List.mapConserve(cdef.tparams)(typedAbsTypeDef)
      val tpt1 = checkNoEscaping.privates(clazz.thisSym, typedType(cdef.tpt))
      val impl1 = newTyper(context.make(cdef.impl, clazz, new Scope()))
        .typedTemplate(cdef.impl, parentTypes(cdef.impl))
      val impl2 = addSyntheticMethods(impl1, clazz, context.unit)
      val ret = copy.ClassDef(cdef, cdef.mods, cdef.name, tparams1, tpt1, impl2)
        .setType(NoType)
      ret
    }

    def typedModuleDef(mdef: ModuleDef): Tree = {
      //System.out.println("sourcefile of " + mdef.symbol + "=" + mdef.symbol.sourceFile);
      val clazz = mdef.symbol.moduleClass
      val impl1 = newTyper(context.make(mdef.impl, clazz, new Scope()))
        .typedTemplate(mdef.impl, parentTypes(mdef.impl))
      val impl2 = addSyntheticMethods(impl1, clazz, context.unit)

      copy.ModuleDef(mdef, mdef.mods, mdef.name, impl2) setType NoType
    }

    def addGetterSetter(stat: Tree): List[Tree] = stat match {
      case ValDef(mods, name, tpt, rhs) if !(mods hasFlag LOCAL) && !stat.symbol.isModuleVar =>
        val vdef = copy.ValDef(stat, mods | PRIVATE | LOCAL, nme.getterToLocal(name), tpt, rhs)
        val value = vdef.symbol
        val getter = if (mods hasFlag DEFERRED) value else value.getter(value.owner)
        assert(getter != NoSymbol, getter);//debug
        val getterDef: DefDef = {
          val result = DefDef(getter, vparamss =>
              if (mods hasFlag DEFERRED) EmptyTree
              else typed(atPos(vdef.pos)(Select(This(value.owner), value)), EXPRmode, value.tpe))
          result.tpt.asInstanceOf[TypeTree] setOriginal tpt /* setPos tpt.pos */
          checkNoEscaping.privates(getter, result.tpt)
          result
        }
        def setterDef: DefDef = {
          val setter = value.owner.info.decl(nme.getterToSetter(getter.name));
          assert(setter != NoSymbol, getter);//debug
          atPos(vdef.pos)(
            DefDef(setter, vparamss =>
              if (mods hasFlag DEFERRED) EmptyTree
              else typed(Assign(Select(This(value.owner), value),
                                Ident(vparamss.head.head)))))
        }
        val gs = if (mods hasFlag MUTABLE) List(getterDef, setterDef)
                 else List(getterDef)
        if (mods hasFlag DEFERRED) gs else vdef :: gs
      case DocDef(comment, defn) =>
        addGetterSetter(defn) map (stat => DocDef(comment, stat))
      case Attributed(attr, defn) =>
        addGetterSetter(defn) map (stat => Attributed(attr.duplicate, stat))
      case _ =>
        List(stat)
    }

    def typedTemplate(templ: Template, parents1: List[Tree]): Template = {
      val clazz = context.owner
      if (templ.symbol == NoSymbol) templ setSymbol clazz.newLocalDummy(templ.pos)
      val selfType =
        if (clazz.isAnonymousClass && !phase.erasedTypes)
          intersectionType(clazz.info.parents, clazz.owner)
        else if (settings.Xgadt.value) clazz.typeOfThis.asSeenFrom(context.prefix, clazz)
        else clazz.typeOfThis
      // the following is necessary for templates generated later
      new Namer(context.outer.make(templ, clazz, clazz.info.decls)).enterSyms(templ.body)
      validateParentClasses(parents1, selfType);
      val body1 = typedStats(templ.body flatMap addGetterSetter, templ.symbol)
      copy.Template(templ, parents1, body1) setType clazz.tpe
    }

    def typedValDef(vdef: ValDef): ValDef = {
      val sym = vdef.symbol
      val typer1 = if (sym.hasFlag(PARAM) && sym.owner.isConstructor)
                     newTyper(context.makeConstructorContext)
                   else this
      var tpt1 = checkNoEscaping.privates(sym, typer1.typedType(vdef.tpt))
      checkNonCyclic(vdef, tpt1)
      val rhs1 =
        if (vdef.rhs.isEmpty) {
          if (sym.isVariable && sym.owner.isTerm && phase.id <= currentRun.typerPhase.id)
            error(vdef.pos, "local variables must be initialized")
          vdef.rhs
        } else {
          newTyper(context.make(vdef, sym)).transformedOrTyped(vdef.rhs, tpt1.tpe)
        }
      copy.ValDef(vdef, vdef.mods, vdef.name, tpt1, rhs1) setType NoType
    }

    /** Enter all aliases of local parameter accessors. */
    def computeParamAliases(clazz: Symbol, vparamss: List[List[ValDef]], rhs: Tree): unit = {
      if (settings.debug.value) log("computing param aliases for "+clazz+":"+clazz.primaryConstructor.tpe+":"+rhs);//debug
      def decompose(call: Tree): Pair[Tree, List[Tree]] = call match {
        case Apply(fn, args) =>
          val Pair(superConstr, args1) = decompose(fn)
          val formals = fn.tpe.paramTypes
          val args2 = if (formals.isEmpty || formals.last.symbol != RepeatedParamClass) args
                      else args.take(formals.length - 1) ::: List(EmptyTree)
          if (args2.length != formals.length) assert(false, "mismatch "+clazz+" "+formals+" "+args2);//debug
          Pair(superConstr, args1 ::: args2)
        case Block(stats, expr) =>
          decompose(stats.head)
        case _ =>
          Pair(call, List())
      }
      val Pair(superConstr, superArgs) = decompose(rhs)
      assert(superConstr.symbol != null);//debug
      if (superConstr.symbol.isPrimaryConstructor) {
        val superClazz = superConstr.symbol.owner
        if (!superClazz.hasFlag(JAVA)) {
          val superParamAccessors = superClazz.constrParamAccessors
          if (superParamAccessors.length != superArgs.length) {
            System.out.println(""+superClazz+":"+superClazz.info.decls.toList.filter(.hasFlag(PARAMACCESSOR)))
            assert(false, "mismatch: "+superParamAccessors+";"+rhs+";"+superClazz.info.decls); //debug
          }
          List.map2(superParamAccessors, superArgs) { (superAcc, superArg) =>
            superArg match {
              case Ident(name) =>
                if (vparamss.exists(.exists(vp => vp.symbol == superArg.symbol))) {
                  var alias = superAcc.initialize.alias
                  if (alias == NoSymbol)
                    alias = superAcc.getter(superAcc.owner)
                  if (alias != NoSymbol &&
                      superClazz.info.nonPrivateMember(alias.name) != alias)
                    alias = NoSymbol
                  if (alias != NoSymbol) {
                    var ownAcc = clazz.info.decl(name).suchThat(.hasFlag(PARAMACCESSOR))
                    if (ownAcc hasFlag ACCESSOR) ownAcc = ownAcc.accessed
                    if (settings.debug.value) log(""+ownAcc+" has alias "+alias + alias.locationString);//debug
                    ownAcc.asInstanceOf[TermSymbol].setAlias(alias)
                  }
                }
              case _ =>
            }
          }
          ()
        }
      }
    }

