New scheme for recording positions

Single traverser, also handles lazy trees.

1 files changed, 695 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/core/pickling/TreeUnpickler.scala b/src/dotty/tools/dotc/core/pickling/TreeUnpickler.scala
new file mode 100644
index 000000000..c037b4336
--- /dev/null
+++ b/src/dotty/tools/dotc/core/pickling/TreeUnpickler.scala
@@ -0,0 +1,695 @@
+package dotty.tools
+package dotc
+package core
+package pickling
+
+import Contexts._, Symbols._, Types._, Scopes._, SymDenotations._, Names._, NameOps._
+import StdNames._, Denotations._, Flags._, Constants._, Annotations._
+import util.Positions._
+import dotty.tools.dotc.ast.{tpd, Trees, untpd}
+import Trees._
+import Decorators._
+import TastyUnpickler._, TastyBuffer._
+import annotation.switch
+import scala.collection.{ mutable, immutable }
+import typer.Mode
+
+/** Unpickler for typed trees
+ *  @param reader         the reader from which to unpickle
+ *  @param tastyName      the nametable
+ *  @param roots          a set of pre-existing symbols whose attributes should be overwritten
+ *                        instead of creating a new symbol.
+ *  @param readPositions  a flag indicating whether positions should be read
+ */
+class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table, readPositions: Boolean) {
+  import dotty.tools.dotc.core.pickling.PickleFormat._
+  import TastyName._
+  import tpd._
+
+  private val symAtAddr  = new mutable.HashMap[Addr, Symbol]
+  private val treeAtAddr = new mutable.HashMap[Addr, Tree]
+  
+  private val typeAtAddr = new mutable.HashMap[Addr, Type] // currently populated only for types that are known to be SHAREd.
+
+  def unpickle()(implicit ctx: Context): List[Tree] =
+    new TreeReader(reader).readTopLevelStats()
+    
+  def toTermName(tname: TastyName): TermName = tname match {
+    case Simple(name) => name
+    case Qualified(qual, name) => toTermName(qual) ++ "." ++ toTermName(name)
+    case Signed(original, params, result) => toTermName(original)
+    case Expanded(original) => ???
+    case ModuleClass(original) => toTermName(original).moduleClassName.toTermName
+    case SuperAccessor(accessed) => ???
+    case DefaultGetter(meth, num) => ???
+  }
+
+  def toTermName(ref: NameRef): TermName = toTermName(tastyName(ref))
+  def toTypeName(ref: NameRef): TypeName = toTermName(ref).toTypeName
+
+  class Completer(reader: TastyReader) extends LazyType {
+    import reader._
+    def complete(denot: SymDenotation)(implicit ctx: Context): Unit = {
+      // println(i"complete ${denot.name}")
+      treeAtAddr(currentAddr) = new TreeReader(reader).readIndexedDef()
+    }
+  }
+
+  class TreeReader(val reader: TastyReader) {
+    import reader._
+        
+    def forkAt(start: Addr) = new TreeReader(subReader(start, endAddr))
+    def fork = forkAt(currentAddr)
+    
+    def skipTree(tag: Int): Unit = {
+      // println(s"skipping ${astTagToString(tag)} at $currentAddr")
+      if (tag >= firstLengthTreeTag) skipTo(readEnd())
+      else if (tag >= firstNatASTTreeTag) { readNat(); skipTree() }
+      else if (tag >= firstNatTreeTag) readNat()
+    }
+    def skipTree(): Unit = skipTree(readByte())
+    
+    def skipParams(): Unit =
+      while (nextByte == PARAMS || nextByte == TYPEPARAM) skipTree()
+
+    def readName(): TermName = toTermName(readNameRef())
+
+    def readNameSplitSig()(implicit ctx: Context): Any /* TermName | (TermName, Signature) */ =
+      tastyName(readNameRef()) match {
+        case Signed(original, params, result) =>
+          var sig = Signature(params map toTypeName, toTypeName(result))
+          if (sig == Signature.NotAMethod) sig = Signature.NotAMethod
+          (toTermName(original), sig)
+        case name =>
+          toTermName(name)
+      }
+    
+// ------ Reading types -----------------------------------------------------
+    
+    /** Read names in an interleaved sequence of (parameter) names and types/bounds */
