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

/* NSC -- new Scala compiler
 * Copyright 2005-2006 LAMP/EPFL
 * @author  Martin Odersky
 */
// $Id$

package scala.tools.nsc.typechecker

import scala.tools.nsc.util.Position
import symtab.Flags
import symtab.Flags._

/** This trait declares methods to create symbols and to enter them into scopes.
 *
 *  @author Martin Odersky
 *  @version 1.0
 */
trait Namers requires Analyzer {
  import global._
  import definitions._

  /** Convert to corresponding type parameters all skolems which satisfy one
   *  of the following two conditions:
   *  1. The skolem is a parameter of a class or alias type
   *  2. The skolem is a method parameter which appears in parameter `tparams'
   */
  class DeSkolemizeMap(tparams: List[Symbol]) extends TypeMap {
    def apply(tp: Type): Type = tp match {
      case TypeRef(pre, sym, args) =>
        val tparam = sym.deSkolemize
        mapOver(
          if (tparam == sym || !(tparams contains tparam)) tp
          else rawTypeRef(NoPrefix, tparam, args))
      case SingleType(pre, sym) if (sym.isThisSkolem) =>
        mkThisType(sym.deSkolemize)
      case PolyType(tparams1, restpe) =>
        new DeSkolemizeMap(tparams1 ::: tparams).mapOver(tp)
      case ClassInfoType(parents, decls, clazz) =>
        val parents1 = List.mapConserve(parents)(this)
        if (parents1 eq parents) tp else ClassInfoType(parents1, decls, clazz)
      case _ =>
        mapOver(tp)
    }
  }
  /** overridden by IDE to not manually enter value parameters */
  protected final def doEnterValueParams = !inIDE;
  protected def inIDE = false;

  class Namer(val context: Context) {

    val typer = newTyper(context)

    def setPrivateWithin(tree: Tree, sym: Symbol, mods: Modifiers): Symbol = {
      if (!mods.privateWithin.isEmpty)
        sym.privateWithin = typer.qualifyingClassContext(tree, mods.privateWithin).owner
      sym
    }

    def updatePosFlags(sym: Symbol, pos: PositionType, flags: int): Symbol = {
      if (settings.debug.value) log("overwriting " + sym)
      val lockedFlag = sym.flags & LOCKED
      sym.reset(NoType)
      sym setPos pos
      sym.flags = flags | lockedFlag
      if (sym.isModule && sym.moduleClass != NoSymbol)
        updatePosFlags(sym.moduleClass, pos, (flags & ModuleToClassFlags) | MODULE | FINAL)
      if (sym.owner.isPackageClass &&
          (sym.linkedSym.rawInfo.isInstanceOf[loaders.SymbolLoader] ||
           sym.linkedSym.rawInfo.isComplete && runId(sym.validTo) != currentRunId))
        // pre-set linked symbol to NoType, in case it is not loaded together with this symbol.
        sym.linkedSym.setInfo(NoType)
      sym
    }

    private def isTemplateContext(context: Context): boolean = context.tree match {
      case Template(_, _) => true
      case Import(_, _) => isTemplateContext(context.outer)
      case _ => false
    }

    private var innerNamerCache: Namer = null

    def namerOf(sym: Symbol): Namer = {

      def innerNamer: Namer = {
        if (innerNamerCache eq null)
          innerNamerCache =
            if (!isTemplateContext(context)) this
            else new Namer(context.make(context.tree, context.owner, newScope))
        innerNamerCache
      }

      def primaryConstructorParamNamer: Namer = {
        val classContext = context.enclClass
        val outerContext = classContext.outer.outer
        val paramContext = outerContext.makeNewScope(outerContext.tree, outerContext.owner)
        classContext.owner.unsafeTypeParams foreach paramContext.scope.enter
        new Namer(paramContext)
      }

      if (sym.isTerm &&
          (sym.hasFlag(PARAM) && sym.owner.isPrimaryConstructor || sym.hasFlag(PARAMACCESSOR)))
        primaryConstructorParamNamer
      else
        innerNamer
    }

    private def doubleDefError(pos: PositionType, sym: Symbol): unit =
      context.error(pos,
        sym.name.toString() + " is already defined as " +
        (if (sym.hasFlag(CASE)) "case class " + sym.name else sym.toString()))

