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Scala example source code file (TreeGen.scala)

This example Scala source code file (TreeGen.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

apply, boolean, collection, emptytree, list, mutable, nil, position, some, symbol, tree, type

The TreeGen.scala Scala example source code

package scala
package reflect
package internal

import Flags._
import util._
import scala.collection.mutable.ListBuffer

abstract class TreeGen {
  val global: SymbolTable

  import global._
  import definitions._

  def rootId(name: Name)             = Select(Ident(nme.ROOTPKG), name)
  def rootScalaDot(name: Name)       = Select(rootId(nme.scala_) setSymbol ScalaPackage, name)
  def scalaDot(name: Name)           = Select(Ident(nme.scala_) setSymbol ScalaPackage, name)
  def scalaAnnotationDot(name: Name) = Select(scalaDot(nme.annotation), name)
  def scalaAnyRefConstr              = scalaDot(tpnme.AnyRef) // used in ide

  def scalaFunctionConstr(argtpes: List[Tree], restpe: Tree, abstractFun: Boolean = false): Tree = {
    val cls = if (abstractFun)
      mkAttributedRef(AbstractFunctionClass(argtpes.length))
    else
      mkAttributedRef(FunctionClass(argtpes.length))
    AppliedTypeTree(cls, argtpes :+ restpe)
  }

  /** A creator for method calls, e.g. fn[T1, T2, ...](v1, v2, ...)
   *  There are a number of variations.
   *
   *  @param    receiver    symbol of the method receiver
   *  @param    methodName  name of the method to call
   *  @param    targs       type arguments (if Nil, no TypeApply node will be generated)
   *  @param    args        value arguments
   *  @return               the newly created trees.
   */
  def mkMethodCall(receiver: Symbol, methodName: Name, targs: List[Type], args: List[Tree]): Tree =
    mkMethodCall(Select(mkAttributedRef(receiver), methodName), targs, args)
  def mkMethodCall(method: Symbol, targs: List[Type], args: List[Tree]): Tree =
    mkMethodCall(mkAttributedRef(method), targs, args)
  def mkMethodCall(method: Symbol, args: List[Tree]): Tree =
    mkMethodCall(method, Nil, args)
  def mkMethodCall(target: Tree, args: List[Tree]): Tree =
    mkMethodCall(target, Nil, args)
  def mkMethodCall(receiver: Symbol, methodName: Name, args: List[Tree]): Tree =
    mkMethodCall(receiver, methodName, Nil, args)
  def mkMethodCall(receiver: Tree, method: Symbol, targs: List[Type], args: List[Tree]): Tree =
    mkMethodCall(Select(receiver, method), targs, args)

  def mkMethodCall(target: Tree, targs: List[Type], args: List[Tree]): Tree =
    Apply(mkTypeApply(target, mapList(targs)(TypeTree)), args)

  def mkNullaryCall(method: Symbol, targs: List[Type]): Tree =
    mkTypeApply(mkAttributedRef(method), mapList(targs)(TypeTree))

  /** Builds a reference to value whose type is given stable prefix.
   *  The type must be suitable for this.  For example, it
   *  must not be a TypeRef pointing to an abstract type variable.
   */
  def mkAttributedQualifier(tpe: Type): Tree =
    mkAttributedQualifier(tpe, NoSymbol)

  /** Builds a reference to value whose type is given stable prefix.
   *  If the type is unsuitable, e.g. it is a TypeRef for an
   *  abstract type variable, then an Ident will be made using
   *  termSym as the Ident's symbol.  In that case, termSym must
   *  not be NoSymbol.
   */
  def mkAttributedQualifier(tpe: Type, termSym: Symbol): Tree = {
    def failMessage = "mkAttributedQualifier(" + tpe + ", " + termSym + ")"
    tpe match {
      case NoPrefix =>
        EmptyTree
      case ThisType(clazz) =>
        if (clazz.isEffectiveRoot) EmptyTree
        else mkAttributedThis(clazz)
      case SingleType(pre, sym) =>
        mkApplyIfNeeded(mkAttributedStableRef(pre, sym))
      case TypeRef(pre, sym, args) =>
        if (sym.isRoot) {
          mkAttributedThis(sym)
        } else if (sym.isModuleClass) {
          mkApplyIfNeeded(mkAttributedRef(pre, sym.sourceModule))
        } else if (sym.isModule || sym.isClass) {
          assert(phase.erasedTypes, failMessage)
          mkAttributedThis(sym)
        } else if (sym.isType) {
          assert(termSym != NoSymbol, failMessage)
          mkAttributedIdent(termSym) setType tpe
        } else {
          mkAttributedRef(pre, sym)
        }

      case ConstantType(value) =>
        Literal(value) setType tpe

      case AnnotatedType(_, atp) =>
        mkAttributedQualifier(atp)

      case RefinedType(parents, _) =>
        // I am unclear whether this is reachable, but
        // the following implementation looks logical -Lex
        val firstStable = parents.find(_.isStable)
        assert(!firstStable.isEmpty, failMessage + " parents = " + parents)
        mkAttributedQualifier(firstStable.get)

      case _ =>
        abort("bad qualifier received: " + failMessage)
    }
  }
  /** If this is a reference to a method with an empty
   *  parameter list, wrap it in an apply.
   */
  def mkApplyIfNeeded(qual: Tree) = qual.tpe match {
    case MethodType(Nil, restpe) => atPos(qual.pos)(Apply(qual, Nil) setType restpe)
    case _                       => qual
  }