+    def readParamNames[N <: Name](end: Addr): List[N] = 
+      until(end) { try readName().asInstanceOf[N] finally skipTree() }
+
+    /** Read types or bounds in an interleaved sequence of (parameter) names and types/bounds */
+    def readParamTypes[T <: Type](end: Addr)(implicit ctx: Context): List[T] = 
+      until(end) { readNat(); readType().asInstanceOf[T] }
+
+    /** Read referece to definition and return symbol created at that definition */
+    def readSymRef()(implicit ctx: Context): Symbol = symAtAddr(readAddr())
+
+    /** Read a type */
+    def readType()(implicit ctx: Context): Type = {
+      val start = currentAddr
+      // println(s"read type at $start")
+      val tag = readByte()
+
+      def registeringType[T](tp: Type, op: => T): T = {
+        typeAtAddr(start) = tp
+        op
+      }
+            
+      def readLengthType(): Type = {
+        val end = readEnd()
+        
+        def readNamesSkipParams[N <: Name]: (List[N], TreeReader) = {
+          val nameReader = fork
+          nameReader.skipTree() // skip result
+          val paramReader = nameReader.fork
+          (nameReader.readParamNames[N](end), paramReader)
+        }
+        
+        try { 
+          (tag: @switch) match {
+            case THIS =>
+              ThisType.raw(readType().asInstanceOf[TypeRef])
+            case SUPERtype =>
+              SuperType(readType(), readType())
+            case REFINEDtype =>
+              val parent = readType()
+              var name: Name = readName()
+              if (nextByte == TYPEBOUNDS || nextByte == TYPEALIAS) name = name.toTypeName
+              RefinedType(parent, name, registeringType(_, readType()))
+            case APPLIEDtype =>
+              readType().appliedTo(until(end)(readType()))
+            case TYPEBOUNDS =>
+              TypeBounds(readType(), readType())
+            case TYPEALIAS =>
+              TypeAlias(readType())
+            case ANNOTATED =>
+              AnnotatedType(Annotation(readTerm()), readType())
+            case ANDtype =>
+              AndType(readType(), readType())
+            case ORtype =>
+              OrType(readType(), readType())
+            case BIND =>
+              symAtAddr(start) = 
+                ctx.newSymbol(ctx.owner, readName().toTypeName, BindDefinedType, readType())
+              readType()
+            case BYNAMEtype =>
+              ExprType(readType())
+            case POLYtype =>
+              val (names, paramReader) = readNamesSkipParams[TypeName]
+              try PolyType(names)(
+                registeringType(_, paramReader.readParamTypes[TypeBounds](end)),
+                _ => readType())
+              finally skipTo(end)
+            case METHODtype =>
+              val (names, paramReader) = readNamesSkipParams[TermName]
+              try MethodType(names, paramReader.readParamTypes[Type](end))(
+                registeringType(_, readType()))
+              finally skipTo(end)
+            case PARAMtype =>
+              readTypeRef() match {
+                case binder: PolyType => PolyParam(binder, readNat())
+                case binder: MethodType => MethodParam(binder, readNat())
+              }
+            case CLASSconst =>
+              readEnd()
+              ConstantType(Constant(readType()))
+            case ENUMconst =>
+              readEnd()
+              ConstantType(Constant(readTermRef().termSymbol))
+          }
+        }
+        finally assert(currentAddr == end)
+      }
+      
+      def readSimpleType(): Type = (tag: @switch) match {
+        case TYPEREFdirect | TERMREFdirect => 
+          NamedType.withFixedSym(NoPrefix, readSymRef())
+        case TYPEREFsymbol | TERMREFsymbol =>
+          val sym = readSymRef()
+          NamedType.withFixedSym(readType(), sym)
+        case TYPEREFpkg =>
+          val name = readName()
+          val pkg = 
