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/*
 * Scala.js (https://www.scala-js.org/)
 *
 * Copyright EPFL.
 *
 * Licensed under Apache License 2.0
 * (https://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

package org.scalajs.ir

import scala.annotation.switch

import java.io._
import java.nio._
import java.net.URI

import scala.collection.mutable
import scala.concurrent._

import Names._
import Position._
import Trees._
import Types._
import Tags._
import Version.Unversioned

import Utils.JumpBackByteArrayOutputStream

object Serializers {
  /** Scala.js IR File Magic Number
   *
   *    CA FE : first part of magic number of Java class files
   *    4A 53 : "JS" in ASCII
   *
   */
  final val IRMagicNumber = 0xCAFE4A53

  def serialize(stream: OutputStream, classDef: ClassDef): Unit = {
    new Serializer().serialize(stream, classDef)
  }

  /** Deserializes entry points from the given buffer.
   *
   *  @throws java.nio.BufferUnderflowException if not enough data is available
   *      in the buffer. In this case the buffer's position is unspecified and
   *      needs to be reset by the caller.
   */
  def deserializeEntryPointsInfo(buf: ByteBuffer): EntryPointsInfo =
    withBigEndian(buf)(new Deserializer(_).deserializeEntryPointsInfo())

  /** Deserializes a class def from the given buffer.
   *
   *  @throws java.nio.BufferUnderflowException if not enough data is available
   *      in the buffer. In this case the buffer's position is unspecified and
   *      needs to be reset by the caller.
   */
  def deserialize(buf: ByteBuffer): ClassDef =
    withBigEndian(buf)(new Deserializer(_).deserialize())

  @inline
  private def withBigEndian[T](buf: ByteBuffer)(body: ByteBuffer => T): T = {
    val o = buf.order()
    buf.order(ByteOrder.BIG_ENDIAN)
    try body(buf)
    finally buf.order(o)
  }

  private object PositionFormat {
    /* Positions are serialized incrementally as diffs wrt the last position.
     *
     * Formats are (the first byte is decomposed in bits):
     *
     *   1st byte | next bytes |  description
     *  -----------------------------------------
     *   ccccccc0 |            | Column diff (7-bit signed)
     *   llllll01 | CC         | Line diff (6-bit signed), column (8-bit unsigned)
     *   ____0011 | LL LL CC   | Line diff (16-bit signed), column (8-bit unsigned)
     *   ____0111 | 12 bytes   | File index, line, column (all 32-bit signed)
     *   11111111 |            | NoPosition (is not compared/stored in last position)
     *
     * Underscores are irrelevant and must be set to 0.
     */

    final val Format1Mask = 0x01
    final val Format1MaskValue = 0x00
    final val Format1Shift = 1

    final val Format2Mask = 0x03
    final val Format2MaskValue = 0x01
    final val Format2Shift = 2

    final val Format3Mask = 0x0f
    final val Format3MaskValue = 0x03

    final val FormatFullMask = 0x0f
    final val FormatFullMaskValue = 0x7

    final val FormatNoPositionValue = -1
  }

  private final class EncodedNameKey(val encoded: UTF8String) {
    override def equals(that: Any): Boolean = that match {
      case that: EncodedNameKey =>
        UTF8String.equals(this.encoded, that.encoded)
      case _ =>
        false
    }

    override def hashCode(): Int =
      UTF8String.hashCode(encoded)
  }

  private final class Serializer {
    private[this] val bufferUnderlying = new JumpBackByteArrayOutputStream
    private[this] val buffer = new DataOutputStream(bufferUnderlying)

    private[this] val files = mutable.ListBuffer.empty[URI]
    private[this] val fileIndexMap = mutable.Map.empty[URI, Int]
    private def fileToIndex(file: URI): Int =
      fileIndexMap.getOrElseUpdate(file, (files += file).size - 1)

    private[this] val encodedNames = mutable.ListBuffer.empty[UTF8String]
    private[this] val encodedNameIndexMap = mutable.Map.empty[EncodedNameKey, Int]
    private def encodedNameToIndex(encoded: UTF8String): Int = {
      val byteString = new EncodedNameKey(encoded)
      encodedNameIndexMap.getOrElseUpdate(byteString,
          (encodedNames += encoded).size - 1)
    }

    private[this] val methodNames = mutable.ListBuffer.empty[MethodName]
    private[this] val methodNameIndexMap = mutable.Map.empty[MethodName, Int]
    private def methodNameToIndex(methodName: MethodName): Int = {
      methodNameIndexMap.getOrElseUpdate(methodName, {
        // need to reserve the internal simple names

        def reserveTypeRef(typeRef: TypeRef): Unit = typeRef match {
          case _: PrimRef =>
            // nothing to do
          case ClassRef(className) =>
            encodedNameToIndex(className.encoded)
          case ArrayTypeRef(base, _) =>
            reserveTypeRef(base)
        }

        encodedNameToIndex(methodName.simpleName.encoded)
        methodName.paramTypeRefs.foreach(reserveTypeRef(_))
        reserveTypeRef(methodName.resultTypeRef)
        (methodNames += methodName).size - 1
      })
    }

    private[this] val strings = mutable.ListBuffer.empty[String]
    private[this] val stringIndexMap = mutable.Map.empty[String, Int]
    private def stringToIndex(str: String): Int =
      stringIndexMap.getOrElseUpdate(str, (strings += str).size - 1)

    private[this] var lastPosition: Position = Position.NoPosition

    def serialize(stream: OutputStream, classDef: ClassDef): Unit = {
      // Write tree to buffer and record files, names and strings
      writeClassDef(classDef)

      val s = new DataOutputStream(stream)

      // Write the Scala.js IR magic number
      s.writeInt(IRMagicNumber)

      // Write the Scala.js Version
      s.writeUTF(ScalaJSVersions.binaryEmitted)

      // Write the entry points info
      val entryPointsInfo = EntryPointsInfo.forClassDef(classDef)
      val entryPointEncodedName = entryPointsInfo.className.encoded.bytes
      s.writeInt(entryPointEncodedName.length)
      s.write(entryPointEncodedName)
      s.writeBoolean(entryPointsInfo.hasEntryPoint)

      // Emit the files
      s.writeInt(files.size)
      files.foreach(f => s.writeUTF(f.toString))

      // Emit the names
      s.writeInt(encodedNames.size)
      encodedNames.foreach { encodedName =>
        s.writeInt(encodedName.length)
        s.write(encodedName.bytes)
      }

      def writeTypeRef(typeRef: TypeRef): Unit = typeRef match {
        case PrimRef(tpe) =>
          tpe match {
            case NoType      => s.writeByte(TagVoidRef)
            case BooleanType => s.writeByte(TagBooleanRef)
            case CharType    => s.writeByte(TagCharRef)
            case ByteType    => s.writeByte(TagByteRef)
            case ShortType   => s.writeByte(TagShortRef)
            case IntType     => s.writeByte(TagIntRef)
            case LongType    => s.writeByte(TagLongRef)
            case FloatType   => s.writeByte(TagFloatRef)
            case DoubleType  => s.writeByte(TagDoubleRef)
            case NullType    => s.writeByte(TagNullRef)
            case NothingType => s.writeByte(TagNothingRef)
          }
        case ClassRef(className) =>
          s.writeByte(TagClassRef)
          s.writeInt(encodedNameIndexMap(new EncodedNameKey(className.encoded)))
        case ArrayTypeRef(base, dimensions) =>
          s.writeByte(TagArrayTypeRef)
          writeTypeRef(base)
          s.writeInt(dimensions)
      }

      // Emit the method names
      s.writeInt(methodNames.size)
      methodNames.foreach { methodName =>
        s.writeInt(encodedNameIndexMap(
            new EncodedNameKey(methodName.simpleName.encoded)))
        s.writeInt(methodName.paramTypeRefs.size)
        methodName.paramTypeRefs.foreach(writeTypeRef(_))
        writeTypeRef(methodName.resultTypeRef)
        s.writeBoolean(methodName.isReflectiveProxy)
        writeName(methodName.simpleName)
      }

      // Emit the strings
      s.writeInt(strings.size)
      strings.foreach(s.writeUTF)

      // Paste the buffer
      bufferUnderlying.writeTo(s)

      s.flush()
    }

    def writeTree(tree: Tree): Unit = {
      import buffer._

      def writeTagAndPos(tag: Int): Unit = {
        writeByte(tag)
        writePosition(tree.pos)
      }

      tree match {
        case VarDef(ident, originalName, vtpe, mutable, rhs) =>
          writeTagAndPos(TagVarDef)
          writeLocalIdent(ident); writeOriginalName(originalName)
          writeType(vtpe); writeBoolean(mutable); writeTree(rhs)

        case Skip() =>
          writeTagAndPos(TagSkip)

        case Block(stats) =>
          writeTagAndPos(TagBlock)
          writeTrees(stats)

        case Labeled(label, tpe, body) =>
          writeTagAndPos(TagLabeled)
          writeLabelIdent(label); writeType(tpe); writeTree(body)

        case Assign(lhs, rhs) =>
          writeTagAndPos(TagAssign)
          writeTree(lhs); writeTree(rhs)

        case Return(expr, label) =>
          writeTagAndPos(TagReturn)
          writeTree(expr); writeLabelIdent(label)

        case If(cond, thenp, elsep) =>
          writeTagAndPos(TagIf)
          writeTree(cond); writeTree(thenp); writeTree(elsep)
          writeType(tree.tpe)

        case While(cond, body) =>
          writeTagAndPos(TagWhile)
          writeTree(cond); writeTree(body)

        case ForIn(obj, keyVar, keyVarOriginalName, body) =>
          writeTagAndPos(TagForIn)
          writeTree(obj); writeLocalIdent(keyVar)
          writeOriginalName(keyVarOriginalName); writeTree(body)

