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

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

package scala.tools.nsc
package typechecker

import scala.collection.{ mutable, immutable }
import mutable.ListBuffer
import symtab.Flags._

/** This phase adds super accessors for all super calls that either
 *  appear in a trait or have as a target a member of some outer class.
 *  It also replaces references to parameter accessors with aliases
 *  by super references to these aliases. The phase also checks that
 *  symbols accessed from super are not abstract, or are overridden by
 *  an abstract override. Finally, the phase also mangles the names
 *  of class-members which are private up to an enclosing non-package
 *  class, in order to avoid overriding conflicts.
 *
 *  @author  Martin Odersky
 *  @version 1.0
 */
abstract class SuperAccessors extends transform.Transform with transform.TypingTransformers {
  import global._
  import definitions.{ UnitClass, ObjectClass, isRepeatedParamType, isByNameParamType, Any_asInstanceOf }
  import analyzer.{ restrictionError }

  /** the following two members override abstract members in Transform */
  val phaseName: String = "superaccessors"

  protected def newTransformer(unit: CompilationUnit): Transformer =
    new SuperAccTransformer(unit)

  class SuperAccTransformer(unit: CompilationUnit) extends TypingTransformer(unit) {
    /** validCurrentOwner arrives undocumented, but I reverse engineer it to be
     *  a flag for needsProtectedAccessor which is false while transforming either
     *  a by-name argument block or a closure.  This excludes them from being
     *  considered able to access protected members via subclassing (why?) which in turn
     *  increases the frequency with which needsProtectedAccessor will be true.
     */
    private var validCurrentOwner = true
    private val accDefs = mutable.Map[Symbol, ListBuffer[Tree]]()
    private def debuglog(msg:  => String): Unit = if (settings.debug.value) log(msg)

    private def storeAccessorDefinition(clazz: Symbol, tree: Tree) = {
      val buf = accDefs.getOrElse(clazz, sys.error("no acc def buf for "+clazz))
      buf += typers(clazz) typed tree
    }
    private def ensureAccessor(sel: Select) = {
      val Select(qual, name) = sel
      val sym                = sel.symbol
      val clazz              = qual.symbol
      val supername          = nme.superName(name)
      val superAcc = clazz.info.decl(supername).suchThat(_.alias == sym) orElse {
        debuglog("add super acc " + sym + sym.locationString + " to `" + clazz);//debug
        val acc = clazz.newMethod(supername, sel.pos).setFlag(SUPERACCESSOR | PRIVATE).setAlias(sym)
        val tpe = clazz.thisType memberType sym match {
          case t if sym.isModule && !sym.isMethod => NullaryMethodType(t)
          case t                                  => t
        }
        acc.setInfo(tpe.cloneInfo(acc))
        clazz.info.decls.enter(acc)
        storeAccessorDefinition(clazz, DefDef(acc, EmptyTree))
        acc
      }

      atPos(sel.pos)(Select(gen.mkAttributedThis(clazz), superAcc) setType sel.tpe)
    }

    private def transformArgs(args: List[Tree], params: List[Symbol]) =
      ((args, params).zipped map { (arg, param) =>
        if (isByNameParamType(param.tpe))
          withInvalidOwner { checkPackedConforms(transform(arg), param.tpe.typeArgs.head) }
        else transform(arg)
      }) :::
      (args drop params.length map transform)

    private def checkPackedConforms(tree: Tree, pt: Type): Tree = {
      if (tree.tpe exists (_.typeSymbol.isExistentialSkolem)) {
        val packed = localTyper.packedType(tree, NoSymbol)
        if (!(packed <:< pt)) {
          val errorContext = localTyper.context.make(localTyper.context.tree)
          errorContext.reportGeneralErrors = true
          analyzer.newTyper(errorContext).infer.typeError(tree.pos, packed, pt)
        }
      }
      tree
    }

