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Scala example source code file (Namers.scala)

This example Scala source code file (Namers.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

annotation, classdef, collection, compiler, context, defdef, list, namer, nosymbol, nsc, symbol, tree, type, valdef

The Namers.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package typechecker

import scala.collection.mutable
import scala.annotation.tailrec
import symtab.Flags._
import scala.language.postfixOps

/** This trait declares methods to create symbols and to enter them into scopes.
 *
 *  @author Martin Odersky
 *  @version 1.0
 */
trait Namers extends MethodSynthesis {
  self: Analyzer =>

  import global._
  import definitions._

  var _lockedCount = 0
  def lockedCount = this._lockedCount

  /** Replaces any Idents for which cond is true with fresh TypeTrees().
   *  Does the same for any trees containing EmptyTrees.
   */
  private class TypeTreeSubstituter(cond: Name => Boolean) extends Transformer {
    override def transform(tree: Tree): Tree = tree match {
      case Ident(name) if cond(name) => TypeTree()
      case _                         => super.transform(tree)
    }
    def apply(tree: Tree) = {
      val r = transform(tree)
      if (r exists { case tt: TypeTree => tt.isEmpty case _ => false })
        TypeTree()
      else r
    }
  }

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

  private class NormalNamer(context: Context) extends Namer(context)
  def newNamer(context: Context): Namer = new NormalNamer(context)

  abstract class Namer(val context: Context) extends MethodSynth with NamerContextErrors { thisNamer =>
    // overridden by the presentation compiler
    def saveDefaultGetter(meth: Symbol, default: Symbol) { }

    import NamerErrorGen._
    val typer = newTyper(context)

    private lazy val innerNamer =
      if (isTemplateContext(context)) createInnerNamer() else this

    def createNamer(tree: Tree): Namer = {
      val sym = tree match {
        case ModuleDef(_, _, _) => tree.symbol.moduleClass
        case _                  => tree.symbol
      }
      def isConstrParam(vd: ValDef) = {
        (sym hasFlag PARAM | PRESUPER) &&
        !vd.mods.isJavaDefined &&
        sym.owner.isConstructor
      }
      val ownerCtx = tree match {
        case vd: ValDef if isConstrParam(vd) =>
          context.makeConstructorContext
        case _ =>
          context
      }
      newNamer(ownerCtx.makeNewScope(tree, sym))
    }
    def createInnerNamer() = {
      newNamer(context.make(context.tree, owner, newScope))
    }
    def createPrimaryConstructorParameterNamer: Namer = { //todo: can we merge this with SCCmode?
      val classContext = context.enclClass
      val outerContext = classContext.outer.outer
      val paramContext = outerContext.makeNewScope(outerContext.tree, outerContext.owner)

      owner.unsafeTypeParams foreach (paramContext.scope enter _)
      newNamer(paramContext)
    }

    def enclosingNamerWithScope(scope: Scope) = {
      var cx = context
      while (cx != NoContext && cx.scope != scope) cx = cx.outer
      if (cx == NoContext || cx == context) thisNamer
      else newNamer(cx)
    }

    def enterValueParams(vparamss: List[List[ValDef]]): List[List[Symbol]] = {
      mmap(vparamss) { param =>
        val sym = assignSymbol(param, param.name, mask = ValueParameterFlags)
        setPrivateWithin(param, sym)
        enterInScope(sym)
        sym setInfo monoTypeCompleter(param)
      }
    }

    protected def owner       = context.owner
    def contextFile = context.unit.source.file
    def typeErrorHandler[T](tree: Tree, alt: T): PartialFunction[Throwable, T] = {
      case ex: TypeError =>
        // H@ need to ensure that we handle only cyclic references
        TypeSigError(tree, ex)
        alt
    }
    // PRIVATE | LOCAL are fields generated for primary constructor arguments
    // @PP: ...or fields declared as private[this].  PARAMACCESSOR marks constructor arguments.
    // Neither gets accessors so the code is as far as I know still correct.
    def noEnterGetterSetter(vd: ValDef) = !vd.mods.isLazy && (
         !owner.isClass
      || (vd.mods.isPrivateLocal && !vd.mods.isCaseAccessor)
      || (vd.name startsWith nme.OUTER)
      || (context.unit.isJava)
      || isEnumConstant(vd)
    )

    def noFinishGetterSetter(vd: ValDef) = (
         (vd.mods.isPrivateLocal && !vd.mods.isLazy) // all lazy vals need accessors, even private[this]
      || vd.symbol.isModuleVar
      || isEnumConstant(vd))

    /** Determines whether this field holds an enum constant.
      * To qualify, the following conditions must be met:
      *  - The field's class has the ENUM flag set
      *  - The field's class extends java.lang.Enum
      *  - The field has the ENUM flag set
      *  - The field is static
      *  - The field is stable
      */
    def isEnumConstant(vd: ValDef) = {
      val ownerHasEnumFlag =
        // Necessary to check because scalac puts Java's static members into the companion object
        // while Scala's enum constants live directly in the class.
        // We don't check for clazz.superClass == JavaEnumClass, because this causes a illegal
        // cyclic reference error. See the commit message for details.
        if (context.unit.isJava) owner.companionClass.hasEnumFlag else owner.hasEnumFlag
      vd.mods.hasAllFlags(ENUM | STABLE | STATIC) && ownerHasEnumFlag
    }

    def setPrivateWithin[T <: Symbol](tree: Tree, sym: T, mods: Modifiers): T =
      if (sym.isPrivateLocal || !mods.hasAccessBoundary) sym
      else sym setPrivateWithin typer.qualifyingClass(tree, mods.privateWithin, packageOK = true)

    def setPrivateWithin(tree: MemberDef, sym: Symbol): Symbol =
      setPrivateWithin(tree, sym, tree.mods)

    def inConstructorFlag: Long = {
      val termOwnedContexts: List[Context] =
        context.enclosingContextChain.takeWhile(c => c.owner.isTerm && !c.owner.isAnonymousFunction)
      val constructorNonSuffix = termOwnedContexts exists (c => c.owner.isConstructor && !c.inConstructorSuffix)
      val earlyInit            = termOwnedContexts exists (_.owner.isEarlyInitialized)
      if (constructorNonSuffix || earlyInit) INCONSTRUCTOR else 0L
    }

    def moduleClassFlags(moduleFlags: Long) =
      (moduleFlags & ModuleToClassFlags) | inConstructorFlag

    def updatePosFlags(sym: Symbol, pos: Position, flags: Long): Symbol = {
      debuglog("[overwrite] " + sym)
      val newFlags = (sym.flags & LOCKED) | flags
      sym.rawInfo match {
        case tr: TypeRef =>
          // !!! needed for: pos/t5954d; the uniques type cache will happilly serve up the same TypeRef
          // over this mutated symbol, and we witness a stale cache for `parents`.
          tr.invalidateCaches()
        case _ =>
      }
      sym reset NoType setFlag newFlags setPos pos
      sym.moduleClass andAlso (updatePosFlags(_, pos, moduleClassFlags(flags)))

      if (sym.isTopLevel) {
        companionSymbolOf(sym, context) andAlso { companion =>
          val assignNoType = companion.rawInfo match {
            case _: SymLoader => true
            case tp           => tp.isComplete && (runId(sym.validTo) != currentRunId)
          }
          // pre-set linked symbol to NoType, in case it is not loaded together with this symbol.
          if (assignNoType)
            companion setInfo NoType
        }
      }
      sym
    }
    def namerOf(sym: Symbol): Namer = {
      val usePrimary = sym.isTerm && (
           (sym.isParamAccessor)
        || (sym.isParameter && sym.owner.isPrimaryConstructor)
      )

      if (usePrimary) createPrimaryConstructorParameterNamer
      else innerNamer
    }

    // FIXME - this logic needs to be thoroughly explained
    // and justified.  I know it's wrong with repect to package
    // objects, but I think it's also wrong in other ways.
    protected def conflict(newS: Symbol, oldS: Symbol) = (
       (   !oldS.isSourceMethod
        || nme.isSetterName(newS.name)
        || newS.isTopLevel
       ) &&
      !(   // @M: allow repeated use of `_` for higher-order type params
           (newS.owner.isTypeParameter || newS.owner.isAbstractType)
           // FIXME: name comparisons not successful, are these underscores
           // sometimes nme.WILDCARD and sometimes tpnme.WILDCARD?
        && (newS.name string_== nme.WILDCARD)
       )
    )

    private def allowsOverload(sym: Symbol) = (
      sym.isSourceMethod && sym.owner.isClass && !sym.isTopLevel
    )

    private def inCurrentScope(m: Symbol): Boolean = {
      if (owner.isClass) owner == m.owner
      else m.owner.isClass && context.scope == m.owner.info.decls
    }

    /** Enter symbol into context's scope and return symbol itself */
    def enterInScope(sym: Symbol): Symbol = enterInScope(sym, context.scope)

    /** Enter symbol into given scope and return symbol itself */
    def enterInScope(sym: Symbol, scope: Scope): Symbol = {
      // FIXME - this is broken in a number of ways.
      //
      // 1) If "sym" allows overloading, that is not itself sufficient to skip
      // the check, because "prev.sym" also must allow overloading.
      //
      // 2) There is nothing which reconciles a package's scope with
      // the package object's scope.  This is the source of many bugs
      // with e.g. defining a case class in a package object.  When
      // compiling against classes, the class symbol is created in the
      // package and in the package object, and the conflict is undetected.
      // There is also a non-deterministic outcome for situations like
      // an object with the same name as a method in the package object.

