Scala example source code file (UnPickler.scala)

This example Scala source code file (UnPickler.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, boolean, collection, constant, int, list, mutable, nosymbol, string, symbol, t, tree, type

The UnPickler.scala Scala example source code

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

package scala
package reflect
package internal
package pickling

import java.io.IOException
import java.lang.Float.intBitsToFloat
import java.lang.Double.longBitsToDouble

import Flags._
import PickleFormat._
import scala.collection.{ mutable, immutable }
import scala.collection.mutable.ListBuffer
import scala.annotation.switch

/** @author Martin Odersky
 *  @version 1.0
 */
abstract class UnPickler {
  val symbolTable: SymbolTable
  import symbolTable._

  /** Unpickle symbol table information descending from a class and/or module root
   *  from an array of bytes.
   *  @param bytes      bytearray from which we unpickle
   *  @param offset     offset from which unpickling starts
   *  @param classRoot  the top-level class which is unpickled, or NoSymbol if inapplicable
   *  @param moduleRoot the top-level module which is unpickled, or NoSymbol if inapplicable
   *  @param filename   filename associated with bytearray, only used for error messages
   */
  def unpickle(bytes: Array[Byte], offset: Int, classRoot: Symbol, moduleRoot: Symbol, filename: String) {
    try {
      new Scan(bytes, offset, classRoot, moduleRoot, filename).run()
    } catch {
      case ex: IOException =>
        throw ex
      case ex: MissingRequirementError =>
        throw ex
      case ex: Throwable =>
        /*if (settings.debug.value)*/ ex.printStackTrace()
        throw new RuntimeException("error reading Scala signature of "+filename+": "+ex.getMessage())
    }
  }

  class Scan(_bytes: Array[Byte], offset: Int, classRoot: Symbol, moduleRoot: Symbol, filename: String) extends PickleBuffer(_bytes, offset, -1) {
    //println("unpickle " + classRoot + " and " + moduleRoot)//debug

    protected def debug = settings.debug.value

    checkVersion()

    private val loadingMirror = mirrorThatLoaded(classRoot)

    /** A map from entry numbers to array offsets */
    private val index = createIndex

    /** A map from entry numbers to symbols, types, or annotations */
    private val entries = new Array[AnyRef](index.length)

    /** A map from symbols to their associated `decls` scopes */
    private val symScopes = mutable.HashMap[Symbol, Scope]()

    private def expect(expected: Int, msg: => String) {
      val tag = readByte()
      if (tag != expected)
        errorBadSignature(s"$msg ($tag)")
    }

    //println("unpickled " + classRoot + ":" + classRoot.rawInfo + ", " + moduleRoot + ":" + moduleRoot.rawInfo);//debug

    @inline private def runAtIndex[T](i: Int)(body: => T): T = {
      val saved = readIndex
      readIndex = index(i)
      try body finally readIndex = saved
    }

    // Laboriously unrolled for performance.
    def run() {
      var i = 0
      while (i < index.length) {
        if (entries(i) == null && isSymbolEntry(i))
          runAtIndex(i)(entries(i) = readSymbol())

        i += 1
      }

      // read children last, fix for #3951
      i = 0
      while (i < index.length) {
        if (entries(i) == null) {
          if (isSymbolAnnotationEntry(i))
            runAtIndex(i)(readSymbolAnnotation())
          else if (isChildrenEntry(i))
            runAtIndex(i)(readChildren())
        }
        i += 1
      }
    }

    private def checkVersion() {
      val major = readNat()
      val minor = readNat()
      if (major != MajorVersion || minor > MinorVersion)
        throw new IOException("Scala signature " + classRoot.decodedName +
                              " has wrong version\n expected: " +
                              MajorVersion + "." + MinorVersion +
                              "\n found: " + major + "." + minor +
                              " in "+filename)
    }

    /** The `decls` scope associated with given symbol */
    protected def symScope(sym: Symbol) = symScopes.getOrElseUpdate(sym, newScope)

    /** Does entry represent an (internal) symbol */
    protected def isSymbolEntry(i: Int): Boolean = {
      val tag = bytes(index(i)).toInt
      (firstSymTag <= tag && tag <= lastSymTag &&
       (tag != CLASSsym || !isRefinementSymbolEntry(i)))
    }

