mixin.scala

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/* NSC -- new Scala compiler
 * Copyright 2005-2007 LAMP/EPFL
 * @author Martin Odersky
 */
// $Id: Mixin.scala 14106 2008-02-22 13:24:21Z odersky $

package scala.tools.nsc.transform

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

abstract class Mixin extends InfoTransform {
  import global._
  import definitions._
  import posAssigner.atPos

  /** The name of the phase: */
  val phaseName: String = "mixin"

  /** The phase might set the fiollowing new flags: */
  override def phaseNewFlags: Long = lateMODULE | notABSTRACT

  /** This map contains a binding (class -> info) if
   *  the class with this info at phase mixinPhase has been treated for mixin composition 
   */
  private val treatedClassInfos = collection.mutable.Map[Symbol, Type]()

// --------- helper functions -----------------------------------------------

  /** A member of a trait is implemented statically if its implementation after the
   *  mixin transform is in the static implementation module. To be statically
   *  implemented, a member must be a method that belonged to the trait's implementation class
   *  before (e.g. it is not abstract). Not statically implemented are
   *   - non-private modules: these are implemented directly in the mixin composition class
   *     (private modules, on the other hand, are implemented statically, but their
   *      module variable is not. all such private modules are lifted, because 
   *      non-lifted private modules have been eliminated in ExplicitOuter)
   *   - field accessors and superaccessors, except for lazy value accessors which become initializer
   *     methods in the impl class (because they can have arbitrary initializers)
   */
  private def isImplementedStatically(sym: Symbol) =
    sym.owner.isImplClass && sym.isMethod &&
    (!sym.isModule || sym.hasFlag(PRIVATE | LIFTED)) &&
    (!(sym hasFlag (ACCESSOR | SUPERACCESSOR)) || sym.hasFlag(LAZY))

  /** A member of a trait is static only if it belongs only to the
   *  implementation class, not the interface, and it is implemented
   *  statically.
   */
  private def isStaticOnly(sym: Symbol) =
    isImplementedStatically(sym) && sym.isImplOnly

  /** A member of a trait is forwarded if it is implemented statically and it
   *  is also visible in the trait's interface. In that case, a forwarder to
   *  the member's static implementation will be added to the class that
   *  inherits the trait.
   */
  private def isForwarded(sym: Symbol) =
    isImplementedStatically(sym) && !sym.isImplOnly

  /** Maps the type of an implementation class to its interface;
   *  maps all other types to themselves.
   */
  private def toInterface(tp: Type): Type =
    atPhase(currentRun.mixinPhase)(tp.typeSymbol.toInterface).tpe

  /** Maps all parts of this type that refer to implementation classes to
   *  their corresponding interfaces.
   */
  private val toInterfaceMap = new TypeMap {
    def apply(tp: Type): Type = mapOver( tp match {
      case TypeRef(pre, sym, args) if (sym.isImplClass) =>
        typeRef(pre, atPhase(currentRun.mixinPhase)(sym.toInterface), args)
      case _ => tp
    })
  }

  /** The implementation class corresponding to a currently compiled interface.
   *  todo: try to use Symbol.implClass instead?
   */
  private def implClass(iface: Symbol): Symbol = {
    val impl = iface.implClass
    if (impl != NoSymbol) impl else erasure.implClass(iface)
  }

  /** Returns the symbol that is accessed by a super-accessor in a mixin composition.
   *
   *  @param base       The class in mwhich everything is mixed together
   *  @param member     The symbol statically referred to by the superaccessor in the trait
   *  @param mixinClass The mixin class that produced the superaccessor
   */
  private def rebindSuper(base: Symbol, member: Symbol, mixinClass: Symbol): Symbol =
    atPhase(currentRun.refchecksPhase) {
      var bcs = base.info.baseClasses.dropWhile(mixinClass !=).tail
      var sym: Symbol = NoSymbol
      if (settings.debug.value)
        log("starting rebindsuper " + base + " " + member + ":" + member.tpe +
            " " + mixinClass + " " + base.info.baseClasses)
      while (!bcs.isEmpty && sym == NoSymbol) {
        if (settings.debug.value) {
          val other = bcs.head.info.nonPrivateDecl(member.name);
          log("rebindsuper " + bcs.head + " " + other + " " + other.tpe +
              " " + other.isDeferred)
        }
        sym = member.overridingSymbol(bcs.head).suchThat(sym => !sym.hasFlag(DEFERRED | BRIDGE))
        bcs = bcs.tail
      }
      assert(sym != NoSymbol, member)
      sym
    }

