path: root/src/dotty/tools/dotc/ast/tpd.scala

package dotty.tools
package dotc
package ast

import core._
import dotty.tools.dotc.transform.TypeUtils
import util.Positions._, Types._, Contexts._, Constants._, Names._, Flags._
import SymDenotations._, Symbols._, StdNames._, Annotations._, Trees._, Symbols._
import Denotations._, Decorators._
import config.Printers._
import typer.Mode
import typer.ErrorReporting._

import scala.annotation.tailrec

/** Some creators for typed trees */
object tpd extends Trees.Instance[Type] with TypedTreeInfo {

  private def ta(implicit ctx: Context) = ctx.typeAssigner

  def Modifiers(sym: Symbol)(implicit ctx: Context): Modifiers = Modifiers(
    sym.flags & ModifierFlags,
    if (sym.privateWithin.exists) sym.privateWithin.asType.name else tpnme.EMPTY,
    sym.annotations map (_.tree))

  def Ident(tp: NamedType)(implicit ctx: Context): Ident =
    ta.assignType(untpd.Ident(tp.name), tp)

  def Select(qualifier: Tree, name: Name)(implicit ctx: Context): Select =
    ta.assignType(untpd.Select(qualifier, name), qualifier)

  def SelectFromTypeTree(qualifier: Tree, name: Name)(implicit ctx: Context): SelectFromTypeTree =
    ta.assignType(untpd.SelectFromTypeTree(qualifier, name), qualifier)

  def SelectFromTypeTree(qualifier: Tree, tp: NamedType)(implicit ctx: Context): SelectFromTypeTree =
    untpd.SelectFromTypeTree(qualifier, tp.name).withType(tp)

  def This(cls: ClassSymbol)(implicit ctx: Context): This =
    untpd.This(cls.name).withType(cls.thisType)

  def Super(qual: Tree, mix: TypeName, inConstrCall: Boolean)(implicit ctx: Context): Super =
    ta.assignType(untpd.Super(qual, mix), qual, inConstrCall)

  def Apply(fn: Tree, args: List[Tree])(implicit ctx: Context): Apply =
    ta.assignType(untpd.Apply(fn, args), fn, args)

  def ensureApplied(fn: Tree)(implicit ctx: Context): Tree =
    if (fn.tpe.widen.isParameterless) fn else Apply(fn, Nil)

  def TypeApply(fn: Tree, args: List[Tree])(implicit ctx: Context): TypeApply =
    ta.assignType(untpd.TypeApply(fn, args), fn, args)

  def Literal(const: Constant)(implicit ctx: Context): Literal =
    ta.assignType(untpd.Literal(const))

  def unitLiteral(implicit ctx: Context): Literal =
    Literal(Constant(()))

  def New(tpt: Tree)(implicit ctx: Context): New =
    ta.assignType(untpd.New(tpt), tpt)

  def New(tp: Type)(implicit ctx: Context): New = New(TypeTree(tp))

  def Pair(left: Tree, right: Tree)(implicit ctx: Context): Pair =
    ta.assignType(untpd.Pair(left, right), left, right)

  def Typed(expr: Tree, tpt: Tree)(implicit ctx: Context): Typed =
    ta.assignType(untpd.Typed(expr, tpt), tpt)

  def NamedArg(name: Name, arg: Tree)(implicit ctx: Context) =
    ta.assignType(untpd.NamedArg(name, arg), arg)

  def Assign(lhs: Tree, rhs: Tree)(implicit ctx: Context): Assign =
    ta.assignType(untpd.Assign(lhs, rhs))

  def Block(stats: List[Tree], expr: Tree)(implicit ctx: Context): Block =
    ta.assignType(untpd.Block(stats, expr), stats, expr)

  def maybeBlock(stats: List[Tree], expr: Tree)(implicit ctx: Context): Tree =
    if (stats.isEmpty) expr else Block(stats, expr)

  def If(cond: Tree, thenp: Tree, elsep: Tree)(implicit ctx: Context): If =
    ta.assignType(untpd.If(cond, thenp, elsep), thenp, elsep)

  def Closure(env: List[Tree], meth: Tree, tpt: Tree)(implicit ctx: Context): Closure =
    ta.assignType(untpd.Closure(env, meth, tpt), meth, tpt)