        case TryCatch(block, errVar, errVarOriginalName, handler) =>
          writeTagAndPos(TagTryCatch)
          writeTree(block); writeLocalIdent(errVar)
          writeOriginalName(errVarOriginalName); writeTree(handler)
          writeType(tree.tpe)

        case TryFinally(block, finalizer) =>
          writeTagAndPos(TagTryFinally)
          writeTree(block); writeTree(finalizer)

        case Throw(expr) =>
          writeTagAndPos(TagThrow)
          writeTree(expr)

        case Match(selector, cases, default) =>
          writeTagAndPos(TagMatch)
          writeTree(selector)
          writeInt(cases.size)
          cases foreach { caze =>
            writeTrees(caze._1); writeTree(caze._2)
          }
          writeTree(default)
          writeType(tree.tpe)

        case Debugger() =>
          writeTagAndPos(TagDebugger)

        case New(className, ctor, args) =>
          writeTagAndPos(TagNew)
          writeName(className); writeMethodIdent(ctor); writeTrees(args)

        case LoadModule(className) =>
          writeTagAndPos(TagLoadModule)
          writeName(className)

        case StoreModule() =>
          writeTagAndPos(TagStoreModule)

        case Select(qualifier, field) =>
          writeTagAndPos(TagSelect)
          writeTree(qualifier); writeFieldIdent(field)
          writeType(tree.tpe)

        case SelectStatic(field) =>
          writeTagAndPos(TagSelectStatic)
          writeFieldIdent(field)
          writeType(tree.tpe)

        case SelectJSNativeMember(className, member) =>
          writeTagAndPos(TagSelectJSNativeMember)
          writeName(className); writeMethodIdent(member)

        case Apply(flags, receiver, method, args) =>
          writeTagAndPos(TagApply)
          writeApplyFlags(flags); writeTree(receiver); writeMethodIdent(method); writeTrees(args)
          writeType(tree.tpe)

        case ApplyStatically(flags, receiver, className, method, args) =>
          writeTagAndPos(TagApplyStatically)
          writeApplyFlags(flags); writeTree(receiver); writeName(className); writeMethodIdent(method); writeTrees(args)
          writeType(tree.tpe)

        case ApplyStatic(flags, className, method, args) =>
          writeTagAndPos(TagApplyStatic)
          writeApplyFlags(flags); writeName(className); writeMethodIdent(method); writeTrees(args)
          writeType(tree.tpe)

        case ApplyDynamicImport(flags, className, method, args) =>
          writeTagAndPos(TagApplyDynamicImport)
          writeApplyFlags(flags); writeName(className); writeMethodIdent(method); writeTrees(args)

        case UnaryOp(op, lhs) =>
          writeTagAndPos(TagUnaryOp)
          writeByte(op); writeTree(lhs)

        case BinaryOp(op, lhs, rhs) =>
          writeTagAndPos(TagBinaryOp)
          writeByte(op); writeTree(lhs); writeTree(rhs)

        case NewArray(tpe, lengths) =>
          writeTagAndPos(TagNewArray)
          writeArrayTypeRef(tpe); writeTrees(lengths)

        case ArrayValue(tpe, elems) =>
          writeTagAndPos(TagArrayValue)
          writeArrayTypeRef(tpe); writeTrees(elems)

        case ArrayLength(array) =>
          writeTagAndPos(TagArrayLength)
          writeTree(array)

        case ArraySelect(array, index) =>
          writeTagAndPos(TagArraySelect)
          writeTree(array); writeTree(index)
          writeType(tree.tpe)

        case RecordValue(tpe, elems) =>
          writeTagAndPos(TagRecordValue)
          writeType(tpe); writeTrees(elems)

        case RecordSelect(record, field) =>
          writeTagAndPos(TagRecordSelect)
          writeTree(record); writeSimpleFieldIdent(field)
          writeType(tree.tpe)

        case IsInstanceOf(expr, testType) =>
          writeTagAndPos(TagIsInstanceOf)
          writeTree(expr); writeType(testType)

        case AsInstanceOf(expr, tpe) =>
          writeTagAndPos(TagAsInstanceOf)
          writeTree(expr); writeType(tpe)

        case GetClass(expr) =>
          writeTagAndPos(TagGetClass)
          writeTree(expr)

        case Clone(expr) =>
          writeTagAndPos(TagClone)
          writeTree(expr)

        case IdentityHashCode(expr) =>
          writeTagAndPos(TagIdentityHashCode)
          writeTree(expr)

        case WrapAsThrowable(expr) =>
          writeTagAndPos(TagWrapAsThrowable)
          writeTree(expr)

        case UnwrapFromThrowable(expr) =>
          writeTagAndPos(TagUnwrapFromThrowable)
          writeTree(expr)

        case JSNew(ctor, args) =>
          writeTagAndPos(TagJSNew)
          writeTree(ctor); writeTreeOrJSSpreads(args)

        case JSPrivateSelect(qualifier, field) =>
          writeTagAndPos(TagJSPrivateSelect)
          writeTree(qualifier); writeFieldIdent(field)

        case JSSelect(qualifier, item) =>
          writeTagAndPos(TagJSSelect)
          writeTree(qualifier); writeTree(item)

        case JSFunctionApply(fun, args) =>
          writeTagAndPos(TagJSFunctionApply)
          writeTree(fun); writeTreeOrJSSpreads(args)

        case JSMethodApply(receiver, method, args) =>
          writeTagAndPos(TagJSMethodApply)
          writeTree(receiver); writeTree(method); writeTreeOrJSSpreads(args)

        case JSSuperSelect(superClass, qualifier, item) =>
          writeTagAndPos(TagJSSuperSelect)
          writeTree(superClass); writeTree(qualifier); writeTree(item)

        case JSSuperMethodCall(superClass, receiver, method, args) =>
          writeTagAndPos(TagJSSuperMethodCall)
          writeTree(superClass); writeTree(receiver); writeTree(method); writeTreeOrJSSpreads(args)

        case JSSuperConstructorCall(args) =>
          writeTagAndPos(TagJSSuperConstructorCall)
          writeTreeOrJSSpreads(args)

        case JSImportCall(arg) =>
          writeTagAndPos(TagJSImportCall)
          writeTree(arg)

        case JSNewTarget() =>
          writeTagAndPos(TagJSNewTarget)

        case JSImportMeta() =>
          writeTagAndPos(TagJSImportMeta)

        case LoadJSConstructor(className) =>
          writeTagAndPos(TagLoadJSConstructor)
          writeName(className)

        case LoadJSModule(className) =>
          writeTagAndPos(TagLoadJSModule)
          writeName(className)

        case JSDelete(qualifier, item) =>
          writeTagAndPos(TagJSDelete)
          writeTree(qualifier)
          writeTree(item)

        case JSUnaryOp(op, lhs) =>
          writeTagAndPos(TagJSUnaryOp)
          writeInt(op); writeTree(lhs)

        case JSBinaryOp(op, lhs, rhs) =>
          writeTagAndPos(TagJSBinaryOp)
          writeInt(op); writeTree(lhs); writeTree(rhs)

        case JSArrayConstr(items) =>
          writeTagAndPos(TagJSArrayConstr)
          writeTreeOrJSSpreads(items)

        case JSObjectConstr(fields) =>
          writeTagAndPos(TagJSObjectConstr)
          writeInt(fields.size)
          fields.foreach { field =>
            writeTree(field._1); writeTree(field._2)
          }

        case JSGlobalRef(name) =>
          writeTagAndPos(TagJSGlobalRef)
          writeString(name)

        case JSTypeOfGlobalRef(globalRef) =>
          writeTagAndPos(TagJSTypeOfGlobalRef)
          writeTree(globalRef)

        case JSLinkingInfo() =>
          writeTagAndPos(TagJSLinkingInfo)

        case Undefined() =>
          writeTagAndPos(TagUndefined)

        case Null() =>
          writeTagAndPos(TagNull)

        case BooleanLiteral(value) =>
          writeTagAndPos(TagBooleanLiteral)
          writeBoolean(value)

        case CharLiteral(value) =>
          writeTagAndPos(TagCharLiteral)
          writeChar(value)

        case ByteLiteral(value) =>
          writeTagAndPos(TagByteLiteral)
          writeByte(value)

        case ShortLiteral(value) =>
          writeTagAndPos(TagShortLiteral)
          writeShort(value)

        case IntLiteral(value) =>
          writeTagAndPos(TagIntLiteral)
          writeInt(value)

        case LongLiteral(value) =>
          writeTagAndPos(TagLongLiteral)
          writeLong(value)

        case FloatLiteral(value) =>
          writeTagAndPos(TagFloatLiteral)
          writeFloat(value)

        case DoubleLiteral(value) =>
          writeTagAndPos(TagDoubleLiteral)
          writeDouble(value)

        case StringLiteral(value) =>
          writeTagAndPos(TagStringLiteral)
          writeString(value)

        case ClassOf(typeRef) =>
          writeTagAndPos(TagClassOf)
          writeTypeRef(typeRef)

        case VarRef(ident) =>
          writeTagAndPos(TagVarRef)
          writeLocalIdent(ident)
          writeType(tree.tpe)

        case This() =>
          writeTagAndPos(TagThis)
          writeType(tree.tpe)

        case Closure(arrow, captureParams, params, restParam, body, captureValues) =>
          writeTagAndPos(TagClosure)
          writeBoolean(arrow)
          writeParamDefs(captureParams)
          writeParamDefs(params)
          writeOptParamDef(restParam)
          writeTree(body)
          writeTrees(captureValues)

        case CreateJSClass(className, captureValues) =>
          writeTagAndPos(TagCreateJSClass)
          writeName(className)
          writeTrees(captureValues)