  /** Builds a reference to given symbol with given stable prefix. */
  def mkAttributedRef(pre: Type, sym: Symbol): RefTree = {
    val qual = mkAttributedQualifier(pre)
    qual match {
      case EmptyTree                                  => mkAttributedIdent(sym)
      case This(clazz) if qual.symbol.isEffectiveRoot => mkAttributedIdent(sym)
      case _                                          => mkAttributedSelect(qual, sym)
    }
  }

  /** Builds a reference to given symbol. */
  def mkAttributedRef(sym: Symbol): RefTree =
    if (sym.owner.isClass) mkAttributedRef(sym.owner.thisType, sym)
    else mkAttributedIdent(sym)

  def mkUnattributedRef(sym: Symbol): RefTree = mkUnattributedRef(sym.fullNameAsName('.'))

  def mkUnattributedRef(fullName: Name): RefTree = {
    val hd :: tl = nme.segments(fullName.toString, assumeTerm = fullName.isTermName)
    tl.foldLeft(Ident(hd): RefTree)(Select(_,_))
  }

  /** Replaces tree type with a stable type if possible */
  def stabilize(tree: Tree): Tree = stableTypeFor(tree) match {
    case NoType => tree
    case tp     => tree setType tp
  }

  /** Computes stable type for a tree if possible */
  def stableTypeFor(tree: Tree): Type = (
    if (!treeInfo.admitsTypeSelection(tree)) NoType
    else tree match {
      case This(_)         => ThisType(tree.symbol)
      case Ident(_)        => singleType(tree.symbol.owner.thisType, tree.symbol)
      case Select(qual, _) => singleType(qual.tpe, tree.symbol)
      case _               => NoType
    }
  )

  /** Builds a reference with stable type to given symbol */
  def mkAttributedStableRef(pre: Type, sym: Symbol): Tree =
    stabilize(mkAttributedRef(pre, sym))

  def mkAttributedStableRef(sym: Symbol): Tree =
    stabilize(mkAttributedRef(sym))

  def mkAttributedThis(sym: Symbol): This =
    This(sym.name.toTypeName) setSymbol sym setType sym.thisType

  def mkAttributedIdent(sym: Symbol): RefTree =
    Ident(sym.name) setSymbol sym setType sym.tpeHK

  def mkAttributedSelect(qual: Tree, sym: Symbol): RefTree = {
    // Tests involving the repl fail without the .isEmptyPackage condition.
    if (qual.symbol != null && (qual.symbol.isEffectiveRoot || qual.symbol.isEmptyPackage))
      mkAttributedIdent(sym)
    else {
      // Have to recognize anytime a selection is made on a package
      // so it can be rewritten to foo.bar.`package`.name rather than
      // foo.bar.name if name is in the package object.
      // TODO - factor out the common logic between this and
      // the Typers method "isInPackageObject", used in typedIdent.
      val qualsym = (
        if (qual.tpe ne null) qual.tpe.typeSymbol
        else if (qual.symbol ne null) qual.symbol
        else NoSymbol
      )
      val needsPackageQualifier = (
           (sym ne null)
        && qualsym.hasPackageFlag
        && !(sym.isDefinedInPackage || sym.moduleClass.isDefinedInPackage) // SI-7817 work around strangeness in post-flatten `Symbol#owner`
      )
      val pkgQualifier =
        if (needsPackageQualifier) {
          val packageObject = rootMirror.getPackageObjectWithMember(qual.tpe, sym)
          Select(qual, nme.PACKAGE) setSymbol packageObject setType singleType(qual.tpe, packageObject)
        }
        else qual

      val tree = Select(pkgQualifier, sym)
      if (pkgQualifier.tpe == null) tree
      else tree setType (qual.tpe memberType sym)
    }
  }

  /** Builds a type application node if args.nonEmpty, returns fun otherwise. */
  def mkTypeApply(fun: Tree, targs: List[Tree]): Tree =
    if (targs.isEmpty) fun else TypeApply(fun, targs)
  def mkAppliedTypeTree(fun: Tree, targs: List[Tree]): Tree =
    if (targs.isEmpty) fun else AppliedTypeTree(fun, targs)
  def mkAttributedTypeApply(target: Tree, method: Symbol, targs: List[Type]): Tree =
    mkTypeApply(mkAttributedSelect(target, method), targs map TypeTree)

  private def mkSingleTypeApply(value: Tree, tpe: Type, what: Symbol, wrapInApply: Boolean) = {
    val tapp = mkAttributedTypeApply(value, what, tpe.dealias :: Nil)
    if (wrapInApply) Apply(tapp, Nil) else tapp
  }
  private def typeTestSymbol(any: Boolean) = if (any) Any_isInstanceOf else Object_isInstanceOf
  private def typeCastSymbol(any: Boolean) = if (any) Any_asInstanceOf else Object_asInstanceOf