+            if (name == nme.ROOT) defn.RootClass
+            else if (name == nme.EMPTY_PACKAGE) defn.EmptyPackageClass
+            else ctx.requiredPackage(name).moduleClass
+          pkg.typeRef
+        case TERMREFpkg =>
+          val name = readName()
+          val pkg = 
+            if (name == nme.ROOT) defn.RootPackage
+            else if (name == nme.EMPTY_PACKAGE) defn.EmptyPackageVal
+            else ctx.requiredPackage(name)
+          pkg.termRef
+        case TYPEREF =>
+          val name =  readName().toTypeName
+          TypeRef(readType(), name)
+        case TERMREF =>
+          readNameSplitSig() match {
+            case name: TermName => TermRef.all(readType(), name)
+            case (name: TermName, sig: Signature) => TermRef.withSig(readType(), name, sig)
+          }
+        case SKOLEMtype =>
+          SkolemType(readTypeRef())
+        case NOTYPE =>
+          NoType
+        case SHARED =>
+          val ref = readAddr()
+          typeAtAddr.getOrElseUpdate(ref, forkAt(ref).readType())
+        case UNITconst =>
+          ConstantType(Constant(()))
+        case TRUEconst =>
+          ConstantType(Constant(true))
+        case FALSEconst =>
+          ConstantType(Constant(false))
+        case BYTEconst =>
+          ConstantType(Constant(readInt().toByte))
+        case SHORTconst =>
+          ConstantType(Constant(readInt().toShort))
+        case CHARconst =>
+          ConstantType(Constant(readNat().toChar))
+        case INTconst =>
+          ConstantType(Constant(readInt()))
+        case LONGconst =>
+          ConstantType(Constant(readLongInt()))
+        case FLOATconst =>
+          ConstantType(Constant(java.lang.Float.intBitsToFloat(readInt())))
+        case DOUBLEconst =>
+          ConstantType(Constant(java.lang.Double.longBitsToDouble(readLongInt())))
+        case STRINGconst =>
+          ConstantType(Constant(readName().toString))
+        case NULLconst =>
+          ConstantType(Constant(null))
+      }
+      
+      if (tag < firstLengthTreeTag) readSimpleType() else readLengthType()
+    }
+    
+    def readTypeRef(): Type = 
+      typeAtAddr(readAddr())
+
+    def readPath()(implicit ctx: Context): Type = {
+      val tp = readType()
+      assert(tp.isInstanceOf[SingletonType])
+      tp
+    }
+    
+    def readTermRef()(implicit ctx: Context): TermRef = 
+      readType().asInstanceOf[TermRef]
+
+// ------ Reading definitions -----------------------------------------------------
+
+    /** Create symbol of definition node and enter in symAtAddr map */
+    def createSymbol()(implicit ctx: Context): Unit = {
+      val start = currentAddr
+      val tag = readByte()
+      val end = readEnd()
+      val name = if (tag == TYPEDEF || tag == TYPEPARAM) readName().toTypeName else readName()
+      skipParams()
+      val isAbstractType = nextByte == TYPEBOUNDS
+      val isClass = nextByte == TEMPLATE
+      val templateStart = currentAddr
+      skipTree()
+      val rhsIsEmpty = 
+        (tag == VALDEF || tag == DEFDEF) && {
+          val result = nextByte == EMPTYTREE
+          skipTree()
+          result
+        }
+      val (givenFlags, annots, privateWithin) = readModifiers(end)
+      println(i"creating symbol $name at $start with flags $givenFlags")
+      val lacksDefinition =
+        rhsIsEmpty && !name.isConstructorName && !givenFlags.is(ParamOrAccessor) ||
+        isAbstractType
+      var flags = givenFlags
+      if (lacksDefinition) flags |= Deferred
+      if (ctx.mode.is(Mode.InSuperCall) && !flags.is(ParamOrAccessor)) flags |= InSuperCall
+      if (ctx.owner.isClass) {
+        if (tag == TYPEPARAM) flags |= Param
+        else if (tag == PARAM) flags |= ParamAccessor // TODO: try to unify param and paramaccessor
+      }
+      else if (isParamTag(tag)) flags |= Param
+      val nameMatches = (_: Denotation).symbol.name == name
+      val prevDenot: SymDenotation = 