  /** A function def
   *
   *    vparams => expr
   *
   *  gets expanded to
   *
   *    { def $anonfun(vparams) = expr; Closure($anonfun) }
   *
   *  where the closure's type is the target type of the expression (FunctionN, unless
   *  otherwise specified).
   */
  def Closure(meth: TermSymbol, rhsFn: List[List[Tree]] => Tree, targs: List[Tree] = Nil, targetType: Type = NoType)(implicit ctx: Context): Block = {
    val targetTpt = if (targetType.exists) TypeTree(targetType) else EmptyTree
    val call =
      if (targs.isEmpty) Ident(TermRef(NoPrefix, meth))
      else TypeApply(Ident(TermRef(NoPrefix, meth)), targs)
    Block(
      DefDef(meth, rhsFn) :: Nil,
      Closure(Nil, call, targetTpt))
  }

  def CaseDef(pat: Tree, guard: Tree, body: Tree)(implicit ctx: Context): CaseDef =
    ta.assignType(untpd.CaseDef(pat, guard, body), body)

  def Match(selector: Tree, cases: List[CaseDef])(implicit ctx: Context): Match =
    ta.assignType(untpd.Match(selector, cases), cases)

  def Return(expr: Tree, from: Tree)(implicit ctx: Context): Return =
    ta.assignType(untpd.Return(expr, from))

  def Try(block: Tree, handler: Tree, finalizer: Tree)(implicit ctx: Context): Try =
    ta.assignType(untpd.Try(block, handler, finalizer), block, handler)

  def Throw(expr: Tree)(implicit ctx: Context): Throw =
    ta.assignType(untpd.Throw(expr))

  def SeqLiteral(elems: List[Tree])(implicit ctx: Context): SeqLiteral =
    ta.assignType(untpd.SeqLiteral(elems), elems)

  def SeqLiteral(tpe: Type, elems: List[Tree])(implicit ctx: Context): SeqLiteral =
    if (tpe derivesFrom defn.SeqClass) SeqLiteral(elems) else JavaSeqLiteral(elems)

  def JavaSeqLiteral(elems: List[Tree])(implicit ctx: Context): SeqLiteral =
    new untpd.JavaSeqLiteral(elems)
      .withType(defn.ArrayClass.typeRef.appliedTo(ctx.typeComparer.lub(elems.tpes)))

  def TypeTree(original: Tree)(implicit ctx: Context): TypeTree =
    TypeTree(original.tpe, original)

  def TypeTree(tp: Type, original: Tree = EmptyTree)(implicit ctx: Context): TypeTree =
    untpd.TypeTree(original).withType(tp)

  def SingletonTypeTree(ref: Tree)(implicit ctx: Context): SingletonTypeTree =
    ta.assignType(untpd.SingletonTypeTree(ref), ref)

  def AndTypeTree(left: Tree, right: Tree)(implicit ctx: Context): AndTypeTree =
    ta.assignType(untpd.AndTypeTree(left, right), left, right)

  def OrTypeTree(left: Tree, right: Tree)(implicit ctx: Context): OrTypeTree =
    ta.assignType(untpd.OrTypeTree(left, right), left, right)

  // RefinedTypeTree is missing, handled specially in Typer and Unpickler.

  def AppliedTypeTree(tycon: Tree, args: List[Tree])(implicit ctx: Context): AppliedTypeTree =
    ta.assignType(untpd.AppliedTypeTree(tycon, args), tycon, args)

  def ByNameTypeTree(result: Tree)(implicit ctx: Context): ByNameTypeTree =
    ta.assignType(untpd.ByNameTypeTree(result), result)

  def TypeBoundsTree(lo: Tree, hi: Tree)(implicit ctx: Context): TypeBoundsTree =
    ta.assignType(untpd.TypeBoundsTree(lo, hi), lo, hi)

  def Bind(sym: TermSymbol, body: Tree)(implicit ctx: Context): Bind =
    ta.assignType(untpd.Bind(sym.name, body), sym)

  def Alternative(trees: List[Tree])(implicit ctx: Context): Alternative =
    ta.assignType(untpd.Alternative(trees), trees)

  def UnApply(fun: Tree, implicits: List[Tree], patterns: List[Tree], proto: Type)(implicit ctx: Context): UnApply =
    ta.assignType(untpd.UnApply(fun, implicits, patterns), proto)