  /** Builds an instance test with given value and type. */
  def mkIsInstanceOf(value: Tree, tpe: Type, any: Boolean = true, wrapInApply: Boolean = true): Tree =
    mkSingleTypeApply(value, tpe, typeTestSymbol(any), wrapInApply)

  /** Builds a cast with given value and type. */
  def mkAsInstanceOf(value: Tree, tpe: Type, any: Boolean = true, wrapInApply: Boolean = true): Tree =
    mkSingleTypeApply(value, tpe, typeCastSymbol(any), wrapInApply)

  /** Cast `tree` to `pt`, unless tpe is a subtype of pt, or pt is Unit.  */
  def maybeMkAsInstanceOf(tree: Tree, pt: Type, tpe: Type, beforeRefChecks: Boolean = false): Tree =
    if ((pt == UnitTpe) || (tpe <:< pt)) tree
    else atPos(tree.pos)(mkAsInstanceOf(tree, pt, any = true, wrapInApply = !beforeRefChecks))

  /** Apparently we smuggle a Type around as a Literal(Constant(tp))
   *  and the implementation of Constant#tpe is such that x.tpe becomes
   *  ClassType(value.asInstanceOf[Type]), i.e. java.lang.Class[Type].
   *  Can't find any docs on how/why it's done this way. See ticket
   *  SI-490 for some interesting comments from lauri alanko suggesting
   *  that the type given by classOf[T] is too strong and should be
   *  weakened so as not to suggest that classOf[List[String]] is any
   *  different from classOf[List[Int]].
   *
   *  !!! See deconstMap in Erasure for one bug this encoding has induced:
   *  I would be very surprised if there aren't more.
   */
  def mkClassOf(tp: Type): Tree =
    Literal(Constant(tp)) setType ConstantType(Constant(tp))

  /** Builds a list with given head and tail. */
  def mkNil: Tree = mkAttributedRef(NilModule)

  /** Builds a tree representing an undefined local, as in
   *    var x: T = _
   *  which is appropriate to the given Type.
   */
  def mkZero(tp: Type): Tree = tp.typeSymbol match {
    case NothingClass => mkMethodCall(Predef_???, Nil) setType NothingTpe
    case _            => Literal(mkConstantZero(tp)) setType tp
  }

  def mkConstantZero(tp: Type): Constant = tp.typeSymbol match {
    case UnitClass    => Constant(())
    case BooleanClass => Constant(false)
    case FloatClass   => Constant(0.0f)
    case DoubleClass  => Constant(0.0d)
    case ByteClass    => Constant(0.toByte)
    case ShortClass   => Constant(0.toShort)
    case IntClass     => Constant(0)
    case LongClass    => Constant(0L)
    case CharClass    => Constant(0.toChar)
    case _            => Constant(null)
  }

  /** Wrap an expression in a named argument. */
  def mkNamedArg(name: Name, tree: Tree): Tree = mkNamedArg(Ident(name), tree)
  def mkNamedArg(lhs: Tree, rhs: Tree): Tree = atPos(rhs.pos)(AssignOrNamedArg(lhs, rhs))

  /** Builds a tuple */
  def mkTuple(elems: List[Tree], flattenUnary: Boolean = true): Tree = elems match {
    case Nil =>
      Literal(Constant(()))
    case tree :: Nil if flattenUnary =>
      tree
    case _ =>
      Apply(scalaDot(TupleClass(elems.length).name.toTermName), elems)
  }

  def mkTupleType(elems: List[Tree], flattenUnary: Boolean = true): Tree = elems match {
    case Nil =>
      scalaDot(tpnme.Unit)
    case List(tree) if flattenUnary =>
      tree
    case _ =>
      AppliedTypeTree(scalaDot(TupleClass(elems.length).name), elems)
  }

  // tree1 AND tree2
  def mkAnd(tree1: Tree, tree2: Tree): Tree =
    Apply(Select(tree1, Boolean_and), List(tree2))

  // tree1 OR tree2
  def mkOr(tree1: Tree, tree2: Tree): Tree =
    Apply(Select(tree1, Boolean_or), List(tree2))

  def mkRuntimeUniverseRef: Tree = {
    assert(ReflectRuntimeUniverse != NoSymbol)
    mkAttributedRef(ReflectRuntimeUniverse) setType singleType(ReflectRuntimeUniverse.owner.thisPrefix, ReflectRuntimeUniverse)
  }

  def mkSeqApply(arg: Tree): Apply = {
    val factory = Select(mkAttributedRef(SeqModule), nme.apply)
    Apply(factory, List(arg))
  }

  def mkSuperInitCall: Select = Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR)

  /** Generates a template with constructor corresponding to
   *
   *  constrmods (vparams1_) ... (vparams_n) preSuper { presupers }
   *  extends superclass(args_1) ... (args_n) with mixins { self => body }
   *
   *  This gets translated to
   *
   *  extends superclass with mixins { self =>
   *    presupers' // presupers without rhs
   *    vparamss   // abstract fields corresponding to value parameters
   *    def <init>(vparamss) {
   *      presupers
   *      super.<init>(args)
   *    }
   *    body
   *  }
   */
  def mkTemplate(parents: List[Tree], self: ValDef, constrMods: Modifiers,
                 vparamss: List[List[ValDef]], body: List[Tree], superPos: Position = NoPosition): Template = {
    /* Add constructor to template */