    /** Check that a class and its companion object to not both define
     *  a class or module with same name
     */
    private def checkCompanionNameClashes(sym: Symbol) =
      if (!sym.owner.isModuleClass) {
        val linked = sym.owner.linkedClassOfClass
        if (linked != NoSymbol) {
          var other = linked.info.decl(sym.name.toTypeName).filter(_.isClass)
          if (other == NoSymbol)
            other = linked.info.decl(sym.name.toTermName).filter(_.isModule)
          if (other != NoSymbol)
            unit.error(sym.pos, "name clash: "+sym.owner+" defines "+sym+
                       "\nand its companion "+sym.owner.companionModule+" also defines "+
                       other)
        }
      }

    private def transformSuperSelect(sel: Select): Tree = {
      val Select(sup @ Super(_, mix), name) = sel
      val sym   = sel.symbol
      val clazz = sup.symbol

      if (sym.isDeferred) {
        val member = sym.overridingSymbol(clazz);
        if (mix != tpnme.EMPTY || member == NoSymbol ||
            !((member hasFlag ABSOVERRIDE) && member.isIncompleteIn(clazz)))
          unit.error(sel.pos, ""+sym.fullLocationString+" is accessed from super. It may not be abstract "+
                               "unless it is overridden by a member declared `abstract' and `override'");
      }

      // determine if the mix in clazz.super[mix].name is a trait
      def mixTpeIsTrait = sup.tpe match {
        case SuperType(_, mixTpe) => mixTpe.typeSymbol.isTrait
        case _                    =>
          log("Warning: could not determine the type of mix " + mix + " by going through a Super node's "+
              "type because instead of a SuperType it was " + sup.tpe)
          false
      }

      // we need an accessor to get to a super on an outer thing, but only if we can't call name more directly on
      // a trait implementation class. So this complicated condition is leaving alone cases where we don't need to do
      // anything special (i.e. we're getting a direct super class) or where a later transform will inject a call to
      // a trait implementation method directly.
      //
      // SI-6536 has more discussion about how this works.
      //
      // So, we're looking for items of the form clazz.super[mix].name (or clazz.super.name wich is seen as
      // clazz.super[EMPTY].name with some limitations. First, name has to be a term rather than a type.
      // Then there are a couple of cases.
      def requiresAccessor = name.isTermName && (mix match {
        // If mix is empty then we only need an accessor if clazz is a trait, it's not this current class,
        // or the validCurentOwner setting is false...which...ugh, is a mess.
        case tpnme.EMPTY => clazz.isTrait || clazz != currentClass || !validCurrentOwner
        // If the mix is set then if it refers to a class and the clazz part isn't the current class
        // it's not just super[mix].name then we need to generate an accessor.
        case _           => clazz != currentClass && !mixTpeIsTrait
      })

      if (requiresAccessor) ensureAccessor(sel)
      else sel
    }

    // Disallow some super.XX calls targeting Any methods which would
    // otherwise lead to either a compiler crash or runtime failure.
    private lazy val isDisallowed = {
      import definitions._
      Set(Any_isInstanceOf, Object_isInstanceOf, Any_asInstanceOf, Object_asInstanceOf, Object_==, Object_!=, Object_##)
    }

    override def transform(tree: Tree): Tree = {
      val sym = tree.symbol

      def mayNeedProtectedAccessor(sel: Select, args: List[Tree], goToSuper: Boolean) =
        if (needsProtectedAccessor(sym, tree.pos)) {
          debuglog("Adding protected accessor for " + tree)

          transform(makeAccessor(sel, args))
        }
        else if (goToSuper) super.transform(tree)
        else tree

      try tree match {
        // Don't transform patterns or strange trees will reach the matcher (ticket #4062)
        case CaseDef(pat, guard, body) =>
          treeCopy.CaseDef(tree, pat, transform(guard), transform(body))