      // allow for overloaded methods
      if (!allowsOverload(sym)) {
        val prev = scope.lookupEntry(sym.name)
        if ((prev ne null) && prev.owner == scope && conflict(sym, prev.sym)) {
          if (sym.isSynthetic || prev.sym.isSynthetic) {
            handleSyntheticNameConflict(sym, prev.sym)
            handleSyntheticNameConflict(prev.sym, sym)
          }
          DoubleDefError(sym, prev.sym)
          sym setInfo ErrorType
          scope unlink prev.sym // let them co-exist...
          // FIXME: The comment "let them co-exist" is confusing given that the
          // line it comments unlinks one of them.  What does it intend?
        }
      }
      scope enter sym
    }

    /** Logic to handle name conflicts of synthetically generated symbols
     *  We handle right now: t6227
     */
    def handleSyntheticNameConflict(sym1: Symbol, sym2: Symbol) = {
      if (sym1.isImplicit && sym1.isMethod && sym2.isModule && sym2.companionClass.isCaseClass)
        validate(sym2.companionClass)
    }

    def enterSym(tree: Tree): Context = pluginsEnterSym(this, tree)

    /** Default implementation of `enterSym`.
     *  Can be overridden by analyzer plugins (see AnalyzerPlugins.pluginsEnterSym for more details)
     */
    def standardEnterSym(tree: Tree): Context = {
      def dispatch() = {
        var returnContext = this.context
        tree match {
          case tree @ PackageDef(_, _)                       => enterPackage(tree)
          case tree @ ClassDef(_, _, _, _)                   => enterClassDef(tree)
          case tree @ ModuleDef(_, _, _)                     => enterModuleDef(tree)
          case tree @ ValDef(_, _, _, _)                     => enterValDef(tree)
          case tree @ DefDef(_, _, _, _, _, _)               => enterDefDef(tree)
          case tree @ TypeDef(_, _, _, _)                    => enterTypeDef(tree)
          case DocDef(_, defn)                               => enterSym(defn)
          case tree @ Import(_, _)                           =>
            assignSymbol(tree)
            returnContext = context.make(tree)
          case _ =>
        }
        returnContext
      }
      tree.symbol match {
        case NoSymbol => try dispatch() catch typeErrorHandler(tree, this.context)
        case sym      => enterExistingSym(sym)
      }
    }

    /** Creates a new symbol and assigns it to the tree, returning the symbol
     */
    def assignSymbol(tree: Tree): Symbol =
      logAssignSymbol(tree, tree match {
        case PackageDef(pid, _) => createPackageSymbol(tree.pos, pid)
        case Import(_, _)       => createImportSymbol(tree)
        case mdef: MemberDef    => createMemberSymbol(mdef, mdef.name, -1L)
        case _                  => abort("Unexpected tree: " + tree)
      })
    def assignSymbol(tree: MemberDef, name: Name, mask: Long): Symbol =
      logAssignSymbol(tree, createMemberSymbol(tree, name, mask))

    def assignAndEnterSymbol(tree: MemberDef): Symbol = {
      val sym = assignSymbol(tree, tree.name, -1L)
      setPrivateWithin(tree, sym)
      enterInScope(sym)
    }
    def assignAndEnterFinishedSymbol(tree: MemberDef): Symbol = {
      val sym = assignAndEnterSymbol(tree)
      sym setInfo completerOf(tree)
      // log("[+info] " + sym.fullLocationString)
      sym
    }

    private def logAssignSymbol(tree: Tree, sym: Symbol): Symbol = {
      if (isPastTyper) sym.name.toTermName match {
        case nme.IMPORT | nme.OUTER | nme.ANON_CLASS_NAME | nme.ANON_FUN_NAME | nme.CONSTRUCTOR => ()
        case _                                                                                  =>
          tree match {
            case md: DefDef => log("[+symbol] " + sym.debugLocationString)
            case _          =>
          }
      }
      tree.symbol = sym
      sym
    }

    /** Create a new symbol at the context owner based on the given tree.
     *  A different name can be given.  If the modifier flags should not be
     *  be transferred to the symbol as they are, supply a mask containing
     *  the flags to keep.
     */
    def createMemberSymbol(tree: MemberDef, name: Name, mask: Long): Symbol = {
      val pos         = tree.pos
      val isParameter = tree.mods.isParameter
      val flags       = tree.mods.flags & mask

      tree match {
        case TypeDef(_, _, _, _) if isParameter     => owner.newTypeParameter(name.toTypeName, pos, flags)
        case TypeDef(_, _, _, _)                    => owner.newTypeSymbol(name.toTypeName, pos, flags)
        case DefDef(_, nme.CONSTRUCTOR, _, _, _, _) => owner.newConstructor(pos, flags)
        case DefDef(_, _, _, _, _, _)               => owner.newMethod(name.toTermName, pos, flags)
        case ClassDef(_, _, _, _)                   => owner.newClassSymbol(name.toTypeName, pos, flags)
        case ModuleDef(_, _, _)                     => owner.newModule(name.toTermName, pos, flags)
        case PackageDef(pid, _)                     => createPackageSymbol(pos, pid)
        case ValDef(_, _, _, _)                     =>
          if (isParameter) owner.newValueParameter(name.toTermName, pos, flags)
          else owner.newValue(name.toTermName, pos, flags)
      }
    }
    def createFieldSymbol(tree: ValDef): TermSymbol =
      owner.newValue(tree.localName, tree.pos, tree.mods.flags & FieldFlags | PrivateLocal)

    def createImportSymbol(tree: Tree) =
      NoSymbol.newImport(tree.pos) setInfo completerOf(tree)

    /** All PackageClassInfoTypes come from here. */
    def createPackageSymbol(pos: Position, pid: RefTree): Symbol = {
      val pkgOwner = pid match {
        case Ident(_)                 => if (owner.isEmptyPackageClass) rootMirror.RootClass else owner
        case Select(qual: RefTree, _) => createPackageSymbol(pos, qual).moduleClass
      }
      val existing = pkgOwner.info.decls.lookup(pid.name)

      if (existing.hasPackageFlag && pkgOwner == existing.owner)
        existing
      else {
        val pkg          = pkgOwner.newPackage(pid.name.toTermName, pos)
        val pkgClass     = pkg.moduleClass
        val pkgClassInfo = new PackageClassInfoType(newPackageScope(pkgClass), pkgClass)

        pkgClass setInfo pkgClassInfo
        pkg setInfo pkgClass.tpe
        enterInScope(pkg, pkgOwner.info.decls)
      }
    }

    private def enterClassSymbol(tree: ClassDef, clazz: ClassSymbol): Symbol = {
      if (clazz.sourceFile != null && clazz.sourceFile != contextFile)
        devWarning(s"Source file mismatch in $clazz: ${clazz.sourceFile} vs. $contextFile")

      clazz.associatedFile = contextFile
      if (clazz.sourceFile != null) {
        assert(currentRun.canRedefine(clazz) || clazz.sourceFile == currentRun.symSource(clazz), clazz.sourceFile)
        currentRun.symSource(clazz) = clazz.sourceFile
      }
      registerTopLevelSym(clazz)
      assert(clazz.name.toString.indexOf('(') < 0, clazz.name)  // )
      clazz
    }

    def enterClassSymbol(tree: ClassDef): Symbol = {
      val existing = context.scope.lookup(tree.name)
      val isRedefinition = (
           existing.isType
        && existing.isTopLevel
        && context.scope == existing.owner.info.decls
        && currentRun.canRedefine(existing)
      )
      val clazz: Symbol = {
        if (isRedefinition) {
          updatePosFlags(existing, tree.pos, tree.mods.flags)
          setPrivateWithin(tree, existing)
          existing
        }
        else assignAndEnterSymbol(tree) setFlag inConstructorFlag
      }
      clazz match {
        case csym: ClassSymbol if csym.isTopLevel => enterClassSymbol(tree, csym)
        case _                                    => clazz
      }
    }

    /** Given a ClassDef or ModuleDef, verifies there isn't a companion which
     *  has been defined in a separate file.
     */
    def validateCompanionDefs(tree: ImplDef) {
      val sym    = tree.symbol orElse { return }
      val ctx    = if (context.owner.isPackageObjectClass) context.outer else context
      val module = if (sym.isModule) sym else ctx.scope lookupModule tree.name
      val clazz  = if (sym.isClass) sym else ctx.scope lookupClass tree.name
      val fails  = (
           module.isModule
        && clazz.isClass
        && !module.isSynthetic
        && !clazz.isSynthetic
        && (clazz.sourceFile ne null)
        && (module.sourceFile ne null)
        && !(module isCoDefinedWith clazz)
        && module.exists
        && clazz.exists
      )
      if (fails) {
        context.unit.error(tree.pos, (
            s"Companions '$clazz' and '$module' must be defined in same file:\n"
          + s"  Found in ${clazz.sourceFile.canonicalPath} and ${module.sourceFile.canonicalPath}")
        )
      }
    }

    def enterModuleDef(tree: ModuleDef) = {
      val sym = enterModuleSymbol(tree)
      sym.moduleClass setInfo namerOf(sym).moduleClassTypeCompleter(tree)
      sym setInfo completerOf(tree)
      validateCompanionDefs(tree)
      sym
    }