    def enterInScope(sym: Symbol): Symbol = {
      // allow for overloaded methods
      if (!(sym.isSourceMethod && sym.owner.isClass && !sym.owner.isPackageClass)) {
      	val prev = context.scope.lookupEntry(sym.name);
      	if ((prev ne null) && prev.owner == context.scope &&
            (!prev.sym.isSourceMethod ||
             nme.isSetterName(sym.name) ||
             sym.owner.isPackageClass)) {
     	   doubleDefError(sym.pos, prev.sym)
           sym setInfo ErrorType
      	} else context.scope enter sym
      } else context.scope enter sym
      sym
    }

    def enterPackageSymbol(pos: PositionType, name: Name): Symbol = {
      val cscope = if (context.owner == EmptyPackageClass) RootClass.info.decls
                   else context.scope
      val p: Symbol = cscope.lookup(name)
      if (p.isPackage && cscope == p.owner.info.decls) {
        p
      } else {
        val cowner = if (context.owner == EmptyPackageClass) RootClass else context.owner
        val pkg = cowner.newPackage(pos, name)
        pkg.moduleClass.setInfo(new PackageClassInfoType(newScope, pkg.moduleClass))
        pkg.setInfo(pkg.moduleClass.tpe)
        enterInScope(pkg)
      }
    }

    def inConstructorFlag: long =
      if (context.owner.isConstructor && !context.inConstructorSuffix) INCONSTRUCTOR
      else 0l

    private def enterClassSymbol(pos: PositionType, flags: int, name: Name): Symbol = {
      var c: Symbol = context.scope.lookup(name)
      if (c.isType && !currentRun.compiles(c) && context.scope == c.owner.info.decls) {
        updatePosFlags(c, pos, flags)
      } else {
        c = enterInScope(context.owner.newClass(pos, name)).setFlag(flags | inConstructorFlag)
      }
      if (c.owner.isPackageClass) {
      	val file = context.unit.source.getFile()
      	val clazz = c.asInstanceOf[ClassSymbol]
      	if (settings.debug.value && (clazz.sourceFile ne null) && !clazz.sourceFile.equals(file)) {
          Console.err.println("SOURCE MISMATCH: " + clazz.sourceFile + " vs. " + file + " SYM=" + c);
        }
        clazz.sourceFile = file
        if (clazz.sourceFile ne null) {
          assert(!currentRun.compiles(clazz) || clazz.sourceFile == currentRun.symSource(c));
          currentRun.symSource(c) = clazz.sourceFile
        }
      }
      c
    }

    private def enterModuleSymbol(pos: PositionType, flags: int, name: Name): Symbol = {
      var m: Symbol = context.scope.lookup(name)
      if (m.isModule && !m.isPackage && !currentRun.compiles(m) &&
         (context.scope == m.owner.info.decls)) {
        updatePosFlags(m, pos, flags)
      } else {
        if (m.isTerm && !m.isPackage && !currentRun.compiles(m) && (context.scope == m.owner.info.decls))
          context.scope.unlink(m)
        m = context.owner.newModule(pos, name)
        m.setFlag(flags)
        m.moduleClass.setFlag(flags | inConstructorFlag)
        enterInScope(m)
      }
      if (m.owner.isPackageClass) {
        m.moduleClass.sourceFile = context.unit.source.getFile()
        currentRun.symSource(m) = m.moduleClass.sourceFile
      }
      m
    }

    private def enterCaseFactorySymbol(pos: PositionType, flags: int, name: Name): Symbol = {
      var m: Symbol = context.scope.lookup(name)
      if (m.isTerm && !m.isPackage && !currentRun.compiles(m) && context.scope == m.owner.info.decls) {
        updatePosFlags(m, pos, flags)
      } else {
        m = enterInScope(context.owner.newMethod(pos, name)).setFlag(flags)
      }
      if (m.owner.isPackageClass)
        currentRun.symSource(m) = context.unit.source.getFile()
      m
    }

    def enterSyms(trees: List[Tree]): Namer = {
      var namer : Namer = this
      for (val tree <- trees) {
        val txt = namer.enterSym(tree)
        if (!(txt eq namer.context)) namer = new Namer(txt)
      }
      namer
    }