        case ClassDef(_, _, _, _) =>
          checkCompanionNameClashes(sym)
          val decls = sym.info.decls
          for (s <- decls) {
            if (s.privateWithin.isClass && !s.isProtected && !s.privateWithin.isModuleClass &&
                !s.hasFlag(EXPANDEDNAME) && !s.isConstructor) {
              val savedName = s.name
              decls.unlink(s)
              s.expandName(s.privateWithin)
              decls.enter(s)
              log("Expanded '%s' to '%s' in %s".format(savedName, s.name, sym))
            }
          }
          if (settings.verbose.value && forScaladoc && !sym.isAnonymousClass) {
            println("========== scaladoc of "+sym+" =============================")
            println(toJavaDoc(expandedDocComment(sym)))
            for (member <- sym.info.members) {
              println(member+":"+sym.thisType.memberInfo(member)+"\n"+
                      toJavaDoc(expandedDocComment(member, sym)))
              for ((useCase, comment, pos) <- useCases(member, sym)) {
                println("usecase "+useCase+":"+useCase.info)
                println(toJavaDoc(comment))
              }
            }
          }
          super.transform(tree)
        case ModuleDef(_, _, _) =>
          checkCompanionNameClashes(sym)
          super.transform(tree)
        case Template(parents, self, body) =>
          val ownAccDefs = new ListBuffer[Tree]
          accDefs(currentOwner) = ownAccDefs

          // ugly hack... normally, the following line should not be
          // necessary, the 'super' method taking care of that. but because
          // that one is iterating through parents (and we dont want that here)
          // we need to inline it.
          curTree = tree
          val body1 = atOwner(currentOwner)(transformTrees(body))
          accDefs -= currentOwner
          ownAccDefs ++= body1
          treeCopy.Template(tree, parents, self, ownAccDefs.toList)

        case TypeApply(sel @ Select(This(_), name), args) =>
          mayNeedProtectedAccessor(sel, args, false)

        case sel @ Select(qual @ This(_), name) =>
          // warn if they are selecting a private[this] member which
          // also exists in a superclass, because they may be surprised
          // to find out that a constructor parameter will shadow a
          // field. See SI-4762.
          if (settings.lint.value) {
            if (sym.isPrivateLocal && sym.paramss.isEmpty) {
              qual.symbol.ancestors foreach { parent =>
                parent.info.decls filterNot (x => x.isPrivate || x.hasLocalFlag) foreach { m2 =>
                  if (sym.name == m2.name && m2.isGetter && m2.accessed.isMutable) {
                    unit.warning(sel.pos,
                        sym.fullLocationString + " shadows mutable " + m2.name
                      + " inherited from " + m2.owner + ".  Changes to " + m2.name + " will not be visible within "
                      + sym.owner + " - you may want to give them distinct names."
                    )
                  }
                }
              }
            }
          }

          // direct calls to aliases of param accessors to the superclass in order to avoid
          // duplicating fields.
          if (sym.isParamAccessor && sym.alias != NoSymbol) {
            val result = (localTyper.typedPos(tree.pos) {
              Select(Super(qual, tpnme.EMPTY) setPos qual.pos, sym.alias)
            }).asInstanceOf[Select]
            debuglog("alias replacement: " + tree + " ==> " + result);//debug
            localTyper.typed(gen.maybeMkAsInstanceOf(transformSuperSelect(result), sym.tpe, sym.alias.tpe, true))
          }
          else {
            /** A trait which extends a class and accesses a protected member
             *  of that class cannot implement the necessary accessor method
             *  because its implementation is in an implementation class (e.g.
             *  Foo$class) which inherits nothing, and jvm access restrictions
             *  require the call site to be in an actual subclass. So non-trait
             *  classes inspect their ancestors for any such situations and
             *  generate the accessors.  See SI-2296.
             */
            // FIXME - this should be unified with needsProtectedAccessor, but some
            // subtlety which presently eludes me is foiling my attempts.
            val shouldEnsureAccessor = (
                 currentClass.isTrait
              && sym.isProtected
              && sym.enclClass != currentClass
              && !sym.owner.isTrait
              && (sym.owner.enclosingPackageClass != currentPackage)
              && (qual.symbol.info.member(sym.name) ne NoSymbol)
              && !needsProtectedAccessor(sym, tree.pos)
            )
            if (shouldEnsureAccessor) {
              log("Ensuring accessor for call to protected " + sym.fullLocationString + " from " + currentClass)
              ensureAccessor(sel)
            }
            else
              mayNeedProtectedAccessor(sel, List(EmptyTree), false)
          }