    /** Enter a module symbol.
     */
    def enterModuleSymbol(tree : ModuleDef): Symbol = {
      var m: Symbol = context.scope lookupModule tree.name
      val moduleFlags = tree.mods.flags | MODULE
      if (m.isModule && !m.isPackage && inCurrentScope(m) && (currentRun.canRedefine(m) || m.isSynthetic)) {
        // This code accounts for the way the package objects found in the classpath are opened up
        // early by the completer of the package itself. If the `packageobjects` phase then finds
        // the same package object in sources, we have to clean the slate and remove package object
        // members from the package class.
        //
        // TODO SI-4695 Pursue the approach in https://github.com/scala/scala/pull/2789 that avoids
        //      opening up the package object on the classpath at all if one exists in source.
        if (m.isPackageObject) {
          val packageScope = m.enclosingPackageClass.rawInfo.decls
          packageScope.filter(_.owner != m.enclosingPackageClass).toList.foreach(packageScope unlink _)
        }
        updatePosFlags(m, tree.pos, moduleFlags)
        setPrivateWithin(tree, m)
        m.moduleClass andAlso (setPrivateWithin(tree, _))
        context.unit.synthetics -= m
        tree.symbol = m
      }
      else {
        m = assignAndEnterSymbol(tree)
        m.moduleClass setFlag moduleClassFlags(moduleFlags)
        setPrivateWithin(tree, m.moduleClass)
      }
      if (m.isTopLevel && !m.isPackage) {
        m.moduleClass.associatedFile = contextFile
        currentRun.symSource(m) = m.moduleClass.sourceFile
        registerTopLevelSym(m)
      }
      m
    }

    def enterSyms(trees: List[Tree]): Namer = {
      trees.foldLeft(this: Namer) { (namer, t) =>
        val ctx = namer enterSym t
        // for Import trees, enterSym returns a changed context, so we need a new namer
        if (ctx eq namer.context) namer
        else newNamer(ctx)
      }
    }
    def applicableTypeParams(owner: Symbol): List[Symbol] =
      if (owner.isTerm || owner.isPackageClass) Nil
      else applicableTypeParams(owner.owner) ::: owner.typeParams

    /** If no companion object for clazz exists yet, create one by applying `creator` to
     *  class definition tree.
     *  @return the companion object symbol.
     */
    def ensureCompanionObject(cdef: ClassDef, creator: ClassDef => Tree = companionModuleDef(_)): Symbol =
      pluginsEnsureCompanionObject(this, cdef, creator)

    /** Default implementation of `ensureCompanionObject`.
     *  Can be overridden by analyzer plugins (see AnalyzerPlugins.pluginsEnsureCompanionObject for more details)
     */
    def standardEnsureCompanionObject(cdef: ClassDef, creator: ClassDef => Tree = companionModuleDef(_)): Symbol = {
      val m = companionSymbolOf(cdef.symbol, context)
      // @luc: not sure why "currentRun.compiles(m)" is needed, things breaks
      // otherwise. documentation welcome.
      //
      // @PP: I tried to reverse engineer said documentation.  The only tests
      // which fail are buildmanager tests, as follows.  Given A.scala:
      //   case class Foo()
      // If you recompile A.scala, the Changes Map is
      //   Map(class Foo -> Nil, object Foo -> Nil)
      // But if you remove the 'currentRun.compiles(m)' condition, it is
      //   Map(class Foo -> Nil)
      // What exactly this implies and whether this is a sensible way to
      // enforce it, I don't know.
      //
      // @martin: currentRun.compiles is needed because we might have a stale
      // companion object from another run in scope. In that case we should still
      // overwrite the object. I.e.
      // Compile run #1: object Foo { ... }
      // Compile run #2: case class Foo ...
      // The object Foo is still in scope, but because it is not compiled in current run
      // it should be ditched and a new one created.
      if (m != NoSymbol && currentRun.compiles(m)) m
      else enterSyntheticSym(atPos(cdef.pos.focus)(creator(cdef)))
    }

    private def checkSelectors(tree: Import): Unit = {
      import DuplicatesErrorKinds._
      val Import(expr, selectors) = tree
      val base = expr.tpe

      def checkNotRedundant(pos: Position, from: Name, to0: Name) {
        def check(to: Name) = {
          val e = context.scope.lookupEntry(to)

          if (e != null && e.owner == context.scope && e.sym.exists)
            typer.permanentlyHiddenWarning(pos, to0, e.sym)
          else if (context ne context.enclClass) {
            val defSym = context.prefix.member(to) filter (
              sym => sym.exists && context.isAccessible(sym, context.prefix, superAccess = false))

            defSym andAlso (typer.permanentlyHiddenWarning(pos, to0, _))
          }
        }
        if (!tree.symbol.isSynthetic && expr.symbol != null && !expr.symbol.isInterpreterWrapper) {
          if (base.member(from) != NoSymbol)
            check(to0)
          if (base.member(from.toTypeName) != NoSymbol)
            check(to0.toTypeName)
        }
      }
      def checkSelector(s: ImportSelector) = {
        val ImportSelector(from, fromPos, to, _) = s
        def isValid(original: Name) =
          original.bothNames forall (x => (base nonLocalMember x) == NoSymbol)

        if (from != nme.WILDCARD && base != ErrorType) {
          if (isValid(from)) {
            // for Java code importing Scala objects
            if (!nme.isModuleName(from) || isValid(from.dropModule)) {
              typer.TyperErrorGen.NotAMemberError(tree, expr, from)
            }
          }
          // Setting the position at the import means that if there is
          // more than one hidden name, the second will not be warned.
          // So it is the position of the actual hidden name.
          //
          // Note: java imports have precence over definitions in the same package
          //       so don't warn for them. There is a corresponding special treatment
          //       in the shadowing rules in typedIdent to (SI-7232). In any case,
          //       we shouldn't be emitting warnings for .java source files.
          if (!context.unit.isJava)
            checkNotRedundant(tree.pos withPoint fromPos, from, to)
        }
      }

      def noDuplicates(names: List[Name], check: DuplicatesErrorKinds.Value) {
        def loop(xs: List[Name]): Unit = xs match {
          case Nil      => ()
          case hd :: tl =>
            if (hd == nme.WILDCARD || !(tl contains hd)) loop(tl)
            else DuplicatesError(tree, hd, check)
        }
        loop(names filterNot (x => x == null || x == nme.WILDCARD))
      }
      selectors foreach checkSelector

      // checks on the whole set
      noDuplicates(selectors map (_.name), RenamedTwice)
      noDuplicates(selectors map (_.rename), AppearsTwice)
    }

    def enterCopyMethod(copyDef: DefDef): Symbol = {
      val sym      = copyDef.symbol
      val lazyType = completerOf(copyDef)

      /* Assign the types of the class parameters to the parameters of the
       * copy method. See comment in `Unapplies.caseClassCopyMeth` */
      def assignParamTypes() {
        val clazz = sym.owner
        val constructorType = clazz.primaryConstructor.tpe
        val subst = new SubstSymMap(clazz.typeParams, copyDef.tparams map (_.symbol))
        val classParamss = constructorType.paramss

        map2(copyDef.vparamss, classParamss)((copyParams, classParams) =>
          map2(copyParams, classParams)((copyP, classP) =>
            copyP.tpt setType subst(classP.tpe)
          )
        )
      }

      sym setInfo {
        mkTypeCompleter(copyDef) { sym =>
          assignParamTypes()
          lazyType complete sym
        }
      }
    }

    def completerOf(tree: Tree): TypeCompleter = {
      val mono = namerOf(tree.symbol) monoTypeCompleter tree
      val tparams = treeInfo.typeParameters(tree)
      if (tparams.isEmpty) mono
      else {
        /* @M! TypeDef's type params are handled differently, e.g., in `type T[A[x <: B], B]`, A and B are entered
         * first as both are in scope in the definition of x. x is only in scope in `A[x <: B]`.
         * No symbols are created for the abstract type's params at this point, i.e. the following assertion holds:
         *     !tree.symbol.isAbstractType || { tparams.forall(_.symbol == NoSymbol)
         * (tested with the above example, `trait C { type T[A[X <: B], B] }`). See also comment in PolyTypeCompleter.
         */
        if (!tree.symbol.isAbstractType) //@M TODO: change to isTypeMember ?
          createNamer(tree) enterSyms tparams

        new PolyTypeCompleter(tparams, mono, context) //@M
      }
    }

    def enterValDef(tree: ValDef) {
      if (noEnterGetterSetter(tree))
        assignAndEnterFinishedSymbol(tree)
      else
        enterGetterSetter(tree)

      if (isEnumConstant(tree))
        tree.symbol setInfo ConstantType(Constant(tree.symbol))
    }