        case Transient(value) =>
          throw new InvalidIRException(tree,
              "Cannot serialize a transient IR node (its value is of class " +
              s"${value.getClass})")
      }
    }

    def writeTrees(trees: List[Tree]): Unit = {
      buffer.writeInt(trees.size)
      trees.foreach(writeTree)
    }

    def writeOptTree(optTree: Option[Tree]): Unit = {
      optTree.fold {
        buffer.writeByte(TagEmptyTree)
      } { tree =>
        writeTree(tree)
      }
    }

    def writeTreeOrJSSpreads(trees: List[TreeOrJSSpread]): Unit = {
      buffer.writeInt(trees.size)
      trees.foreach(writeTreeOrJSSpread)
    }

    def writeTreeOrJSSpread(tree: TreeOrJSSpread): Unit = {
      tree match {
        case JSSpread(items) =>
          buffer.writeByte(TagJSSpread)
          writePosition(tree.pos)
          writeTree(items)
        case tree: Tree =>
          writeTree(tree)
      }
    }

    def writeClassDef(classDef: ClassDef): Unit = {
      import buffer._
      import classDef._

      writePosition(classDef.pos)
      writeClassIdent(name)
      writeOriginalName(originalName)
      writeByte(ClassKind.toByte(kind))
      writeBoolean(jsClassCaptures.isDefined)
      jsClassCaptures.foreach(writeParamDefs(_))
      writeOptClassIdent(superClass)
      writeClassIdents(interfaces)
      writeOptTree(jsSuperClass)
      writeJSNativeLoadSpec(jsNativeLoadSpec)
      writeMemberDefs(fields ::: methods ::: jsConstructor.toList ::: jsMethodProps ::: jsNativeMembers)
      writeTopLevelExportDefs(topLevelExportDefs)
      writeInt(OptimizerHints.toBits(optimizerHints))
    }

    def writeMemberDef(memberDef: MemberDef): Unit = {
      import buffer._
      writePosition(memberDef.pos)
      memberDef match {
        case FieldDef(flags, name, originalName, ftpe) =>
          writeByte(TagFieldDef)
          writeInt(MemberFlags.toBits(flags))
          writeFieldIdentForEnclosingClass(name)
          writeOriginalName(originalName)
          writeType(ftpe)

        case JSFieldDef(flags, name, ftpe) =>
          writeByte(TagJSFieldDef)
          writeInt(MemberFlags.toBits(flags))
          writeTree(name)
          writeType(ftpe)

        case methodDef: MethodDef =>
          val MethodDef(flags, name, originalName, args, resultType, body) = methodDef

          writeByte(TagMethodDef)
          writeOptHash(methodDef.version)

          // Prepare for back-jump and write dummy length
          bufferUnderlying.markJump()
          writeInt(-1)

          // Write out method def
          writeInt(MemberFlags.toBits(flags)); writeMethodIdent(name)
          writeOriginalName(originalName)
          writeParamDefs(args); writeType(resultType); writeOptTree(body)
          writeInt(OptimizerHints.toBits(methodDef.optimizerHints))

          // Jump back and write true length
          val length = bufferUnderlying.jumpBack()
          writeInt(length)
          bufferUnderlying.continue()

        case ctorDef: JSConstructorDef =>
          val JSConstructorDef(flags, args, restParam, body) = ctorDef

          writeByte(TagJSConstructorDef)
          writeOptHash(ctorDef.version)

          // Prepare for back-jump and write dummy length
          bufferUnderlying.markJump()
          writeInt(-1)

          // Write out ctor def
          writeInt(MemberFlags.toBits(flags))
          writeParamDefs(args); writeOptParamDef(restParam)
          writePosition(body.pos)
          writeTrees(body.beforeSuper)
          writeTree(body.superCall)
          writeTrees(body.afterSuper)
          writeInt(OptimizerHints.toBits(ctorDef.optimizerHints))

          // Jump back and write true length
          val length = bufferUnderlying.jumpBack()
          writeInt(length)
          bufferUnderlying.continue()

        case methodDef: JSMethodDef =>
          val JSMethodDef(flags, name, args, restParam, body) = methodDef

          writeByte(TagJSMethodDef)
          writeOptHash(methodDef.version)

          // Prepare for back-jump and write dummy length
          bufferUnderlying.markJump()
          writeInt(-1)

          // Write out method def
          writeInt(MemberFlags.toBits(flags)); writeTree(name)
          writeParamDefs(args); writeOptParamDef(restParam); writeTree(body)
          writeInt(OptimizerHints.toBits(methodDef.optimizerHints))

          // Jump back and write true length
          val length = bufferUnderlying.jumpBack()
          writeInt(length)
          bufferUnderlying.continue()

        case propDef: JSPropertyDef =>
          val JSPropertyDef(flags, name, getter, setterArgAndBody) = propDef

          writeByte(TagJSPropertyDef)
          writeOptHash(propDef.version)

          // Prepare for back-jump and write dummy length
          bufferUnderlying.markJump()
          writeInt(-1)

          // Write out prop def
          writeInt(MemberFlags.toBits(flags))
          writeTree(name)
          writeOptTree(getter)
          writeBoolean(setterArgAndBody.isDefined)
          setterArgAndBody foreach { case (arg, body) =>
            writeParamDef(arg); writeTree(body)
          }

          // Jump back and write true length
          val length = bufferUnderlying.jumpBack()
          writeInt(length)
          bufferUnderlying.continue()

        case JSNativeMemberDef(flags, name, jsNativeLoadSpec) =>
          writeByte(TagJSNativeMemberDef)
          writeInt(MemberFlags.toBits(flags))
          writeMethodIdent(name)
          writeJSNativeLoadSpec(Some(jsNativeLoadSpec))
      }
    }

    def writeMemberDefs(memberDefs: List[MemberDef]): Unit = {
      buffer.writeInt(memberDefs.size)
      memberDefs.foreach(writeMemberDef)
    }

    def writeTopLevelExportDef(topLevelExportDef: TopLevelExportDef): Unit = {
      import buffer._
      writePosition(topLevelExportDef.pos)
      topLevelExportDef match {
        case TopLevelJSClassExportDef(moduleID, exportName) =>
          writeByte(TagTopLevelJSClassExportDef)
          writeString(moduleID); writeString(exportName)

        case TopLevelModuleExportDef(moduleID, exportName) =>
          writeByte(TagTopLevelModuleExportDef)
          writeString(moduleID); writeString(exportName)

        case TopLevelMethodExportDef(moduleID, methodDef) =>
          writeByte(TagTopLevelMethodExportDef)
          writeString(moduleID); writeMemberDef(methodDef)

        case TopLevelFieldExportDef(moduleID, exportName, field) =>
          writeByte(TagTopLevelFieldExportDef)
          writeString(moduleID); writeString(exportName); writeFieldIdentForEnclosingClass(field)
      }
    }

    def writeTopLevelExportDefs(
        topLevelExportDefs: List[TopLevelExportDef]): Unit = {
      buffer.writeInt(topLevelExportDefs.size)
      topLevelExportDefs.foreach(writeTopLevelExportDef)
    }

    def writeLocalIdent(ident: LocalIdent): Unit = {
      writePosition(ident.pos)
      writeName(ident.name)
    }

    def writeLabelIdent(ident: LabelIdent): Unit = {
      writePosition(ident.pos)
      writeName(ident.name)
    }

    def writeSimpleFieldIdent(ident: SimpleFieldIdent): Unit = {
      writePosition(ident.pos)
      writeName(ident.name)
    }

    def writeFieldIdent(ident: FieldIdent): Unit = {
      // For historical reasons, the className comes *before* the position
      writeName(ident.name.className)
      writePosition(ident.pos)
      writeName(ident.name.simpleName)
    }

    def writeFieldIdentForEnclosingClass(ident: FieldIdent): Unit = {
      writePosition(ident.pos)
      writeName(ident.name.simpleName)
    }

    def writeMethodIdent(ident: MethodIdent): Unit = {
      writePosition(ident.pos)
      writeMethodName(ident.name)
    }

    def writeClassIdent(ident: ClassIdent): Unit = {
      writePosition(ident.pos)
      writeName(ident.name)
    }

    def writeClassIdents(idents: List[ClassIdent]): Unit = {
      buffer.writeInt(idents.size)
      idents.foreach(writeClassIdent)
    }

    def writeOptClassIdent(optIdent: Option[ClassIdent]): Unit = {
      buffer.writeBoolean(optIdent.isDefined)
      optIdent.foreach(writeClassIdent)
    }

    def writeName(name: Name): Unit =
      buffer.writeInt(encodedNameToIndex(name.encoded))

    def writeMethodName(name: MethodName): Unit =
      buffer.writeInt(methodNameToIndex(name))

    def writeOriginalName(originalName: OriginalName): Unit = {
      buffer.writeBoolean(originalName.isDefined)
      if (originalName.isDefined)
        buffer.writeInt(encodedNameToIndex(originalName.get))
    }

    def writeParamDef(paramDef: ParamDef): Unit = {
      writePosition(paramDef.pos)
      writeLocalIdent(paramDef.name)
      writeOriginalName(paramDef.originalName)
      writeType(paramDef.ptpe)
      buffer.writeBoolean(paramDef.mutable)
    }

    def writeParamDefs(paramDefs: List[ParamDef]): Unit = {
      buffer.writeInt(paramDefs.size)
      paramDefs.foreach(writeParamDef(_))
    }

    def writeOptParamDef(paramDef: Option[ParamDef]): Unit = {
      buffer.writeBoolean(paramDef.isDefined)
      paramDef.foreach(writeParamDef(_))
    }