    def newTypeSkolems(tparams: List[Symbol]): List[Symbol] = {
      val tskolems = tparams map (.newTypeSkolem)
      val ltp = new LazyType {
        override def complete(sym: Symbol): unit =
          sym setInfo sym.deSkolemize.info.substSym(tparams, tskolems)
      }
      tskolems foreach (.setInfo(ltp))
      tskolems
    }

    def skolemize(tparams: List[AbsTypeDef]): unit = {
      val tskolems = newTypeSkolems(tparams map (.symbol))
      for (val (tparam, tskolem) <- tparams zip tskolems) tparam.symbol = tskolem
    }

    def applicableTypeParams(owner: Symbol): List[Symbol] =
      if (owner.isTerm || owner.isPackageClass) List()
      else applicableTypeParams(owner.owner) ::: owner.typeParams

    def deSkolemize: TypeMap = new DeSkolemizeMap(applicableTypeParams(context.owner))

    def enterSym(tree: Tree): Context = {

      def finishWith(tparams: List[AbsTypeDef]): unit = {
        val sym = tree.symbol
        if (settings.debug.value) log("entered " + sym + " in " + context.owner + ", scope-id = " + context.scope.hashCode());
        var ltype: LazyType = namerOf(sym).typeCompleter(tree)
        if (!tparams.isEmpty) {
          new Namer(context.makeNewScope(tree, sym)).enterSyms(tparams)
          ltype = new LazyPolyType(tparams map (.symbol), ltype)
          if (sym.isTerm) skolemize(tparams)
        }
        sym.setInfo(ltype)
      }
      def finish = finishWith(List())


      if (tree.symbol == NoSymbol) {
	val owner = context.owner
	tree match {
	  case PackageDef(name, stats) =>
	    tree.symbol = enterPackageSymbol(tree.pos, name)
	    val namer = new Namer(
	      context.make(tree, tree.symbol.moduleClass, tree.symbol.info.decls))
	    namer.enterSyms(stats)
	  case ClassDef(mods, name, tparams, _, impl) =>
	    if ((mods.flags & CASE) != 0) { // enter case factory method.
	      tree.symbol = enterCaseFactorySymbol(
        		tree.pos, mods.flags & AccessFlags | METHOD | CASE, name.toTermName)
              tree.symbol.setInfo(namerOf(tree.symbol).caseFactoryCompleter(tree))
              setPrivateWithin(tree, tree.symbol, mods)
            }
            tree.symbol = enterClassSymbol(tree.pos, mods.flags, name)
            setPrivateWithin(tree, tree.symbol, mods)
            finishWith(tparams)
          case ModuleDef(mods, name, _) =>
            tree.symbol = enterModuleSymbol(tree.pos, mods.flags | MODULE | FINAL, name)
            setPrivateWithin(tree, tree.symbol, mods)
            setPrivateWithin(tree, tree.symbol.moduleClass, mods)
            tree.symbol.moduleClass.setInfo(namerOf(tree.symbol).moduleClassTypeCompleter(tree))
            finish
          case ValDef(mods, name, tp, rhs) =>
            if (context.owner.isClass && (mods.flags & (PRIVATE | LOCAL)) != (PRIVATE | LOCAL)) {
              val accflags = ACCESSOR |
                (if ((mods.flags & MUTABLE) != 0) mods.flags & ~MUTABLE else mods.flags | STABLE)
              val getter = owner.newMethod(tree.pos, name).setFlag(accflags)
              getter.setInfo(namerOf(getter).getterTypeCompleter(tree))
              setPrivateWithin(tree, getter, mods)
              enterInScope(getter)
              if ((mods.flags & MUTABLE) != 0) {
                val setter = owner.newMethod(tree.pos, nme.getterToSetter(name))
        	  .setFlag(accflags & ~STABLE & ~CASEACCESSOR)
                setter.setInfo(namerOf(setter).setterTypeCompleter(tree))
                setPrivateWithin(tree, setter, mods)
                enterInScope(setter)
              }
              tree.symbol =
        	if ((mods.flags & DEFERRED) == 0) {
                  val value =
        	    enterInScope(owner.newValue(tree.pos, nme.getterToLocal(name)))
 	              .setFlag(mods.flags & FieldFlags | PRIVATE | LOCAL)
                  value.setInfo(namerOf(value).typeCompleter(tree))
                  value
                } else getter;
            } else {
              tree.symbol = enterInScope(owner.newValue(tree.pos, name))
                .setFlag(mods.flags)
              finish
            }
          case DefDef(mods, nme.CONSTRUCTOR, tparams, _, _, _) =>
            tree.symbol = enterInScope(owner.newConstructor(tree.pos))
              .setFlag(mods.flags | owner.getFlag(ConstrFlags))
            setPrivateWithin(tree, tree.symbol, mods)
            finishWith(tparams)
          case DefDef(mods, name, tparams, _, _, _) =>
            tree.symbol = enterInScope(owner.newMethod(tree.pos, name))
              .setFlag(mods.flags)
            setPrivateWithin(tree, tree.symbol, mods)
            finishWith(tparams)
          case AbsTypeDef(mods, name, _, _) =>
            tree.symbol = enterInScope(owner.newAbstractType(tree.pos, name))
              .setFlag(mods.flags)
            setPrivateWithin(tree, tree.symbol, mods)
            finish
          case AliasTypeDef(mods, name, tparams, _) =>
            tree.symbol = enterInScope(owner.newAliasType(tree.pos, name))
              .setFlag(mods.flags)
            setPrivateWithin(tree, tree.symbol, mods)
            finishWith(tparams)
          case DocDef(_, defn) =>
            enterSym(defn)
          case imp @ Import(_, _) =>
            tree.symbol = NoSymbol.newImport(tree.pos)
            tree.symbol.setInfo(namerOf(tree.symbol).typeCompleter(tree))
            return (context.makeNewImport(imp))
          case _ =>
        }
      }
      this.context
    }