    def typedDefDef(ddef: DefDef): DefDef = {
      val meth = ddef.symbol

      def checkPrecedes(tree: Tree): unit = tree match {
        case Block(stat :: _, _) => checkPrecedes(stat)
        case Apply(fun, _) =>
          if (fun.symbol.isConstructor &&
              fun.symbol.owner == meth.owner && fun.symbol.pos >= meth.pos)
            error(fun.pos, "called constructor must precede calling constructor");
        case _ =>
      }
      def typedSuperCall(tree: Tree): Tree = {
        val result = typed(tree, EXPRmode | SCCmode, UnitClass.tpe)
        checkPrecedes(result)
        result
      }

      reenterTypeParams(ddef.tparams)
      reenterValueParams(ddef.vparamss)
      val tparams1 = List.mapConserve(ddef.tparams)(typedAbsTypeDef)
      val vparamss1 = List.mapConserve(ddef.vparamss)(vparams1 =>
        List.mapConserve(vparams1)(typedValDef))
      for (val vparams <- vparamss1; val vparam <- vparams) {
        checkNoEscaping.locals(context.scope, WildcardType, vparam.tpt); ()
      }
      var tpt1 =
        checkNoEscaping.locals(context.scope, WildcardType,
          checkNoEscaping.privates(meth,
              typedType(ddef.tpt)))
      checkNonCyclic(ddef, tpt1)
      ddef.tpt.setType(tpt1.tpe)
      val rhs1 =
        if (ddef.name == nme.CONSTRUCTOR) {
          if (!meth.hasFlag(SYNTHETIC) &&
              !(meth.owner.isClass ||
                meth.owner.isModuleClass ||
                meth.owner.isAnonymousClass ||
                meth.owner.isRefinementClass))
            error(ddef.pos, "constructor definition not allowed here "+meth.owner);//debug
          val result = ddef.rhs match {
            case Block(stat :: stats, expr) =>
              val stat1 = typedSuperCall(stat)
              newTyper(context.makeConstructorSuffixContext).typed(
                copy.Block(ddef.rhs, stats, expr), UnitClass.tpe) match {
                case block1 @ Block(stats1, expr1) =>
                  copy.Block(block1, stat1 :: stats1, expr1)
              }
            case _ =>
              typedSuperCall(ddef.rhs)
          }
          if (meth.isPrimaryConstructor && !phase.erasedTypes && reporter.errors == 0)
            computeParamAliases(meth.owner, vparamss1, result)
          result
        } else transformedOrTyped(ddef.rhs, tpt1.tpe)
      copy.DefDef(ddef, ddef.mods, ddef.name, tparams1, vparamss1, tpt1, rhs1) setType NoType
    }

    def typedAbsTypeDef(tdef: AbsTypeDef): AbsTypeDef = {
      val lo1 = checkNoEscaping.privates(tdef.symbol, typedType(tdef.lo))
      val hi1 = checkNoEscaping.privates(tdef.symbol, typedType(tdef.hi))
      checkNonCyclic(tdef.symbol)
      if (!(lo1.tpe <:< hi1.tpe))
        error(tdef.pos,
              "lower bound "+lo1.tpe+" does not conform to upper bound "+hi1.tpe)
      copy.AbsTypeDef(tdef, tdef.mods, tdef.name, lo1, hi1) setType NoType
    }

    def typedAliasTypeDef(tdef: AliasTypeDef): AliasTypeDef = {
      reenterTypeParams(tdef.tparams)
      val tparams1 = List.mapConserve(tdef.tparams)(typedAbsTypeDef)
      val rhs1 = checkNoEscaping.privates(tdef.symbol, typedType(tdef.rhs))
      checkNonCyclic(tdef.symbol)
      copy.AliasTypeDef(tdef, tdef.mods, tdef.name, tparams1, rhs1) setType NoType
    }

    private def enterLabelDef(stat: Tree): unit = stat match {
      case ldef @ LabelDef(_, _, _) =>
        if (ldef.symbol == NoSymbol)
          ldef.symbol = namer.enterInScope(
            context.owner.newLabel(ldef.pos, ldef.name) setInfo MethodType(List(), UnitClass.tpe))
      case _ =>
    }

    def typedLabelDef(ldef: LabelDef): LabelDef = {
      val restpe = ldef.symbol.tpe.resultType
      val rhs1 = typed(ldef.rhs, restpe)
      ldef.params foreach (param => param.tpe = param.symbol.tpe)
      copy.LabelDef(ldef, ldef.name, ldef.params, rhs1) setType restpe
    }

    def typedBlock(block: Block, mode: int, pt: Type): Block = {
      namer.enterSyms(block.stats)
      block.stats foreach enterLabelDef
      val stats1 = typedStats(block.stats, context.owner)
      val expr1 = typed(block.expr, mode & ~(FUNmode | QUALmode), pt)
      val block1 = copy.Block(block, stats1, expr1)
        .setType(if (treeInfo.isPureExpr(block)) expr1.tpe else expr1.tpe.deconst)
      if (isFullyDefined(pt)) block1
      else { //todo: correct?
        if (block1.tpe.symbol.isAnonymousClass)
          block1 setType intersectionType(block1.tpe.parents, block1.tpe.symbol.owner)
        checkNoEscaping.locals(context.scope, pt, block1)
      }
    }

    def typedCase(cdef: CaseDef, pattpe: Type, pt: Type): CaseDef = {
      val pat1: Tree = typedPattern(cdef.pat, pattpe)
      val guard1: Tree = if (cdef.guard == EmptyTree) EmptyTree
                         else typed(cdef.guard, BooleanClass.tpe)
      var body1: Tree = typed(cdef.body, pt)
      if (!context.savedTypeBounds.isEmpty) {
        context.restoreTypeBounds
        // the following is a hack to make the pattern matcher work
        body1 =
          typed {
            atPos(body1.pos) {
              TypeApply(Select(body1, Any_asInstanceOf), List(TypeTree(pt)))
            }
          }
      }
      copy.CaseDef(cdef, pat1, guard1, body1) setType body1.tpe
    }

    def typedCases(tree: Tree, cases: List[CaseDef], pattp0: Type, pt: Type): List[CaseDef] = {
      var pattp = pattp0
      List.mapConserve(cases) ( cdef =>
          newTyper(context.makeNewScope(cdef, context.owner)).typedCase(cdef, pattp, pt))
/* not yet!
        cdef.pat match {
          case Literal(Constant(null)) =>
            if (!(pattp <:< NonNullClass.tpe))
              pattp = intersectionType(List(pattp, NonNullClass.tpe), context.owner)
          case _ =>
        }
        result
*/
    }