    def writeType(tpe: Type): Unit = {
      tpe match {
        case AnyType     => buffer.write(TagAnyType)
        case NothingType => buffer.write(TagNothingType)
        case UndefType   => buffer.write(TagUndefType)
        case BooleanType => buffer.write(TagBooleanType)
        case CharType    => buffer.write(TagCharType)
        case ByteType    => buffer.write(TagByteType)
        case ShortType   => buffer.write(TagShortType)
        case IntType     => buffer.write(TagIntType)
        case LongType    => buffer.write(TagLongType)
        case FloatType   => buffer.write(TagFloatType)
        case DoubleType  => buffer.write(TagDoubleType)
        case StringType  => buffer.write(TagStringType)
        case NullType    => buffer.write(TagNullType)
        case NoType      => buffer.write(TagNoType)

        case ClassType(className) =>
          buffer.write(TagClassType)
          writeName(className)

        case ArrayType(arrayTypeRef) =>
          buffer.write(TagArrayType)
          writeArrayTypeRef(arrayTypeRef)

        case RecordType(fields) =>
          buffer.write(TagRecordType)
          buffer.writeInt(fields.size)
          for (RecordType.Field(name, originalName, tpe, mutable) <- fields) {
            writeName(name)
            writeOriginalName(originalName)
            writeType(tpe)
            buffer.writeBoolean(mutable)
          }
      }
    }

    def writeTypeRef(typeRef: TypeRef): Unit = typeRef match {
      case PrimRef(tpe) =>
        tpe match {
          case NoType      => buffer.writeByte(TagVoidRef)
          case BooleanType => buffer.writeByte(TagBooleanRef)
          case CharType    => buffer.writeByte(TagCharRef)
          case ByteType    => buffer.writeByte(TagByteRef)
          case ShortType   => buffer.writeByte(TagShortRef)
          case IntType     => buffer.writeByte(TagIntRef)
          case LongType    => buffer.writeByte(TagLongRef)
          case FloatType   => buffer.writeByte(TagFloatRef)
          case DoubleType  => buffer.writeByte(TagDoubleRef)
          case NullType    => buffer.writeByte(TagNullRef)
          case NothingType => buffer.writeByte(TagNothingRef)
        }
      case ClassRef(className) =>
        buffer.writeByte(TagClassRef)
        writeName(className)
      case typeRef: ArrayTypeRef =>
        buffer.writeByte(TagArrayTypeRef)
        writeArrayTypeRef(typeRef)
    }

    def writeArrayTypeRef(typeRef: ArrayTypeRef): Unit = {
      writeTypeRef(typeRef.base)
      buffer.writeInt(typeRef.dimensions)
    }

    def writeApplyFlags(flags: ApplyFlags): Unit =
      buffer.writeInt(ApplyFlags.toBits(flags))

    def writePosition(pos: Position): Unit = {
      import buffer._
      import PositionFormat._

      def writeFull(): Unit = {
        writeByte(FormatFullMaskValue)
        writeInt(fileToIndex(pos.source))
        writeInt(pos.line)
        writeInt(pos.column)
      }

      if (pos == Position.NoPosition) {
        writeByte(FormatNoPositionValue)
      } else if (lastPosition == Position.NoPosition ||
          pos.source != lastPosition.source) {
        writeFull()
        lastPosition = pos
      } else {
        val line = pos.line
        val column = pos.column
        val lineDiff = line - lastPosition.line
        val columnDiff = column - lastPosition.column
        val columnIsByte = column >= 0 && column < 256

        if (lineDiff == 0 && columnDiff >= -64 && columnDiff < 64) {
          writeByte((columnDiff << Format1Shift) | Format1MaskValue)
        } else if (lineDiff >= -32 && lineDiff < 32 && columnIsByte) {
          writeByte((lineDiff << Format2Shift) | Format2MaskValue)
          writeByte(column)
        } else if (lineDiff >= Short.MinValue && lineDiff <= Short.MaxValue && columnIsByte) {
          writeByte(Format3MaskValue)
          writeShort(lineDiff)
          writeByte(column)
        } else {
          writeFull()
        }

        lastPosition = pos
      }
    }

    def writeJSNativeLoadSpec(jsNativeLoadSpec: Option[JSNativeLoadSpec]): Unit = {
      import buffer._

      def writeGlobalSpec(spec: JSNativeLoadSpec.Global): Unit = {
        writeString(spec.globalRef)
        writeStrings(spec.path)
      }

      def writeImportSpec(spec: JSNativeLoadSpec.Import): Unit = {
        writeString(spec.module)
        writeStrings(spec.path)
      }

      jsNativeLoadSpec.fold {
        writeByte(TagJSNativeLoadSpecNone)
      } { spec =>
        spec match {
          case spec: JSNativeLoadSpec.Global =>
            writeByte(TagJSNativeLoadSpecGlobal)
            writeGlobalSpec(spec)

          case spec: JSNativeLoadSpec.Import =>
            writeByte(TagJSNativeLoadSpecImport)
            writeImportSpec(spec)

          case JSNativeLoadSpec.ImportWithGlobalFallback(importSpec, globalSpec) =>
            writeByte(TagJSNativeLoadSpecImportWithGlobalFallback)
            writeImportSpec(importSpec)
            writeGlobalSpec(globalSpec)
        }
      }
    }

    def writeOptHash(version: Version): Unit = {
      val isHash = version.isHash
      buffer.writeBoolean(isHash)
      if (isHash)
        version.writeHash(buffer)
    }

    def writeString(s: String): Unit =
      buffer.writeInt(stringToIndex(s))

    def writeStrings(strings: List[String]): Unit = {
      buffer.writeInt(strings.size)
      strings.foreach(writeString)
    }
  }

  private final class Deserializer(buf: ByteBuffer) {
    require(buf.order() == ByteOrder.BIG_ENDIAN)

    private[this] var hacks: Hacks = _
    private[this] var files: Array[URI] = _
    private[this] var encodedNames: Array[UTF8String] = _
    private[this] var localNames: Array[LocalName] = _
    private[this] var labelNames: Array[LabelName] = _
    private[this] var simpleFieldNames: Array[SimpleFieldName] = _
    private[this] var simpleMethodNames: Array[SimpleMethodName] = _
    private[this] var classNames: Array[ClassName] = _
    private[this] var methodNames: Array[MethodName] = _
    private[this] var strings: Array[String] = _

    /** Uniqueness cache for FieldName's.
     *
     *  For historical reasons, the `ClassName` and `SimpleFieldName`
     *  components of `FieldName`s are store separately in the `.sjsir` format.
     *  Since most if not all occurrences of any particular `FieldName`
     *  typically come from a single `.sjsir` file, we use a uniqueness cache
     *  to make them all `eq`, consuming less memory and speeding up equality
     *  tests.
     */
    private[this] val uniqueFieldNames = mutable.AnyRefMap.empty[FieldName, FieldName]

    private[this] var lastPosition: Position = Position.NoPosition

    private[this] var enclosingClassName: ClassName = _
    private[this] var thisTypeForHack8: Type = NoType

    def deserializeEntryPointsInfo(): EntryPointsInfo = {
      hacks = new Hacks(sourceVersion = readHeader())
      readEntryPointsInfo()
    }

    def deserialize(): ClassDef = {
      hacks = new Hacks(sourceVersion = readHeader())
      readEntryPointsInfo() // discarded
      files = Array.fill(readInt())(new URI(readUTF()))
      encodedNames = Array.fill(readInt()) {
        val len = readInt()
        val encodedName = new Array[Byte](len)
        buf.get(encodedName)
        UTF8String.createAcquiringByteArray(encodedName)
      }
      localNames = new Array(encodedNames.length)
      labelNames = new Array(encodedNames.length)
      simpleFieldNames = new Array(encodedNames.length)
      simpleMethodNames = new Array(encodedNames.length)
      classNames = new Array(encodedNames.length)
      methodNames = Array.fill(readInt()) {
        val simpleName = readSimpleMethodName()
        val paramTypeRefs = List.fill(readInt())(readTypeRef())
        val resultTypeRef = readTypeRef()
        val isReflectiveProxy = readBoolean()
        MethodName(simpleName, paramTypeRefs, resultTypeRef, isReflectiveProxy)
      }
      strings = Array.fill(readInt())(readUTF())
      readClassDef()
    }

    /** Reads the Scala.js IR header and verifies the version compatibility.
     *
     *  @return the binary version that was read
     */
    private def readHeader(): String = {
      // Check magic number
      if (readInt() != IRMagicNumber)
        throw new IOException("Not a Scala.js IR file")

      // Check that we support this version of the IR
      val version = readUTF()
      ScalaJSVersions.checkSupported(version)

      version
    }

    private def readEntryPointsInfo(): EntryPointsInfo = {
      val encodedNameLen = readInt()
      val encodedName = new Array[Byte](encodedNameLen)
      buf.get(encodedName)
      val name = ClassName(UTF8String.createAcquiringByteArray(encodedName))
      val hasEntryPoint = readBoolean()
      new EntryPointsInfo(name, hasEntryPoint)
    }

    def readTree(): Tree =
      readTreeFromTag(readByte())

    def readOptTree(): Option[Tree] = {
      val tag = readByte()
      if (tag == TagEmptyTree) None
      else Some(readTreeFromTag(tag))
    }

    def readTreeOrJSSpread(): TreeOrJSSpread = {
      val tag = readByte()
      if (tag == TagJSSpread) {
        implicit val pos = readPosition()
        JSSpread(readTree())
      } else {
        readTreeFromTag(tag)
      }
    }

    def readTreeOrJSSpreads(): List[TreeOrJSSpread] =
      List.fill(readInt())(readTreeOrJSSpread())

    private def readTreeFromTag(tag: Byte): Tree = {
      implicit val pos = readPosition()
      (tag: @switch) match {
        case TagEmptyTree =>
          throw new IOException("Found invalid TagEmptyTree")

        case TagVarDef  => VarDef(readLocalIdent(), readOriginalName(), readType(), readBoolean(), readTree())
        case TagSkip    => Skip()
        case TagBlock   => Block(readTrees())
        case TagLabeled => Labeled(readLabelIdent(), readType(), readTree())

        case TagAssign =>
          val lhs0 = readTree()
          val lhs = if (hacks.use4 && lhs0.tpe == NothingType) {
            /* Note [Nothing FieldDef rewrite]
             * (throw qual.field[null]) = rhs  -->  qual.field[null] = rhs
             */
            lhs0 match {
              case Throw(sel: Select) if sel.tpe == NullType => sel
              case _                                         => lhs0
            }
          } else {
            lhs0
          }

          val rhs = readTree()