    def enterLazyVal(tree: ValDef, lazyAccessor: Symbol): TermSymbol = {
      // If the owner is not a class, this is a lazy val from a method,
      // with no associated field.  It has an accessor with $lzy appended to its name and
      // its flags are set differently.  The implicit flag is reset because otherwise
      // a local implicit "lazy val x" will create an ambiguity with itself
      // via "x$lzy" as can be seen in test #3927.
      val sym = (
        if (owner.isClass) createFieldSymbol(tree)
        else owner.newValue(tree.name append nme.LAZY_LOCAL, tree.pos, (tree.mods.flags | ARTIFACT) & ~IMPLICIT)
      )
      enterValSymbol(tree, sym setFlag MUTABLE setLazyAccessor lazyAccessor)
    }
    def enterStrictVal(tree: ValDef): TermSymbol = {
      enterValSymbol(tree, createFieldSymbol(tree))
    }
    def enterValSymbol(tree: ValDef, sym: TermSymbol): TermSymbol = {
      enterInScope(sym)
      sym setInfo namerOf(sym).monoTypeCompleter(tree)
    }
    def enterPackage(tree: PackageDef) {
      val sym = assignSymbol(tree)
      newNamer(context.make(tree, sym.moduleClass, sym.info.decls)) enterSyms tree.stats
    }
    def enterTypeDef(tree: TypeDef) = assignAndEnterFinishedSymbol(tree)

    def enterDefDef(tree: DefDef): Unit = tree match {
      case DefDef(_, nme.CONSTRUCTOR, _, _, _, _) =>
        assignAndEnterFinishedSymbol(tree)
      case DefDef(mods, name, tparams, _, _, _) =>
        val bridgeFlag = if (mods hasAnnotationNamed tpnme.bridgeAnnot) BRIDGE | ARTIFACT else 0
        val sym = assignAndEnterSymbol(tree) setFlag bridgeFlag

        if (name == nme.copy && sym.isSynthetic)
          enterCopyMethod(tree)
        else
          sym setInfo completerOf(tree)
    }

    def enterClassDef(tree: ClassDef) {
      val ClassDef(mods, _, _, impl) = tree
      val primaryConstructorArity = treeInfo.firstConstructorArgs(impl.body).size
      tree.symbol = enterClassSymbol(tree)
      tree.symbol setInfo completerOf(tree)

      if (mods.isCase) {
        val m = ensureCompanionObject(tree, caseModuleDef)
        m.moduleClass.updateAttachment(new ClassForCaseCompanionAttachment(tree))
      }
      val hasDefault = impl.body exists treeInfo.isConstructorWithDefault
      if (hasDefault) {
        val m = ensureCompanionObject(tree)
        m.updateAttachment(new ConstructorDefaultsAttachment(tree, null))
      }
      val owner = tree.symbol.owner
      if (settings.lint && owner.isPackageObjectClass && !mods.isImplicit) {
        context.unit.warning(tree.pos,
          "it is not recommended to define classes/objects inside of package objects.\n" +
          "If possible, define " + tree.symbol + " in " + owner.skipPackageObject + " instead."
        )
      }

      // Suggested location only.
      if (mods.isImplicit) {
        if (primaryConstructorArity == 1) {
          log("enter implicit wrapper "+tree+", owner = "+owner)
          enterImplicitWrapper(tree)
        }
        else context.unit.error(tree.pos, "implicit classes must accept exactly one primary constructor parameter")
      }
      validateCompanionDefs(tree)
    }

    // Hooks which are overridden in the presentation compiler
    def enterExistingSym(sym: Symbol): Context = this.context
    def enterIfNotThere(sym: Symbol) { }

    def enterSyntheticSym(tree: Tree): Symbol = {
      enterSym(tree)
      context.unit.synthetics(tree.symbol) = tree
      tree.symbol
    }

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

    def findCyclicalLowerBound(tp: Type): Symbol = {
      tp match {
        case TypeBounds(lo, _) =>
          // check that lower bound is not an F-bound
          // but carefully: class Foo[T <: Bar[_ >: T]] should be allowed
          for (tp1 @ TypeRef(_, sym, _) <- lo) {
            if (settings.breakCycles) {
              if (!sym.maybeInitialize) {
                log(s"Cycle inspecting $lo for possible f-bounds: ${sym.fullLocationString}")
                return sym
              }
            }
            else sym.initialize
          }
        case _ =>
      }
      NoSymbol
    }

    def monoTypeCompleter(tree: Tree) = mkTypeCompleter(tree) { sym =>
      // this early test is there to avoid infinite baseTypes when
      // adding setters and getters --> bug798
      // It is a def in an attempt to provide some insulation against
      // uninitialized symbols misleading us. It is not a certainty
      // this accomplishes anything, but performance is a non-consideration
      // on these flag checks so it can't hurt.
      def needsCycleCheck = sym.isNonClassType && !sym.isParameter && !sym.isExistential
      logAndValidate(sym) {
        val tp = typeSig(tree)

        findCyclicalLowerBound(tp) andAlso { sym =>
          if (needsCycleCheck) {
            // neg/t1224:  trait C[T] ; trait A { type T >: C[T] <: C[C[T]] }
            // To avoid an infinite loop on the above, we cannot break all cycles
            log(s"Reinitializing info of $sym to catch any genuine cycles")
            sym reset sym.info
            sym.initialize
          }
        }
        sym setInfo {
          if (sym.isJavaDefined) RestrictJavaArraysMap(tp)
          else tp
        }
        if (needsCycleCheck) {
          log(s"Needs cycle check: ${sym.debugLocationString}")
          if (!typer.checkNonCyclic(tree.pos, tp))
            sym setInfo ErrorType
        }
      }
    }

    def moduleClassTypeCompleter(tree: ModuleDef) = {
      mkTypeCompleter(tree) { sym =>
        val moduleSymbol = tree.symbol
        assert(moduleSymbol.moduleClass == sym, moduleSymbol.moduleClass)
        moduleSymbol.info // sets moduleClass info as a side effect.
      }
    }

    /* Explicit isSetter required for bean setters (beanSetterSym.isSetter is false) */
    def accessorTypeCompleter(tree: ValDef, isSetter: Boolean) = mkTypeCompleter(tree) { sym =>
      logAndValidate(sym) {
        sym setInfo {
          val tp = if (isSetter) MethodType(List(sym.newSyntheticValueParam(typeSig(tree))), UnitTpe)
                   else NullaryMethodType(typeSig(tree))
          pluginsTypeSigAccessor(tp, typer, tree, sym)
        }
      }
    }

    def selfTypeCompleter(tree: Tree) = mkTypeCompleter(tree) { sym =>
      val selftpe = typer.typedType(tree).tpe
      sym setInfo {
        if (selftpe.typeSymbol isNonBottomSubClass sym.owner) selftpe
        else intersectionType(List(sym.owner.tpe, selftpe))
      }
    }

    /** This method has a big impact on the eventual compiled code.
     *  At this point many values have the most specific possible
     *  type (e.g. in val x = 42, x's type is Int(42), not Int) but
     *  most need to be widened to avoid undesirable propagation of
     *  those singleton types.
     *
     *  However, the compilation of pattern matches into switch
     *  statements depends on constant folding, which will only take
     *  place for those values which aren't widened.  The "final"
     *  modifier is the present means of signaling that a constant
     *  value should not be widened, so it has a use even in situations
     *  whether it is otherwise redundant (such as in a singleton.)
     */
    private def widenIfNecessary(sym: Symbol, tpe: Type, pt: Type): Type = {
      val getter =
        if (sym.isValue && sym.owner.isClass && sym.isPrivate)
          sym.getter(sym.owner)
        else sym
      def isHidden(tp: Type): Boolean = tp match {
        case SingleType(pre, sym) =>
          (sym isLessAccessibleThan getter) || isHidden(pre)
        case ThisType(sym) =>
          sym isLessAccessibleThan getter
        case p: SimpleTypeProxy =>
          isHidden(p.underlying)
        case _ =>
          false
      }
      val shouldWiden = (
           !tpe.typeSymbolDirect.isModuleClass // Infer Foo.type instead of "object Foo"
        && (tpe.widen <:< pt)                  // Don't widen our way out of conforming to pt
        && (   sym.isVariable
            || sym.isMethod && !sym.hasAccessorFlag
            || isHidden(tpe)
           )
      )
      dropIllegalStarTypes(
        if (shouldWiden) tpe.widen
        else if (sym.isFinal) tpe    // "final val" allowed to retain constant type
        else tpe.deconst
      )
    }
    /** Computes the type of the body in a ValDef or DefDef, and
     *  assigns the type to the tpt's node.  Returns the type.
     */
    private def assignTypeToTree(tree: ValOrDefDef, defnTyper: Typer, pt: Type): Type = {
      val rhsTpe = tree match {
        case ddef: DefDef if tree.symbol.isTermMacro => defnTyper.computeMacroDefType(ddef, pt)
        case _ => defnTyper.computeType(tree.rhs, pt)
      }

      val defnTpe = widenIfNecessary(tree.symbol, rhsTpe, pt)
      tree.tpt defineType defnTpe setPos tree.pos.focus
      tree.tpt.tpe
    }