    /** Does entry represent an (internal or external) symbol */
    protected def isSymbolRef(i: Int): Boolean = {
      val tag = bytes(index(i))
      (firstSymTag <= tag && tag <= lastExtSymTag)
    }

    /** Does entry represent a name? */
    protected def isNameEntry(i: Int): Boolean = {
      val tag = bytes(index(i)).toInt
      tag == TERMname || tag == TYPEname
    }

    /** Does entry represent a symbol annotation? */
    protected def isSymbolAnnotationEntry(i: Int): Boolean = {
      val tag = bytes(index(i)).toInt
      tag == SYMANNOT
    }

    /** Does the entry represent children of a symbol? */
    protected def isChildrenEntry(i: Int): Boolean = {
      val tag = bytes(index(i)).toInt
      tag == CHILDREN
    }

    private def maybeReadSymbol(): Either[Int, Symbol] = readNat() match {
      case index if isSymbolRef(index) => Right(at(index, readSymbol))
      case index                       => Left(index)
    }

    /** Does entry represent a refinement symbol?
     *  pre: Entry is a class symbol
     */
    protected def isRefinementSymbolEntry(i: Int): Boolean = {
      val savedIndex = readIndex
      readIndex = index(i)
      val tag = readByte().toInt
      assert(tag == CLASSsym)

      readNat(); // read length
      val result = readNameRef() == tpnme.REFINE_CLASS_NAME
      readIndex = savedIndex
      result
    }

    /** If entry at `i` is undefined, define it by performing
     *  operation `op` with `readIndex at start of i'th
     *  entry. Restore `readIndex` afterwards.
     */
    protected def at[T <: AnyRef](i: Int, op: () => T): T = {
      var r = entries(i)
      if (r eq null) {
        val savedIndex = readIndex
        readIndex = index(i)
        r = op()
        assert(entries(i) eq null, entries(i))
        entries(i) = r
        readIndex = savedIndex
      }
      r.asInstanceOf[T]
    }

    /** Read a name */
    protected def readName(): Name = {
      val tag = readByte()
      val len = readNat()
      tag match {
        case TERMname => newTermName(bytes, readIndex, len)
        case TYPEname => newTypeName(bytes, readIndex, len)
        case _ => errorBadSignature("bad name tag: " + tag)
      }
    }
    private def readEnd() = readNat() + readIndex

    /** Read a symbol */
    protected def readSymbol(): Symbol = {
      val tag   = readByte()
      val end   = readEnd()
      def atEnd = readIndex == end

      def readExtSymbol(): Symbol = {
        val name  = readNameRef()
        val owner = if (atEnd) loadingMirror.RootClass else readSymbolRef()

        def adjust(sym: Symbol) = if (tag == EXTref) sym else sym.moduleClass

        def fromName(name: Name) = name.toTermName match {
          case nme.ROOT     => loadingMirror.RootClass
          case nme.ROOTPKG  => loadingMirror.RootPackage
          case _            => adjust(owner.info.decl(name))
        }
        def nestedObjectSymbol: Symbol = {
          // If the owner is overloaded (i.e. a method), it's not possible to select the
          // right member, so return NoSymbol. This can only happen when unpickling a tree.
          // the "case Apply" in readTree() takes care of selecting the correct alternative
          //  after parsing the arguments.
          if (owner.isOverloaded)
            return NoSymbol

          if (tag == EXTMODCLASSref) {
            val moduleVar = owner.info.decl(nme.moduleVarName(name.toTermName))
            if (moduleVar.isLazyAccessor)
              return moduleVar.lazyAccessor.lazyAccessor
          }
          NoSymbol
        }

        def moduleAdvice(missing: String): String = {
          val module =
            if      (missing.startsWith("scala.xml"))                Some(("org.scala-lang.modules", "scala-xml"))
            else if (missing.startsWith("scala.util.parsing"))       Some(("org.scala-lang.modules", "scala-parser-combinators"))
            else if (missing.startsWith("scala.swing"))              Some(("org.scala-lang.modules", "scala-swing"))
            else if (missing.startsWith("scala.util.continuations")) Some(("org.scala-lang.plugins", "scala-continuations-library"))
            else None