    def typedFunction(fun: Function, mode: int, pt: Type): Tree = {
      def decompose(pt: Type): Triple[Symbol, List[Type], Type] =
        if (isFunctionType(pt)
            ||
            pt.symbol == PartialFunctionClass &&
            fun.vparams.length == 1 && fun.body.isInstanceOf[Match])
          Triple(pt.symbol, pt.typeArgs.init, pt.typeArgs.last)
        else
          Triple(FunctionClass(fun.vparams.length), fun.vparams map (x => NoType), WildcardType)

      val Triple(clazz, argpts, respt) =
        decompose(if (pt.symbol isSubClass CodeClass) pt.typeArgs.head else pt)

      if (fun.vparams.length != argpts.length)
        errorTree(fun, "wrong number of parameters; expected = "+argpts.length)
      else {
        val vparamSyms = List.map2(fun.vparams, argpts) { (vparam, argpt) =>
          if (vparam.tpt.isEmpty)
            vparam.tpt.tpe =
              if (argpt == NoType || argpt == WildcardType) {
                error(vparam.pos, "missing parameter type"); ErrorType
              }
              else argpt
          namer.enterSym(vparam)
          vparam.symbol
        }
        val vparams = List.mapConserve(fun.vparams)(typedValDef)
        for (val vparam <- vparams) {
          checkNoEscaping.locals(context.scope, WildcardType, vparam.tpt); ()
        }
        val body = checkNoEscaping.locals(context.scope, respt, typed(fun.body, respt))
        val formals = vparamSyms map (.tpe)
        val restpe = body.tpe.deconst
        val funtpe = typeRef(clazz.tpe.prefix, clazz, formals ::: List(restpe))
        val fun1 = copy.Function(fun, vparams, checkNoEscaping.locals(context.scope, restpe, body))
          .setType(funtpe)
        if (pt.symbol isSubClass CodeClass) {
          val liftPoint = Apply(Select(Ident(CodeModule), nme.lift_), List(fun1))
          typed(atPos(fun.pos)(liftPoint))
        } else fun1
      }
    }

    def typedRefinement(stats: List[Tree]): List[Tree] = {
      namer.enterSyms(stats)
      for (val stat <- stats) stat.symbol setFlag OVERRIDE
      typedStats(stats, NoSymbol)
    }

    def typedStats(stats: List[Tree], exprOwner: Symbol): List[Tree] = {
      val inBlock = exprOwner == context.owner
      val result =
        List.mapConserve(stats) { stat =>
          if (context.owner.isRefinementClass && !treeInfo.isDeclaration(stat))
            errorTree(stat, "only declarations allowed here")
          stat match {
            case imp @ Import(_, _) =>
              context = context.makeNewImport(imp)
              stat.symbol.initialize
              EmptyTree
            case _ =>
              (if (!inBlock && (!stat.isDef || stat.isInstanceOf[LabelDef]))
                newTyper(context.make(stat, exprOwner)) else this).typed(stat)
          }
        }
      val scope = if (inBlock) context.scope else context.owner.info.decls;
      var e = scope.elems;
      while (e != null && e.owner == scope) {
        if (!e.sym.hasFlag(LOCAL)) {
          var e1 = scope.lookupNextEntry(e);
          while (e1 != null && e1.owner == scope) {
            if (!e1.sym.hasFlag(LOCAL) &&
                (e.sym.isType || inBlock || (e.sym.tpe matches e1.sym.tpe)))
              if (!e.sym.isErroneous && !e1.sym.isErroneous)
                error(e.sym.pos, ""+e1.sym+" is defined twice");
            e1 = scope.lookupNextEntry(e1);
          }
        }
        e = e.next
      }
      result
    }

    protected def typed1(tree: Tree, mode: int, pt: Type): Tree = {

      def funmode = mode & stickyModes | FUNmode | POLYmode

      def ptOrLub(tps: List[Type]) = if (isFullyDefined(pt)) pt else lub(tps)

      def typedTypeApply(fun: Tree, args: List[Tree]): Tree = fun.tpe match {
        case OverloadedType(pre, alts) =>
          inferPolyAlternatives(fun, args.length)
          typedTypeApply(fun, args)
        case PolyType(tparams, restpe) if (tparams.length != 0) =>
          if (tparams.length == args.length) {
            val targs = args map (.tpe)
            checkBounds(tree.pos, tparams, targs, "")
            copy.TypeApply(tree, fun, args) setType restpe.subst(tparams, targs)
          } else {
            errorTree(tree, "wrong number of type parameters for "+treeSymTypeMsg(fun))
          }
        case ErrorType =>
          setError(tree)
        case _ =>
          errorTree(tree, treeSymTypeMsg(fun)+" does not take type parameters.")
        }

      def typedArg(arg: Tree, pt: Type): Tree = {
        val argTyper = if ((mode & SCCmode) != 0) newTyper(context.makeConstructorContext)
                       else this
        argTyper.typed(arg, mode & stickyModes, pt)
      }

      def typedArgs(args: List[Tree]) =
        List.mapConserve(args)(arg => typedArg(arg, WildcardType))

      def typedApply(fun0: Tree, args: List[Tree]): Tree = {
        var fun = fun0;
        if (fun.hasSymbol && (fun.symbol hasFlag OVERLOADED)) {
          // preadapt symbol to number of arguments given
          val argtypes = args map (arg => AllClass.tpe)
          val pre = fun.symbol.tpe.prefix
          val sym = fun.symbol filter (alt =>
            isApplicable(context.undetparams, pre.memberType(alt), argtypes, pt))
          if (sym != NoSymbol)
            fun = adapt(fun setSymbol sym setType pre.memberType(sym), funmode, WildcardType)
        }
        fun.tpe match {
          case OverloadedType(pre, alts) =>
            val args1 = typedArgs(args)
            inferMethodAlternative(fun, context.undetparams, args1 map (.tpe.deconst), pt)
            typedApply(adapt(fun, funmode, WildcardType), args1)
          case MethodType(formals0, restpe) =>
            val formals = formalTypes(formals0, args.length)
            if (formals.length != args.length) {
              //System.out.println(""+formals.length+" "+args.length);//DEBUG
              errorTree(tree, "wrong number of arguments for "+treeSymTypeMsg(fun))
            } else {
              val tparams = context.undetparams
              context.undetparams = List()
              if (tparams.isEmpty) {
                val args1 = List.map2(args, formals)(typedArg)
                def ifPatternSkipFormals(tp: Type) = tp match {
                  case MethodType(_, rtp) if ((mode & PATTERNmode) != 0) => rtp
                  case _ => tp
                }
                constfold(copy.Apply(tree, fun, args1).setType(ifPatternSkipFormals(restpe)))
              } else {
                assert((mode & PATTERNmode) == 0); // this case cannot arise for patterns
                val lenientTargs = protoTypeArgs(tparams, formals, restpe, pt)
                val strictTargs = List.map2(lenientTargs, tparams)((targ, tparam) =>
                  if (targ == WildcardType) tparam.tpe else targ)
                def typedArgToPoly(arg: Tree, formal: Type): Tree = {
                  val lenientPt = formal.subst(tparams, lenientTargs)
                  val arg1 = typedArg(arg, lenientPt)
                  val argtparams = context.undetparams
                  context.undetparams = List()
                  if (!argtparams.isEmpty) {
                    val strictPt = formal.subst(tparams, strictTargs)
                    inferArgumentInstance(arg1, argtparams, strictPt, lenientPt)
                  }
                  arg1
                }
                val args1 = List.map2(args, formals)(typedArgToPoly)
                if (args1 exists (.tpe.isError)) setError(tree)
                else {
                  if (settings.debug.value) log("infer method inst "+fun+", tparams = "+tparams+", args = "+args1.map(.tpe)+", pt = "+pt+", lobounds = "+tparams.map(.tpe.bounds.lo));//debug
                  val undetparams = inferMethodInstance(fun, tparams, args1, pt)
                  val result = typedApply(fun, args1)
                  context.undetparams = undetparams
                  result
                }
              }
            }
          case ErrorType =>
            setError(tree)
          case _ =>
            errorTree(tree, ""+fun+" does not take parameters")
        }
      }