    // create parameters for <init> as synthetic trees.
    var vparamss1 = mmap(vparamss) { vd =>
      val param = atPos(vd.pos.makeTransparent) {
        val mods = Modifiers(vd.mods.flags & (IMPLICIT | DEFAULTPARAM | BYNAMEPARAM) | PARAM | PARAMACCESSOR)
        ValDef(mods withAnnotations vd.mods.annotations, vd.name, vd.tpt.duplicate, duplicateAndKeepPositions(vd.rhs))
      }
      param
    }

    val (edefs, rest) = body span treeInfo.isEarlyDef
    val (evdefs, etdefs) = edefs partition treeInfo.isEarlyValDef
    val gvdefs = evdefs map {
      case vdef @ ValDef(_, _, tpt, _) =>
        copyValDef(vdef)(
        // atPos for the new tpt is necessary, since the original tpt might have no position
        // (when missing type annotation for ValDef for example), so even though setOriginal modifies the
        // position of TypeTree, it would still be NoPosition. That's what the author meant.
        tpt = atPos(vdef.pos.focus)(TypeTree() setOriginal tpt setPos tpt.pos.focus),
        rhs = EmptyTree
      )
    }
    val lvdefs = evdefs collect { case vdef: ValDef => copyValDef(vdef)(mods = vdef.mods | PRESUPER) }

    val constr = {
      if (constrMods.isTrait) {
        if (body forall treeInfo.isInterfaceMember) None
        else Some(
          atPos(wrappingPos(superPos, lvdefs)) (
            DefDef(NoMods, nme.MIXIN_CONSTRUCTOR, Nil, ListOfNil, TypeTree(), Block(lvdefs, Literal(Constant())))))
      }
      else {
        // convert (implicit ... ) to ()(implicit ... ) if its the only parameter section
        if (vparamss1.isEmpty || !vparamss1.head.isEmpty && vparamss1.head.head.mods.isImplicit)
          vparamss1 = List() :: vparamss1
        val superCall = pendingSuperCall // we can't know in advance which of the parents will end up as a superclass
                                         // this requires knowing which of the parents is a type macro and which is not
                                         // and that's something that cannot be found out before typer
                                         // (the type macros aren't in the trunk yet, but there is a plan for them to land there soon)
                                         // this means that we don't know what will be the arguments of the super call
                                         // therefore here we emit a dummy which gets populated when the template is named and typechecked
        Some(
          atPos(wrappingPos(superPos, lvdefs ::: vparamss1.flatten).makeTransparent) (
            DefDef(constrMods, nme.CONSTRUCTOR, List(), vparamss1, TypeTree(), Block(lvdefs ::: List(superCall), Literal(Constant())))))
      }
    }
    constr foreach (ensureNonOverlapping(_, parents ::: gvdefs, focus = false))
    // Field definitions for the class - remove defaults.

    val fieldDefs = vparamss.flatten map (vd => {
      val field = copyValDef(vd)(mods = vd.mods &~ DEFAULTPARAM, rhs = EmptyTree)
      // Prevent overlapping of `field` end's position with default argument's start position.
      // This is needed for `Positions.Locator(pos).traverse` to return the correct tree when
      // the `pos` is a point position with all its values equal to `vd.rhs.pos.start`.
      if(field.pos.isRange && vd.rhs.pos.isRange) field.pos = field.pos.withEnd(vd.rhs.pos.start - 1)
      field
    })

    global.Template(parents, self, gvdefs ::: fieldDefs ::: constr ++: etdefs ::: rest)
  }

  def mkParents(ownerMods: Modifiers, parents: List[Tree], parentPos: Position = NoPosition) =
    if (ownerMods.isCase) parents ::: List(scalaDot(tpnme.Product), scalaDot(tpnme.Serializable))
    else if (parents.isEmpty) atPos(parentPos)(scalaAnyRefConstr) :: Nil
    else parents

  def mkClassDef(mods: Modifiers, name: TypeName, tparams: List[TypeDef], templ: Template): ClassDef = {
    val isInterface = mods.isTrait && (templ.body forall treeInfo.isInterfaceMember)
    val mods1 = if (isInterface) (mods | Flags.INTERFACE) else mods
    ClassDef(mods1, name, tparams, templ)
  }

  /** Create positioned tree representing an object creation <new parents { stats }
   *  @param npos  the position of the new
   *  @param cpos  the position of the anonymous class starting with parents
   */
  def mkNew(parents: List[Tree], self: ValDef, stats: List[Tree],
            npos: Position, cpos: Position): Tree =
    if (parents.isEmpty)
      mkNew(List(scalaAnyRefConstr), self, stats, npos, cpos)
    else if (parents.tail.isEmpty && stats.isEmpty) {
      // `Parsers.template` no longer differentiates tpts and their argss
      // e.g. `C()` will be represented as a single tree Apply(Ident(C), Nil)
      // instead of parents = Ident(C), argss = Nil as before
      // this change works great for things that are actually templates
      // but in this degenerate case we need to perform postprocessing
      val app = treeInfo.dissectApplied(parents.head)
      atPos(npos union cpos) { New(app.callee, app.argss) }
    } else {
      val x = tpnme.ANON_CLASS_NAME
      atPos(npos union cpos) {
        Block(
          List(
            atPos(cpos) {
              ClassDef(
                Modifiers(FINAL), x, Nil,
                mkTemplate(parents, self, NoMods, ListOfNil, stats, cpos.focus))
            }),
          atPos(npos) {
            New(
              Ident(x) setPos npos.focus,
              Nil)
          }
        )
      }
    }