    // owner is the class with the self type
    def enterSelf(self: ValDef) {
      val ValDef(_, name, tpt, _) = self
      if (self eq noSelfType)
        return

      val hasName = name != nme.WILDCARD
      val hasType = !tpt.isEmpty
      if (!hasType)
        tpt defineType NoType

      val sym = (
        if (hasType || hasName) {
          owner.typeOfThis = if (hasType) selfTypeCompleter(tpt) else owner.tpe_*
          val selfSym = owner.thisSym setPos self.pos
          if (hasName) selfSym setName name else selfSym
        }
        else {
          val symName = if (name != nme.WILDCARD) name else nme.this_
          owner.newThisSym(symName, owner.pos) setInfo owner.tpe
        }
      )
      self.symbol = context.scope enter sym
    }

    private def templateSig(templ: Template): Type = {
      val clazz = context.owner
      def checkParent(tpt: Tree): Type = {
        if (tpt.tpe.isError) AnyRefTpe
        else tpt.tpe
      }

      val parents = typer.typedParentTypes(templ) map checkParent

      enterSelf(templ.self)

      val decls = newScope
      val templateNamer = newNamer(context.make(templ, clazz, decls))
      templateNamer enterSyms templ.body

      // add apply and unapply methods to companion objects of case classes,
      // unless they exist already; here, "clazz" is the module class
      if (clazz.isModuleClass) {
        clazz.attachments.get[ClassForCaseCompanionAttachment] foreach { cma =>
          val cdef = cma.caseClass
          assert(cdef.mods.isCase, "expected case class: "+ cdef)
          addApplyUnapply(cdef, templateNamer)
        }
      }

      // add the copy method to case classes; this needs to be done here, not in SyntheticMethods, because
      // the namer phase must traverse this copy method to create default getters for its parameters.
      // here, clazz is the ClassSymbol of the case class (not the module). (!clazz.hasModuleFlag) excludes
      // the moduleClass symbol of the companion object when the companion is a "case object".
      if (clazz.isCaseClass && !clazz.hasModuleFlag) {
        val modClass = companionSymbolOf(clazz, context).moduleClass
        modClass.attachments.get[ClassForCaseCompanionAttachment] foreach { cma =>
          val cdef = cma.caseClass
          def hasCopy = (decls containsName nme.copy) || parents.exists(_ member nme.copy exists)

          // SI-5956 needs (cdef.symbol == clazz): there can be multiple class symbols with the same name
          if (cdef.symbol == clazz && !hasCopy)
            addCopyMethod(cdef, templateNamer)
        }
      }

      // if default getters (for constructor defaults) need to be added to that module, here's the namer
      // to use. clazz is the ModuleClass. sourceModule works also for classes defined in methods.
      val module = clazz.sourceModule
      for (cda <- module.attachments.get[ConstructorDefaultsAttachment]) {
        debuglog(s"Storing the template namer in the ConstructorDefaultsAttachment of ${module.debugLocationString}.")
        cda.companionModuleClassNamer = templateNamer
      }
      val classTp = ClassInfoType(parents, decls, clazz)
      pluginsTypeSig(classTp, templateNamer.typer, templ, WildcardType)
    }

    private def classSig(cdef: ClassDef): Type = {
      val clazz = cdef.symbol
      val ClassDef(_, _, tparams, impl) = cdef
      val tparams0   = typer.reenterTypeParams(tparams)
      val resultType = templateSig(impl)

      val res = GenPolyType(tparams0, resultType)
      val pluginsTp = pluginsTypeSig(res, typer, cdef, WildcardType)

      // Already assign the type to the class symbol (monoTypeCompleter will do it again).
      // Allows isDerivedValueClass to look at the info.
      clazz setInfo pluginsTp
      if (clazz.isDerivedValueClass) {
        log("Ensuring companion for derived value class " + cdef.name + " at " + cdef.pos.show)
        clazz setFlag FINAL
        // Don't force the owner's info lest we create cycles as in SI-6357.
        enclosingNamerWithScope(clazz.owner.rawInfo.decls).ensureCompanionObject(cdef)
      }
      pluginsTp
    }

    private def moduleSig(mdef: ModuleDef): Type = {
      val moduleSym = mdef.symbol
      // The info of both the module and the moduleClass symbols need to be assigned. monoTypeCompleter assigns
      // the result of typeSig to the module symbol. The module class info is assigned here as a side-effect.
      val result = templateSig(mdef.impl)
      val pluginsTp = pluginsTypeSig(result, typer, mdef, WildcardType)
      // Assign the moduleClass info (templateSig returns a ClassInfoType)
      val clazz = moduleSym.moduleClass
      clazz setInfo pluginsTp
      // clazz.tpe_* returns a `ModuleTypeRef(clazz)`, a typeRef that links to the module class `clazz`
      // (clazz.info would the ClassInfoType, which is not what should be assigned to the module symbol)
      clazz.tpe_*
    }

    /**
     * The method type for `ddef`.
     *
     * If a PolyType(tparams, restp) is returned, `tparams` are the external symbols (not type skolems),
     * i.e. instances of AbstractTypeSymbol. All references in `restp` to the type parameters are TypeRefs
     * to these non-skolems.
     *
     * For type-checking the rhs (in case the result type is inferred), the type skolems of the type parameters
     * are entered in scope. Equally, the parameter symbols entered into scope have types which refer to those
     * skolems: when type-checking the rhs, references to parameters need to have types that refer to the skolems.
     * In summary, typing an rhs happens with respect to the skolems.
     *
     * This means that the method's result type computed by the typer refers to skolems. In order to put it
     * into the method type (the result of methodSig), typeRefs to skolems have to be replaced by references
     * to the non-skolems.
     */
    private def methodSig(ddef: DefDef): Type = {

      // DEPMETTODO: do we need to skolemize value parameter symbols?

      val DefDef(_, _, tparams, vparamss, tpt, _) = ddef

      val meth = owner
      val methOwner = meth.owner
      val site = methOwner.thisType

      /* tparams already have symbols (created in enterDefDef/completerOf), namely the skolemized ones (created
       * by the PolyTypeCompleter constructor, and assigned to tparams). reenterTypeParams enters the type skolems
       * into scope and returns the non-skolems.
       */
      val tparamSyms = typer.reenterTypeParams(tparams)

      val tparamSkolems = tparams.map(_.symbol)

      /* since the skolemized tparams are in scope, the TypeRefs in types of vparamSymss refer to the type skolems
       * note that for parameters with missing types, `methodSig` reassigns types of these symbols (the parameter
       * types from the overridden method).
       */
      var vparamSymss = enterValueParams(vparamss)


      /*
       * Creates a method type using tparamSyms and vparamsSymss as argument symbols and `respte` as result type.
       * All typeRefs to type skolems are replaced by references to the corresponding non-skolem type parameter,
       * so the resulting type is a valid external method type, it does not contain (references to) skolems.
       */
      def thisMethodType(restpe: Type) = {
        val checkDependencies = new DependentTypeChecker(context)(this)
        checkDependencies check vparamSymss
        // DEPMETTODO: check not needed when they become on by default
        checkDependencies(restpe)

        val makeMethodType = (vparams: List[Symbol], restpe: Type) => {
          // TODODEPMET: check that we actually don't need to do anything here
          // new dependent method types: probably OK already, since 'enterValueParams' above
          // enters them in scope, and all have a lazy type. so they may depend on other params. but: need to
          // check that params only depend on ones in earlier sections, not the same. (done by checkDependencies,
          // so re-use / adapt that)
          if (meth.isJavaDefined)
          // TODODEPMET necessary?? new dependent types: replace symbols in restpe with the ones in vparams
            JavaMethodType(vparams map (p => p setInfo objToAny(p.tpe)), restpe)
          else
            MethodType(vparams, restpe)
        }


        val res = GenPolyType(
          tparamSyms, // deSkolemized symbols  -- TODO: check that their infos don't refer to method args?
          if (vparamSymss.isEmpty) NullaryMethodType(restpe)
          // vparamss refer (if they do) to skolemized tparams
          else (vparamSymss :\ restpe) (makeMethodType)
        )
        res.substSym(tparamSkolems, tparamSyms)
      }

      /*
       * Creates a schematic method type which has WildcardTypes for non specified
       * return or parameter types. For instance, in `def f[T](a: T, b) = ...`, the
       * type schema is
       *
       *   PolyType(T, MethodType(List(a: T, b: WildcardType), WildcardType))
       *
       * where T are non-skolems.
       */
      def methodTypeSchema(resTp: Type) = {
        // for all params without type set WildcaradType
        mforeach(vparamss)(v => if (v.tpt.isEmpty) v.symbol setInfo WildcardType)
        thisMethodType(resTp)
      }

      def overriddenSymbol(resTp: Type) = {
        lazy val schema: Type = methodTypeSchema(resTp) // OPT create once. Must be lazy to avoid cycles in neg/t5093.scala
        intersectionType(methOwner.info.parents).nonPrivateMember(meth.name).filter { sym =>
          sym != NoSymbol && (site.memberType(sym) matches schema)
        }
      }
      // TODO: see whether this or something similar would work instead:
      // def overriddenSymbol = meth.nextOverriddenSymbol