      def tryTypedArgs(args: List[Tree]) = {
        val reportGeneralErrors = context.reportGeneralErrors
        val reportAmbiguousErrors = context.reportAmbiguousErrors
        try {
          context.reportGeneralErrors = false
          context.reportAmbiguousErrors = false
          typedArgs(args)
        } catch {
          case ex: TypeError =>
            null
        } finally {
          context.reportGeneralErrors = reportGeneralErrors
          context.reportAmbiguousErrors = reportAmbiguousErrors
        }
      }

      /** Try to apply function to arguments; if it does not work try to insert an implicit
       *  conversion
       */
      def tryTypedApply(fun: Tree, args: List[Tree]): Tree = {
        val reportGeneralErrors = context.reportGeneralErrors
        try {
          context.reportGeneralErrors = false
          typedApply(fun, args)
        } catch {
          case ex: TypeError =>
            val Select(qual, name) = fun
            val args1 = tryTypedArgs(args map UnTyper.apply)
            context.reportGeneralErrors = reportGeneralErrors
            val qual1 = if (args1 == null || pt.isError) qual
                        else adaptToMember(qual, name, MethodType(args1 map (.tpe), pt))
            val tree1 = Apply(Select(qual1, name) setPos fun.pos, args map UnTyper.apply) setPos tree.pos
            typed1(tree1, mode | SNDTRYmode, pt)
        } finally {
          context.reportGeneralErrors = reportGeneralErrors
        }
      }

      /** Attribute a selection where `tree' is `qual.name'.
       *  `qual' is already attributed.
       */
      def typedSelect(qual: Tree, name: Name): Tree = {
        val sym =
          if (tree.symbol != NoSymbol) {
            if (phase.erasedTypes && qual.isInstanceOf[Super]) qual.tpe = tree.symbol.owner.tpe
            if (false && settings.debug.value) { // todo: replace by settings.check.value?
              val alts = qual.tpe.member(tree.symbol.name).alternatives
              if (!(alts exists (alt =>
                alt == tree.symbol || alt.isTerm && (alt.tpe matches tree.symbol.tpe))))
                assert(false, "symbol "+tree.symbol+tree.symbol.locationString+" not in "+alts+" of "+qual.tpe+
                       "\n members = "+qual.tpe.members+
                       "\n type history = "+qual.tpe.symbol.infosString+
                       "\n phase = "+phase)
            }
            tree.symbol
          } else qual.tpe match {
            case ThisType(clazz) if (clazz == context.enclClass.owner) =>
              qual.tpe.member(name)
            case _  =>
              qual.tpe.nonLocalMember(name)
          }
        if (sym == NoSymbol) {
          val qual1 = adaptToName(qual, name)
          if (qual1 ne qual) return typed(copy.Select(tree, qual1, name), mode, pt)
        }
        if (sym.info == NoType) {
          if (settings.debug.value) System.err.println("qual = "+qual+":"+qual.tpe+"\nSymbol="+qual.tpe.symbol+"\nsymbol-info = "+qual.tpe.symbol.info+"\nscope-id = "+qual.tpe.symbol.info.decls.hashCode()+"\nmembers = "+qual.tpe.members+"\nfound = "+sym)
          if (!qual.tpe.widen.isErroneous) {
            if (context.unit == null) assert(false, "("+qual+":"+qual.tpe+")."+name)
            error(tree.pos,
              decode(name)+" is not a member of "+qual.tpe.widen +
              (if (Position.line(context.unit.source, qual.pos) <
                   Position.line(context.unit.source, tree.pos))
                "\npossible cause: maybe a semicolon is missing before `"+name+"'?" else ""))
          }
          setError(tree)
        } else {
          val tree1 = tree match {
            case Select(_, _) => copy.Select(tree, qual, name)
            case SelectFromTypeTree(_, _) => copy.SelectFromTypeTree(tree, qual, name)
          }
          stabilize(checkAccessible(tree1, sym, qual.tpe, qual), qual.tpe, mode, pt)
        }
      }

      /** Attribute an identifier consisting of a simple name or an outer reference.
       *  @param tree      The tree representing the identifier.
       *  @param name      The name of the identifier.
       *  Transformations: (1) Prefix class members with this.
       *                   (2) Change imported symbols to selections
       */
      def typedIdent(name: Name): Tree = {
        def ambiguousError(msg: String) =
          error(tree.pos, "reference to "+name+" is ambiguous;\n"+msg)

        var defSym: Symbol = tree.symbol;   // the directly found symbol
        var pre: Type = NoPrefix;        // the prefix type of defSym, if a class member
        var qual: Tree = EmptyTree;   // the qualififier tree if transformed tree is a select

        if (defSym == NoSymbol) {
          var defEntry: ScopeEntry = null; // the scope entry of defSym, if defined in a local scope

          var cx = context
          while (defSym == NoSymbol && cx != NoContext) {
            //if (phase.name == "uncurry") System.out.println("typing " + name + " " + cx.owner + " " + (if (cx.enclClass == null) "null" else cx.enclClass.owner));//DEBUG
            pre = cx.enclClass.prefix
            defEntry = cx.scope.lookupEntry(name)
            if (defEntry != null && defEntry.sym.tpe != NoType) {
              defSym = defEntry.sym
            } else {
              cx = cx.enclClass
              defSym = pre.member(name) filter (
                sym => sym.tpe != NoType && context.isAccessible(sym, pre, false))
              if (defSym == NoSymbol) cx = cx.outer
            }
          }
          val symDepth = if (defEntry == null) cx.depth
                         else cx.depth - (cx.scope.nestingLevel - defEntry.owner.nestingLevel)
          var impSym: Symbol = NoSymbol;      // the imported symbol
          var imports = context.imports;      // impSym != NoSymbol => it is imported from imports.head
          while (impSym == NoSymbol && !imports.isEmpty && imports.head.depth > symDepth) {
            impSym = imports.head.importedSymbol(name)
            if (impSym == NoSymbol) imports = imports.tail
          }

