alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Scala example source code file (SuperAccessors.scala)

This example Scala source code file (SuperAccessors.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Scala tags/keywords

a, apply, list, list, nosymbol, nosymbol, object_, polytype, select, select, symbol, tree, tree, type

The Scala SuperAccessors.scala source code

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

package scala.tools.nsc
package typechecker

import scala.collection.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 {
  // inherits abstract value `global' and class `Phase' from Transform

  import global._
  import definitions.{ UnitClass, 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) {
    private var validCurrentOwner = true
    private var accDefs: List[(Symbol, ListBuffer[Tree])] = List()
    
    private def accDefBuf(clazz: Symbol) = 
      accDefs collectFirst { case (`clazz`, buf) => buf } getOrElse sys.error("no acc def buf for "+clazz)

    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(tree: Tree): Tree = tree match {
      case Select(sup @ Super(_, mix), name)  =>
        val sym = tree.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(tree.pos, ""+sym+sym.locationString+" is accessed from super. It may not be abstract "+
                                 "unless it is overridden by a member declared `abstract' and `override'");
        }
        if (tree.isTerm && mix == tpnme.EMPTY && 
            (clazz.isTrait || clazz != currentOwner.enclClass || !validCurrentOwner)) {
          val supername = nme.superName(sym.name)
          var superAcc = clazz.info.decl(supername).suchThat(_.alias == sym)
          if (superAcc == NoSymbol) {
            if (settings.debug.value) log("add super acc " + sym + sym.locationString + " to `" + clazz);//debug
            superAcc = 
              clazz.newMethod(tree.pos, supername)
                .setFlag(SUPERACCESSOR | PRIVATE)
                .setAlias(sym)
            var superAccTpe = clazz.thisType.memberType(sym) 
            if (sym.isModule && !sym.isMethod) {
              // the super accessor always needs to be a method. See #231
              superAccTpe = NullaryMethodType(superAccTpe)
            }
            superAcc.setInfo(superAccTpe.cloneInfo(superAcc))
            //println("creating super acc "+superAcc+":"+superAcc.tpe)//DEBUG
            clazz.info.decls enter superAcc;
            accDefBuf(clazz) += typers(clazz).typed(DefDef(superAcc, EmptyTree))
          }
          atPos(sup.pos) {
            Select(gen.mkAttributedThis(clazz), superAcc) setType tree.tpe;
          }
        } else {
          tree
        }
      case _ =>
        assert(tree.tpe.isError, tree)
        tree
    }

    // 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)) {
          if (settings.debug.value)
            log("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.toList) {
            if (s.privateWithin.isClass && !s.privateWithin.isModuleClass &&
                !s.hasFlag(EXPANDEDNAME) && !s.isConstructor) {
              decls.unlink(s)
              s.expandName(s.privateWithin)
              decls.enter(s)
            }
          }
          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) :: accDefs;
        
          // 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 = accDefs.tail;
          treeCopy.Template(tree, parents, self, ownAccDefs.toList ::: body1)
          
        case TypeApply(sel @ Select(This(_), name), args) =>
          mayNeedProtectedAccessor(sel, args, false)
      
        case sel @ Select(qual @ This(_), name) => 
           // 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.typed {
                Select(
                  Super(qual, tpnme.EMPTY/*qual.symbol.info.parents.head.symbol.name*/) setPos qual.pos,
                  sym.alias) setPos tree.pos
            }
            if (settings.debug.value) 
              log("alias replacement: " + tree + " ==> " + result);//debug
            localTyper.typed(gen.maybeMkAsInstanceOf(transformSuperSelect(result), sym.tpe, sym.alias.tpe, true))
          }
          else mayNeedProtectedAccessor(sel, List(EmptyTree), false)

        case 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(tree)
      
        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)) {
            if (settings.debug.value) log("Adding protected setter for " + tree)
            val setter = makeSetter(lhs);
            if (settings.debug.value)
              log("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 prevValidCurrentOwner = validCurrentOwner
      validCurrentOwner = false
      val result = trans
      validCurrentOwner = prevValidCurrentOwner
      result
    }
    
    /** Add a protected accessor, if needed, and return a tree that calls
     *  the accessor and returns the 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, currentOwner.enclClass)
          