          Assign(lhs.asInstanceOf[AssignLhs], rhs)

        case TagReturn  => Return(readTree(), readLabelIdent())
        case TagIf      => If(readTree(), readTree(), readTree())(readType())
        case TagWhile   => While(readTree(), readTree())

        case TagDoWhile =>
          if (!hacks.use12)
            throw new IOException(s"Found invalid pre-1.13 DoWhile loop at $pos")
          // Rewrite `do { body } while (cond)` to `while ({ body; cond }) {}`
          val body = readTree()
          val cond = readTree()
          While(Block(body, cond), Skip())

        case TagForIn   => ForIn(readTree(), readLocalIdent(), readOriginalName(), readTree())

        case TagTryCatch =>
          TryCatch(readTree(), readLocalIdent(), readOriginalName(), readTree())(readType())

        case TagTryFinally =>
          TryFinally(readTree(), readTree())

        case TagThrow =>
          val expr = readTree()
          val patchedExpr =
            if (hacks.use8) throwArgumentHack8(expr)
            else expr
          Throw(patchedExpr)

        case TagMatch =>
          Match(readTree(), List.fill(readInt()) {
            (readTrees().map(_.asInstanceOf[MatchableLiteral]), readTree())
          }, readTree())(readType())
        case TagDebugger => Debugger()

        case TagNew          => New(readClassName(), readMethodIdent(), readTrees())
        case TagLoadModule   => LoadModule(readClassName())

        case TagStoreModule =>
          if (hacks.use13) {
            val cls = readClassName()
            val rhs = readTree()
            if (cls != enclosingClassName || !rhs.isInstanceOf[This]) {
              throw new IOException(
                  s"Illegal legacy StoreModule(${cls.nameString}, $rhs) " +
                  s"found in class ${enclosingClassName.nameString}")
            }
          }
          StoreModule()

        case TagSelect =>
          val qualifier = readTree()
          val field = readFieldIdent()
          val tpe = readType()

          if (hacks.use4 && tpe == NothingType) {
            /* Note [Nothing FieldDef rewrite]
             * qual.field[nothing]  -->  throw qual.field[null]
             */
            Throw(Select(qualifier, field)(NullType))
          } else {
            Select(qualifier, field)(tpe)
          }

        case TagSelectStatic => SelectStatic(readFieldIdent())(readType())
        case TagSelectJSNativeMember => SelectJSNativeMember(readClassName(), readMethodIdent())

        case TagApply =>
          Apply(readApplyFlags(), readTree(), readMethodIdent(), readTrees())(
              readType())
        case TagApplyStatically =>
          ApplyStatically(readApplyFlags(), readTree(), readClassName(),
              readMethodIdent(), readTrees())(readType())
        case TagApplyStatic =>
          ApplyStatic(readApplyFlags(), readClassName(), readMethodIdent(),
              readTrees())(readType())
        case TagApplyDynamicImport =>
          ApplyDynamicImport(readApplyFlags(), readClassName(),
              readMethodIdent(), readTrees())

        case TagUnaryOp          => UnaryOp(readByte(), readTree())
        case TagBinaryOp         => BinaryOp(readByte(), readTree(), readTree())
        case TagNewArray         => NewArray(readArrayTypeRef(), readTrees())
        case TagArrayValue       => ArrayValue(readArrayTypeRef(), readTrees())
        case TagArrayLength      => ArrayLength(readTree())
        case TagArraySelect      => ArraySelect(readTree(), readTree())(readType())
        case TagRecordValue      => RecordValue(readType().asInstanceOf[RecordType], readTrees())
        case TagIsInstanceOf     => IsInstanceOf(readTree(), readType())
        case TagAsInstanceOf     => AsInstanceOf(readTree(), readType())
        case TagGetClass         => GetClass(readTree())
        case TagClone            => Clone(readTree())
        case TagIdentityHashCode => IdentityHashCode(readTree())

        case TagWrapAsThrowable =>
          WrapAsThrowable(readTree())
        case TagUnwrapFromThrowable =>
          UnwrapFromThrowable(readTree())

        case TagJSNew                => JSNew(readTree(), readTreeOrJSSpreads())
        case TagJSPrivateSelect      => JSPrivateSelect(readTree(), readFieldIdent())
        case TagJSSelect             => JSSelect(readTree(), readTree())
        case TagJSFunctionApply      => JSFunctionApply(readTree(), readTreeOrJSSpreads())
        case TagJSMethodApply        => JSMethodApply(readTree(), readTree(), readTreeOrJSSpreads())
        case TagJSSuperSelect        => JSSuperSelect(readTree(), readTree(), readTree())
        case TagJSSuperMethodCall    =>
          JSSuperMethodCall(readTree(), readTree(), readTree(), readTreeOrJSSpreads())
        case TagJSSuperConstructorCall => JSSuperConstructorCall(readTreeOrJSSpreads())
        case TagJSImportCall         => JSImportCall(readTree())
        case TagJSNewTarget          => JSNewTarget()
        case TagJSImportMeta         => JSImportMeta()
        case TagLoadJSConstructor    => LoadJSConstructor(readClassName())
        case TagLoadJSModule         => LoadJSModule(readClassName())
        case TagJSDelete             => JSDelete(readTree(), readTree())
        case TagJSUnaryOp            => JSUnaryOp(readInt(), readTree())
        case TagJSBinaryOp           => JSBinaryOp(readInt(), readTree(), readTree())
        case TagJSArrayConstr        => JSArrayConstr(readTreeOrJSSpreads())
        case TagJSObjectConstr       =>
          JSObjectConstr(List.fill(readInt())((readTree(), readTree())))
        case TagJSGlobalRef          => JSGlobalRef(readString())
        case TagJSTypeOfGlobalRef    => JSTypeOfGlobalRef(readTree().asInstanceOf[JSGlobalRef])
        case TagJSLinkingInfo        => JSLinkingInfo()

        case TagUndefined      => Undefined()
        case TagNull           => Null()
        case TagBooleanLiteral => BooleanLiteral(readBoolean())
        case TagCharLiteral    => CharLiteral(readChar())
        case TagByteLiteral    => ByteLiteral(readByte())
        case TagShortLiteral   => ShortLiteral(readShort())
        case TagIntLiteral     => IntLiteral(readInt())
        case TagLongLiteral    => LongLiteral(readLong())
        case TagFloatLiteral   => FloatLiteral(readFloat())
        case TagDoubleLiteral  => DoubleLiteral(readDouble())
        case TagStringLiteral  => StringLiteral(readString())
        case TagClassOf        => ClassOf(readTypeRef())

        case TagVarRef =>
          VarRef(readLocalIdent())(readType())

        case TagThis =>
          val tpe = readType()
          if (hacks.use8)
            This()(thisTypeForHack8)
          else
            This()(tpe)

        case TagClosure =>
          val arrow = readBoolean()
          val captureParams = readParamDefs()
          val (params, restParam) = readParamDefsWithRest()
          val body = if (!hacks.use8) {
            readTree()
          } else {
            val prevThisTypeForHack8 = thisTypeForHack8
            thisTypeForHack8 = if (arrow) NoType else AnyType
            try {
              readTree()
            } finally {
              thisTypeForHack8 = prevThisTypeForHack8
            }
          }
          val captureValues = readTrees()
          Closure(arrow, captureParams, params, restParam, body, captureValues)

        case TagCreateJSClass =>
          CreateJSClass(readClassName(), readTrees())
      }
    }

    /** Patches the argument of a `Throw` for IR version until 1.8.
     *
     *  Prior to Scala.js 1.11, `Throw(e)` was emitted by the compiler with
     *  the somewhat implied assumption that it would "throw an NPE" (but
     *  subject to UB so not really) when `e` is a `null` `Throwable`.
     *
     *  Moreover, there was no other user-space way to emit a `Throw(e)` in the
     *  IR (`js.special.throw` was introduced in 1.11), so *all* `Throw` nodes
     *  are part of the semantics of a Scala `throw expr` or of an implicit
     *  re-throw in a Scala `try..catch`.
     *
     *  In Scala.js 1.11, we explicitly ruled out the NPE behavior of `Throw`,
     *  so that `Throw(e)` only ever throws the value of `e`, while the NPE UB
     *  is specified by `UnwrapFromThrowable`. Among other things, this allows
     *  the user-space code `js.special.throw(e)` to indiscriminately throw `e`
     *  even if it is `null`.
     *
     *  With this hack, we patch `Throw(e)` where `e` is a nullable `Throwable`
     *  by inserting an appropriate `UnwrapFromThrowable`.
     *
     *  Naively, we would just return `UnwrapFromThrowable(e)`. Unfortunately,
     *  we cannot prove that this is type-correct when the type of `e` is a
     *  `ClassType(cls)`, as we cannot test whether `cls` is a subclass of
     *  `java.lang.Throwable`. So we have to produce the following instead:
     *
     *  {{{
     *    if (expr === null) unwrapFromThrowable(null) else expr
     *  }}}
     *
     *  except that evaluates `expr` twice. If it is a `VarRef`, which is a
     *  common case, that is fine. Otherwise, we have to wrap this pattern in
     *  an IIFE.
     *
     *  We also have to avoid the transformation altogether when the `expr` is
     *  an `AnyType`. This happens when the previous Scala.js compiler already
     *  provides the unwrapped exception, which is either
     *
     *  - when automatically re-throwing an unhandled exception at the end of a
     *    `try..catch`, or
     *  - when throwing a maybe-JavaScriptException, with an explicit call to
     *    `runtime.package$.unwrapJavaScriptException(x)`.
     */
    private def throwArgumentHack8(expr: Tree)(implicit pos: Position): Tree = {
      expr.tpe match {
        case NullType =>
          // Evaluate the expression then definitely run into an NPE UB
          UnwrapFromThrowable(expr)