      /*
       * If `meth` doesn't have an explicit return type, extracts the return type from the method
       * overridden by `meth` (if there's an unique one). This type is lateron used as the expected
       * type for computing the type of the rhs. The resulting type references type skolems for
       * type parameters (consistent with the result of `typer.typedType(tpt).tpe`).
       *
       * As a first side effect, this method assigns a MethodType constructed using this
       * return type to `meth`. This allows omitting the result type for recursive methods.
       *
       * As another side effect, this method also assigns paramter types from the overridden
       * method to parameters of `meth` that have missing types (the parser accepts missing
       * parameter types under -Yinfer-argument-types).
       */
      def typesFromOverridden(methResTp: Type): Type = {
        val overridden = overriddenSymbol(methResTp)
        if (overridden == NoSymbol || overridden.isOverloaded) {
          methResTp
        } else {
          overridden.cookJavaRawInfo() // #3404 xform java rawtypes into existentials
          var overriddenTp = site.memberType(overridden) match {
              case PolyType(tparams, rt) => rt.substSym(tparams, tparamSkolems)
              case mt => mt
            }
          for (vparams <- vparamss) {
            var overriddenParams = overriddenTp.params
            for (vparam <- vparams) {
              if (vparam.tpt.isEmpty) {
                val overriddenParamTp = overriddenParams.head.tpe
                // references to type parameteres in overriddenParamTp link to the type skolems, so the
                // assigned type is consistent with the other / existing parameter types in vparamSymss.
                vparam.symbol setInfo overriddenParamTp
                vparam.tpt defineType overriddenParamTp setPos vparam.pos.focus
              }
              overriddenParams = overriddenParams.tail
            }
            overriddenTp = overriddenTp.resultType
          }

          // SI-7668 Substitute parameters from the parent method with those of the overriding method.
          overriddenTp = overriddenTp.substSym(overridden.paramss.flatten, vparamss.flatten.map(_.symbol))

          overriddenTp match {
            case NullaryMethodType(rtpe) => overriddenTp = rtpe
            case MethodType(List(), rtpe) => overriddenTp = 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(overriddenTp)
            overriddenTp
          } else {
            methResTp
          }
        }
      }

      if (tpt.isEmpty && meth.name == nme.CONSTRUCTOR) {
        tpt defineType context.enclClass.owner.tpe_*
        tpt setPos meth.pos.focus
      }

      val methResTp = if (tpt.isEmpty) WildcardType else typer.typedType(tpt).tpe
      val resTpFromOverride = if (methOwner.isClass && (tpt.isEmpty || mexists(vparamss)(_.tpt.isEmpty))) {
          typesFromOverridden(methResTp)
        } else {
          methResTp
        }

      // Add a () parameter section if this overrides some method with () parameters
      if (methOwner.isClass && vparamss.isEmpty &&
        overriddenSymbol(methResTp).alternatives.exists(_.info.isInstanceOf[MethodType])) {
        vparamSymss = ListOfNil
      }

      // issue an error for missing parameter types
      mforeach(vparamss) { vparam =>
        if (vparam.tpt.isEmpty) {
          MissingParameterOrValTypeError(vparam)
          vparam.tpt defineType ErrorType
        }
      }

      addDefaultGetters(meth, ddef, vparamss, tparams, overriddenSymbol(methResTp))

      // fast track macros, i.e. macros defined inside the compiler, are hardcoded
      // hence we make use of that and let them have whatever right-hand side they need
      // (either "macro ???" as they used to or just "???" to maximally simplify their compilation)
      if (fastTrack contains meth) meth setFlag MACRO

      // macro defs need to be typechecked in advance
      // because @macroImpl annotation only gets assigned during typechecking
      // otherwise macro defs wouldn't be able to robustly coexist with their clients
      // because a client could be typechecked before a macro def that it uses
      if (meth.isMacro) {
        typer.computeMacroDefType(ddef, resTpFromOverride)
      }

      val res = thisMethodType({
        val rt = (
          if (!tpt.isEmpty) {
            methResTp
          } else {
            // return type is inferred, we don't just use resTpFromOverride. Here, C.f has type String:
            //   trait T { def f: Object }; class C <: T { def f = "" }
            // using resTpFromOverride as expected type allows for the following (C.f has type A):
            //   trait T { def f: A }; class C <: T { implicit def b2a(t: B): A = ???; def f = new B }
            assignTypeToTree(ddef, typer, resTpFromOverride)
          })
        // #2382: return type of default getters are always @uncheckedVariance
        if (meth.hasDefault)
          rt.withAnnotation(AnnotationInfo(uncheckedVarianceClass.tpe, List(), List()))
        else rt
      })
      pluginsTypeSig(res, typer, ddef, methResTp)
    }

    /**
     * For every default argument, insert a method computing that default
     *
     * Also adds the "override" and "defaultparam" (for inherited defaults) flags
     * Typer is too late, if an inherited default is used before the method is
     * typechecked, the corresponding param would not yet have the "defaultparam"
     * flag.
     */
    private def addDefaultGetters(meth: Symbol, ddef: DefDef, vparamss: List[List[ValDef]], tparams: List[TypeDef], overriddenSymbol: => Symbol) {
      val DefDef(_, _, rtparams0, rvparamss0, _, _) = resetAttrs(ddef.duplicate)
      // having defs here is important to make sure that there's no sneaky tree sharing
      // in methods with multiple default parameters
      def rtparams = rtparams0.map(_.duplicate)
      def rvparamss = rvparamss0.map(_.map(_.duplicate))
      val methOwner  = meth.owner
      val isConstr   = meth.isConstructor
      val overridden = if (isConstr || !methOwner.isClass) NoSymbol else overriddenSymbol
      val overrides  = overridden != NoSymbol && !overridden.isOverloaded
      // value parameters of the base class (whose defaults might be overridden)
      var baseParamss = (vparamss, overridden.tpe.paramss) match {
        // match empty and missing parameter list
        case (Nil, ListOfNil) => Nil
        case (ListOfNil, Nil) => ListOfNil
        case (_, paramss)     => paramss
      }
      assert(
        !overrides || vparamss.length == baseParamss.length,
        "" + meth.fullName + ", "+ overridden.fullName
      )

      // cache the namer used for entering the default getter symbols
      var ownerNamer: Option[Namer] = None
      var moduleNamer: Option[(ClassDef, Namer)] = None
      var posCounter = 1

      // For each value parameter, create the getter method if it has a
      // default argument. previous denotes the parameter lists which
      // are on the left side of the current one. These get added to the
      // default getter. Example:
      //
      //   def foo(a: Int)(b: Int = a)      becomes
      //   foo$default$1(a: Int) = a
      //
      vparamss.foldLeft(Nil: List[List[ValDef]]) { (previous, vparams) =>
        assert(!overrides || vparams.length == baseParamss.head.length, ""+ meth.fullName + ", "+ overridden.fullName)
        val rvparams = rvparamss(previous.length)
        var baseParams = if (overrides) baseParamss.head else Nil
        map2(vparams, rvparams)((vparam, rvparam) => {
          val sym = vparam.symbol
          // true if the corresponding parameter of the base class has a default argument
          val baseHasDefault = overrides && baseParams.head.hasDefault
          if (sym.hasDefault) {
            // Create a "default getter", i.e. a DefDef that will calculate vparam.rhs
            // for those who are going to call meth without providing an argument corresponding to vparam.
            // After the getter is created, a corresponding synthetic symbol is created and entered into the parent namer.
            //
            // In the ideal world, this DefDef would be a simple one-liner that just returns vparam.rhs,
            // but in scalac things are complicated in two different ways.
            //
            // 1) Because the underlying language is quite sophisticated, we must allow for those sophistications in our getter.
            //    Namely: a) our getter has to copy type parameters from the associated method (or the associated class
            //    if meth is a constructor), because vparam.rhs might refer to one of them, b) our getter has to copy
            //    preceding value parameter lists from the associated method, because again vparam.rhs might refer to one of them.
            //
            // 2) Because we have already assigned symbols to type and value parameters that we have to copy, we must jump through
            //    hoops in order to destroy them and allow subsequent naming create new symbols for our getter. Previously this
            //    was done in an overly brutal way akin to resetAllAttrs, but now we utilize a resetLocalAttrs-based approach.
            //    Still far from ideal, but at least enables things like run/macro-default-params that were previously impossible.

            val oflag = if (baseHasDefault) OVERRIDE else 0
            val name = nme.defaultGetterName(meth.name, posCounter)

            var defTparams = rtparams
            val defVparamss = mmap(rvparamss.take(previous.length)){ rvp =>
              copyValDef(rvp)(mods = rvp.mods &~ DEFAULTPARAM, rhs = EmptyTree)
            }

            val parentNamer = if (isConstr) {
              val (cdef, nmr) = moduleNamer.getOrElse {
                val module = companionSymbolOf(methOwner, context)
                module.initialize // call type completer (typedTemplate), adds the
                                  // module's templateNamer to classAndNamerOfModule
                module.attachments.get[ConstructorDefaultsAttachment] match {
                  // by martin: the null case can happen in IDE; this is really an ugly hack on top of an ugly hack but it seems to work
                  case Some(cda) =>
                    if (cda.companionModuleClassNamer == null) {
                      debugwarn(s"SI-6576 The companion module namer for $meth was unexpectedly null")
                      return
                    }
                    val p = (cda.classWithDefault, cda.companionModuleClassNamer)
                    moduleNamer = Some(p)
                    p
                  case _ =>
                    return // fix #3649 (prevent crash in erroneous source code)
                }
              }
              val ClassDef(_, _, rtparams, _) = resetAttrs(cdef.duplicate)
              defTparams = rtparams.map(rt => copyTypeDef(rt)(mods = rt.mods &~ (COVARIANT | CONTRAVARIANT)))
              nmr
            }
            else ownerNamer getOrElse {
              val ctx = context.nextEnclosing(c => c.scope.toList.contains(meth))
              assert(ctx != NoContext, meth)
              val nmr = newNamer(ctx)
              ownerNamer = Some(nmr)
              nmr
            }