          (module map { case (group, art) =>
            s"""\n(NOTE: It looks like the $art module is missing; try adding a dependency on "$group" : "$art".
               |       See http://docs.scala-lang.org/overviews/core/scala-2.11.html for more information.)""".stripMargin
           } getOrElse "")
        }

        // (1) Try name.
        fromName(name) orElse {
          // (2) Try with expanded name.  Can happen if references to private
          // symbols are read from outside: for instance when checking the children
          // of a class.  See #1722.
          fromName(nme.expandedName(name.toTermName, owner)) orElse {
            // (3) Try as a nested object symbol.
            nestedObjectSymbol orElse {
              // (4) Call the mirror's "missing" hook.
              adjust(mirrorThatLoaded(owner).missingHook(owner, name)) orElse {
                // (5) Create a stub symbol to defer hard failure a little longer.
                val fullName = s"${owner.fullName}.$name"
                val missingMessage =
                  s"""|bad symbolic reference to $fullName encountered in class file '$filename'.
                      |Cannot access ${name.longString} in ${owner.kindString} ${owner.fullName}. The current classpath may be
                      |missing a definition for $fullName, or $filename may have been compiled against a version that's
                      |incompatible with the one found on the current classpath.${moduleAdvice(fullName)}""".stripMargin
                owner.newStubSymbol(name, missingMessage)
              }
            }
          }
        }
      }

      tag match {
        case NONEsym                 => return NoSymbol
        case EXTref | EXTMODCLASSref => return readExtSymbol()
        case _                       => ()
      }

      // symbols that were pickled with Pickler.writeSymInfo
      val nameref      = readNat()
      val name         = at(nameref, readName)
      val owner        = readSymbolRef()
      val flags        = pickledToRawFlags(readLongNat())

      val (privateWithin, inforef) = maybeReadSymbol() match {
        case Left(index) => NoSymbol -> index
        case Right(sym)  => sym -> readNat()
      }

      def isModuleFlag = (flags & MODULE) != 0L
      def isClassRoot  = (name == classRoot.name) && (owner == classRoot.owner)
      def isModuleRoot = (name == moduleRoot.name) && (owner == moduleRoot.owner)
      def pflags       = flags & PickledFlags

      def finishSym(sym: Symbol): Symbol = {
        markFlagsCompleted(sym)(mask = AllFlags)
        sym.privateWithin = privateWithin
        sym.info = (
          if (atEnd) {
            assert(!sym.isSuperAccessor, sym)
            newLazyTypeRef(inforef)
          }
          else {
            assert(sym.isSuperAccessor || sym.isParamAccessor, sym)
            newLazyTypeRefAndAlias(inforef, readNat())
          }
        )
        if (sym.owner.isClass && sym != classRoot && sym != moduleRoot &&
            !sym.isModuleClass && !sym.isRefinementClass && !sym.isTypeParameter && !sym.isExistentiallyBound)
          symScope(sym.owner) enter sym

        sym
      }

      finishSym(tag match {
        case TYPEsym  | ALIASsym =>
          owner.newNonClassSymbol(name.toTypeName, NoPosition, pflags)
        case CLASSsym =>
          val sym = (
            if (isClassRoot) {
              if (isModuleFlag) moduleRoot.moduleClass setFlag pflags
              else classRoot setFlag pflags
            }
            else owner.newClassSymbol(name.toTypeName, NoPosition, pflags)
          )
          if (!atEnd)
            sym.typeOfThis = newLazyTypeRef(readNat())

          sym
        case MODULEsym =>
          val clazz = at(inforef, () => readType()).typeSymbol // after NMT_TRANSITION, we can leave off the () => ... ()
          if (isModuleRoot) moduleRoot setFlag pflags
          else owner.newLinkedModule(clazz, pflags)
        case VALsym =>
          if (isModuleRoot) { abort(s"VALsym at module root: owner = $owner, name = $name") }
          else owner.newTermSymbol(name.toTermName, NoPosition, pflags)

        case _ =>
          errorBadSignature("bad symbol tag: " + tag)
      })
    }

    protected def readType(forceProperType: Boolean = false): Type = {
      val tag = readByte()
      val end = readEnd()
      @inline def all[T](body: => T): List[T] = until(end, () => body)

      def readTypes()   = all(readTypeRef)
      def readSymbols() = all(readSymbolRef)
      def readAnnots()  = all(readAnnotationRef)