  def ValDef(sym: TermSymbol, rhs: Tree = EmptyTree)(implicit ctx: Context): ValDef =
    ta.assignType(untpd.ValDef(Modifiers(sym), sym.name, TypeTree(sym.info), rhs), sym)

  def SyntheticValDef(name: TermName, rhs: Tree)(implicit ctx: Context): ValDef =
    ValDef(ctx.newSymbol(ctx.owner, name, Synthetic, rhs.tpe.widen, coord = rhs.pos), rhs)

  def DefDef(sym: TermSymbol, rhs: Tree = EmptyTree)(implicit ctx: Context): DefDef =
    ta.assignType(DefDef(sym, Function.const(rhs) _), sym)

  def DefDef(sym: TermSymbol, rhsFn: List[List[Tree]] => Tree)(implicit ctx: Context): DefDef =
    polyDefDef(sym, Function.const(rhsFn))

  def polyDefDef(sym: TermSymbol, rhsFn: List[Type] => List[List[Tree]] => Tree)(implicit ctx: Context): DefDef = {
    val (tparams, mtp) = sym.info match {
      case tp: PolyType =>
        val tparams = ctx.newTypeParams(sym, tp.paramNames, EmptyFlags, tp.instantiateBounds)
        (tparams, tp.instantiate(tparams map (_.typeRef)))
      case tp => (Nil, tp)
    }

    def valueParamss(tp: Type): (List[List[TermSymbol]], Type) = tp match {
      case tp @ MethodType(paramNames, paramTypes) =>
        def valueParam(name: TermName, info: Type): TermSymbol =
          ctx.newSymbol(sym, name, TermParam, info)
        val params = (paramNames, paramTypes).zipped.map(valueParam)
        val (paramss, rtp) = valueParamss(tp.instantiate(params map (_.termRef)))
        (params :: paramss, rtp)
      case tp => (Nil, tp.widenExpr)
    }
    val (vparamss, rtp) = valueParamss(mtp)
    val targs = tparams map (_.typeRef)
    val argss = vparamss.nestedMap(vparam => Ident(vparam.termRef))
    ta.assignType(
      untpd.DefDef(
        Modifiers(sym), sym.name, tparams map TypeDef,
        vparamss.nestedMap(ValDef(_)), TypeTree(rtp), rhsFn(targs)(argss)), sym)
  }

  def TypeDef(sym: TypeSymbol)(implicit ctx: Context): TypeDef =
    ta.assignType(untpd.TypeDef(Modifiers(sym), sym.name, TypeTree(sym.info)), sym)

  def ClassDef(cls: ClassSymbol, constr: DefDef, body: List[Tree], superArgs: List[Tree] = Nil)(implicit ctx: Context): TypeDef = {
    val firstParent :: otherParents = cls.info.parents
    val superRef =
      if (cls is Trait) TypeTree(firstParent)
      else {
        def isApplicable(ctpe: Type): Boolean = ctpe match {
          case ctpe: PolyType =>
            isApplicable(ctpe.instantiate(firstParent.argTypes))
          case ctpe: MethodType =>
            (superArgs corresponds ctpe.paramTypes)(_.tpe <:< _)
          case _ =>
            false
        }
        val constr = firstParent.decl(nme.CONSTRUCTOR).suchThat(constr => isApplicable(constr.info))
        New(firstParent, constr.symbol.asTerm, superArgs)
      }
    val parents = superRef :: otherParents.map(TypeTree(_))

    val selfType =
      if (cls.classInfo.selfInfo ne NoType) ValDef(ctx.newSelfSym(cls))
      else EmptyValDef
    def isOwnTypeParam(stat: Tree) =
      (stat.symbol is TypeParam) && stat.symbol.owner == cls
    val bodyTypeParams = body filter isOwnTypeParam map (_.symbol)
    val newTypeParams =
      for (tparam <- cls.typeParams if !(bodyTypeParams contains tparam))
      yield TypeDef(tparam)
    val findLocalDummy = new FindLocalDummyAccumulator(cls)
    val localDummy = ((NoSymbol: Symbol) /: body)(findLocalDummy)
      .orElse(ctx.newLocalDummy(cls))
    val impl = untpd.Template(constr, parents, selfType, newTypeParams ++ body)
      .withType(localDummy.nonMemberTermRef)
    ta.assignType(untpd.TypeDef(Modifiers(cls), cls.name, impl), cls)
  }

  def Import(expr: Tree, selectors: List[untpd.Tree])(implicit ctx: Context): Import =
    ta.assignType(untpd.Import(expr, selectors), ctx.newImportSymbol(expr))

  def PackageDef(pid: RefTree, stats: List[Tree])(implicit ctx: Context): PackageDef =
    ta.assignType(untpd.PackageDef(pid, stats), pid)

  def Annotated(annot: Tree, arg: Tree)(implicit ctx: Context): Annotated =
    ta.assignType(untpd.Annotated(annot, arg), annot, arg)