        case ClassType(_) =>
          expr match {
            case New(_, _, _) =>
              // Common case (`throw new SomeException(...)`) that is known not to be `null`
              expr
            case VarRef(_) =>
              /* Common case (explicit re-throw of the form `throw th`) where we don't need the IIFE.
               * if (expr === null) unwrapFromThrowable(null) else expr
               */
              If(BinaryOp(BinaryOp.===, expr, Null()), UnwrapFromThrowable(Null()), expr)(AnyType)
            case _ =>
              /* General case where we need to avoid evaluating `expr` twice.
               * ((x) => if (x === null) unwrapFromThrowable(null) else x)(expr)
               */
              val x = LocalIdent(LocalName("x"))
              val xParamDef = ParamDef(x, OriginalName.NoOriginalName, AnyType, mutable = false)
              val xRef = xParamDef.ref
              val closure = Closure(arrow = true, Nil, List(xParamDef), None, {
                If(BinaryOp(BinaryOp.===, xRef, Null()), UnwrapFromThrowable(Null()), xRef)(AnyType)
              }, Nil)
              JSFunctionApply(closure, List(expr))
          }

        case _ =>
          // Do not transform expressions of other types, in particular `AnyType`
          expr
      }
    }

    def readTrees(): List[Tree] =
      List.fill(readInt())(readTree())

    def readClassDef(): ClassDef = {
      implicit val pos = readPosition()

      val name = readClassIdent()
      val cls = name.name
      enclosingClassName = cls

      val originalName = readOriginalName()
      val kind = ClassKind.fromByte(readByte())

      if (hacks.use8) {
        thisTypeForHack8 = {
          if (kind.isJSType)
            AnyType
          else if (kind == ClassKind.HijackedClass)
            BoxedClassToPrimType.getOrElse(cls, ClassType(cls)) // getOrElse as safety guard
          else
            ClassType(cls)
        }
      }

      val hasJSClassCaptures = readBoolean()
      val jsClassCaptures =
        if (!hasJSClassCaptures) None
        else Some(readParamDefs())
      val superClass = readOptClassIdent()
      val parents = readClassIdents()

      /* jsSuperClass is not hacked like in readMemberDef.bodyHack5. The
       * compilers before 1.6 always use a simple VarRef() as jsSuperClass,
       * when there is one, so no hack is required.
       */
      val jsSuperClass = readOptTree()

      val jsNativeLoadSpec = readJSNativeLoadSpec()

      // Read member defs
      val fieldsBuilder = List.newBuilder[AnyFieldDef]
      val methodsBuilder = List.newBuilder[MethodDef]
      val jsConstructorBuilder = new OptionBuilder[JSConstructorDef]
      val jsMethodPropsBuilder = List.newBuilder[JSMethodPropDef]
      val jsNativeMembersBuilder = List.newBuilder[JSNativeMemberDef]

      for (_ <- 0 until readInt()) {
        implicit val pos = readPosition()
        readByte() match {
          case TagFieldDef          => fieldsBuilder += readFieldDef()
          case TagJSFieldDef        => fieldsBuilder += readJSFieldDef()
          case TagMethodDef         => methodsBuilder += readMethodDef(cls, kind)
          case TagJSConstructorDef  => jsConstructorBuilder += readJSConstructorDef()
          case TagJSMethodDef       => jsMethodPropsBuilder += readJSMethodDef()
          case TagJSPropertyDef     => jsMethodPropsBuilder += readJSPropertyDef()
          case TagJSNativeMemberDef => jsNativeMembersBuilder += readJSNativeMemberDef()
        }
      }

      val topLevelExportDefs = readTopLevelExportDefs()
      val optimizerHints = OptimizerHints.fromBits(readInt())

      val fields = fieldsBuilder.result()

      val methods = {
        val methods0 = methodsBuilder.result()
        if (hacks.use4 && kind.isJSClass) {
          // #4409: Filter out abstract methods in non-native JS classes for version < 1.5
          methods0.filter(_.body.isDefined)
        } else {
          methods0
        }
      }

      val (jsConstructor, jsMethodProps) = {
        if (hacks.use8 && kind.isJSClass) {
          assert(jsConstructorBuilder.result().isEmpty, "found JSConstructorDef in pre 1.8 IR")
          jsConstructorHack(jsMethodPropsBuilder.result())
        } else {
          (jsConstructorBuilder.result(), jsMethodPropsBuilder.result())
        }
      }

      val jsNativeMembers = jsNativeMembersBuilder.result()

      ClassDef(name, originalName, kind, jsClassCaptures, superClass, parents,
          jsSuperClass, jsNativeLoadSpec, fields, methods, jsConstructor,
          jsMethodProps, jsNativeMembers, topLevelExportDefs)(
          optimizerHints)
    }

    private def jsConstructorHack(
        jsMethodProps: List[JSMethodPropDef]): (Option[JSConstructorDef], List[JSMethodPropDef]) = {
      val jsConstructorBuilder = new OptionBuilder[JSConstructorDef]
      val jsMethodPropsBuilder = List.newBuilder[JSMethodPropDef]

      jsMethodProps.foreach {
        case methodDef @ JSMethodDef(flags, StringLiteral("constructor"), args, restParam, body)
            if flags.namespace == MemberNamespace.Public =>
          val bodyStats = body match {
            case Block(stats) => stats
            case _            => body :: Nil
          }

          bodyStats.span(!_.isInstanceOf[JSSuperConstructorCall]) match {
            case (beforeSuper, (superCall: JSSuperConstructorCall) :: afterSuper) =>
              val newFlags = flags.withNamespace(MemberNamespace.Constructor)
              val newBody = JSConstructorBody(beforeSuper, superCall, afterSuper)(body.pos)
              val ctorDef = JSConstructorDef(newFlags, args, restParam, newBody)(
                  methodDef.optimizerHints, Unversioned)(methodDef.pos)
              jsConstructorBuilder += Hashers.hashJSConstructorDef(ctorDef)

            case _ =>
              /* This is awkward: we have an old-style JS constructor that is
               * structurally invalid. We crash in order not to silently
               * ignore errors.
               */
              throw new IOException(
                  s"Found invalid pre-1.11 JS constructor def at ${methodDef.pos}:\n${methodDef.show}")
          }

        case exportedMember =>
          jsMethodPropsBuilder += exportedMember
      }

      (jsConstructorBuilder.result(), jsMethodPropsBuilder.result())
    }

    private def readFieldDef()(implicit pos: Position): FieldDef = {
      val flags = MemberFlags.fromBits(readInt())
      val name = readFieldIdentForEnclosingClass()
      val originalName = readOriginalName()

      val ftpe0 = readType()
      val ftpe = if (hacks.use4 && ftpe0 == NothingType) {
        /* Note [Nothing FieldDef rewrite]
         * val field: nothing  -->  val field: null
         */
        NullType
      } else {
        ftpe0
      }

      FieldDef(flags, name, originalName, ftpe)
    }

    private def readJSFieldDef()(implicit pos: Position): JSFieldDef =
      JSFieldDef(MemberFlags.fromBits(readInt()), readTree(), readType())

    private def readMethodDef(owner: ClassName, ownerKind: ClassKind)(
        implicit pos: Position): MethodDef = {
      val optHash = readOptHash()
      // read and discard the length
      val len = readInt()
      assert(len >= 0)

      val flags = MemberFlags.fromBits(readInt())

      val name = {
        /* In versions 1.0 and 1.1 of the IR, static initializers and
         * class initializers were conflated into one concept, which was
         * handled differently in the linker based on whether the owner
         * was a JS type or not. They were serialized as ``.
         * Starting with 1.2, `` is only for class initializers.
         * If we read a definition for a `` in a non-JS type, we
         * rewrite it as a static initializers instead (``).
         */
        val name0 = readMethodIdent()
        if (hacks.use1 &&
            name0.name == ClassInitializerName &&
            !ownerKind.isJSType) {
          MethodIdent(StaticInitializerName)(name0.pos)
        } else {
          name0
        }
      }

      val originalName = readOriginalName()
      val args = readParamDefs()
      val resultType = readType()
      val body = readOptTree()
      val optimizerHints = OptimizerHints.fromBits(readInt())

      if (hacks.use0 &&
          flags.namespace == MemberNamespace.Public &&
          owner == HackNames.SystemModule &&
          name.name == HackNames.identityHashCodeName) {
        /* #3976: 1.0 javalib relied on wrong linker dispatch.
         * We simply replace it with a correct implementation.
         */
        assert(args.size == 1)

        val patchedBody = Some(IdentityHashCode(args(0).ref))
        val patchedOptimizerHints = OptimizerHints.empty.withInline(true)