// --- Lazy Type Assignment --------------------------------------------------

    def typeCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        if (settings.debug.value) log("defining " + sym);
        val tp = typeSig(tree)
        sym.setInfo(tp)
        if ((sym.isAliasType || sym.isAbstractType) && !(sym hasFlag PARAM) &&
            !typer.checkNonCyclic(tree.pos, tp))
          sym.setInfo(ErrorType) // this early test is there to avoid infinite baseTypes when
                                 // adding setters and getters --> bug798
        if (settings.debug.value) log("defined " + sym);
        validate(sym)
      }
    }

    def moduleClassTypeCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        tree.symbol.info // sets moduleClass info as a side effect.
      }
    }

    def getterTypeCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        if (settings.debug.value) log("defining " + sym);
        sym.setInfo(PolyType(List(), typeSig(tree)))
        if (settings.debug.value) log("defined " + sym);
        validate(sym)
      }
    }

    def setterTypeCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        if (settings.debug.value) log("defining " + sym);
        sym.setInfo(MethodType(List(typeSig(tree)), UnitClass.tpe))
        if (settings.debug.value) log("defined " + sym);
        validate(sym)
      }
    }

    def selfTypeCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        sym.setInfo(typer.typedType(tree).tpe)
      }
    }

    def caseFactoryCompleter(tree: Tree) = new TypeCompleter(tree) {
      override def complete(sym: Symbol): unit = {
        val clazz = tree.symbol
        var tpe = clazz.primaryConstructor.tpe
        val tparams = clazz.typeParams
        if (!tparams.isEmpty) tpe = PolyType(tparams, tpe).cloneInfo(sym);
        sym.setInfo(tpe)
      }
    }

    private def deconstIfNotFinal(sym: Symbol, tpe: Type): Type =
      if (sym.isVariable ||
          !(sym hasFlag FINAL) ||
          sym.isMethod && !(sym hasFlag ACCESSOR)) tpe.deconst
      else tpe;


    def enterValueParams(owner: Symbol, vparamss: List[List[ValDef]]): List[List[Symbol]] = {
      def enterValueParam(param: ValDef): Symbol = if (doEnterValueParams) {
        param.symbol = owner.newValueParameter(param.pos, param.name)
          .setInfo(typeCompleter(param))
          .setFlag(param.mods.flags & (BYNAMEPARAM | IMPLICIT))
        setPrivateWithin(param, param.symbol, param.mods)
        enterInScope(param.symbol)
        param.symbol
      } else param.symbol
      vparamss.map(.map(enterValueParam))
    }