  /** Create a tree representing the function type (argtpes) => restpe */
  def mkFunctionTypeTree(argtpes: List[Tree], restpe: Tree): Tree =
    AppliedTypeTree(rootScalaDot(newTypeName("Function" + argtpes.length)), argtpes ::: List(restpe))

  /** Create a literal unit tree that is inserted by the compiler but not
   *  written by end user. It's important to distinguish the two so that
   *  quasiquotes can strip synthetic ones away.
   */
  def mkSyntheticUnit() = Literal(Constant(())).updateAttachment(SyntheticUnitAttachment)

  /** Create block of statements `stats`  */
  def mkBlock(stats: List[Tree]): Tree =
    if (stats.isEmpty) mkSyntheticUnit()
    else if (!stats.last.isTerm) Block(stats, mkSyntheticUnit())
    else if (stats.length == 1) stats.head
    else Block(stats.init, stats.last)

  /** Create a block that wraps multiple statements but don't
   *  do any wrapping if there is just one statement. Used by
   *  quasiquotes, macro c.parse api and toolbox.
   */
  def mkTreeOrBlock(stats: List[Tree]) = stats match {
    case Nil         => EmptyTree
    case head :: Nil => head
    case _           => mkBlock(stats)
  }

  /** Create a tree representing an assignment <lhs = rhs> */
  def mkAssign(lhs: Tree, rhs: Tree): Tree = lhs match {
    case Apply(fn, args) => Apply(atPos(fn.pos)(Select(fn, nme.update)), args :+ rhs)
    case _               => Assign(lhs, rhs)
  }

  def mkPackageObject(defn: ModuleDef, pidPos: Position = NoPosition, pkgPos: Position = NoPosition) = {
    val module = copyModuleDef(defn)(name = nme.PACKAGEkw)
    val pid    = atPos(pidPos)(Ident(defn.name))
    atPos(pkgPos)(PackageDef(pid, module :: Nil))
  }

  // Following objects represent encoding of for loop enumerators
  // into the regular trees. Such representations are used for:
  //
  //   - as intermediate value of enumerators inside of the parser
  //     right before the mkFor desugaring is being called
  //
  //   - as intermediate value of enumerators obtained after
  //     re-sugaring of for loops through build.SyntacticFor
  //     and build.SyntacticForYield (which are used by quasiquotes)
  //
  // The encoding uses regular trees with ForAttachment that helps
  // to reliably differentiate them from normal trees that can have
  // similar shape. fq"$pat <- $rhs" for example is represented in
  // the same way as "`<-`($pat, $rhs)"" but with added attachment to
  // the `<-` identifier.
  //
  // The primary rationale behind such representation in favor of
  // simple case classes is a wish to re-use the same representation
  // between quasiquotes and parser without exposing compiler internals.
  // Opaque tree encoding can be changed/adapted at any time without
  // breaking end users code.

  /** Encode/decode fq"$pat <- $rhs" enumerator as q"`<-`($pat, $rhs)" */
  object ValFrom {
    def apply(pat: Tree, rhs: Tree): Tree =
      Apply(Ident(nme.LARROWkw).updateAttachment(ForAttachment),
        List(pat, rhs))

    def unapply(tree: Tree): Option[(Tree, Tree)] = tree match {
      case Apply(id @ Ident(nme.LARROWkw), List(pat, rhs))
        if id.hasAttachment[ForAttachment.type] =>
        Some((pat, rhs))
      case _ => None
    }
  }

  /** Encode/decode fq"$pat = $rhs" enumerator as q"$pat = $rhs" */
  object ValEq {
    def apply(pat: Tree, rhs: Tree): Tree =
      Assign(pat, rhs).updateAttachment(ForAttachment)

    def unapply(tree: Tree): Option[(Tree, Tree)] = tree match {
      case Assign(pat, rhs)
        if tree.hasAttachment[ForAttachment.type] =>
        Some((pat, rhs))
      case _ => None
    }
  }

  /** Encode/decode fq"if $cond" enumerator as q"`if`($cond)" */
  object Filter {
    def apply(tree: Tree) =
      Apply(Ident(nme.IFkw).updateAttachment(ForAttachment), List(tree))

    def unapply(tree: Tree): Option[Tree] = tree match {
      case Apply(id @ Ident(nme.IFkw), List(cond))
        if id.hasAttachment[ForAttachment.type] =>
        Some((cond))
      case _ => None
    }
  }

  /** Encode/decode body of for yield loop as q"`yield`($tree)" */
  object Yield {
    def apply(tree: Tree): Tree =
      Apply(Ident(nme.YIELDkw).updateAttachment(ForAttachment), List(tree))

    def unapply(tree: Tree): Option[Tree] = tree match {
      case Apply(id @ Ident(nme.YIELDkw), List(tree))
        if id.hasAttachment[ForAttachment.type] =>
        Some(tree)
      case _  => None
    }
  }