          // detect ambiguous definition/import,
          // update `defSym' to be the final resolved symbol,
          // update `pre' to be `sym's prefix type in case it is an imported member,
          // and compute value of:

          // imported symbols take precedence over package-owned symbols in different
          // compilation units
          if (defSym.tpe != NoType && impSym.tpe != NoType &&
              defSym.owner.isPackageClass &&
              (!currentRun.compiles(defSym) ||
               context.unit != null && defSym.sourceFile != context.unit.source.file))
            defSym = NoSymbol

          if (defSym.tpe != NoType) {
            if (impSym.tpe != NoType)
              ambiguousError(
                "it is both defined in "+defSym.owner +
                " and imported subsequently by \n"+imports.head)
            else if (!defSym.owner.isClass || defSym.owner.isPackageClass || defSym.isTypeParameterOrSkolem)
              pre = NoPrefix
            else
              qual = atPos(tree.pos)(gen.mkQualifier(pre))
          } else {
            if (impSym.tpe != NoType) {
              var impSym1 = NoSymbol
              var imports1 = imports.tail
              def ambiguousImport() = {
                if (!(imports.head.qual.tpe =:= imports1.head.qual.tpe))
                  ambiguousError(
                    "it is imported twice in the same scope by\n"+imports.head +  "\nand "+imports1.head)
              }
              while (!imports1.isEmpty &&
                     (!imports.head.isExplicitImport(name) ||
                      imports1.head.depth == imports.head.depth)) {
                var impSym1 = imports1.head.importedSymbol(name)
                if (impSym1 != NoSymbol) {
                  if (imports1.head.isExplicitImport(name)) {
                    if (imports.head.isExplicitImport(name) ||
                        imports1.head.depth != imports.head.depth) ambiguousImport()
                    impSym = impSym1;
                    imports = imports1
                  } else if (!imports.head.isExplicitImport(name) &&
                             imports1.head.depth == imports.head.depth) ambiguousImport()
                }
                imports1 = imports1.tail
              }
              defSym = impSym
              qual = imports.head.qual
              pre = qual.tpe
            } else {
              if (settings.debug.value) {
                log(context.imports);//debug
              }
              error(tree.pos, "not found: "+decode(name))
              defSym = context.owner.newErrorSymbol(name)
            }
          }
        }
        if (defSym.owner.isPackageClass) pre = defSym.owner.thisType
        val tree1 = if (qual == EmptyTree) tree
                    else atPos(tree.pos)(Select(qual, name));
                      // atPos necessary because qualifier might come from startContext
        stabilize(checkAccessible(tree1, defSym, pre, qual), pre, mode, pt)
      }

      // begin typed1
      val sym: Symbol = tree.symbol
      if (sym != null) sym.initialize
      //if (settings.debug.value && tree.isDef) log("typing definition of "+sym);//DEBUG
      tree match {
        case PackageDef(name, stats) =>
          val stats1 = newTyper(context.make(tree, sym.moduleClass, sym.info.decls))
            .typedStats(stats, NoSymbol)
          copy.PackageDef(tree, name, stats1) setType NoType

        case cdef @ ClassDef(_, _, _, _, _) =>
          newTyper(context.makeNewScope(tree, sym)).typedClassDef(cdef)

        case mdef @ ModuleDef(_, _, _) =>
          newTyper(context.make(tree, sym.moduleClass)).typedModuleDef(mdef)

        case vdef @ ValDef(_, _, _, _) =>
          typedValDef(vdef)

        case ddef @ DefDef(_, _, _, _, _, _) =>
          newTyper(context.makeNewScope(tree, sym)).typedDefDef(ddef)

        case tdef @ AbsTypeDef(_, _, _, _) =>
          newTyper(context.makeNewScope(tree, sym)).typedAbsTypeDef(tdef)

        case tdef @ AliasTypeDef(_, _, _, _) =>
          newTyper(context.makeNewScope(tree, sym)).typedAliasTypeDef(tdef)

        case ldef @ LabelDef(_, _, _) =>
          var lsym = ldef.symbol
          var typer1 = this
          if (lsym == NoSymbol) { // labeldef is part of template
            typer1 = newTyper(context.makeNewScope(tree, context.owner))
            typer1.enterLabelDef(ldef)
          }
          typer1.typedLabelDef(ldef)

        case Attributed(attr, defn) =>
          val attr1 = typed(attr, AttributeClass.tpe)
          val attrInfo = attr1 match {
            case Apply(Select(New(tpt), nme.CONSTRUCTOR), args) =>
              Pair(tpt.tpe, args map {
                case Literal(value) =>
                  value
                case arg =>
                  error(arg.pos, "attribute argument needs to be a constant; found: "+arg)
                  null
              })
          }
          if (attrInfo != null) {
            val attributed =
              if (defn.symbol.isModule) defn.symbol.moduleClass else defn.symbol;
            attributed.attributes = attributed.attributes ::: List(attrInfo)
          }
          typed(defn, mode, pt)

        case DocDef(comment, defn) => {
          val ret = typed(defn, mode, pt)
          if (onlyPresentation) comments(defn . symbol) = comment;
          ret
        }
        case block @ Block(_, _) =>
          newTyper(context.makeNewScope(tree, context.owner))
            .typedBlock(block, mode, pt)

        case Sequence(elems) =>
          val elems1 = List.mapConserve(elems)(elem => typed(elem, mode, pt))
          copy.Sequence(tree, elems1) setType pt

        case Alternative(alts) =>
          val alts1 = List.mapConserve(alts)(alt => typed(alt, mode, pt))
          copy.Alternative(tree, alts1) setType pt

        case Star(elem) =>
          val elem1 = typed(elem, mode, pt)
          copy.Star(tree, elem1) setType pt

        case Bind(name, body) =>
          var vble = tree.symbol
          if (vble == NoSymbol) vble = context.owner.newValue(tree.pos, name)
          if (vble.name != nme.WILDCARD) namer.enterInScope(vble)
          val body1 = typed(body, mode, pt)
          vble.setInfo(if (treeInfo.isSequenceValued(body)) seqType(body1.tpe) else body1.tpe)
          copy.Bind(tree, name, body1) setSymbol vble setType body1.tpe; // buraq, was: pt

        case ArrayValue(elemtpt, elems) =>
          val elemtpt1 = typedType(elemtpt)
          val elems1 = List.mapConserve(elems)(elem => typed(elem, mode, elemtpt1.tpe))
          copy.ArrayValue(tree, elemtpt1, elems1)
            .setType(if (isFullyDefined(pt) && !phase.erasedTypes) pt
                     else appliedType(ArrayClass.typeConstructor, List(elemtpt1.tpe)))