    /** A creator for polytypes. If tparams is empty, simply returns result type */
    private def makePolyType(tparams: List[Symbol], tpe: Type): Type =
      if (tparams.isEmpty) tpe
      else
        PolyType(tparams, tpe match {
          case PolyType(List(), tpe1) => tpe1
          case _ => tpe
        });

    private def templateSig(templ0: Template): Type = {
      var templ = templ0
      val clazz = context.owner
      def checkParent(tpt: Tree): Type = {
        val tp = tpt.tpe
        if (tp.symbol == context.owner) {
          context.error(tpt.pos, ""+tp.symbol+" inherits itself")
          AnyRefClass.tpe
        } else if (tp.isError) {
          AnyRefClass.tpe
        } else {
          tp
        }
      }
      val parents = typer.parentTypes(templ) map checkParent
      val decls = newDecls(templ, clazz)
      new Namer(context.make(templ, clazz, decls)).enterSyms(templ.body)
      ClassInfoType(parents, decls, clazz)
    }

    private def classSig(tparams: List[AbsTypeDef], self: ValDef, impl: Template): Type = {
      val clazz = context.owner
      val tparamSyms = typer.reenterTypeParams(tparams)
      if (!self.tpt.isEmpty) {
        clazz.typeOfThis = selfTypeCompleter(self.tpt)
        self.symbol = clazz.thisSym
      } else {
        self.tpt.tpe = NoType
        if (self.name != nme.WILDCARD) {
          clazz.typeOfThis = clazz.tpe
          self.symbol = clazz.thisSym
        } else {
          self.symbol = clazz.newThisSym(self.pos) setInfo clazz.tpe
        }
      }
      if (self.name != nme.WILDCARD) {
        context.scope enter self.symbol
        clazz.thisSym.name = self.name
      }
      makePolyType(tparamSyms, templateSig(impl))
    }

    private def methodSig(tparams: List[AbsTypeDef], vparamss: List[List[ValDef]],
                          tpt: Tree, rhs: Tree): Type = {
      val meth = context.owner

      val tparamSyms = typer.reenterTypeParams(tparams)
      val vparamSymss = enterValueParams(meth, vparamss)
      if (tpt.isEmpty && meth.name == nme.CONSTRUCTOR) tpt.tpe = context.enclClass.owner.tpe

      def makeMethodType(vparams: List[Symbol], restpe: Type) = {
        val formals = vparams map (.tpe)
        if (!vparams.isEmpty && vparams.head.hasFlag(IMPLICIT)) ImplicitMethodType(formals, restpe)
        else MethodType(formals, restpe)
      }

      def thisMethodType(restype: Type) =
        makePolyType(
          tparamSyms,
          if (vparamSymss.isEmpty) PolyType(List(), restype)
          else (vparamSymss :\ restype)(makeMethodType))

      var resultPt = if (tpt.isEmpty) WildcardType else typer.typedType(tpt).tpe

      if (onlyPresentation)
        methodArgumentNames(meth) = vparamss.map(.map(.symbol));
      if (meth.owner.isClass && (tpt.isEmpty || vparamss.exists(.exists(.tpt.isEmpty)))) {
        // try to complete from matching definition in base type
        for (val vparams <- vparamss; val vparam <- vparams)
          if (vparam.tpt.isEmpty) vparam.symbol setInfo WildcardType
        val schema = thisMethodType(resultPt)
        val site = meth.owner.thisType


        val overridden = intersectionType(meth.owner.info.parents).member(meth.name).filter(sym =>
          sym != NoSymbol && (site.memberType(sym) matches schema))
        if (overridden != NoSymbol && !(overridden hasFlag OVERLOADED)) {
          resultPt = site.memberType(overridden) match {
            case PolyType(tparams, rt) => rt.substSym(tparams, tparamSyms)
            case mt => mt
          }

          for (val vparams <- vparamss) {
            var pfs = resultPt.paramTypes
            for (val vparam <- vparams) {
              if (vparam.tpt.isEmpty) {
                vparam.tpt.tpe = pfs.head
                vparam.symbol setInfo pfs.head
              }
              pfs = pfs.tail
            }
            resultPt = resultPt.resultType
          }
          resultPt match {
            case PolyType(List(), rtpe) => resultPt = rtpe
            case MethodType(List(), rtpe) => resultPt = rtpe
            case _ =>
          }
          if (tpt.isEmpty) {
            // provisionally assign `meth' a method type with inherited result type
            // that way, we can leave out the result type even if method is recursive.
            meth setInfo thisMethodType(resultPt)
          }
        }
      }