// --------- type transformation -----------------------------------------------

  /** Add given member to given class, and mark member as mixed-in.
   */
  def addMember(clazz: Symbol, member: Symbol): Symbol = {
    if (settings.debug.value) log("new member of " + clazz + ":" + member.defString)
    clazz.info.decls enter member
    member setFlag MIXEDIN
  }

  /** Add getters and setters for all non-module fields of an implementation
   *  class to its interface unless they are already present. This is done
   *  only once per class. The mixedin flag is used to remember whether late
   *  members have been added to an interface.
   *    - lazy fields don't get a setter.
   *  
   *  @param clazz ...
   */
  def addLateInterfaceMembers(clazz: Symbol) {
    if ((treatedClassInfos get clazz) != Some(clazz.info)) {
      treatedClassInfos(clazz) = clazz.info
      assert(phase == currentRun.mixinPhase)

      /** Create a new getter. Getters are never private or local. They are
       *  always accessors and deferred. */
      def newGetter(field: Symbol): Symbol =
        clazz.newMethod(field.pos, nme.getterName(field.name))
          .setFlag(field.flags & ~(PRIVATE | LOCAL) | ACCESSOR | lateDEFERRED)
          .setInfo(MethodType(List(), field.info))

      /** Create a new setter. Setters are never private or local. They are
       *  always accessors and deferred. */
      def newSetter(field: Symbol): Symbol =
        clazz.newMethod(field.pos, nme.getterToSetter(nme.getterName(field.name)))
          .setFlag(field.flags & ~(PRIVATE | LOCAL) | ACCESSOR | lateDEFERRED)
          .setInfo(MethodType(List(field.info), UnitClass.tpe))

      clazz.info // make sure info is up to date, so that implClass is set.
      val impl = implClass(clazz)
      assert(impl != NoSymbol)

      for (val member <- impl.info.decls.toList) {
        if (!member.isMethod && !member.isModule && !member.isModuleVar) {
          assert(member.isTerm && !member.isDeferred, member)
          if (member.getter(impl) hasFlag PRIVATE) {
            member.makeNotPrivate(clazz) // this will also make getter&setter not private
          }
          val getter = member.getter(clazz)
          if (getter == NoSymbol) addMember(clazz, newGetter(member))
          if (!member.tpe.isInstanceOf[ConstantType] && !member.hasFlag(LAZY)) {
            val setter = member.setter(clazz)
            if (setter == NoSymbol) addMember(clazz, newSetter(member))
          }
        }
      }
      if (settings.debug.value) log("new defs of " + clazz + " = " + clazz.info.decls);
    }
  }

  /** Map a lazy, mixedin field accessor to it's trait member accessor */
  val initializer = new HashMap[Symbol, Symbol]
  
  /** Add all members to be mixed in into a (non-trait-) class
   *  These are:
   *    for every mixin trait T that is not also inherited by the superclass:
   *     add late interface members to T and then:
   *      - if a member M of T is forwarded to the implementation class, add
   *        a forwarder for M unless one exists already.
   *        The alias of the forwarder is the static member it forwards to.
   *      - for every abstract accessor in T, add a field and an implementation for that acessor
   *      - for every super accessor in T, add an implementation of that accessor
   *      - for every module in T, add a module
   */
  def addMixedinMembers(clazz: Symbol) {
    if (!(clazz hasFlag JAVA) && (treatedClassInfos get clazz) != Some(clazz.info)) {
      treatedClassInfos(clazz) = clazz.info

      assert(!clazz.isTrait, clazz)
      assert(!clazz.info.parents.isEmpty, clazz)