        case sel @ Select(Super(_, mix), name) =>
          if (sym.isValue && !sym.isMethod || sym.hasAccessorFlag) {
            unit.error(tree.pos, "super may be not be used on "+
                       (if (sym.hasAccessorFlag) sym.accessed else sym))
          }
          else if (isDisallowed(sym)) {
            unit.error(tree.pos, "super not allowed here: use this." + name.decode + " instead")
          }
          transformSuperSelect(sel)

        case TypeApply(sel @ Select(qual, name), args) =>
          mayNeedProtectedAccessor(sel, args, true)

        case sel @ Select(qual, name) =>
          mayNeedProtectedAccessor(sel, List(EmptyTree), true)

        case Assign(lhs @ Select(qual, name), rhs) =>
          if (lhs.symbol.isVariable &&
              lhs.symbol.isJavaDefined &&
              needsProtectedAccessor(lhs.symbol, tree.pos)) {
            debuglog("Adding protected setter for " + tree)
            val setter = makeSetter(lhs);
            debuglog("Replaced " + tree + " with " + setter);
            transform(localTyper.typed(Apply(setter, List(qual, rhs))))
          } else
            super.transform(tree)

        case Apply(fn, args) =>
          assert(fn.tpe != null, tree)
          treeCopy.Apply(tree, transform(fn), transformArgs(args, fn.tpe.params))
        case Function(vparams, body) =>
          withInvalidOwner {
            treeCopy.Function(tree, vparams, transform(body))
          }
        case _ =>
          super.transform(tree)
      }
      catch {
        case ex : AssertionError =>
          if (sym != null && sym != NoSymbol)
            Console.println("TRANSFORM: " + tree.symbol.sourceFile)

          Console.println("TREE: " + tree)
          throw ex
      }
    }

    override def atOwner[A](owner: Symbol)(trans: => A): A = {
      if (owner.isClass) validCurrentOwner = true
      super.atOwner(owner)(trans)
    }

    private def withInvalidOwner[A](trans: => A): A = {
      val saved = validCurrentOwner
      validCurrentOwner = false
      try trans
      finally validCurrentOwner = saved
    }

    /** Add a protected accessor, if needed, and return a tree that calls
     *  the accessor and returns the same member. The result is already
     *  typed.
     */
    private def makeAccessor(tree: Select, targs: List[Tree]): Tree = {
      val Select(qual, name) = tree
      val sym = tree.symbol
      val clazz = hostForAccessorOf(sym, currentClass)

      /** Return a list of list of types of all value parameter sections. */
      def allParamTypes(tpe: Type): List[List[Type]] = tpe match {
        case PolyType(_, restpe) => allParamTypes(restpe)
        case MethodType(params, res) => params.map(_.tpe) :: allParamTypes(res)
        case _ => Nil
      }


      assert(clazz != NoSymbol, sym)
      debuglog("Decided for host class: " + clazz)

      val accName    = nme.protName(sym.originalName)
      val hasArgs    = sym.tpe.paramSectionCount > 0
      val memberType = refchecks.toScalaRepeatedParam(sym.tpe) // fix for #2413