      for (val vparams <- vparamss; val vparam <- vparams; vparam.tpt.isEmpty) {
        context.error(vparam.pos, "missing parameter type")
        vparam.tpt.tpe = ErrorType
      }

      thisMethodType(
        if (tpt.isEmpty) {
          val pt = resultPt.substSym(tparamSyms, tparams map (.symbol))
          tpt.tpe = deconstIfNotFinal(meth, typer.computeType(rhs, pt))
          tpt.tpe
        } else typer.typedType(tpt).tpe)
     }

    /** If `sym' is an implicit value, check that its type signature `tp' is contractive.
     *  This means: The type of every implicit parameter is properly contained
     *  in the type that is obtained by removing all implicit parameters and converting
     *  the rest to a function type.
     *  If the check succeeds return `tp' itself, otherwise `ErrorType'.
     */
    private def checkContractive(sym: Symbol, tp: Type): Type = {
      /* The type signature without implicit parameters converted to function type */
      def provided(tp: Type): Type = tp match {
        case PolyType(_, restpe) => provided(restpe)
        case mt: ImplicitMethodType => mt.resultType
        case MethodType(formals, restpe) => functionType(formals, provided(restpe))
        case _ => tp
      }
      /* The types of all implicit parameters */
      def required(tp: Type): List[Type] = tp match {
        case PolyType(_, restpe) => required(restpe)
        case mt: ImplicitMethodType => mt.paramTypes
        case MethodType(formals, restpe) => required(restpe)
        case _ => List()
      }
      var result = tp;
      if (sym hasFlag IMPLICIT) {
        val p = provided(tp);
        //Console.println("check contractive: "+sym+" "+p+"/"+required(tp))
        for (val r <- required(tp)) {
          if (!isContainedIn(r, p) || (r =:= p)) {
            context.error(sym.pos, "implicit " + sym + " is not contractive," +
        		  "\n because the implicit parameter type " + r +
        		  "\n is not strictly contained in the signature " + p);
            result = ErrorType;
          }
        }
      }
      result
    }

    private def aliasTypeSig(tpsym: Symbol, tparams: List[AbsTypeDef], rhs: Tree): Type =
      makePolyType(typer.reenterTypeParams(tparams), typer.typedType(rhs).tpe);

    def typeSig(tree: Tree): Type = {
      val sym: Symbol = tree.symbol
      tree match {
        case defn: MemberDef =>
          val ainfos = for {
            val annot <- defn.mods.annotations
            val ainfo = typer.typedAnnotation(annot, typer.getConstant)
            !ainfo.atp.isError
          } yield ainfo
          if (!ainfos.isEmpty) {
            val annotated = if (sym.isModule) sym.moduleClass else sym
            annotated.attributes = ainfos
          }
        case _ =>
      }
      val result =
        try {
          tree match {
            case ClassDef(_, _, tparams, self, impl) =>
              new Namer(makeNewScope(context, tree, sym)).classSig(tparams, self, impl)

            case ModuleDef(_, _, impl) =>
              val clazz = sym.moduleClass
              clazz.setInfo(new Namer(context.make(tree, clazz)).templateSig(impl));
              //clazz.typeOfThis = singleType(sym.owner.thisType, sym);
              clazz.tpe;

            case DefDef(_, _, tparams, vparamss, tpt, rhs) =>
              val result =
                new Namer(makeNewScope(context, tree, sym)).methodSig(tparams, vparamss, tpt, rhs);
              checkContractive(sym, result)

            case ValDef(_, _, tpt, rhs) =>
              if (tpt.isEmpty) {
                if (rhs.isEmpty) {
        	  context.error(tpt.pos, "missing parameter type");
        	  ErrorType
                } else {
        	  tpt.tpe = deconstIfNotFinal(sym, newTyper(context.make(tree, sym)).computeType(rhs, WildcardType));
        	  tpt.tpe
                }
              } else {
                val typer1 =
                  if (sym.hasFlag(PARAM) && sym.owner.isConstructor && !phase.erasedTypes)
                    newTyper(context.makeConstructorContext)
                  else typer;
                typer1.typedType(tpt).tpe
              }