      // if the method is overloaded, the params cannot be determined (see readSymbol) => return NoType.
      // Only happen for trees, "case Apply" in readTree() takes care of selecting the correct
      // alternative after parsing the arguments.
      def MethodTypeRef(restpe: Type, params: List[Symbol]): Type = (
        if (restpe == NoType || (params contains NoSymbol)) NoType
        else MethodType(params, restpe)
      )
      def PolyOrNullaryType(restpe: Type, tparams: List[Symbol]): Type = tparams match {
        case Nil => NullaryMethodType(restpe)
        case _   => PolyType(tparams, restpe)
      }
      def CompoundType(clazz: Symbol, parents: List[Type]): Type = tag match {
        case REFINEDtpe   => RefinedType(parents, symScope(clazz), clazz)
        case CLASSINFOtpe => ClassInfoType(parents, symScope(clazz), clazz)
      }

      // We're stuck with the order types are pickled in, but with judicious use
      // of named parameters we can recapture a declarative flavor in a few cases.
      // But it's still a rat's nest of adhockery.
      (tag: @switch) match {
        case NOtpe                     => NoType
        case NOPREFIXtpe               => NoPrefix
        case THIStpe                   => ThisType(readSymbolRef())
        case SINGLEtpe                 => SingleType(readTypeRef(), readSymbolRef())
        case SUPERtpe                  => SuperType(readTypeRef(), readTypeRef())
        case CONSTANTtpe               => ConstantType(readConstantRef())
        case TYPEREFtpe                => TypeRef(readTypeRef(), readSymbolRef(), readTypes())
        case TYPEBOUNDStpe             => TypeBounds(readTypeRef(), readTypeRef())
        case REFINEDtpe | CLASSINFOtpe => CompoundType(readSymbolRef(), readTypes())
        case METHODtpe                 => MethodTypeRef(readTypeRef(), readSymbols())
        case POLYtpe                   => PolyOrNullaryType(readTypeRef(), readSymbols())
        case EXISTENTIALtpe            => ExistentialType(underlying = readTypeRef(), quantified = readSymbols())
        case ANNOTATEDtpe              => AnnotatedType(underlying = readTypeRef(), annotations = readAnnots())
      }
    }

    def noSuchTypeTag(tag: Int, end: Int): Type =
      errorBadSignature("bad type tag: " + tag)

    /** Read a constant */
    protected def readConstant(): Constant = {
      val tag = readByte().toInt
      val len = readNat()
      (tag: @switch) match {
        case LITERALunit    => Constant(())
        case LITERALboolean => Constant(readLong(len) != 0L)
        case LITERALbyte    => Constant(readLong(len).toByte)
        case LITERALshort   => Constant(readLong(len).toShort)
        case LITERALchar    => Constant(readLong(len).toChar)
        case LITERALint     => Constant(readLong(len).toInt)
        case LITERALlong    => Constant(readLong(len))
        case LITERALfloat   => Constant(intBitsToFloat(readLong(len).toInt))
        case LITERALdouble  => Constant(longBitsToDouble(readLong(len)))
        case LITERALstring  => Constant(readNameRef().toString)
        case LITERALnull    => Constant(null)
        case LITERALclass   => Constant(readTypeRef())
        case LITERALenum    => Constant(readSymbolRef())
        case _              => noSuchConstantTag(tag, len)
      }
    }

    def noSuchConstantTag(tag: Int, len: Int): Constant =
      errorBadSignature("bad constant tag: " + tag)

    /** Read children and store them into the corresponding symbol.
     */
    protected def readChildren() {
      val tag = readByte()
      assert(tag == CHILDREN)
      val end = readEnd()
      val target = readSymbolRef()
      while (readIndex != end) target addChild readSymbolRef()
    }

    /** Read an annotation argument, which is pickled either
     *  as a Constant or a Tree.
     */
    protected def readAnnotArg(i: Int): Tree = bytes(index(i)) match {
      case TREE => at(i, readTree)
      case _    =>
        val const = at(i, readConstant)
        Literal(const) setType const.tpe
    }