        case fun @ Function(_, _) =>
/*
          newTyper(context.makeNewScope(tree, context.owner)).typedFunction(fun, mode, pt)
*/
          tree.symbol = context.owner.newValue(tree.pos, nme.ANON_FUN_NAME)
            .setFlag(SYNTHETIC).setInfo(NoType)
          newTyper(context.makeNewScope(tree, tree.symbol)).typedFunction(fun, mode, pt)

        case Assign(lhs, rhs) =>
          def isGetter(sym: Symbol) = sym.info match {
            case PolyType(List(), _) => sym.owner.isClass && !sym.isStable
            case _: ImplicitMethodType => sym.owner.isClass && !sym.isStable
            case _ => false
          }
          val lhs1 = typed(lhs, EXPRmode | LHSmode, WildcardType)
          val varsym = lhs1.symbol
          if (varsym != null && isGetter(varsym)) {
            lhs1 match {
              case Select(qual, name) =>
                typed(
                  Apply(
                    Select(qual, nme.getterToSetter(name)) setPos lhs.pos,
                    List(rhs)) setPos tree.pos, mode, pt)
            }
          } else if (varsym != null && (varsym.isVariable || varsym.isValue && phase.erasedTypes)) {
            val rhs1 = typed(rhs, lhs1.tpe)
            copy.Assign(tree, lhs1, rhs1) setType UnitClass.tpe
          } else {
            if (!lhs1.tpe.isError) error(tree.pos, "assignment to non-variable ")
            setError(tree)
          }

        case If(cond, thenp, elsep) =>
          val cond1 = typed(cond, BooleanClass.tpe)
          if (elsep.isEmpty) {
            val thenp1 = typed(thenp, UnitClass.tpe)
            copy.If(tree, cond1, thenp1, elsep) setType UnitClass.tpe
          } else {
            val thenp1 = typed(thenp, pt)
            val elsep1 = typed(elsep, pt)
            copy.If(tree, cond1, thenp1, elsep1) setType ptOrLub(List(thenp1.tpe, elsep1.tpe))
          }

        case Match(selector, cases) =>
          val selector1 = typed(selector)
          val cases1 = typedCases(tree, cases, selector1.tpe.widen, pt)
          copy.Match(tree, selector1, cases1) setType ptOrLub(cases1 map (.tpe))

        case Return(expr) =>
          val enclMethod = context.enclMethod;
          if (enclMethod == NoContext || enclMethod.owner.isConstructor)
            errorTree(tree, "return outside method definition")
          else if (!enclMethod.owner.isInitialized)
            errorTree(tree, "method "+enclMethod.owner+" has return statement; needs result type")
          else {
            val DefDef(_, _, _, _, restpt, _) = enclMethod.tree
            assert(restpt.tpe != null, restpt)
            val expr1: Tree = typed(expr, restpt.tpe)
            copy.Return(tree, expr1) setSymbol enclMethod.owner setType AllClass.tpe
          }

        case Try(block, catches, finalizer) =>
          val block1 = typed(block, pt)
          val catches1 = typedCases(tree, catches, ThrowableClass.tpe, pt)
          val finalizer1 = if (finalizer.isEmpty) finalizer
                           else typed(finalizer, UnitClass.tpe)
          copy.Try(tree, block1, catches1, finalizer1)
            .setType(ptOrLub(block1.tpe :: (catches1 map (.tpe))))

        case Throw(expr) =>
          val expr1 = typed(expr, ThrowableClass.tpe)
          copy.Throw(tree, expr1) setType AllClass.tpe

        case New(tpt: Tree) =>
          var tpt1 = typedTypeConstructor(tpt)
          if (tpt1.hasSymbol && !tpt1.symbol.typeParams.isEmpty) {
            context.undetparams = cloneSymbols(tpt1.symbol.typeParams)
            tpt1 = TypeTree()
              .setOriginal(tpt1) /* .setPos(tpt1.pos) */
              .setType(appliedType(tpt1.tpe, context.undetparams map (.tpe)))
          }
          if (tpt1.tpe.symbol hasFlag ABSTRACT)
            error(tree.pos, ""+tpt1.tpe.symbol+" is abstract; cannot be instantiated")
          copy.New(tree, tpt1).setType(tpt1.tpe)

        case Typed(expr, Function(List(), EmptyTree)) =>
          val expr1 = typed1(expr, mode, pt);
          expr1.tpe match {
            case MethodType(formals, _) =>
              adapt(expr1, mode, functionType(formals map (t => WildcardType), WildcardType))
            case ErrorType =>
              expr1
            case _ =>
              errorTree(expr1, "`&' must be applied to method type; cannot be applied to " + expr1.tpe)
          }

        case Typed(expr, tpt @ Ident(name)) if (name == nme.WILDCARD_STAR.toTypeName) =>
          val expr1 = typed(expr, mode & stickyModes, seqType(pt))
          expr1.tpe.baseType(SeqClass) match {
            case TypeRef(_, _, List(elemtp)) =>
              copy.Typed(tree, expr1, tpt setType elemtp) setType elemtp
            case _ =>
              setError(tree)
          }
        case Typed(expr, tpt) =>
          val tpt1 = typedType(tpt)
          val expr1 = typed(expr, mode & stickyModes, tpt1.tpe)
          copy.Typed(tree, expr1, tpt1) setType tpt1.tpe

        case TypeApply(fun, args) =>
          val args1 = List.mapConserve(args)(typedType)
          // do args first in order to maintain conext.undetparams on the function side.
          typedTypeApply(typed(fun, funmode | TAPPmode, WildcardType), args1)

        case Apply(Block(stats, expr), args) =>
          typed1(Block(stats, Apply(expr, args)), mode, pt)

        case Apply(fun, args) =>
          val stableApplication = fun.symbol != null && fun.symbol.isMethod && fun.symbol.isStable
          if (stableApplication && (mode & PATTERNmode) != 0) {
            // treat stable function applications f() as expressions.
            typed1(tree, mode & ~PATTERNmode | EXPRmode, pt)
          } else {
            val funpt = if ((mode & PATTERNmode) != 0) pt else WildcardType
            var fun1 = typed(fun, funmode, funpt)
            if (stableApplication) fun1 = stabilizeFun(fun1, mode, pt)
            // if function is overloaded, filter all alternatives that match
            // number of arguments and expected result type.
            if (settings.debug.value) log("trans app "+fun1+":"+fun1.symbol+":"+fun1.tpe+" "+args);//DEBUG
            if (util.Statistics.enabled) appcnt = appcnt + 1
            if (xviews &&
                fun1.isInstanceOf[Select] &&
                !fun1.tpe.isInstanceOf[ImplicitMethodType] &&
                (mode & (EXPRmode | SNDTRYmode)) == EXPRmode) tryTypedApply(fun1, args)
            else typedApply(fun1, args)
          }