            case tree @ AliasTypeDef(_, _, tparams, rhs) =>
              new Namer(makeNewScope(context, tree, sym)).aliasTypeSig(sym, tparams, rhs)

            case AbsTypeDef(_, _, lo, hi) =>
              var lt = typer.typedType(lo).tpe
              if (lt.isError) lt = AllClass.tpe
              var ht = typer.typedType(hi).tpe
              if (ht.isError) ht = AnyClass.tpe
              mkTypeBounds(lt, ht)

            case Import(expr, selectors) =>
              val expr1 = typer.typedQualifier(expr)
              val base = expr1.tpe
              typer.checkStable(expr1)
              def checkNotRedundant(pos: PositionType, from: Name, to: Name): boolean = {
                if (!tree.symbol.hasFlag(SYNTHETIC) &&
                    !((expr1.symbol ne null) && expr1.symbol.isInterpreterWrapper) &&
                    base.member(from) != NoSymbol) {
                  val e = context.scope.lookupEntry(to)
                  def warnRedundant(sym: Symbol) =
                    context.unit.warning(pos, "imported `"+to+
                                         "' is permanently hidden by definition of "+sym+
                                         sym.locationString)
                  if ((e ne null) && e.owner == context.scope) {
                    warnRedundant(e.sym); return false
                  } else if (context eq context.enclClass) {
                    val defSym = context.prefix.member(to) filter (
                      sym => sym.exists && context.isAccessible(sym, context.prefix, false))
                    if (defSym != NoSymbol) { warnRedundant(defSym); return false }
                  }
                }
                true
              }
              def checkSelectors(selectors: List[(Name, Name)]): unit = selectors match {
                case (from, to) :: rest =>
        	  if (from != nme.WILDCARD && base != ErrorType) {
        	    if (base.member(from) == NoSymbol && base.member(from.toTypeName) == NoSymbol)
        	      context.error(tree.pos, from.decode + " is not a member of " + expr);
                    if (checkNotRedundant(tree.pos, from, to))
                      checkNotRedundant(tree.pos, from.toTypeName, to.toTypeName)
                  }
        	  if (from != nme.WILDCARD && (rest.exists (sel => sel._1 == from)))
        	    context.error(tree.pos, from.decode + " is renamed twice");
        	  if ((to ne null) && to != nme.WILDCARD && (rest exists (sel => sel._2 == to)))
        	    context.error(tree.pos, to.decode + " appears twice as a target of a renaming");
        	  checkSelectors(rest)
                case Nil =>
              }
              checkSelectors(selectors)
              ImportType(expr1)
          }
        } catch {
          case ex: TypeError =>
            //Console.println("caught " + ex + " in typeSig")//DEBUG
            typer.reportTypeError(tree.pos, ex)
            ErrorType
        }
      deSkolemize(result)
    }