      // if the result type depends on the this type of an enclosing class, the accessor
      // has to take an object of exactly this type, otherwise it's more general
      val objType = if (isThisType(memberType.finalResultType)) clazz.thisType else clazz.typeOfThis
      val accType = (protAcc: Symbol) => memberType match {
        case PolyType(tparams, restpe) =>
          // luc: question to author: should the tparams symbols not be cloned and get a new owner (protAcc)?
          PolyType(tparams, MethodType(List(protAcc.newSyntheticValueParam(objType)),
                                       restpe.cloneInfo(protAcc).asSeenFrom(qual.tpe, sym.owner)))
        case _ =>
          MethodType(List(protAcc.newSyntheticValueParam(objType)),
                     memberType.cloneInfo(protAcc).asSeenFrom(qual.tpe, sym.owner))
      }

      val protAcc = clazz.info.decl(accName).suchThat(s => s == NoSymbol || s.tpe =:= accType(s)) orElse {
        val newAcc = clazz.newMethod(nme.protName(sym.originalName), tree.pos)
        newAcc.setInfo(accType(newAcc))
        clazz.info.decls.enter(newAcc)

        val code = DefDef(newAcc, {
          val (receiver :: _) :: tail = newAcc.paramss
          val base: Tree              = Select(Ident(receiver), sym)
          val args = (tail, allParamTypes(sym.info)).zipped.map((params, tpes) => (params, tpes).zipped.map(makeArg(_, receiver, _)))
          args.foldLeft(base)(Apply(_, _))
        })

        debuglog("" + code)
        storeAccessorDefinition(clazz, code)
        newAcc
      }
      val selection = Select(This(clazz), protAcc)
      def mkApply(fn: Tree) = Apply(fn, qual :: Nil)
      val res = atPos(tree.pos) {
        targs.head match {
          case EmptyTree  => mkApply(selection)
          case _          => mkApply(TypeApply(selection, targs))
        }
      }
      debuglog("Replaced " + tree + " with " + res)
      if (hasArgs) localTyper.typedOperator(res) else localTyper.typed(res)
    }

    /** Adapt the given argument in call to protected member.
     *  Adaptation may add a cast to a path-dependent type, for instance
     *
     *  def prot$m(obj: Outer)(x: Inner) = obj.m(x.asInstanceOf[obj.Inner]).
     *
     *  such a cast might be necessary when m expects an Outer.this.Inner (the
     *  outer of 'obj' and 'x' have to be the same). This restriction can't be
     *  expressed in the type system (but is implicit when defining method m).
     *
     *  Also, it calls using repeated parameters are ascribed with ': _*'
     */
    private def makeArg(v: Symbol, obj: Symbol, pt: Type): Tree = {
      // owner class
      val clazz = pt match {
        case TypeRef(pre, _, _) => thisTypeOfPath(pre)
        case _                  => NoSymbol
      }
      val result = gen.paramToArg(v)
      if (clazz != NoSymbol && (obj.tpe.typeSymbol isSubClass clazz)) // path-dependent type
        gen.mkAsInstanceOf(result, pt.asSeenFrom(singleType(NoPrefix, obj), clazz))
      else
        result
    }

    /** Add an accessor for field, if needed, and return a selection tree for it .
     *  The result is not typed.
     */
    private def makeSetter(tree: Select): Tree = {
      val field = tree.symbol
      val clazz = hostForAccessorOf(field, currentClass)
      assert(clazz != NoSymbol, field)
      debuglog("Decided for host class: " + clazz)

      val accName = nme.protSetterName(field.originalName)
      val protectedAccessor = clazz.info decl accName orElse {
        val protAcc      = clazz.newMethod(accName, field.pos)
        val paramTypes   = List(clazz.typeOfThis, field.tpe)
        val params       = protAcc newSyntheticValueParams paramTypes
        val accessorType = MethodType(params, UnitClass.tpe)

        protAcc.setInfo(accessorType)
        clazz.info.decls.enter(protAcc)
        val obj :: value :: Nil = params
        storeAccessorDefinition(clazz, DefDef(protAcc, Assign(Select(Ident(obj), field.name), Ident(value))))

        protAcc
      }
      atPos(tree.pos)(Select(This(clazz), protectedAccessor))
    }