+        if (ctx.owner.is(Package)) ctx.effectiveScope.lookup(name)
+        else NoDenotation // TODO check for double reads
+      var completer: LazyType = 
+        if (prevDenot.exists) new Completer(subReader(start, end)) with SymbolLoaders.SecondCompleter
+        else new Completer(subReader(start, end))
+      if (flags is Module) completer = ctx.adjustModuleCompleter(completer, name)
+      val sym =
+        if (prevDenot.exists) {
+          println(i"overwriting ${prevDenot.symbol} # ${prevDenot.hashCode}")
+          prevDenot.info = completer
+          prevDenot.setFlag(flags)
+          prevDenot.resetFlag(Touched) // allow one more completion
+          prevDenot.privateWithin = privateWithin
+          prevDenot.symbol
+        } else if (isClass)
+          ctx.newClassSymbol(ctx.owner, name.asTypeName, flags, completer, privateWithin, coord = start.index)
+        else {
+          ctx.newSymbol(ctx.owner, name, flags, completer, privateWithin, coord = start.index)
+        } // TODO set position
+      sym.annotations = annots
+      ctx.enter(sym)
+      symAtAddr(start) = sym
+      if (isClass) {
+        completer.withDecls(newScope)
+        forkAt(templateStart).indexTemplateParams()(ctx.fresh.setOwner(sym))
+      }
+    }
+
+    /** Read modifier list into triplet of flags, annotations and a privateWithin 
+     *  boindary symbol.
+     */
+    def readModifiers(end: Addr)(implicit ctx: Context): (FlagSet, List[Annotation], Symbol) = {
+      var flags: FlagSet = EmptyFlags
+      var annots = new mutable.ListBuffer[Annotation]
+      var privateWithin: Symbol = NoSymbol
+      while (currentAddr.index != end.index) {
+        def addFlag(flag: FlagSet) = {
+          flags |= flag
+          readByte()
+        }
+        nextByte match {
+          case PRIVATE => addFlag(Private)
+          case INTERNAL => ??? // addFlag(Internal)
+          case PROTECTED => addFlag(Protected)
+          case ABSTRACT => addFlag(Abstract)
+          case FINAL => addFlag(Final)
+          case SEALED => addFlag(Sealed)
+          case CASE => addFlag(Case)
+          case IMPLICIT => addFlag(Implicit)
+          case LAZY => addFlag(Lazy)
+          case OVERRIDE => addFlag(Override)
+          case INLINE => addFlag(Inline)
+          case ABSOVERRIDE => addFlag(AbsOverride)
+          case STATIC => addFlag(JavaStatic)
+          case MODULE => addFlag(Module)
+          case LOCAL => addFlag(Local)
+          case SYNTHETIC => addFlag(Synthetic)
+          case ARTIFACT => addFlag(Artifact)
+          case MUTABLE => addFlag(Mutable)
+          case LABEL => addFlag(Label)
+          case FIELDaccessor => addFlag(Accessor)
+          case PARAMaccessor => addFlag(ParamAccessor)
+          case CASEaccessor => addFlag(CaseAccessor)
+          case COVARIANT => addFlag(Covariant)
+          case CONTRAVARIANT => addFlag(Contravariant)
+          case SCALA2X => addFlag(Scala2x)
+          case DEFAULTparameterized => addFlag(DefaultParameterized)
+          case DEFAULTinit => addFlag(DefaultInit)
+          case INSUPERCALL => addFlag(InSuperCall)
+          case PRIVATEqualified => 
+            readByte()
+            readEnd()
+            privateWithin = readType().typeSymbol
+          case PROTECTEDqualified =>
+            addFlag(Protected)
+            readEnd()
+            privateWithin = readType().typeSymbol
+          case ANNOTATION =>
+            readByte()
+            val end = readEnd()
+            val sym = readType().typeSymbol
+            val lazyAnnotTree = readLater(end, _.readTerm())
+            annots += Annotation.deferred(sym, _ => lazyAnnotTree.complete)
+          case _ =>
+            assert(false, s"illegal modifier tag at $currentAddr")
+        }
+      }
+      (flags, annots.toList, privateWithin)
+    }
+    
+    /** Create symbols for a definitions in statement sequence between
+     *  current address and `end`.