        MethodDef(flags, name, originalName, args, resultType, patchedBody)(
            patchedOptimizerHints, optHash)
      } else if (hacks.use4 &&
          flags.namespace == MemberNamespace.Public &&
          owner == ObjectClass &&
          name.name == HackNames.cloneName) {
        /* #4391: In version 1.5, we introduced a dedicated IR node for the
         * primitive operation behind `Object.clone()`. This allowed to
         * simplify the linker by removing several special-cases that
         * treated it specially (for example, preventing it from being
         * inlined if the receiver could be an array). The simplifications
         * mean that the old implementation is not valid anymore, and so we
         * must force using the new implementation if we read IR from an
         * older version.
         */
        assert(args.isEmpty)

        val thisValue = This()(ClassType(ObjectClass))
        val cloneableClassType = ClassType(CloneableClass)

        val patchedBody = Some {
          If(IsInstanceOf(thisValue, cloneableClassType),
              Clone(AsInstanceOf(thisValue, cloneableClassType)),
              Throw(New(
                  HackNames.CloneNotSupportedExceptionClass,
                  MethodIdent(NoArgConstructorName),
                  Nil)))(cloneableClassType)
        }
        val patchedOptimizerHints = OptimizerHints.empty.withInline(true)

        MethodDef(flags, name, originalName, args, resultType, patchedBody)(
            patchedOptimizerHints, optHash)
      } else {
        val patchedBody = body.map(bodyHack5(_, isStat = resultType == NoType))
        MethodDef(flags, name, originalName, args, resultType, patchedBody)(
            optimizerHints, optHash)
      }
    }

    private def readJSConstructorDef()(implicit pos: Position): JSConstructorDef = {
      val optHash = readOptHash()
      // read and discard the length
      val len = readInt()
      assert(len >= 0)

      /* JSConstructorDef was introduced in 1.11. Therefore, by
       * construction, they never need the body hack of 1.5.
       */

      val flags = MemberFlags.fromBits(readInt())
      val (params, restParam) = readParamDefsWithRest()
      val bodyPos = readPosition()
      val beforeSuper = readTrees()
      val superCall = readTree().asInstanceOf[JSSuperConstructorCall]
      val afterSuper = readTrees()
      val body = JSConstructorBody(beforeSuper, superCall, afterSuper)(bodyPos)
      JSConstructorDef(flags, params, restParam, body)(
          OptimizerHints.fromBits(readInt()), optHash)
    }

    private def readJSMethodDef()(implicit pos: Position): JSMethodDef = {
      val optHash = readOptHash()
      // read and discard the length
      val len = readInt()
      assert(len >= 0)

      val flags = MemberFlags.fromBits(readInt())
      val name = bodyHack5Expr(readTree())
      val (params, restParam) = readParamDefsWithRest()
      val body = bodyHack5Expr(readTree())
      JSMethodDef(flags, name, params, restParam, body)(
          OptimizerHints.fromBits(readInt()), optHash)
    }

    private def readJSPropertyDef()(implicit pos: Position): JSPropertyDef = {
      val optHash: Version = {
        if (hacks.use12) {
          Unversioned
        } else {
          val optHash = readOptHash()
          // read and discard the length
          val len = readInt()
          assert(len >= 0)
          optHash
        }
      }

      val flags = MemberFlags.fromBits(readInt())
      val name = bodyHack5Expr(readTree())
      val getterBody = readOptTree().map(bodyHack5Expr(_))
      val setterArgAndBody = {
        if (readBoolean())
          Some((readParamDef(), bodyHack5Expr(readTree())))
        else
          None
      }
      JSPropertyDef(flags, name, getterBody, setterArgAndBody)(optHash)
    }

    private def readJSNativeMemberDef()(implicit pos: Position): JSNativeMemberDef = {
      val flags = MemberFlags.fromBits(readInt())
      val name = readMethodIdent()
      val jsNativeLoadSpec = readJSNativeLoadSpec().get
      JSNativeMemberDef(flags, name, jsNativeLoadSpec)
    }

    private def bodyHack5(body: Tree, isStat: Boolean): Tree = {
      if (!hacks.use5) {
        body
      } else {
        /* #4442 and #4601: Patch Labeled, If, Match and TryCatch nodes in
         * statement position to have type NoType. These 4 nodes are the
         * control structures whose result type is explicitly specified (and
         * not derived from their children like Block or TryFinally, or
         * constant like While).
         */
        new Transformers.Transformer {
          override def transform(tree: Tree, isStat: Boolean): Tree = {
            val newTree = super.transform(tree, isStat)
            if (isStat && newTree.tpe != NoType) {
              newTree match {
                case Labeled(label, _, body) =>
                  Labeled(label, NoType, body)(newTree.pos)
                case If(cond, thenp, elsep) =>
                  If(cond, thenp, elsep)(NoType)(newTree.pos)
                case Match(selector, cases, default) =>
                  Match(selector, cases, default)(NoType)(newTree.pos)
                case TryCatch(block, errVar, errVarOriginalName, handler) =>
                  TryCatch(block, errVar, errVarOriginalName, handler)(NoType)(newTree.pos)
                case _ =>
                  newTree
              }
            } else {
              newTree
            }
          }
        }.transform(body, isStat)
      }
    }

    private def bodyHack5Expr(body: Tree): Tree = bodyHack5(body, isStat = false)

    def readTopLevelExportDef(): TopLevelExportDef = {
      implicit val pos = readPosition()
      val tag = readByte()

      def readJSMethodDef(): JSMethodDef = {
        implicit val pos = readPosition()
        val tag = readByte()
        assert(tag == TagJSMethodDef, s"unexpected tag $tag")
        this.readJSMethodDef()
      }

      def readModuleID(): String =
        if (hacks.use2) DefaultModuleID
        else readString()

      (tag: @switch) match {
        case TagTopLevelJSClassExportDef => TopLevelJSClassExportDef(readModuleID(), readString())
        case TagTopLevelModuleExportDef  => TopLevelModuleExportDef(readModuleID(), readString())
        case TagTopLevelMethodExportDef  => TopLevelMethodExportDef(readModuleID(), readJSMethodDef())

        case TagTopLevelFieldExportDef =>
          TopLevelFieldExportDef(readModuleID(), readString(), readFieldIdentForEnclosingClass())
      }
    }

    def readTopLevelExportDefs(): List[TopLevelExportDef] =
      List.fill(readInt())(readTopLevelExportDef())

    def readLocalIdent(): LocalIdent = {
      implicit val pos = readPosition()
      LocalIdent(readLocalName())
    }

    def readLabelIdent(): LabelIdent = {
      implicit val pos = readPosition()
      LabelIdent(readLabelName())
    }

    def readFieldIdent(): FieldIdent = {
      // For historical reasons, the className comes *before* the position
      val className = readClassName()
      implicit val pos = readPosition()
      val simpleName = readSimpleFieldName()
      FieldIdent(makeFieldName(className, simpleName))
    }

    def readFieldIdentForEnclosingClass(): FieldIdent = {
      implicit val pos = readPosition()
      val simpleName = readSimpleFieldName()
      FieldIdent(makeFieldName(enclosingClassName, simpleName))
    }

    private def makeFieldName(className: ClassName, simpleName: SimpleFieldName): FieldName = {
      val newFieldName = FieldName(className, simpleName)
      uniqueFieldNames.getOrElseUpdate(newFieldName, newFieldName)
    }

    def readMethodIdent(): MethodIdent = {
      implicit val pos = readPosition()
      MethodIdent(readMethodName())
    }

    def readClassIdent(): ClassIdent = {
      implicit val pos = readPosition()
      ClassIdent(readClassName())
    }

    def readClassIdents(): List[ClassIdent] =
      List.fill(readInt())(readClassIdent())

    def readOptClassIdent(): Option[ClassIdent] = {
      if (readBoolean()) Some(readClassIdent())
      else None
    }

    def readParamDef(): ParamDef = {
      implicit val pos = readPosition()
      val name = readLocalIdent()
      val originalName = readOriginalName()
      val ptpe = readType()
      val mutable = readBoolean()

      if (hacks.use4) {
        val rest = readBoolean()
        assert(!rest, "Illegal rest parameter")
      }

      ParamDef(name, originalName, ptpe, mutable)
    }

    def readParamDefs(): List[ParamDef] =
      List.fill(readInt())(readParamDef())

    def readParamDefsWithRest(): (List[ParamDef], Option[ParamDef]) = {
      if (hacks.use4) {
        val (params, isRest) = List.fill(readInt()) {
          implicit val pos = readPosition()
          (ParamDef(readLocalIdent(), readOriginalName(), readType(), readBoolean()), readBoolean())
        }.unzip

        if (isRest.forall(!_)) {
          (params, None)
        } else {
          assert(isRest.init.forall(!_), "illegal non-last rest parameter")
          (params.init, Some(params.last))
        }
      } else {
        val params = readParamDefs()

        val restParam =
          if (readBoolean()) Some(readParamDef())
          else None