        case Super(qual, mix) =>
          val Pair(clazz, selftype) =
            if (tree.symbol != NoSymbol) {
              Pair(tree.symbol, tree.symbol.thisType)
            } else {
              val clazzContext = qualifyingClassContext(tree, qual)
              Pair(clazzContext.owner, clazzContext.prefix)
            }
          if (clazz == NoSymbol) setError(tree)
          else {
            val owntype =
              if (mix.isEmpty)
                if ((mode & SUPERCONSTRmode) != 0) clazz.info.parents.head
                else intersectionType(clazz.info.parents)
              else {
                val ps = clazz.info.parents dropWhile (p => p.symbol.name != mix)
                if (ps.isEmpty) {
                  if (settings.debug.value) System.out.println(clazz.info.parents map (.symbol.name));//debug
                  error(tree.pos, ""+mix+" does not name a base class of "+clazz)
                  ErrorType
                } else ps.head
              }
            tree setSymbol clazz setType SuperType(selftype, owntype)
          }

        case This(qual) =>
          val Pair(clazz, selftype) =
            if (tree.symbol != NoSymbol) {
              Pair(tree.symbol, tree.symbol.thisType)
            } else {
              val clazzContext = qualifyingClassContext(tree, qual)
              Pair(clazzContext.owner, clazzContext.prefix)
            }
          if (clazz == NoSymbol) setError(tree)
          else {
            val owntype = if (pt.isStable || (mode & QUALmode) != 0) selftype
                          else selftype.singleDeref
            tree setSymbol clazz setType owntype
          }

        case Select(qual @ Super(_, _), nme.CONSTRUCTOR) =>
          val qual1 = typed(qual, EXPRmode | QUALmode | POLYmode | SUPERCONSTRmode, WildcardType)
          // the qualifier type of a supercall constructor is its first parent class
          typedSelect(qual1, nme.CONSTRUCTOR)

        case Select(qual, name) =>
          if (util.Statistics.enabled) selcnt = selcnt + 1
          var qual1 = typedQualifier(qual)
          if (name.isTypeName) qual1 = checkStable(qual1)
          typedSelect(qual1, name)

        case Ident(name) =>
          idcnt = idcnt + 1
          if (name == nme.WILDCARD && (mode & (PATTERNmode | FUNmode)) == PATTERNmode)
            tree setType pt
          else
            typedIdent(name)

        // todo: try with case Literal(Constant(()))
        case Literal(value) =>
          tree setType (
            if (value.tag == UnitTag) UnitClass.tpe
            else ConstantType(value))

        case SingletonTypeTree(ref) =>
          val ref1 = checkStable(typed(ref, EXPRmode | QUALmode, AnyRefClass.tpe))
          tree setType ref1.tpe.resultType

        case SelectFromTypeTree(qual, selector) =>
          tree setType typedSelect(typedType(qual), selector).tpe

        case CompoundTypeTree(templ: Template) =>
          tree setType {
            val parents1 = List.mapConserve(templ.parents)(typedType)
            if (parents1 exists (.tpe.isError)) ErrorType
            else {
              val decls = new Scope()
              val self = refinedType(parents1 map (.tpe), context.enclClass.owner, decls)
              newTyper(context.make(templ, self.symbol, decls)).typedRefinement(templ.body)
              self
            }
          }

        case AppliedTypeTree(tpt, args) =>
          val tpt1 = typed1(tpt, mode | FUNmode | TAPPmode, WildcardType)
          val tparams = tpt1.symbol.typeParams
          val args1 = List.mapConserve(args)(typedType)
          if (tpt1.tpe.isError) {
            setError(tree)
          } else if (tparams.length == args1.length) {
            val argtypes = args1 map (.tpe)
            val owntype = if (tpt1.symbol.isClass) appliedType(tpt1.tpe, argtypes)
                          else tpt1.tpe.subst(tparams, argtypes)
            TypeTree(owntype) setOriginal(tree) // setPos tree.pos
          } else if (tparams.length == 0) {
            errorTree(tree, ""+tpt1.tpe+" does not take type parameters")
          } else {
            //System.out.println("\{tpt1}:\{tpt1.symbol}:\{tpt1.symbol.info}")
            if (settings.debug.value) System.out.println(""+tpt1+":"+tpt1.symbol+":"+tpt1.symbol.info);//debug
            errorTree(tree, "wrong number of type arguments for "+tpt1.tpe+", should be "+tparams.length)
          }
        case _ =>
          throw new Error("unexpected tree: "+tree);//debug
      }
    }

    def typed(tree: Tree, mode: int, pt: Type): Tree =
      try {
        if (settings.debug.value) {
          assert(pt != null, tree);//debug
          //System.out.println("typing "+tree);//debug
        }
        val tree1 = if (tree.tpe != null) tree else typed1(tree, mode, pt)
        //System.out.println("typed "+tree1+":"+tree1.tpe);//debug
        val result = if (tree1.isEmpty) tree1 else adapt(tree1, mode, pt)
        //System.out.println("adapted "+tree1+":"+tree1.tpe+" to "+pt);//debug
        result
      } catch {
        case ex: TypeError =>
          //System.out.println("caught "+ex+" in typed");//DEBUG
              reportTypeError(tree.pos, ex)
              setError(tree)
            case ex: Throwable =>
              if (settings.debug.value)
                System.out.println("exception when typing "+tree+", pt = "+pt)
            if (context != null && context.unit != null && context.unit.source != null && tree != null)
              logError("AT: " + context.unit.source.dbg(tree.pos), ex);
              throw(ex)
      }

    def atOwner(owner: Symbol): Typer =
      new Typer(context.make(context.tree, owner))

    def atOwner(tree: Tree, owner: Symbol): Typer =
      new Typer(context.make(tree, owner))

    /** Types expression or definition `tree' */
    def typed(tree: Tree): Tree =
      typed(tree, EXPRmode, WildcardType)

    /** Types expression `tree' with given prototype `pt' */
    def typed(tree: Tree, pt: Type): Tree =
      typed(tree, EXPRmode, pt)

    /** Types qualifier `tree' of a select node. E.g. is tree occurs in acontext like `tree.m'. */
    def typedQualifier(tree: Tree): Tree =
      typed(tree, EXPRmode | QUALmode | POLYmode, WildcardType)

    /** Types function part of an application */
    def typedOperator(tree: Tree): Tree =
      typed(tree, EXPRmode | FUNmode | POLYmode | TAPPmode, WildcardType)

    /** Types a pattern with prototype `pt' */
    def typedPattern(tree: Tree, pt: Type): Tree =
      typed(tree, PATTERNmode, pt)

    /** Types a (fully parameterized) type tree */
    def typedType(tree: Tree): Tree =
      typed(tree, TYPEmode, WildcardType)

    /** Types a type constructor tree used in a new or supertype */
    def typedTypeConstructor(tree: Tree): Tree = {
      val result = typed(tree, TYPEmode | FUNmode, WildcardType)
      if (!phase.erasedTypes && result.tpe.isInstanceOf[TypeRef] && !result.tpe.prefix.isStable)
        error(tree.pos, ""+result.tpe.prefix+" is not a legal prefix for a constructor")
      result
    }

    def computeType(tree: Tree): Type = {
      val tree1 = typed(tree)
      transformed(tree) = tree1
      tree1.tpe
    }

    def transformedOrTyped(tree: Tree, pt: Type): Tree = transformed.get(tree) match {
      case Some(tree1) => transformed -= tree; tree1
      case None => typed(tree, pt)
    }