+     */
+    def indexStats(end: Addr)(implicit ctx: Context) =
+      until(end) { if (isDefTag(nextByte)) createSymbol() else skipTree() }
+
+    /** Create symbols the longest consecutive sequence of parameters with given
+     *  `tag starting at current address.
+     */
+    def indexParams(tag: Int)(implicit ctx: Context) =
+      while (nextByte == tag) createSymbol()
+      
+    /** Create symbols for all type and value parameters of template starting
+     *  at current address.
+     */
+    def indexTemplateParams()(implicit ctx: Context) = {
+      assert(readByte() == TEMPLATE)
+      readEnd()
+      indexParams(TYPEPARAM)
+      indexParams(PARAM)
+    }
+
+    /** If definition was already read by a completer, return the previously read tree
+     *  or else read definition. 
+     */
+    def readIndexedDef()(implicit ctx: Context): Tree = treeAtAddr.remove(currentAddr) match {
+      case Some(tree) => skipTree(); tree
+      case none => readNewDef()
+    }
+    
+    private def readNewDef()(implicit ctx: Context): Tree = {
+      val start = currentAddr
+      // println(s"reading def at $start")
+      val sym = symAtAddr(start)
+      val tag = readByte()
+      val end = readEnd()
+
+      def readParams[T <: MemberDef](tag: Int)(implicit ctx: Context): List[T] = {
+        fork.indexParams(tag)
+        readIndexedParams(tag)
+      }
+    
+      def readParamss(implicit ctx: Context): List[List[ValDef]] = {
+        collectWhile(nextByte == PARAMS) {
+          readByte()
+          readEnd()
+          readParams[ValDef](PARAM)
+        }
+      }
+      
+      def readRhs(implicit ctx: Context) = readLater(end, _.readTerm())
+
+      def localCtx = ctx.fresh.setOwner(sym)
+      
+      def ta =  ctx.typeAssigner
+
+      val name = readName()
+      // println(s"reading def of $name at $start")
+      val tree: MemberDef = tag match {
+        case DEFDEF =>
+          val tparams = readParams[TypeDef](TYPEPARAM)(localCtx)
+          val vparamss = readParamss(localCtx)
+          val tpt = readTpt()
+          val typeParams = tparams.map(_.symbol)
+          val valueParamss = vparamss.nestedMap(_.symbol)
+          val resType = ctx.effectiveResultType(sym, typeParams, tpt.tpe)
+          sym.info = ctx.methodType(typeParams, valueParamss, resType)
+          ta.assignType(
+            untpd.DefDef(
+              sym.name.asTermName, tparams, vparamss, tpt, readRhs(localCtx)),
+            sym)
+        case VALDEF =>
+          sym.info = readType()
+          ValDef(sym.asTerm, readRhs(localCtx))
+        case TYPEDEF | TYPEPARAM =>
+          if (sym.isClass) {
+            val cls = sym.asClass
+            val impl = readTemplate(localCtx)
+            cls.info = ClassInfo(
+                cls.owner.thisType, 
+                cls, 
+                impl.parents.map(_.tpe.asInstanceOf[TypeRef]),
+                cls.unforcedDecls,
+                if (impl.self.isEmpty) NoType else impl.self.tpt.tpe)
+            ta.assignType(untpd.TypeDef(sym.name.asTypeName, impl), sym)
+          }
+          else {
+            sym.info = readType()
+            TypeDef(sym.asType)
+          }
+        case PARAM =>
+          sym.info = readType()
+          ValDef(sym.asTerm)
+      }
+      val mods = 
+        if (sym.annotations.isEmpty) EmptyModifiers
+        else Modifiers(annotations = sym.annotations.map(_.tree))
+      tree.withMods(mods) // record annotations in tree so that tree positions can be filled in.