  // ------ Making references ------------------------------------------------------

  def prefixIsElidable(tp: NamedType)(implicit ctx: Context) = {
    def test(implicit ctx: Context) = tp.prefix match {
      case NoPrefix =>
        true
      case pre: ThisType =>
        pre.cls.isStaticOwner ||
          tp.symbol.is(ParamOrAccessor) && ctx.owner.enclosingClass.derivesFrom(pre.cls)
      case pre: TermRef =>
        pre.symbol.is(Module) && pre.symbol.isStatic
      case _ =>
        false
    }
    try test
    catch { // See remark in SymDenotations#accessWithin
      case ex: NotDefinedHere => test(ctx.addMode(Mode.FutureDefsOK))
    }
  }

  def needsSelect(tp: Type)(implicit ctx: Context) = tp match {
    case tp: TermRef => !prefixIsElidable(tp)
    case _ => false
  }

  /** A tree representing the same reference as the given type */
  def ref(tp: NamedType)(implicit ctx: Context): Tree =
    if (tp.isType) TypeTree(tp)
    else if (prefixIsElidable(tp)) Ident(tp)
    else tp.prefix match {
      case pre: SingletonType => singleton(pre).select(tp)
      case pre => SelectFromTypeTree(TypeTree(pre), tp)
    } // no checks necessary

  def ref(sym: Symbol)(implicit ctx: Context): Tree =
    ref(NamedType(sym.owner.thisType, sym.name, sym.denot))

  def singleton(tp: Type)(implicit ctx: Context): Tree = tp match {
    case tp: TermRef => ref(tp)
    case tp: ThisType => This(tp.cls)
    case SuperType(qual, _) => singleton(qual)
    case ConstantType(value) => Literal(value)
  }

  // ------ Creating typed equivalents of trees that exist only in untyped form -------

  /** new C(args), calling the primary constructor of C */
  def New(tp: Type, args: List[Tree])(implicit ctx: Context): Apply =
    New(tp, tp.typeSymbol.primaryConstructor.asTerm, args)

  /** new C(args), calling given constructor `constr` of C */
  def New(tp: Type, constr: TermSymbol, args: List[Tree])(implicit ctx: Context): Apply = {
    val targs = tp.argTypes
    New(tp withoutArgs targs)
      .select(TermRef.withSig(tp.normalizedPrefix, constr))
      .appliedToTypes(targs)
      .appliedToArgs(args)
  }

  /** An object def
   *
   *     object obs extends parents { decls }
   *
   *  gets expanded to
   *
   *     <module> val obj = new obj$
   *     <module> class obj$ extends parents { this: obj.type => decls }
   *
   *  (The following no longer applies:
   *  What's interesting here is that the block is well typed
   *  (because class obj$ is hoistable), but the type of the `obj` val is
   *  not expressible. What needs to happen in general when
   *  inferring the type of a val from its RHS, is: if the type contains
   *  a class that has the val itself as owner, then that class
   *  is remapped to have the val's owner as owner. Remapping could be
   *  done by cloning the class with the new owner and substituting
   *  everywhere in the tree. We know that remapping is safe
   *  because the only way a local class can appear in the RHS of a val is
   *  by being hoisted outside of a block, and the necessary checks are
   *  done at this point already.
   *
   *  On the other hand, for method result type inference, if the type of
   *  the RHS of a method contains a class owned by the method, this would be
   *  an error.)
   */
  def ModuleDef(sym: TermSymbol, body: List[Tree])(implicit ctx: Context): tpd.Thicket = {
    val modcls = sym.moduleClass.asClass
    val constrSym = modcls.primaryConstructor orElse ctx.newDefaultConstructor(modcls).entered
    val constr = DefDef(constrSym.asTerm, EmptyTree)
    val clsdef = ClassDef(modcls, constr, body)
    val valdef = ValDef(sym, New(modcls.typeRef))
    Thicket(valdef, clsdef)
  }