    /** Read a ClassfileAnnotArg (argument to a classfile annotation)
     */
    private def readArrayAnnot() = {
      readByte() // skip the `annotargarray` tag
      val end = readEnd()
      until(end, () => readClassfileAnnotArg(readNat())).toArray(JavaArgumentTag)
    }
    protected def readClassfileAnnotArg(i: Int): ClassfileAnnotArg = bytes(index(i)) match {
      case ANNOTINFO     => NestedAnnotArg(at(i, readAnnotation))
      case ANNOTARGARRAY => at(i, () => ArrayAnnotArg(readArrayAnnot()))
      case _             => LiteralAnnotArg(at(i, readConstant))
    }

    /** Read an AnnotationInfo. Not to be called directly, use
     *  readAnnotation or readSymbolAnnotation
     */
    protected def readAnnotationInfo(end: Int): AnnotationInfo = {
      val atp = readTypeRef()
      val args = new ListBuffer[Tree]
      val assocs = new ListBuffer[(Name, ClassfileAnnotArg)]
      while (readIndex != end) {
        val argref = readNat()
        if (isNameEntry(argref)) {
          val name = at(argref, readName)
          val arg = readClassfileAnnotArg(readNat())
          assocs += ((name, arg))
        }
        else
          args += readAnnotArg(argref)
      }
      AnnotationInfo(atp, args.toList, assocs.toList)
    }

    /** Read an annotation and as a side effect store it into
     *  the symbol it requests. Called at top-level, for all
     *  (symbol, annotInfo) entries. */
    protected def readSymbolAnnotation() {
      expect(SYMANNOT, "symbol annotation expected")
      val end = readEnd()
      val target = readSymbolRef()
      target.addAnnotation(readAnnotationInfo(end))
    }

    /** Read an annotation and return it. Used when unpickling
     *  an ANNOTATED(WSELF)tpe or a NestedAnnotArg */
    protected def readAnnotation(): AnnotationInfo = {
      val tag = readByte()
      if (tag != ANNOTINFO)
        errorBadSignature("annotation expected (" + tag + ")")
      val end = readEnd()
      readAnnotationInfo(end)
    }

    private def readNonEmptyTree(tag: Int, end: Int): Tree = {
      @inline def all[T](body: => T): List[T] = until(end, () => body)
      @inline def rep[T](body: => T): List[T] = times(readNat(), () => body)

      // !!! What is this doing here?
      def fixApply(tree: Apply, tpe: Type): Apply = {
        val Apply(fun, args) = tree
        if (fun.symbol.isOverloaded) {
          fun setType fun.symbol.info
          inferMethodAlternative(fun, args map (_.tpe), tpe)
        }
        tree
      }
      def ref()         = readTreeRef()
      def caseRef()     = readCaseDefRef()
      def modsRef()     = readModifiersRef()
      def implRef()     = readTemplateRef()
      def nameRef()     = readNameRef()
      def tparamRef()   = readTypeDefRef()
      def vparamRef()   = readValDefRef()
      def memberRef()   = readMemberDefRef()
      def constRef()    = readConstantRef()
      def idRef()       = readIdentRef()
      def termNameRef() = readNameRef().toTermName
      def typeNameRef() = readNameRef().toTypeName
      def refTreeRef()  = ref() match {
        case t: RefTree => t
        case t          => errorBadSignature("RefTree expected, found " + t.shortClass)
      }
      def selectorsRef() = all(ImportSelector(nameRef(), -1, nameRef(), -1))