            val defTpt =
              // don't mess with tpt's of case copy default getters, because assigning something other than TypeTree()
              // will break the carefully orchestrated naming/typing logic that involves enterCopyMethod and caseClassCopyMeth
              if (meth.isCaseCopy) TypeTree()
              else {
                // If the parameter type mentions any type parameter of the method, let the compiler infer the
                // return type of the default getter => allow "def foo[T](x: T = 1)" to compile.
                // This is better than always using Wildcard for inferring the result type, for example in
                //    def f(i: Int, m: Int => Int = identity _) = m(i)
                // if we use Wildcard as expected, we get "Nothing => Nothing", and the default is not usable.
                // TODO: this is a very brittle approach; I sincerely hope that Denys's research into hygiene
                //       will open the doors to a much better way of doing this kind of stuff
                val tparamNames = defTparams map { case TypeDef(_, name, _, _) => name }
                val eraseAllMentionsOfTparams = new TypeTreeSubstituter(tparamNames contains _)
                eraseAllMentionsOfTparams(rvparam.tpt match {
                  // default getter for by-name params
                  case AppliedTypeTree(_, List(arg)) if sym.hasFlag(BYNAMEPARAM) => arg
                  case t => t
                })
              }
            val defRhs = rvparam.rhs

            val defaultTree = atPos(vparam.pos.focus) {
              DefDef(Modifiers(paramFlagsToDefaultGetter(meth.flags)) | oflag, name, defTparams, defVparamss, defTpt, defRhs)
            }
            if (!isConstr)
              methOwner.resetFlag(INTERFACE) // there's a concrete member now
            val default = parentNamer.enterSyntheticSym(defaultTree)
            if (default.owner.isTerm)
              saveDefaultGetter(meth, default)
          }
          else if (baseHasDefault) {
            // the parameter does not have a default itself, but the
            // corresponding parameter in the base class does.
            sym.setFlag(DEFAULTPARAM)
          }
          posCounter += 1
          if (overrides) baseParams = baseParams.tail
        })
        if (overrides) baseParamss = baseParamss.tail
        previous :+ vparams
      }
    }

    private def valDefSig(vdef: ValDef) = {
      val ValDef(_, _, tpt, rhs) = vdef
      val result = if (tpt.isEmpty) {
        if (rhs.isEmpty) {
          MissingParameterOrValTypeError(tpt)
          ErrorType
        }
        else assignTypeToTree(vdef, typer, WildcardType)
      } else {
        typer.typedType(tpt).tpe
      }
      pluginsTypeSig(result, typer, vdef, if (tpt.isEmpty) WildcardType else result)

    }

    //@M! an abstract type definition (abstract type member/type parameter)
    // may take type parameters, which are in scope in its bounds
    private def typeDefSig(tdef: TypeDef) = {
      val TypeDef(_, _, tparams, rhs) = tdef
      // log("typeDefSig(" + tpsym + ", " + tparams + ")")
      val tparamSyms = typer.reenterTypeParams(tparams) //@M make tparams available in scope (just for this abstypedef)
      val tp = typer.typedType(rhs).tpe match {
        case TypeBounds(lt, rt) if (lt.isError || rt.isError) =>
          TypeBounds.empty
        case tp @ TypeBounds(lt, rt) if (tdef.symbol hasFlag JAVA) =>
          TypeBounds(lt, objToAny(rt))
        case tp =>
          tp
      }
      // see neg/bug1275, #3419
      // used to do a rudimentary kind check here to ensure overriding in refinements
      // doesn't change a type member's arity (number of type parameters), e.g.
      //
      //    trait T { type X[A] }
      //    type S = T { type X }
      //    val x: S
      //
      // X in x.X[A] will get rebound to the X in the refinement, which
      // does not take any type parameters. This mismatch does not crash
      // the compiler (anymore), but leads to weird type errors, as
      // x.X[A] will become NoType internally. It's not obvious the
      // error refers to the X in the refinement and not the original X.
      //
      // However, separate compilation requires the symbol info to be
      // loaded to do this check, but loading the info will probably
      // lead to spurious cyclic errors.  So omit the check.
      val res = GenPolyType(tparamSyms, tp)
      pluginsTypeSig(res, typer, tdef, WildcardType)
    }

    private def importSig(imp: Import) = {
      val Import(expr, selectors) = imp
      val expr1 = typer.typedQualifier(expr)

      if (expr1.symbol != null && expr1.symbol.isRootPackage)
        RootImportError(imp)

      if (expr1.isErrorTyped)
        ErrorType
      else {
        expr1 match {
          case This(_) =>
            // SI-8207 okay, typedIdent expands Ident(self) to C.this which doesn't satisfy the next case
            // TODO should we change `typedIdent` not to expand to the `Ident` to a `This`?
          case _ if treeInfo.isStableIdentifierPattern(expr1) =>
          case _ =>
            typer.TyperErrorGen.UnstableTreeError(expr1)
        }

        val newImport = treeCopy.Import(imp, expr1, selectors).asInstanceOf[Import]
        checkSelectors(newImport)
        context.unit.transformed(imp) = newImport
        // copy symbol and type attributes back into old expression
        // so that the structure builder will find it.
        expr setSymbol expr1.symbol setType expr1.tpe
        ImportType(expr1)
      }
    }


    /** Given a case class
     *   case class C[Ts] (ps: Us)
     *  Add the following methods to toScope:
     *  1. if case class is not abstract, add
     *   <synthetic> <case> def apply[Ts](ps: Us): C[Ts] = new C[Ts](ps)
     *  2. add a method
     *   <synthetic> <case> def unapply[Ts](x: C[Ts]) = <ret-val>
     *  where <ret-val> is the caseClassUnapplyReturnValue of class C (see UnApplies.scala)
     *
     * @param cdef is the class definition of the case class
     * @param namer is the namer of the module class (the comp. obj)
     */
    def addApplyUnapply(cdef: ClassDef, namer: Namer) {
      if (!cdef.symbol.hasAbstractFlag)
        namer.enterSyntheticSym(caseModuleApplyMeth(cdef))

      val primaryConstructorArity = treeInfo.firstConstructorArgs(cdef.impl.body).size
      if (primaryConstructorArity <= MaxTupleArity)
        namer.enterSyntheticSym(caseModuleUnapplyMeth(cdef))
    }

    def addCopyMethod(cdef: ClassDef, namer: Namer) {
      caseClassCopyMeth(cdef) foreach namer.enterSyntheticSym
    }

    /**
     * TypeSig is invoked by monoTypeCompleters. It returns the type of a definition which
     * is then assigned to the corresponding symbol (typeSig itself does not need to assign
     * the type to the symbol, but it can if necessary).
     */
    def typeSig(tree: Tree): Type = {
      // log("typeSig " + tree)
      /* For definitions, transform Annotation trees to AnnotationInfos, assign
       * them to the sym's annotations. Type annotations: see Typer.typedAnnotated
       * We have to parse definition annotations here (not in the typer when traversing
       * the MemberDef tree): the typer looks at annotations of certain symbols; if
       * they were added only in typer, depending on the compilation order, they may
       * or may not be visible.
       */
      def annotate(annotated: Symbol) = {
        // typeSig might be called multiple times, e.g. on a ValDef: val, getter, setter
        // parse the annotations only once.
        if (!annotated.isInitialized) tree match {
          case defn: MemberDef =>
            val ainfos = defn.mods.annotations filterNot (_ eq null) map { ann =>
              val ctx    = typer.context
              val annCtx = ctx.make(ann)
              annCtx.setReportErrors()
              // need to be lazy, #1782. beforeTyper to allow inferView in annotation args, SI-5892.
              AnnotationInfo lazily {
                enteringTyper(newTyper(annCtx) typedAnnotation ann)
              }
            }
            if (ainfos.nonEmpty) {
              annotated setAnnotations ainfos
              if (annotated.isTypeSkolem)
                annotated.deSkolemize setAnnotations ainfos
            }
          case _ =>
        }
      }

      val sym: Symbol = tree.symbol

      // TODO: meta-annotations to indicate where module annotations should go (module vs moduleClass)
      annotate(sym)
      if (sym.isModule) annotate(sym.moduleClass)

      def getSig = tree match {
        case cdef: ClassDef =>
          createNamer(tree).classSig(cdef)

        case mdef: ModuleDef =>
          createNamer(tree).moduleSig(mdef)

        case ddef: DefDef =>
          createNamer(tree).methodSig(ddef)

        case vdef: ValDef =>
          createNamer(tree).valDefSig(vdef)

        case tdef: TypeDef =>
          createNamer(tree).typeDefSig(tdef) //@M!