  /** Create tree for for-comprehension <for (enums) do body> or
  *   <for (enums) yield body> where mapName and flatMapName are chosen
  *  corresponding to whether this is a for-do or a for-yield.
  *  The creation performs the following rewrite rules:
  *
  *  1.
  *
  *    for (P <- G) E   ==>   G.foreach (P => E)
  *
  *     Here and in the following (P => E) is interpreted as the function (P => E)
  *     if P is a variable pattern and as the partial function { case P => E } otherwise.
  *
  *  2.
  *
  *    for (P <- G) yield E  ==>  G.map (P => E)
  *
  *  3.
  *
  *    for (P_1 <- G_1; P_2 <- G_2; ...) ...
  *      ==>
  *    G_1.flatMap (P_1 => for (P_2 <- G_2; ...) ...)
  *
  *  4.
  *
  *    for (P <- G; E; ...) ...
  *      =>
  *    for (P <- G.filter (P => E); ...) ...
  *
  *  5. For N < MaxTupleArity:
  *
  *    for (P_1 <- G; P_2 = E_2; val P_N = E_N; ...)
  *      ==>
  *    for (TupleN(P_1, P_2, ... P_N) <-
  *      for (x_1 @ P_1 <- G) yield {
  *        val x_2 @ P_2 = E_2
  *        ...
  *        val x_N & P_N = E_N
  *        TupleN(x_1, ..., x_N)
  *      } ...)
  *
  *    If any of the P_i are variable patterns, the corresponding `x_i @ P_i' is not generated
  *    and the variable constituting P_i is used instead of x_i
  *
  *  @param mapName      The name to be used for maps (either map or foreach)
  *  @param flatMapName  The name to be used for flatMaps (either flatMap or foreach)
  *  @param enums        The enumerators in the for expression
  *  @param body          The body of the for expression
  */
  def mkFor(enums: List[Tree], sugarBody: Tree)(implicit fresh: FreshNameCreator): Tree = {
    val (mapName, flatMapName, body) = sugarBody match {
      case Yield(tree) => (nme.map, nme.flatMap, tree)
      case _           => (nme.foreach, nme.foreach, sugarBody)
    }

    /* make a closure pat => body.
     * The closure is assigned a transparent position with the point at pos.point and
     * the limits given by pat and body.
     */
    def makeClosure(pos: Position, pat: Tree, body: Tree): Tree = {
      def wrapped  = wrappingPos(List(pat, body))
      def splitpos = (if (pos != NoPosition) wrapped.withPoint(pos.point) else pos).makeTransparent
      matchVarPattern(pat) match {
        case Some((name, tpt)) =>
          Function(
            List(atPos(pat.pos) { ValDef(Modifiers(PARAM), name.toTermName, tpt, EmptyTree) }),
            body) setPos splitpos
        case None =>
          atPos(splitpos) {
            mkVisitor(List(CaseDef(pat, EmptyTree, body)), checkExhaustive = false)
          }
      }
    }

    /* Make an application  qual.meth(pat => body) positioned at `pos`.
     */
    def makeCombination(pos: Position, meth: TermName, qual: Tree, pat: Tree, body: Tree): Tree =
      // ForAttachment on the method selection is used to differentiate
      // result of for desugaring from a regular method call
      Apply(Select(qual, meth) setPos qual.pos updateAttachment ForAttachment,
        List(makeClosure(pos, pat, body))) setPos pos

    /* If `pat` is not yet a `Bind` wrap it in one with a fresh name */
    def makeBind(pat: Tree): Tree = pat match {
      case Bind(_, _) => pat
      case _ => Bind(freshTermName(), pat) setPos pat.pos
    }

    /* A reference to the name bound in Bind `pat`. */
    def makeValue(pat: Tree): Tree = pat match {
      case Bind(name, _) => Ident(name) setPos pat.pos.focus
    }

    /* The position of the closure that starts with generator at position `genpos`. */
    def closurePos(genpos: Position) =
      if (genpos == NoPosition) NoPosition
      else {
        val end = body.pos match {
          case NoPosition => genpos.point
          case bodypos => bodypos.end
        }
        rangePos(genpos.source, genpos.start, genpos.point, end)
      }