        (params, restParam)
      }
    }

    def readType(): Type = {
      val tag = readByte()
      (tag: @switch) match {
        case TagAnyType     => AnyType
        case TagNothingType => NothingType
        case TagUndefType   => UndefType
        case TagBooleanType => BooleanType
        case TagCharType    => CharType
        case TagByteType    => ByteType
        case TagShortType   => ShortType
        case TagIntType     => IntType
        case TagLongType    => LongType
        case TagFloatType   => FloatType
        case TagDoubleType  => DoubleType
        case TagStringType  => StringType
        case TagNullType    => NullType
        case TagNoType      => NoType

        case TagClassType => ClassType(readClassName())
        case TagArrayType => ArrayType(readArrayTypeRef())

        case TagRecordType =>
          RecordType(List.fill(readInt()) {
            val name = readSimpleFieldName()
            val originalName = readString()
            val tpe = readType()
            val mutable = readBoolean()
            RecordType.Field(name, readOriginalName(), tpe, mutable)
          })
      }
    }

    def readTypeRef(): TypeRef = {
      readByte() match {
        case TagVoidRef      => VoidRef
        case TagBooleanRef   => BooleanRef
        case TagCharRef      => CharRef
        case TagByteRef      => ByteRef
        case TagShortRef     => ShortRef
        case TagIntRef       => IntRef
        case TagLongRef      => LongRef
        case TagFloatRef     => FloatRef
        case TagDoubleRef    => DoubleRef
        case TagNullRef      => NullRef
        case TagNothingRef   => NothingRef
        case TagClassRef     => ClassRef(readClassName())
        case TagArrayTypeRef => readArrayTypeRef()
      }
    }

    def readArrayTypeRef(): ArrayTypeRef =
      ArrayTypeRef(readTypeRef().asInstanceOf[NonArrayTypeRef], readInt())

    def readApplyFlags(): ApplyFlags =
      ApplyFlags.fromBits(readInt())

    def readPosition(): Position = {
      import PositionFormat._

      val first = readByte()

      if (first == FormatNoPositionValue) {
        Position.NoPosition
      } else {
        val result = if ((first & FormatFullMask) == FormatFullMaskValue) {
          val file = files(readInt())
          val line = readInt()
          val column = readInt()
          Position(file, line, column)
        } else {
          assert(lastPosition != NoPosition,
              "Position format error: first position must be full")
          if ((first & Format1Mask) == Format1MaskValue) {
            val columnDiff = first >> Format1Shift
            Position(lastPosition.source, lastPosition.line,
                lastPosition.column + columnDiff)
          } else if ((first & Format2Mask) == Format2MaskValue) {
            val lineDiff = first >> Format2Shift
            val column = readByte() & 0xff // unsigned
            Position(lastPosition.source,
                lastPosition.line + lineDiff, column)
          } else {
            assert((first & Format3Mask) == Format3MaskValue,
                s"Position format error: first byte $first does not match any format")
            val lineDiff = readShort()
            val column = readByte() & 0xff // unsigned
            Position(lastPosition.source,
                lastPosition.line + lineDiff, column)
          }
        }
        lastPosition = result
        result
      }
    }

    def readJSNativeLoadSpec(): Option[JSNativeLoadSpec] = {
      def readGlobalSpec(): JSNativeLoadSpec.Global =
        JSNativeLoadSpec.Global(readString(), readStrings())

      def readImportSpec(): JSNativeLoadSpec.Import =
        JSNativeLoadSpec.Import(readString(), readStrings())

      (readByte(): @switch) match {
        case TagJSNativeLoadSpecNone =>
          None
        case TagJSNativeLoadSpecGlobal =>
          Some(readGlobalSpec())
        case TagJSNativeLoadSpecImport =>
          Some(readImportSpec())
        case TagJSNativeLoadSpecImportWithGlobalFallback =>
          Some(JSNativeLoadSpec.ImportWithGlobalFallback(
              readImportSpec(), readGlobalSpec()))
      }
    }

    def readOptHash(): Version = {
      if (readBoolean()) {
        val hash = new Array[Byte](20)
        buf.get(hash)
        Version.fromHash(hash)
      } else {
        Unversioned
      }
    }

    def readString(): String = {
      strings(readInt())
    }

    def readStrings(): List[String] =
      List.fill(readInt())(readString())

    private def readLocalName(): LocalName = {
      val i = readInt()
      val existing = localNames(i)
      if (existing ne null) {
        existing
      } else {
        val result = LocalName(encodedNames(i))
        localNames(i) = result
        result
      }
    }

    private def readLabelName(): LabelName = {
      val i = readInt()
      val existing = labelNames(i)
      if (existing ne null) {
        existing
      } else {
        val result = LabelName(encodedNames(i))
        labelNames(i) = result
        result
      }
    }

    private def readSimpleFieldName(): SimpleFieldName = {
      val i = readInt()
      val existing = simpleFieldNames(i)
      if (existing ne null) {
        existing
      } else {
        val result = SimpleFieldName(encodedNames(i))
        simpleFieldNames(i) = result
        result
      }
    }

    private def readSimpleMethodName(): SimpleMethodName = {
      val i = readInt()
      val existing = simpleMethodNames(i)
      if (existing ne null) {
        existing
      } else {
        val result = SimpleMethodName(encodedNames(i))
        simpleMethodNames(i) = result
        result
      }
    }

    private def readClassName(): ClassName = {
      val i = readInt()
      val existing = classNames(i)
      if (existing ne null) {
        existing
      } else {
        val result = ClassName(encodedNames(i))
        classNames(i) = result
        result
      }
    }

    private def readMethodName(): MethodName =
      methodNames(readInt())

    def readOriginalName(): OriginalName =
      if (readBoolean()) OriginalName(encodedNames(readInt()))
      else OriginalName.NoOriginalName

    private def readBoolean() = buf.get() != 0
    private def readByte() = buf.get()
    private def readChar() = buf.getChar()
    private def readShort() = buf.getShort()
    private def readInt() = buf.getInt()
    private def readLong() = buf.getLong()
    private def readFloat() = buf.getFloat()
    private def readDouble() = buf.getDouble()

    private def readUTF(): String = {
      // DataInput.readUTF for buffers.

      val length = buf.getShort() & 0xffff // unsigned
      var res = ""
      var i = 0

      def badFormat(msg: String) = throw new UTFDataFormatException(msg)

      while (i < length) {
        val a = buf.get()

        i += 1

        val char = {
          if ((a & 0x80) == 0x00) { // 0xxxxxxx
            a.toChar
          } else if ((a & 0xE0) == 0xC0 && i < length) { // 110xxxxx
            val b = buf.get()
            i += 1

            if ((b & 0xC0) != 0x80) // 10xxxxxx
              badFormat("Expected 2 bytes, found: %#02x (init: %#02x)".format(b, a))

            (((a & 0x1F) << 6) | (b & 0x3F)).toChar
          } else if ((a & 0xF0) == 0xE0 && i < length - 1) { // 1110xxxx
            val b = buf.get()
            val c = buf.get()
            i += 2

            if ((b & 0xC0) != 0x80)   // 10xxxxxx
              badFormat("Expected 3 bytes, found: %#02x (init: %#02x)".format(b, a))

            if ((c & 0xC0) != 0x80)   // 10xxxxxx
              badFormat("Expected 3 bytes, found: %#02x, %#02x (init: %#02x)".format(b, c, a))

            (((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F)).toChar
          } else {
            val rem = length - i
            badFormat("Unexpected start of char: %#02x (%d bytes to go)".format(a, rem))
          }
        }

        res += char
      }

      res
    }
  }

  /** Hacks for backwards compatible deserializing. */
  private final class Hacks(sourceVersion: String) {
    val use0: Boolean = sourceVersion == "1.0"

    val use1: Boolean = use0 || sourceVersion == "1.1"

    val use2: Boolean = use1 || sourceVersion == "1.2"

    private val use3: Boolean = use2 || sourceVersion == "1.3"

    val use4: Boolean = use3 || sourceVersion == "1.4"

    val use5: Boolean = use4 || sourceVersion == "1.5"

    private val use6: Boolean = use5 || sourceVersion == "1.6"

    private val use7: Boolean = use6 || sourceVersion == "1.7"

    val use8: Boolean = use7 || sourceVersion == "1.8"

    assert(sourceVersion != "1.9", "source version 1.9 does not exist")
    assert(sourceVersion != "1.10", "source version 1.10 does not exist")

    private val use11: Boolean = use8 || sourceVersion == "1.11"

    val use12: Boolean = use11 || sourceVersion == "1.12"

    val use13: Boolean = use12 || sourceVersion == "1.13"
  }

  /** Names needed for hacks. */
  private object HackNames {
    val CloneNotSupportedExceptionClass =
      ClassName("java.lang.CloneNotSupportedException")
    val SystemModule: ClassName =
      ClassName("java.lang.System$")

    val cloneName: MethodName =
      MethodName("clone", Nil, ClassRef(ObjectClass))
    val identityHashCodeName: MethodName =
      MethodName("identityHashCode", List(ClassRef(ObjectClass)), IntRef)
  }

  private class OptionBuilder[T] {
    private[this] var value: Option[T] = None

    def +=(x: T): Unit = {
      require(value.isEmpty)
      value = Some(x)
    }

    def result(): Option[T] = value
  }

  /* Note [Nothing FieldDef rewrite]
   *
   * Prior to Scala.js 1.5.0, the compiler back-end emitted `FieldDef`s with
   * type `nothing` (`NothingType`). Until Scala.js 1.3.1, such fields happened
   * to link by chance. Scala.js 1.4.0 changed the Emitter in a way that they
   * did not link anymore (#4370), which broke some existing code.
   *
   * In Scala.js 1.5.0, we declared that such definitions are invalid IR, since
   * fields need a zero value to initialize them, and `nothing` doesn't have
   * one.
   *
   * To preserve backward binary compatibility of IR produced by earlier
   * versions, we use the following rewrites as a deserialization hack:
   *
   * - `FieldDef`s with type `nothing` are rewritten with type `null`:
   *   val field: nothing  -->  val field: null
   * - `Select`s with type `nothing` are rewritten with type `null`, but are
   *   then wrapped in a `throw` to preserve the well-typedness of the
   *   surrounding IR:
   *   qual.field[nothing]  -->  throw qual.field[null]
   * - In an `Assign`, the inserted `throw` would be invalid. Therefore we have
   *   to unwrap the `throw`. The rhs being of type `nothing` (in IR that was
   *   originally well typed), it can be assigned to a field of type `null`.
   *   (throw qual.field[null]) = rhs  -->  qual.field[null] = rhs
   */
}




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