    /** Does `sym` need an accessor when accessed from `currentClass`?
     *  A special case arises for classes with explicit self-types. If the
     *  self type is a Java class, and a protected accessor is needed, we issue
     *  an error. If the self type is a Scala class, we don't add an accessor.
     *  An accessor is not needed if the access boundary is larger than the
     *  enclosing package, since that translates to 'public' on the host sys.
     *  (as Java has no real package nesting).
     *
     * If the access happens inside a 'trait', access is more problematic since
     * the implementation code is moved to an '$class' class which does not
     * inherit anything. Since we can't (yet) add accessors for 'required'
     * classes, this has to be signaled as error.
     */
    private def needsProtectedAccessor(sym: Symbol, pos: Position): Boolean = {
      val clazz = currentClass
      def accessibleThroughSubclassing =
        validCurrentOwner && clazz.thisSym.isSubClass(sym.owner) && !clazz.isTrait

      def packageAccessBoundry(sym: Symbol) =
        sym.accessBoundary(sym.enclosingPackageClass)

      val isCandidate = (
           sym.isProtected
        && sym.isJavaDefined
        && !sym.definedInPackage
        && !accessibleThroughSubclassing
        && (sym.enclosingPackageClass != currentPackage)
        && (sym.enclosingPackageClass == sym.accessBoundary(sym.enclosingPackageClass))
      )
      val host = hostForAccessorOf(sym, clazz)
      def isSelfType = !(host.tpe <:< host.typeOfThis) && {
        if (host.typeOfThis.typeSymbol.isJavaDefined)
          restrictionError(pos, unit,
            "%s accesses protected %s from self type %s.".format(clazz, sym, host.typeOfThis)
          )
        true
      }
      def isJavaProtected = host.isTrait && sym.isJavaDefined && {
        restrictionError(pos, unit,
          """|%s accesses protected %s inside a concrete trait method.
             |Add an accessor in a class extending %s as a workaround.""".stripMargin.format(
                clazz, sym, sym.enclClass)
        )
        true
      }
      isCandidate && !host.isPackageClass && !isSelfType && !isJavaProtected
    }

    /** Return the innermost enclosing class C of referencingClass for which either
     *  of the following holds:
     *     - C is a subclass of sym.owner or
     *     - C is declared in the same package as sym's owner
     */
    private def hostForAccessorOf(sym: Symbol, referencingClass: Symbol): Symbol = {
      if (referencingClass.isSubClass(sym.owner.enclClass)
          || referencingClass.thisSym.isSubClass(sym.owner.enclClass)
          || referencingClass.enclosingPackageClass == sym.owner.enclosingPackageClass) {
        assert(referencingClass.isClass, referencingClass)
        referencingClass
      } else if(referencingClass.owner.enclClass != NoSymbol)
        hostForAccessorOf(sym, referencingClass.owner.enclClass)
      else referencingClass
    }

    /** For a path-dependent type, return the this type. */
    private def thisTypeOfPath(path: Type): Symbol = path match {
      case ThisType(outerSym)  => outerSym
      case SingleType(rest, _) => thisTypeOfPath(rest)
      case _                   => NoSymbol
    }

    /** Is 'tpe' the type of a member of an enclosing class? */
    private def isThisType(tpe: Type): Boolean = tpe match {
      case ThisType(sym)           => sym.isClass && !sym.isPackageClass
      case TypeRef(pre, _, _)      => isThisType(pre)
      case SingleType(pre, _)      => isThisType(pre)
      case RefinedType(parents, _) => parents exists isThisType
      case AnnotatedType(_, tp, _) => isThisType(tp)
      case _                       => false
    }
  }
}