    /** Check that symbol's definition is well-formed. This means:
     *   - no conflicting modifiers
     *   - `abstract' modifier only for classes
     *   - `override' modifier never for classes
     *   - `def' modifier never for parameters of case classes
     *   - declarations only in mixins or abstract classes
     */
    def validate(sym: Symbol): unit = {
      def checkNoConflict(flag1: int, flag2: int): unit =
        if (sym.hasFlag(flag1) && sym.hasFlag(flag2))
          context.error(sym.pos,
            if (flag1 == DEFERRED)
              "abstract member may not have " + Flags.flagsToString(flag2) + " modifier";
            else
              "illegal combination of modifiers: " +
              Flags.flagsToString(flag1) + " and " + Flags.flagsToString(flag2));
      if (sym.hasFlag(IMPLICIT) && !sym.isTerm)
        context.error(sym.pos, "`implicit' modifier can be used only for values, variables and methods")
      if (sym.hasFlag(IMPLICIT) && sym.owner.isPackageClass)
        context.error(sym.pos, "`implicit' modifier cannot be used for top-level objects")
      if (sym.hasFlag(ABSTRACT) && !sym.isClass)
        context.error(sym.pos, "`abstract' modifier can be used only for classes; " +
          "\nit should be omitted for abstract members")
      if (sym.hasFlag(OVERRIDE | ABSOVERRIDE) && sym.isClass)
        context.error(sym.pos, "`override' modifier not allowed for classes")
      if (sym.hasFlag(OVERRIDE | ABSOVERRIDE) && sym.isConstructor)
        context.error(sym.pos, "`override' modifier not allowed for constructors")
      if (sym.hasFlag(ABSOVERRIDE) && !sym.owner.isTrait)
        context.error(sym.pos, "`abstract override' modifier only allowed for members of traits")
      if (sym.info.symbol == FunctionClass(0) &&
          sym.isValueParameter && sym.owner.isClass && sym.owner.hasFlag(CASE))
        context.error(sym.pos, "pass-by-name arguments not allowed for case class parameters");
      if ((sym.flags & DEFERRED) != 0) {
        if (!sym.isValueParameter && !sym.isTypeParameterOrSkolem &&
            (!sym.owner.isClass || sym.owner.isModuleClass || sym.owner.isAnonymousClass)) {
          context.error(sym.pos,
            "only classes can have declared but undefined members" + varNotice(sym))
          sym.resetFlag(DEFERRED)
        }
      }
      checkNoConflict(DEFERRED, PRIVATE)
      checkNoConflict(FINAL, SEALED)
      checkNoConflict(PRIVATE, PROTECTED)
      checkNoConflict(PRIVATE, OVERRIDE)
      checkNoConflict(DEFERRED, FINAL)
      checkNoConflict(ABSTRACT, CASE)
    }
  }

  /* Is type `tp1' properly contained in type `tp2'? */
  def isContainedIn(tp1: Type, tp2: Type) = {
    //Console.println("is " + tp1 + " contained in " + tp2 + "?");//DEBUG
    new ContainsTraverser(tp1).traverse(tp2).result
  }

  /* Type `elemtp' is contained in type `tp' is one of the following holds:
   *  - elemtp is the same as some proper part of tp
   *  - tp is a function type and elemtp is not
   *  - tp and elemtp are function types, and arity of tp is greater than arity of elemtp
   *  - tp and elemtp are both parameterized types with same type constructor and prefix,
   *    and each type argument of elemtp is contained in the corresponding type argument of tp.
   */
  private class ContainsTraverser(elemtp: Type) extends TypeTraverser {
    var nested = false
    var result = false
    def traverse(tp: Type): ContainsTraverser = {
      if (!result) {
        if (elemtp =:= tp)
          result = nested
        else if (isFunctionType(tp) &&
                 (!isFunctionType(elemtp) || tp.typeArgs.length > elemtp.typeArgs.length))
          result = true
        else (tp, elemtp) match {
          case (TypeRef(pre, sym, args), TypeRef(elempre, elemsym, elemargs)) =>
            if ((sym == elemsym) && (pre =:= elempre) && (args.length == elemargs.length))
              result = List.forall2(elemargs, args) (isContainedIn)
          case _ =>
        }
      }
      if (!result) {
        tp match {
          case SingleType(_, _) => nested = true
          case TypeRef(_, _, _) => nested = true
          case _ =>
        }
        mapOver(tp)
      }
      this
    }
  }

  abstract class TypeCompleter(val tree: Tree) extends LazyType

  /** The symbol that which this accessor represents (possibly in part).
   *  This is used for error messages, where we want to speak in terms
   *  of the actual declaration or definition, not in terms of the generated setters
   *  and getters */
  def underlying(member: Symbol) : Symbol =
    if (member hasFlag ACCESSOR) {
      if (member hasFlag DEFERRED) {
        val getter = if (member.isSetter) member.getter(member.owner) else member
        if (inIDE && getter == NoSymbol) return NoSymbol;
        val result = getter.owner.newValue(getter.pos, getter.name)
          .setInfo(getter.tpe.resultType)
          .setFlag(DEFERRED)
        if (getter.setter(member.owner) != NoSymbol) result.setFlag(MUTABLE)
        result
      } else member.accessed
    } else member

  /** An explanatory note to be added to error messages
   *  when there's a problem with abstract var defs */
  def varNotice(sym: Symbol) =
    if (underlying(sym).isVariable)
      "\n(Note that variables need to be initialized to be defined)"
    else ""
}