        case imp: Import =>
          importSig(imp)
      }

      try getSig
      catch typeErrorHandler(tree, ErrorType)
    }

    def includeParent(tpe: Type, parent: Symbol): Type = tpe match {
      case PolyType(tparams, restpe) =>
        PolyType(tparams, includeParent(restpe, parent))
      case ClassInfoType(parents, decls, clazz) =>
        if (parents exists (_.typeSymbol == parent)) tpe
        else ClassInfoType(parents :+ parent.tpe, decls, clazz)
      case _ =>
        tpe
    }

    class LogTransitions[S](onEnter: S => String, onExit: S => String) {
      val enabled = settings.debug.value
      @inline final def apply[T](entity: S)(body: => T): T = {
        if (enabled) log(onEnter(entity))
        try body
        finally if (enabled) log(onExit(entity))
      }
    }
    private val logDefinition = new LogTransitions[Symbol](
      sym => "[define] >> " + sym.flagString + " " + sym.fullLocationString,
      sym => "[define] << " + sym
    )
    private def logAndValidate(sym: Symbol)(body: => Unit) {
      logDefinition(sym)(body)
      validate(sym)
    }

    /** Convert Java generic array type T[] to (T with Object)[]
     *  (this is necessary because such arrays have a representation which is incompatible
     *   with arrays of primitive types.)
     *
     *  @note the comparison to Object only works for abstract types bounded by classes that are strict subclasses of Object
     *  if the bound is exactly Object, it will have been converted to Any, and the comparison will fail
     *
     *  see also sigToType
     */
    private object RestrictJavaArraysMap extends TypeMap {
      def apply(tp: Type): Type = tp match {
        case TypeRef(pre, ArrayClass, List(elemtp))
        if elemtp.typeSymbol.isAbstractType && !(elemtp <:< ObjectTpe) =>
          TypeRef(pre, ArrayClass, List(intersectionType(List(elemtp, ObjectTpe))))
        case _ =>
          mapOver(tp)
      }
    }

    /** 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 (when not @native)
     */
    def validate(sym: Symbol) {
      import SymValidateErrors._
      def fail(kind: SymValidateErrors.Value) = SymbolValidationError(sym, kind)

      def checkWithDeferred(flag: Int) {
        if (sym hasFlag flag)
          AbstractMemberWithModiferError(sym, flag)
      }
      def checkNoConflict(flag1: Int, flag2: Int) {
        if (sym hasAllFlags flag1.toLong | flag2)
          IllegalModifierCombination(sym, flag1, flag2)
      }
      if (sym.isImplicit) {
        if (sym.isConstructor)
          fail(ImplicitConstr)
        if (!(sym.isTerm || (sym.isClass && !sym.isTrait)))
          fail(ImplicitNotTermOrClass)
        if (sym.isTopLevel)
          fail(ImplicitAtToplevel)
      }
      if (sym.isClass) {
        checkNoConflict(IMPLICIT, CASE)
        if (sym.isAnyOverride && !sym.hasFlag(TRAIT))
          fail(OverrideClass)
      } else {
        if (sym.isSealed)
          fail(SealedNonClass)
        if (sym.hasFlag(ABSTRACT))
          fail(AbstractNonClass)
      }

      if (sym.isConstructor && sym.isAnyOverride)
        fail(OverrideConstr)
      if (sym.isAbstractOverride) {
          if (!sym.owner.isTrait)
            fail(AbstractOverride)
          if(sym.isType)
            fail(AbstractOverrideOnTypeMember)
      }
      if (sym.isLazy && sym.hasFlag(PRESUPER))
        fail(LazyAndEarlyInit)
      if (sym.info.typeSymbol == FunctionClass(0) && sym.isValueParameter && sym.owner.isCaseClass)
        fail(ByNameParameter)
      if (sym.isTrait && sym.isFinal && !sym.isSubClass(AnyValClass))
        checkNoConflict(ABSTRACT, FINAL)

      if (sym.isDeferred) {
        // Is this symbol type always allowed the deferred flag?
        def symbolAllowsDeferred = (
             sym.isValueParameter
          || sym.isTypeParameterOrSkolem
          || context.tree.isInstanceOf[ExistentialTypeTree]
        )
        // Does the symbol owner require no undefined members?
        def ownerRequiresConcrete = (
             !sym.owner.isClass
          ||  sym.owner.isModuleClass
          ||  sym.owner.isAnonymousClass
        )
        if (sym hasAnnotation NativeAttr)
          sym resetFlag DEFERRED
        else if (!symbolAllowsDeferred && ownerRequiresConcrete)
          fail(AbstractVar)

        checkWithDeferred(PRIVATE)
        checkWithDeferred(FINAL)
      }

      checkNoConflict(FINAL, SEALED)
      checkNoConflict(PRIVATE, PROTECTED)
      // checkNoConflict(PRIVATE, OVERRIDE) // this one leads to bad error messages like #4174, so catch in refchecks
      // checkNoConflict(PRIVATE, FINAL)    // can't do this because FINAL also means compile-time constant
      // checkNoConflict(ABSTRACT, FINAL)   // this one gives a bad error for non-@inline classes which extend AnyVal
      // @PP: I added this as a sanity check because these flags are supposed to be
      // converted to ABSOVERRIDE before arriving here.
      checkNoConflict(ABSTRACT, OVERRIDE)
    }
  }

  abstract class TypeCompleter extends LazyType {
    val tree: Tree
  }

  def mkTypeCompleter(t: Tree)(c: Symbol => Unit) = new LockingTypeCompleter with FlagAgnosticCompleter {
    val tree = t
    def completeImpl(sym: Symbol) = c(sym)
  }

  trait LockingTypeCompleter extends TypeCompleter {
    def completeImpl(sym: Symbol): Unit

    override def complete(sym: Symbol) = {
      _lockedCount += 1
      try completeImpl(sym)
      finally _lockedCount -= 1
    }
  }

  /**
   * A class representing a lazy type with known type parameters. `ctx` is the namer context in which the
   * `owner` is defined.
   *
   * Constructing a PolyTypeCompleter for a DefDef creates type skolems for the type parameters and
   * assigns them to the `tparams` trees.
   */
  class PolyTypeCompleter(tparams: List[TypeDef], restp: TypeCompleter, ctx: Context) extends LockingTypeCompleter with FlagAgnosticCompleter {
    // @M. If `owner` is an abstract type member, `typeParams` are all NoSymbol (see comment in `completerOf`),
    // otherwise, the non-skolemized (external) type parameter symbols
    override val typeParams = tparams map (_.symbol)

    /* The definition tree (poly ClassDef, poly DefDef or HK TypeDef) */
    override val tree = restp.tree

    private val defnSym = tree.symbol

    if (defnSym.isTerm) {
      // for polymorphic DefDefs, create type skolems and assign them to the tparam trees.
      val skolems = deriveFreshSkolems(tparams map (_.symbol))
      map2(tparams, skolems)(_ setSymbol _)
    }

    def completeImpl(sym: Symbol) = {
      // @M an abstract type's type parameters are entered.
      // TODO: change to isTypeMember ?
      if (defnSym.isAbstractType)
        newNamer(ctx.makeNewScope(tree, tree.symbol)) enterSyms tparams //@M
      restp complete sym
    }
  }

  // Can we relax these restrictions? For motivation, see
  //    test/files/pos/depmet_implicit_oopsla_session_2.scala
  //    neg/depmet_try_implicit.scala
  //
  // We should allow forward references since type selections on
  // implicit args are like type parameters.
  //    def foo[T](a: T, x: w.T2)(implicit w: ComputeT2[T])
  // is more compact than:
  //    def foo[T, T2](a: T, x: T2)(implicit w: ComputeT2[T, T2])
  // moreover, the latter is not an encoding of the former, which hides type
  // inference of T2, so you can specify T while T2 is purely computed
  private class DependentTypeChecker(ctx: Context)(namer: Namer) extends TypeTraverser {
    private[this] val okParams = mutable.Set[Symbol]()
    private[this] val method   = ctx.owner

    def traverse(tp: Type) = tp match {
      case SingleType(_, sym) =>
        if (sym.owner == method && sym.isValueParameter && !okParams(sym))
          namer.NamerErrorGen.IllegalDependentMethTpeError(sym)(ctx)

      case _ => mapOver(tp)
    }
    def check(vparamss: List[List[Symbol]]) {
      for (vps <- vparamss) {
        for (p <- vps)
          this(p.info)
        // can only refer to symbols in earlier parameter sections
        // (if the extension is enabled)
        okParams ++= vps
      }
    }
  }

  /** The companion class or companion module of `original`.
   *  Calling .companionModule does not work for classes defined inside methods.
   *
   *  !!! Then why don't we fix companionModule? Does the presence of these
   *  methods imply all the places in the compiler calling sym.companionModule are
   *  bugs waiting to be reported? If not, why not? When exactly do we need to
   *  call this method?
   */
  def companionSymbolOf(original: Symbol, ctx: Context): Symbol = {
    val owner = original.owner
    // SI-7264 Force the info of owners from previous compilation runs.
    //         Doing this generally would trigger cycles; that's what we also
    //         use the lower-level scan through the current Context as a fall back.
    if (!currentRun.compiles(owner)) owner.initialize
    original.companionSymbol orElse {
      ctx.lookup(original.name.companionName, owner).suchThat(sym =>
        (original.isTerm || sym.hasModuleFlag) &&
        (sym isCoDefinedWith original)
      )
    }
  }

  /** A version of `Symbol#linkedClassOfClass` that works with local companions, ala `companionSymbolOf`. */
  final def linkedClassOfClassOf(original: Symbol, ctx: Context): Symbol =
    if (original.isModuleClass)
      companionSymbolOf(original.sourceModule, ctx)
    else
      companionSymbolOf(original, ctx).moduleClass
}

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