+      skipTo(end)
+      addAddr(start, tree)
+    }
+    
+    private def readTemplate(implicit ctx: Context): Template = {
+      val start = currentAddr
+      val cls = ctx.owner.asClass
+      val localDummy = ctx.newLocalDummy(cls)
+      assert(readByte() == TEMPLATE)
+      val end = readEnd()
+      readIndexedParams(TYPEPARAM)
+      readIndexedParams(PARAM)
+      val parents = collectWhile(nextByte != SELFDEF && nextByte != DEFDEF) {
+        nextByte match {
+          case APPLY | TYPEAPPLY => readTerm()
+          case _ => readTpt()
+        }
+      }
+      val self = 
+        if (nextByte == SELFDEF) {
+          readByte()
+          readEnd()
+          untpd.ValDef(readName(), readTpt(), EmptyTree).withType(NoType)
+        }
+        else EmptyValDef
+      fork.indexStats(end)
+      val constr = readIndexedDef().asInstanceOf[DefDef]
+      val lazyStats = readLater(end, _.readIndexedStats(localDummy, end))
+      addAddr(start,
+        untpd.Template(constr, parents, self, lazyStats)
+          .withType(localDummy.nonMemberTermRef))
+    }
+    
+    def readIndexedStat(exprOwner: Symbol)(implicit ctx: Context): Tree = nextByte match {
+      case TYPEDEF | VALDEF | DEFDEF | IMPORT => readIndexedDef()
+      case _ => readTerm()(ctx.withOwner(exprOwner))
+    }
+    
+    def readStats(exprOwner: Symbol, end: Addr)(implicit ctx: Context): List[Tree] = {
+      fork.indexStats(end)
+      readIndexedStats(exprOwner, end)
+    } 
+    
+    def readIndexedStats(exprOwner: Symbol, end: Addr)(implicit ctx: Context): List[Tree] =
+      until(end)(readIndexedStat(exprOwner))
+    
+    def readIndexedParams[T <: MemberDef](tag: Int)(implicit ctx: Context): List[T] =
+      collectWhile(nextByte == tag) { readIndexedDef().asInstanceOf[T] }
+
+// ------ Reading terms -----------------------------------------------------
+
+    def readTerm()(implicit ctx: Context): Tree = {
+      val start = currentAddr
+      // println(s"reading term at $start")
+      val tag = readByte()
+
+      def readSimpleTerm(): Tree = tag match {
+        case IDENT =>
+          untpd.Ident(readName()).withType(readType())
+        case SELECT =>
+          def readQual(name: Name) = {
+            val localCtx = 
+              if (name == nme.CONSTRUCTOR) ctx.fresh.addMode(Mode.InSuperCall) else ctx
+            readTerm()(localCtx)
+          }
+          readNameSplitSig match {
+            case name: Name => readQual(name).select(name)
+            case (name: Name, sig: Signature) => readQual(name).selectWithSig(name, sig)
+          }
+        case EMPTYTREE =>
+          EmptyTree
+        case _ =>
+          ref(readTermRef())
+      }
+
+      def readLengthTerm(): Tree = {
+        val end = readEnd()
+
+        try {
+          (tag: @switch) match {
+            case SUPER => 
+              val qual = readTerm()
+              val mixClass = ifBefore(end)(readType().typeSymbol, NoSymbol)
+              val mixName = if (mixClass.exists) mixClass.name.asTypeName else tpnme.EMPTY
+              tpd.Super(qual, mixName, ctx.mode.is(Mode.InSuperCall), mixClass)
+            case APPLY => 
+              val fn = readTerm()
+              val isJava = fn.tpe.isInstanceOf[JavaMethodType]
+              def readArg() = readTerm() match {
+                case SeqLiteral(elems) if isJava => JavaSeqLiteral(elems)
+                case arg => arg
+              }
+              tpd.Apply(fn, until(end)(readArg()))
+            case TYPEAPPLY =>
+              tpd.TypeApply(readTerm(), until(end)(readTpt()))
+            case NEW =>
+              New(readTpt())
+            case PAIR =>
+              Pair(readTerm(), readTerm())
+            case TYPED =>
+              Typed(readTerm(), readTpt())
+            case NAMEDARG =>
+              NamedArg(readName(), readTerm())
+            case ASSIGN =>
+              Assign(readTerm(), readTerm())
+            case BLOCK =>
+              val exprReader = fork
+              skipTree()