/*
    def convertToTypeTree(tree: Tree): Tree = tree match {
      case TypeTree() => tree
      case _ => TypeTree(tree.tpe)
    }
*/
    /* -- Views --------------------------------------------------------------- */

    private def depoly(tp: Type): Type = tp match {
      case PolyType(tparams, restpe) => restpe.subst(tparams, tparams map (t => WildcardType))
      case _ => tp
    }

    private def containsError(tp: Type): boolean = tp match {
      case PolyType(tparams, restpe) => containsError(restpe)
      case MethodType(formals, restpe) => (formals exists (.isError)) || containsError(restpe)
      case _ => tp.isError
    }

    /** Try to construct a typed tree from given implicit info with given expected type
     *  @param pos     Position for error reporting
     *  @param info    The given implicit info describing the implicit definition
     *  @param pt      The expected type
     *  @param isLocal Is implicit definition visible without prefix?
     *  @returns A typed tree if the implicit info can be made to conform to `pt', EmptyTree otherwise.
     *  @pre info.tpe does not contain an error
     */
    private def typedImplicit(pos: int, info: ImplicitInfo, pt: Type, isLocal: boolean): Tree =
      if (isCompatible(depoly(info.tpe), pt)) {
        val tree = Ident(info.name) setPos pos
        def fail(reason: String, sym1: Symbol, sym2: Symbol): Tree = {
          if (settings.debug.value)
            log(""+tree+" is not a valid implicit value because:\n"+reason + sym1+" "+sym2);
          EmptyTree
        }
        try {
          if (!isLocal) tree setSymbol info.sym
          val tree1 = typed1(tree, EXPRmode, pt)
          if (settings.debug.value) log("typed implicit "+tree1+":"+tree1.tpe+", pt = "+pt);
          val tree2 = adapt(tree1, EXPRmode, pt)
          if (settings.debug.value) log("adapted implicit "+tree1.symbol+":"+tree2.tpe+" to "+pt);
          if (!tree2.tpe.isError && info.sym == tree1.symbol) tree2
          else fail("syms differ: ", tree1.symbol, info.sym)
        } catch {
          case ex: TypeError => fail(ex.getMessage(), NoSymbol, NoSymbol)
        }
      } else EmptyTree

    /** Infer implicit argument or view
     *  @param  pos     position for error reporting
     *  @param  pt      the expected type of the implicit
     *  @param  isView  are we searching for a view? (this affects the error message)
     *  @param  reportAmbiguous  should ambiguous errors be reported? False iff we search for a view
     *              to find out whether one type is coercible to another (@see isCoercible)
     */
    private def inferImplicit(pos: int, pt: Type, isView: boolean, reportAmbiguous: boolean): Tree = {

      if (util.Statistics.enabled) implcnt = implcnt + 1
      val startTime = if (util.Statistics.enabled) System.currentTimeMillis() else 0l

      val tc = newTyper(context.makeImplicit(reportAmbiguous))

      def ambiguousError(info1: ImplicitInfo, info2: ImplicitInfo) =
        error(
          pos,
          "ambiguous implicit value:\n" +
          " both "+info1.sym + info1.sym.locationString+" of type "+info1.tpe+
          "\n and "+info2.sym + info2.sym.locationString+" of type "+info2.tpe+
          (if (isView) "\n are possible conversion functions from "+ pt.typeArgs(0)+" to "+pt.typeArgs(1)
           else "\n match expected type "+pt))

      /** Search list of implicit info lists for one matching prototype `pt'
       *  If found return a tree from found implicit info which is typed with expected type `pt'.
       *  Otherwise return EmptyTree
       *  @param implicitInfoss    The given list of lists of implicit infos
       *  @isLocal                 Is implicit definition visible without prefix?
       *                           If this is the case then symbols in preceding lists shadow
       *                           symbols of the same name in succeeding lists.
       */
      def searchImplicit(implicitInfoss: List[List[ImplicitInfo]], isLocal: boolean): Tree = {
        def isSubClassOrObject(sym1: Symbol, sym2: Symbol) = {
          (sym1 isSubClass sym2) ||
          sym1.isModuleClass && sym2.isModuleClass &&
          (sym1.sourceModule.linkedClass isSubClass sym2.sourceModule.linkedClass)
        }
        def improves(info1: ImplicitInfo, info2: ImplicitInfo) =
          (info2 == NoImplicitInfo) ||
          (info1 != NoImplicitInfo) &&
          isSubClassOrObject(info1.sym.owner, info2.sym.owner) &&
          isStrictlyBetter(info1.tpe, info2.tpe)
        val shadowed = new HashSet[Name](8)
        def isApplicable(info: ImplicitInfo): boolean =
          !containsError(info.tpe) &&
          !(isLocal && shadowed.contains(info.name)) &&
          tc.typedImplicit(pos, info, pt, isLocal) != EmptyTree
        def applicableInfos(is: List[ImplicitInfo]) = {
          val result = is filter isApplicable
          if (isLocal)
            for (val i <- is) shadowed addEntry i.name
          result
        }
        val applicable = List.flatten(implicitInfoss map applicableInfos)
        val best = (NoImplicitInfo /: applicable) ((best, alt) => if (improves(alt, best)) alt else best)
        val competing = applicable dropWhile (alt => best == alt || improves(best, alt))
        if (best == NoImplicitInfo) EmptyTree
        else {
          if (!competing.isEmpty) ambiguousError(best, competing.head)
          tc.typedImplicit(pos, best, pt, isLocal)
        }
      }

      def implicitsOfType(tp: Type): List[List[ImplicitInfo]] = {
        val tp1 = if (isFunctionType(tp)) intersectionType(tp.typeArgs.reverse) else tp
        tp1.baseClasses map implicitsOfClass
      }

      def implicitsOfClass(clazz: Symbol): List[ImplicitInfo] = (
        clazz.initialize.linkedModule.moduleClass.info.members.toList.filter(.hasFlag(IMPLICIT)) map
          (sym => new ImplicitInfo(sym.name, clazz.linkedModule.tpe, sym))
      )

      var tree = searchImplicit(context.implicitss, true)
      if (tree == EmptyTree) tree = searchImplicit(implicitsOfType(pt.widen), false)
      if (util.Statistics.enabled) impltime = impltime + System.currentTimeMillis() - startTime
      tree
    }

    def applyImplicitArgs(tree: Tree): Tree = tree.tpe match {
      case MethodType(formals, _) =>
        def implicitArg(pt: Type) = {
          val arg = inferImplicit(tree.pos, pt, false, true)
          if (arg != EmptyTree) arg
          else errorTree(tree, "no implicit argument matching parameter type "+pt+" was found.")
        }
        Apply(tree, formals map implicitArg) setPos tree.pos
      case ErrorType =>
        tree
    }
  }
}