      // first complete the superclass with mixed in members
      addMixedinMembers(clazz.superClass)

      //Console.println("adding members of " + clazz.info.baseClasses.tail.takeWhile(superclazz !=) + " to " + clazz);//DEBUG

      /** Mix in members of implementation class mixinClass into class clazz */
      def mixinImplClassMembers(impl: Symbol, iface: Symbol) {
        assert (impl.isImplClass)
        for (val member <- impl.info.decls.toList) {
          if (isForwarded(member)) {
            val imember = member.overriddenSymbol(iface)
            //Console.println("mixin member "+member+":"+member.tpe+member.locationString+" "+imember+" "+imember.overridingSymbol(clazz)+" to "+clazz+" with scope "+clazz.info.decls)//DEBUG
            if (imember.overridingSymbol(clazz) == NoSymbol &&
                clazz.info.findMember(member.name, 0, lateDEFERRED, false).alternatives.contains(imember)) {
                  val member1 = addMember(
                    clazz,
                    member.cloneSymbol(clazz) setPos clazz.pos resetFlag (DEFERRED | lateDEFERRED))
                  member1.asInstanceOf[TermSymbol] setAlias member;
                }
          }
        }
      }

      /** Mix in members of trait mixinClass into class clazz. Also,
       *  for each lazy field in mixinClass, add a link from its mixed in member to it's 
       *  initializer method inside the implclass.
       */
      def mixinTraitMembers(mixinClass: Symbol) {
        // For all members of a trait's interface do:
        def isConcreteAccessor(member: Symbol) = 
          (member hasFlag ACCESSOR) && 
          (!(member hasFlag DEFERRED) || (member hasFlag lateDEFERRED))
        def isOverridden(member: Symbol) =
          isConcreteAccessor(member.overridingSymbol(clazz))
        for (val member <- mixinClass.info.decls.toList) {
          if (isConcreteAccessor(member)) {
            if (isOverridden(member)) {
              if (settings.debug.value) println("!!! is overridden val: "+member)
            } else {
              // mixin field accessors
              val member1 = addMember(
                clazz,
                member.cloneSymbol(clazz)
                  setPos clazz.pos
                  setFlag FINAL resetFlag (DEFERRED | lateDEFERRED))
              if (member.hasFlag(LAZY)) {
                var init = implClass(mixinClass).info.decl(member.name)
                assert(init != NoSymbol, "Could not find initializer for " + member.name)
                initializer(member1) = init
              }
              if (!member.isSetter)
                member.tpe match {
                  case MethodType(List(), ConstantType(_)) =>
                    // member is a constant; only getter is needed
                    ;
                  case MethodType(List(), TypeRef(_, tpeSym, _))
                    if member.hasFlag(LAZY) && tpeSym == definitions.UnitClass =>
                    // member is a lazy value of type unit. No field needed
                    ;
                  case _ =>
                    // otherwise mixin a field as well
                    addMember(clazz,
                              clazz.newValue(member.pos, nme.getterToLocal(member.name))
                              setFlag (LOCAL | PRIVATE | member.getFlag(MUTABLE | LAZY))
                              setFlag (if (!member.hasFlag(STABLE)) MUTABLE else 0)
                              setInfo member.tpe.resultType
                              setAttributes member.attributes)
                }
            }
          } else if (member hasFlag SUPERACCESSOR) { // mixin super accessors
            val member1 = addMember(clazz, member.cloneSymbol(clazz)) setPos clazz.pos
            assert(member1.alias != NoSymbol, member1)
            val alias1 = rebindSuper(clazz, member.alias, mixinClass)
            member1.asInstanceOf[TermSymbol] setAlias alias1

          } else if (member.isMethod && member.isModule && !(member hasFlag (LIFTED | BRIDGE))) {
            // mixin objects: todo what happens with abstract objects?
            addMember(clazz, member.cloneSymbol(clazz))
              .setPos(clazz.pos)