+              Block(readStats(ctx.owner, end), exprReader.readTerm())(ctx.fresh.setNewScope)
+            case IF =>
+              If(readTerm(), readTerm(), readTerm())
+            case CLOSURE =>
+              val meth = readTerm()
+              val tpt = readTpt()
+              Closure(until(end)(readTerm()), meth, tpt)
+            case MATCH =>
+              Match(readTerm(), readCases())
+            case RETURN =>
+              val from = readSymRef()
+              val expr = ifBefore(end)(readTerm(), EmptyTree)
+              Return(expr, Ident(from.termRef))
+            case TRY =>
+              Try(readTerm(), readCases(), ifBefore(end)(readTerm(), EmptyTree))
+            case THROW =>
+              Throw(readTerm())
+            case REPEATED =>
+              SeqLiteral(until(end)(readTerm()))
+            case BIND =>
+              val name = readName()
+              val info = readType()
+              val sym = ctx.newSymbol(ctx.owner, name, EmptyFlags, info)
+              symAtAddr(start) = sym
+              Bind(sym, readTerm())
+            case ALTERNATIVE =>
+              Alternative(until(end)(readTerm()))
+            case UNAPPLY =>
+              val fn = readTerm()
+              val implicitArgs = 
+                collectWhile(nextByte == IMPLICITARG) {
+                  readByte()
+                  readEnd()
+                  readTerm()
+                }
+              val patType = readType()
+              val argPats = until(end)(readTerm())
+              UnApply(fn, implicitArgs, argPats, patType)
+          }
+        }
+        finally assert(currentAddr == end, s"$currentAddr $end ${astTagToString(tag)}")
+      }
+
+      addAddr(start, 
+        if (tag < firstLengthTreeTag) readSimpleTerm()
+        else readLengthTerm())
+    }
+    
+    def readTpt()(implicit ctx: Context) = {
+      val start = currentAddr
+      addAddr(start, TypeTree(readType()))
+    }
+
+    def readCases()(implicit ctx: Context): List[CaseDef] = 
+      collectWhile(nextByte == CASEDEF) {
+        val start = currentAddr
+        readByte()
+        val end = readEnd()
+        val pat = readTerm()
+        val rhs = readTerm()
+        val guard = ifBefore(end)(readTerm(), EmptyTree)
+        addAddr(start, CaseDef(pat, guard, rhs))
+      }
+
+    def readTopLevelStats()(implicit ctx: Context): List[Tree] = {
+      fork.indexStats(endAddr)
+      until(endAddr) {
+        if (nextByte == PACKAGE) {
+          val start = currentAddr
+          readByte()
+          val end = readEnd()
+          val pid = ref(readTermRef()).asInstanceOf[RefTree]
+          addAddr(start,
+            PackageDef(pid, readStats(NoSymbol, end)(ctx.fresh.setOwner(pid.symbol.moduleClass))))     
+        }
+        else readIndexedStat(ctx.owner)
+      }
+    }
+
+    def readLater[T](end: Addr, op: TreeReader => T): Trees.Lazy[T] = {
+      val localReader = fork
+      skipTo(end)
+      new LazyReader(localReader, op)
+    }
+    
+// ------ Hooks for positions ------------------------------------------------
+    
+    /** A temporary position encoding.
+     *  Start and end fields are each given the address of bytes from which tree is unpickled
+     *  These are later overridden with the actual offsets taken from the Positions section.
+     */
+    def indexPosition(addr: Addr): Position = {
+      assert(addr.index < MaxOffset)
+      Position(addr.index, addr.index, 0)
+    }
+      
+    /** Record address from which tree was created as a temporary position in the tree. */
+    def addAddr[T <: Tree](addr: Addr, tree: T): T = {
+      if (readPositions) { tree.setPosUnchecked(indexPosition(addr)); tree }
+      else tree
+    }
+  }
+
+  class LazyReader[T](reader: TreeReader, op: TreeReader => T) extends Trees.Lazy[T] {
+    var posReader: Option[PositionReader] = None
+    def complete: T = {
+      val res = op(reader)
+      posReader.foreach(_.unpickle(res))
+      res
+    }  
+  }
+    
+}