      /** A few of the most popular trees have been pulled to the top for
       *  switch efficiency purposes.
       */
      def readTree(tpe: Type): Tree = (tag: @switch) match {
        case IDENTtree           => Ident(nameRef)
        case SELECTtree          => Select(ref, nameRef)
        case APPLYtree           => fixApply(Apply(ref, all(ref)), tpe) // !!!
        case BINDtree            => Bind(nameRef, ref)
        case BLOCKtree           => all(ref) match { case stats :+ expr => Block(stats, expr) }
        case IFtree              => If(ref, ref, ref)
        case LITERALtree         => Literal(constRef)
        case TYPEAPPLYtree       => TypeApply(ref, all(ref))
        case TYPEDtree           => Typed(ref, ref)
        case ALTERNATIVEtree     => Alternative(all(ref))
        case ANNOTATEDtree       => Annotated(ref, ref)
        case APPLIEDTYPEtree     => AppliedTypeTree(ref, all(ref))
        case APPLYDYNAMICtree    => ApplyDynamic(ref, all(ref))
        case ARRAYVALUEtree      => ArrayValue(ref, all(ref))
        case ASSIGNtree          => Assign(ref, ref)
        case CASEtree            => CaseDef(ref, ref, ref)
        case CLASStree           => ClassDef(modsRef, typeNameRef, rep(tparamRef), implRef)
        case COMPOUNDTYPEtree    => CompoundTypeTree(implRef)
        case DEFDEFtree          => DefDef(modsRef, termNameRef, rep(tparamRef), rep(rep(vparamRef)), ref, ref)
        case EXISTENTIALTYPEtree => ExistentialTypeTree(ref, all(memberRef))
        case FUNCTIONtree        => Function(rep(vparamRef), ref)
        case IMPORTtree          => Import(ref, selectorsRef)
        case LABELtree           => LabelDef(termNameRef, rep(idRef), ref)
        case MATCHtree           => Match(ref, all(caseRef))
        case MODULEtree          => ModuleDef(modsRef, termNameRef, implRef)
        case NEWtree             => New(ref)
        case PACKAGEtree         => PackageDef(refTreeRef, all(ref))
        case RETURNtree          => Return(ref)
        case SELECTFROMTYPEtree  => SelectFromTypeTree(ref, typeNameRef)
        case SINGLETONTYPEtree   => SingletonTypeTree(ref)
        case STARtree            => Star(ref)
        case SUPERtree           => Super(ref, typeNameRef)
        case TEMPLATEtree        => Template(rep(ref), vparamRef, all(ref))
        case THIStree            => This(typeNameRef)
        case THROWtree           => Throw(ref)
        case TREtree             => Try(ref, rep(caseRef), ref)
        case TYPEBOUNDStree      => TypeBoundsTree(ref, ref)
        case TYPEDEFtree         => TypeDef(modsRef, typeNameRef, rep(tparamRef), ref)
        case TYPEtree            => TypeTree()
        case UNAPPLYtree         => UnApply(ref, all(ref))
        case VALDEFtree          => ValDef(modsRef, termNameRef, ref, ref)
        case _                   => noSuchTreeTag(tag, end)
      }

      val tpe    = readTypeRef()
      val sym    = if (isTreeSymbolPickled(tag)) readSymbolRef() else null
      val result = readTree(tpe)

      if (sym ne null) result setSymbol sym
      result setType tpe
    }

    /* Read an abstract syntax tree */
    protected def readTree(): Tree = {
      expect(TREE, "tree expected")
      val end = readEnd()
      readByte() match {
        case EMPTYtree => EmptyTree
        case tag       => readNonEmptyTree(tag, end)
      }
    }

    def noSuchTreeTag(tag: Int, end: Int) =
      errorBadSignature("unknown tree type (" + tag + ")")

    def readModifiers(): Modifiers = {
      val tag = readNat()
      if (tag != MODIFIERS)
        errorBadSignature("expected a modifiers tag (" + tag + ")")

      readEnd()
      val pflagsHi = readNat()
      val pflagsLo = readNat()
      val pflags = (pflagsHi.toLong << 32) + pflagsLo
      val flags = pickledToRawFlags(pflags)
      val privateWithin = readNameRef()
      Modifiers(flags, privateWithin, Nil)
    }