    enums match {
      case (t @ ValFrom(pat, rhs)) :: Nil =>
        makeCombination(closurePos(t.pos), mapName, rhs, pat, body)
      case (t @ ValFrom(pat, rhs)) :: (rest @ (ValFrom(_, _) :: _)) =>
        makeCombination(closurePos(t.pos), flatMapName, rhs, pat,
                        mkFor(rest, sugarBody))
      case (t @ ValFrom(pat, rhs)) :: Filter(test) :: rest =>
        mkFor(ValFrom(pat, makeCombination(rhs.pos union test.pos, nme.withFilter, rhs, pat.duplicate, test)).setPos(t.pos) :: rest, sugarBody)
      case (t @ ValFrom(pat, rhs)) :: rest =>
        val valeqs = rest.take(definitions.MaxTupleArity - 1).takeWhile { ValEq.unapply(_).nonEmpty }
        assert(!valeqs.isEmpty)
        val rest1 = rest.drop(valeqs.length)
        val pats = valeqs map { case ValEq(pat, _) => pat }
        val rhss = valeqs map { case ValEq(_, rhs) => rhs }
        val defpat1 = makeBind(pat)
        val defpats = pats map makeBind
        val pdefs = (defpats, rhss).zipped flatMap mkPatDef
        val ids = (defpat1 :: defpats) map makeValue
        val rhs1 = mkFor(
          List(ValFrom(defpat1, rhs).setPos(t.pos)),
          Yield(Block(pdefs, atPos(wrappingPos(ids)) { mkTuple(ids) }) setPos wrappingPos(pdefs)))
        val allpats = (pat :: pats) map (_.duplicate)
        val pos1 =
          if (t.pos == NoPosition) NoPosition
          else rangePos(t.pos.source, t.pos.start, t.pos.point, rhs1.pos.end)
        val vfrom1 = ValFrom(atPos(wrappingPos(allpats)) { mkTuple(allpats) }, rhs1).setPos(pos1)
        mkFor(vfrom1 :: rest1, sugarBody)
      case _ =>
        EmptyTree //may happen for erroneous input

    }
  }

  /** Create tree for pattern definition <val pat0 = rhs> */
  def mkPatDef(pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[ValDef] =
    mkPatDef(Modifiers(0), pat, rhs)

  /** Create tree for pattern definition <mods val pat0 = rhs> */
  def mkPatDef(mods: Modifiers, pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator): List[ValDef] = matchVarPattern(pat) match {
    case Some((name, tpt)) =>
      List(atPos(pat.pos union rhs.pos) {
        ValDef(mods, name.toTermName, tpt, rhs)
      })

    case None =>
      //  in case there is exactly one variable x_1 in pattern
      //  val/var p = e  ==>  val/var x_1 = e.match (case p => (x_1))
      //
      //  in case there are zero or more than one variables in pattern
      //  val/var p = e  ==>  private synthetic val t$ = e.match (case p => (x_1, ..., x_N))
      //                  val/var x_1 = t$._1
      //                  ...
      //                  val/var x_N = t$._N

      val rhsUnchecked = mkUnchecked(rhs)

      // TODO: clean this up -- there is too much information packked into mkPatDef's `pat` argument
      // when it's a simple identifier (case Some((name, tpt)) -- above),
      // pat should have the type ascription that was specified by the user
      // however, in `case None` (here), we must be careful not to generate illegal pattern trees (such as `(a, b): Tuple2[Int, String]`)
      // i.e., this must hold: pat1 match { case Typed(expr, tp) => assert(expr.isInstanceOf[Ident]) case _ => }
      // if we encounter such an erroneous pattern, we strip off the type ascription from pat and propagate the type information to rhs
      val (pat1, rhs1) = patvarTransformer.transform(pat) match {
        // move the Typed ascription to the rhs
        case Typed(expr, tpt) if !expr.isInstanceOf[Ident] =>
          val rhsTypedUnchecked =
            if (tpt.isEmpty) rhsUnchecked
            else Typed(rhsUnchecked, tpt) setPos (rhs.pos union tpt.pos)
          (expr, rhsTypedUnchecked)
        case ok =>
          (ok, rhsUnchecked)
      }
      val vars = getVariables(pat1)
      val matchExpr = atPos((pat1.pos union rhs.pos).makeTransparent) {
        Match(
          rhs1,
          List(
            atPos(pat1.pos) {
              CaseDef(pat1, EmptyTree, mkTuple(vars map (_._1) map Ident.apply))
            }
          ))
      }
      vars match {
        case List((vname, tpt, pos)) =>
          List(atPos(pat.pos union pos union rhs.pos) {
            ValDef(mods, vname.toTermName, tpt, matchExpr)
          })
        case _ =>
          val tmp = freshTermName()
          val firstDef =
            atPos(matchExpr.pos) {
              ValDef(Modifiers(PrivateLocal | SYNTHETIC | ARTIFACT | (mods.flags & LAZY)),
                     tmp, TypeTree(), matchExpr)
            }
          var cnt = 0
          val restDefs = for ((vname, tpt, pos) <- vars) yield atPos(pos) {
            cnt += 1
            ValDef(mods, vname.toTermName, tpt, Select(Ident(tmp), newTermName("_" + cnt)))
          }
          firstDef :: restDefs
      }
  }

  /** Create tree for for-comprehension generator <val pat0 <- rhs0> */
  def mkGenerator(pos: Position, pat: Tree, valeq: Boolean, rhs: Tree)(implicit fresh: FreshNameCreator): Tree = {
    val pat1 = patvarTransformer.transform(pat)
    if (valeq) ValEq(pat1, rhs).setPos(pos)
    else ValFrom(pat1, mkCheckIfRefutable(pat1, rhs)).setPos(pos)
  }

  def mkCheckIfRefutable(pat: Tree, rhs: Tree)(implicit fresh: FreshNameCreator) =
    if (treeInfo.isVarPatternDeep(pat)) rhs
    else {
      val cases = List(
        CaseDef(pat.duplicate, EmptyTree, Literal(Constant(true))),
        CaseDef(Ident(nme.WILDCARD), EmptyTree, Literal(Constant(false)))
      )
      val visitor = mkVisitor(cases, checkExhaustive = false, nme.CHECK_IF_REFUTABLE_STRING)
      atPos(rhs.pos)(Apply(Select(rhs, nme.withFilter), visitor :: Nil))
    }