      /** 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)
      if (settings.debug.value)  log("Decided for host class: " + clazz)

      val accName = nme.protName(sym.originalName)
      val hasArgs = sym.tpe.paramTypes != Nil
      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))
      }
        
      var protAcc = clazz.info.decl(accName).suchThat(s => s == NoSymbol || s.tpe =:= accType(s))
      if (protAcc == NoSymbol) { 
        protAcc = clazz.newMethod(tree.pos, nme.protName(sym.originalName))
        protAcc.setInfo(accType(protAcc))
        clazz.info.decls.enter(protAcc);
        val code = DefDef(protAcc, {
          val obj = protAcc.paramss.head.head // receiver
          protAcc.paramss.tail.zip(allParamTypes(sym.tpe)).foldLeft(Select(Ident(obj), sym): Tree) (
              (fun, pvparams) => {
                Apply(fun, (pvparams._1, pvparams._2).zipped map (makeArg(_, obj, _)))
              })
        })

        if (settings.debug.value)
          log(code)
        accDefBuf(clazz) += typers(clazz).typed(code)
      }
      var res: Tree = atPos(tree.pos) {
        if (targs.head == EmptyTree) 
          Apply(Select(This(clazz), protAcc), List(qual))
        else
          Apply(TypeApply(Select(This(clazz), protAcc), targs), List(qual))
      }
      if (settings.debug.value)
        log("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, expectedTpe: Type): Tree = {
      var res: Tree = Ident(v)
      val sym = obj.tpe.typeSymbol
      var ownerClass: Symbol = NoSymbol
      
      val isDependentType = expectedTpe match {
        case TypeRef(path, _, _) => 
          ownerClass = thisTypeOfPath(path)
          if (sym.isSubClass(ownerClass)) true else false 
        case _ => false
      }
      if (isRepeatedParamType(v.info)) {
        res = gen.wildcardStar(res)
        log("adapted to wildcard star: " + res)
      }
      if (isDependentType) {
        val preciseTpe = expectedTpe.asSeenFrom(singleType(NoPrefix, obj), ownerClass) //typeRef(singleType(NoPrefix, obj), v.tpe.symbol, List())
        TypeApply(Select(res, Any_asInstanceOf), 
                  List(TypeTree(preciseTpe)))
      } else res
    }
    
    /** 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
    }
    
    /** 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, currentOwner.enclClass)
      assert(clazz != NoSymbol, field)
      if (settings.debug.value)
        log("Decided for host class: " + clazz)
      val accName = nme.protSetterName(field.originalName)
      var protAcc = clazz.info.decl(accName)
      if (protAcc == NoSymbol) {
        protAcc = clazz.newMethod(field.pos, nme.protSetterName(field.originalName))
        protAcc.setInfo(MethodType(protAcc.newSyntheticValueParams(List(clazz.typeOfThis, field.tpe)),
                                   UnitClass.tpe))
        clazz.info.decls.enter(protAcc)
        val code = DefDef(protAcc, {
          val obj :: value :: Nil = protAcc.paramss.head;
          atPos(tree.pos) {
            Assign(
              Select(Ident(obj), field.name),
              Ident(value))
          }              
        })
        if (settings.debug.value)
          log(code);
        accDefBuf(clazz) += typers(clazz).typed(code)
      }
      var res: Tree = atPos(tree.pos) { Select(This(clazz), protAcc) }
      res
    }
        
    /** Does `sym' need an accessor when accessed from `currentOwner'? 
     *  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 = currentOwner.enclClass
      def accessibleThroughSubclassing =
        validCurrentOwner && clazz.thisSym.isSubClass(sym.owner) && !clazz.isTrait

      def packageAccessBoundry(sym: Symbol) = {
        val b = sym.accessBoundary(sym.owner)
        if (b.isPackageClass) b
        else b.enclosingPackageClass
      }

      val isCandidate = (
           sym.isProtected
        && sym.isJavaDefined
        && !sym.definedInPackage
        && !accessibleThroughSubclassing
        && (sym.owner.enclosingPackageClass != currentOwner.enclosingPackageClass)
        && (sym.owner.enclosingPackageClass == packageAccessBoundry(sym))
      )
      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
      } else if(referencingClass.owner.enclClass != NoSymbol)
        hostForAccessorOf(sym, referencingClass.owner.enclClass)
      else referencingClass
    }
    
    /** 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(pref, _, _) => isThisType(pref)
      case SingleType(pref, _) => isThisType(pref)
      case RefinedType(parents, defs) =>
        parents.exists(isThisType(_)) 
      case AnnotatedType(_, tp, _) =>
        isThisType(tp)
      case _ => false
    }
  }
}

Other Scala examples (source code examples)

Here is a short list of links related to this Scala SuperAccessors.scala source code file:

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.