    /* Read a reference to a pickled item */
    protected def readSymbolRef(): Symbol             = {//OPT inlined from: at(readNat(), readSymbol) to save on closure creation
      val i = readNat()
      var r = entries(i)
      if (r eq null) {
        val savedIndex = readIndex
        readIndex = index(i)
        r = readSymbol()
        assert(entries(i) eq null, entries(i))
        entries(i) = r
        readIndex = savedIndex
      }
      r.asInstanceOf[Symbol]
    }

    protected def readNameRef(): Name                 = at(readNat(), readName)
    protected def readTypeRef(): Type                 = at(readNat(), () => readType()) // after the NMT_TRANSITION period, we can leave off the () => ... ()
    protected def readConstantRef(): Constant         = at(readNat(), readConstant)
    protected def readAnnotationRef(): AnnotationInfo = at(readNat(), readAnnotation)
    protected def readModifiersRef(): Modifiers       = at(readNat(), readModifiers)
    protected def readTreeRef(): Tree                 = at(readNat(), readTree)

    protected def readTypeNameRef(): TypeName         = readNameRef().toTypeName

    protected def readTemplateRef(): Template =
      readTreeRef() match {
        case templ:Template => templ
        case other =>
          errorBadSignature("expected a template (" + other + ")")
      }
    protected def readCaseDefRef(): CaseDef =
      readTreeRef() match {
        case tree:CaseDef => tree
        case other =>
          errorBadSignature("expected a case def (" + other + ")")
      }
    protected def readValDefRef(): ValDef =
      readTreeRef() match {
        case tree:ValDef => tree
        case other =>
          errorBadSignature("expected a ValDef (" + other + ")")
      }
    protected def readIdentRef(): Ident =
      readTreeRef() match {
        case tree:Ident => tree
        case other =>
          errorBadSignature("expected an Ident (" + other + ")")
      }
    protected def readTypeDefRef(): TypeDef =
      readTreeRef() match {
        case tree:TypeDef => tree
        case other =>
          errorBadSignature("expected an TypeDef (" + other + ")")
      }
    protected def readMemberDefRef(): MemberDef =
      readTreeRef() match {
        case tree:MemberDef => tree
        case other =>
          errorBadSignature("expected an MemberDef (" + other + ")")
      }

    protected def errorBadSignature(msg: String) =
      throw new RuntimeException("malformed Scala signature of " + classRoot.name + " at " + readIndex + "; " + msg)

    def inferMethodAlternative(fun: Tree, argtpes: List[Type], restpe: Type) {} // can't do it; need a compiler for that.

    def newLazyTypeRef(i: Int): LazyType = new LazyTypeRef(i)
    def newLazyTypeRefAndAlias(i: Int, j: Int): LazyType = new LazyTypeRefAndAlias(i, j)

    /** Convert to a type error, that is printed gracefully instead of crashing.
     *
     *  Similar in intent to what SymbolLoader does (but here we don't have access to
     *  error reporting, so we rely on the typechecker to report the error).
     */
    def toTypeError(e: MissingRequirementError) = {
      new TypeError(e.msg)
    }

    /** A lazy type which when completed returns type at index `i`. */
    private class LazyTypeRef(i: Int) extends LazyType with FlagAgnosticCompleter {
      private val definedAtRunId = currentRunId
      private val p = phase
      protected def completeInternal(sym: Symbol) : Unit = try {
        val tp = at(i, () => readType(sym.isTerm)) // after NMT_TRANSITION, revert `() => readType(sym.isTerm)` to `readType`
        if (p ne null)
          slowButSafeEnteringPhase(p) (sym setInfo tp)
        if (currentRunId != definedAtRunId)
          sym.setInfo(adaptToNewRunMap(tp))
      }
      catch {
        case e: MissingRequirementError => throw toTypeError(e)
      }
      override def complete(sym: Symbol) : Unit = {
        completeInternal(sym)
        if (!isCompilerUniverse) markAllCompleted(sym)
      }
      override def load(sym: Symbol) { complete(sym) }
    }

    /** A lazy type which when completed returns type at index `i` and sets alias
     *  of completed symbol to symbol at index `j`.
     */
    private class LazyTypeRefAndAlias(i: Int, j: Int) extends LazyTypeRef(i) {
      override def completeInternal(sym: Symbol) = try {
        super.completeInternal(sym)

        var alias = at(j, readSymbol)
        if (alias.isOverloaded)
          alias = slowButSafeEnteringPhase(picklerPhase)((alias suchThat (alt => sym.tpe =:= sym.owner.thisType.memberType(alt))))

        sym.asInstanceOf[TermSymbol].setAlias(alias)
      }
      catch {
        case e: MissingRequirementError => throw toTypeError(e)
      }
    }
  }
}