  /** If tree is a variable pattern, return Some("its name and type").
   *  Otherwise return none */
  private def matchVarPattern(tree: Tree): Option[(Name, Tree)] = {
    def wildType(t: Tree): Option[Tree] = t match {
      case Ident(x) if x.toTermName == nme.WILDCARD             => Some(TypeTree())
      case Typed(Ident(x), tpt) if x.toTermName == nme.WILDCARD => Some(tpt)
      case _                                                    => None
    }
    tree match {
      case Ident(name)             => Some((name, TypeTree()))
      case Bind(name, body)        => wildType(body) map (x => (name, x))
      case Typed(Ident(name), tpt) => Some((name, tpt))
      case _                       => None
    }
  }

  /** Create visitor <x => x match cases> */
  def mkVisitor(cases: List[CaseDef], checkExhaustive: Boolean, prefix: String = "x$")(implicit fresh: FreshNameCreator): Tree = {
    val x   = freshTermName(prefix)
    val id  = Ident(x)
    val sel = if (checkExhaustive) id else mkUnchecked(id)
    Function(List(mkSyntheticParam(x)), Match(sel, cases))
  }

  /** Traverse pattern and collect all variable names with their types in buffer
   *  The variables keep their positions; whereas the pattern is converted to be
   *  synthetic for all nodes that contain a variable position.
   */
  class GetVarTraverser extends Traverser {
    val buf = new ListBuffer[(Name, Tree, Position)]

    def namePos(tree: Tree, name: Name): Position =
      if (!tree.pos.isRange || name.containsName(nme.raw.DOLLAR)) tree.pos.focus
      else {
        val start = tree.pos.start
        val end = start + name.decode.length
        rangePos(tree.pos.source, start, start, end)
      }

    override def traverse(tree: Tree): Unit = {
      def seenName(name: Name)     = buf exists (_._1 == name)
      def add(name: Name, t: Tree) = if (!seenName(name)) buf += ((name, t, namePos(tree, name)))
      val bl = buf.length

      tree match {
        case Bind(nme.WILDCARD, _)          =>
          super.traverse(tree)

        case Bind(name, Typed(tree1, tpt))  =>
          val newTree = if (treeInfo.mayBeTypePat(tpt)) TypeTree() else tpt.duplicate
          add(name, newTree)
          traverse(tree1)

        case Bind(name, tree1)              =>
          // can assume only name range as position, as otherwise might overlap
          // with binds embedded in pattern tree1
          add(name, TypeTree())
          traverse(tree1)

        case _ =>
          super.traverse(tree)
      }
      if (buf.length > bl)
        tree setPos tree.pos.makeTransparent
    }
    def apply(tree: Tree) = {
      traverse(tree)
      buf.toList
    }
  }

  /** Returns list of all pattern variables, possibly with their types,
   *  without duplicates
   */
  private def getVariables(tree: Tree): List[(Name, Tree, Position)] =
    new GetVarTraverser apply tree

  /** Convert all occurrences of (lower-case) variables in a pattern as follows:
   *    x                  becomes      x @ _
   *    x: T               becomes      x @ (_: T)
   */
  object patvarTransformer extends Transformer {
    override def transform(tree: Tree): Tree = tree match {
      case Ident(name) if (treeInfo.isVarPattern(tree) && name != nme.WILDCARD) =>
        atPos(tree.pos)(Bind(name, atPos(tree.pos.focus) (Ident(nme.WILDCARD))))
      case Typed(id @ Ident(name), tpt) if (treeInfo.isVarPattern(id) && name != nme.WILDCARD) =>
        atPos(tree.pos.withPoint(id.pos.point)) {
          Bind(name, atPos(tree.pos.withStart(tree.pos.point)) {
            Typed(Ident(nme.WILDCARD), tpt)
          })
        }
      case Apply(fn @ Apply(_, _), args) =>
        treeCopy.Apply(tree, transform(fn), transformTrees(args))
      case Apply(fn, args) =>
        treeCopy.Apply(tree, fn, transformTrees(args))
      case Typed(expr, tpt) =>
        treeCopy.Typed(tree, transform(expr), tpt)
      case Bind(name, body) =>
        treeCopy.Bind(tree, name, transform(body))
      case Alternative(_) | Star(_) =>
        super.transform(tree)
      case _ =>
        tree
    }
  }

  // annotate the expression with @unchecked
  def mkUnchecked(expr: Tree): Tree = atPos(expr.pos) {
    // This can't be "Annotated(New(UncheckedClass), expr)" because annotations
    // are very picky about things and it crashes the compiler with "unexpected new".
    Annotated(New(scalaDot(tpnme.unchecked), Nil), expr)
  }

  def mkSyntheticParam(pname: TermName) =
    ValDef(Modifiers(PARAM | SYNTHETIC), pname, TypeTree(), EmptyTree)

  def mkCast(tree: Tree, pt: Type): Tree =
    atPos(tree.pos)(mkAsInstanceOf(tree, pt, any = true, wrapInApply = false))
}

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