  def initValue(tpe: Types.Type)(implicit ctx: Context) = {
    val tpw = tpe.widen

    if (tpw isRef defn.IntClass) Literal(Constant(0))
    else if (tpw isRef defn.LongClass) Literal(Constant(0L))
    else if (tpw isRef defn.BooleanClass) Literal(Constant(false))
    else if (tpw isRef defn.CharClass) Literal(Constant('\u0000'))
    else if (tpw isRef defn.FloatClass) Literal(Constant(0f))
    else if (tpw isRef defn.DoubleClass) Literal(Constant(0d))
    else if (tpw isRef defn.ByteClass) Literal(Constant(0.toByte))
    else if (tpw isRef defn.ShortClass) Literal(Constant(0.toShort))
    else Literal(Constant(null)).select(defn.Any_asInstanceOf).appliedToType(tpe)
  }

  private class FindLocalDummyAccumulator(cls: ClassSymbol)(implicit ctx: Context) extends TreeAccumulator[Symbol] {
    def apply(sym: Symbol, tree: Tree) =
      if (sym.exists) sym
      else if (tree.isDef) {
        val owner = tree.symbol.owner
        if (owner.isLocalDummy && owner.owner == cls) owner
        else if (owner == cls) foldOver(sym, tree)
        else sym
      } else foldOver(sym, tree)
  }

  override val cpy = new TypedTreeCopier

  class TypedTreeCopier extends TreeCopier {
    def postProcess(tree: Tree, copied: untpd.Tree): copied.ThisTree[Type] =
      copied.withTypeUnchecked(tree.tpe)

    override def Select(tree: Tree)(qualifier: Tree, name: Name)(implicit ctx: Context): Select = {
      val tree1 = untpd.cpy.Select(tree)(qualifier, name)
      tree match {
        case tree: Select if (qualifier.tpe eq tree.qualifier.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => tree.tpe match {
          case tpe: NamedType => tree1.withType(tpe.derivedSelect(qualifier.tpe))
          case _ => tree1.withTypeUnchecked(tree.tpe)
        }
      }
    }

    override def Apply(tree: Tree)(fun: Tree, args: List[Tree])(implicit ctx: Context): Apply =
      ta.assignType(untpd.cpy.Apply(tree)(fun, args), fun, args)
      // Note: Reassigning the original type if `fun` and `args` have the same types as before
      // does not work here: The computed type depends on the widened function type, not
      // the function type itself. A treetransform may keep the function type the
      // same but its widened type might change.

    override def TypeApply(tree: Tree)(fun: Tree, args: List[Tree])(implicit ctx: Context): TypeApply =
      ta.assignType(untpd.cpy.TypeApply(tree)(fun, args), fun, args)
      // Same remark as for Apply

    override def Literal(tree: Tree)(const: Constant)(implicit ctx: Context): Literal =
      ta.assignType(untpd.cpy.Literal(tree)(const))

    override def New(tree: Tree)(tpt: Tree)(implicit ctx: Context): New =
      ta.assignType(untpd.cpy.New(tree)(tpt), tpt)

    override def Pair(tree: Tree)(left: Tree, right: Tree)(implicit ctx: Context): Pair = {
      val tree1 = untpd.cpy.Pair(tree)(left, right)
      tree match {
        case tree: Pair if (left.tpe eq tree.left.tpe) && (right.tpe eq tree.right.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, left, right)
      }
    }

    override def Typed(tree: Tree)(expr: Tree, tpt: Tree)(implicit ctx: Context): Typed =
      ta.assignType(untpd.cpy.Typed(tree)(expr, tpt), tpt)

    override def NamedArg(tree: Tree)(name: Name, arg: Tree)(implicit ctx: Context): NamedArg =
      ta.assignType(untpd.cpy.NamedArg(tree)(name, arg), arg)

    override def Assign(tree: Tree)(lhs: Tree, rhs: Tree)(implicit ctx: Context): Assign =
      ta.assignType(untpd.cpy.Assign(tree)(lhs, rhs))

    override def Block(tree: Tree)(stats: List[Tree], expr: Tree)(implicit ctx: Context): Block = {
      val tree1 = untpd.cpy.Block(tree)(stats, expr)
      tree match {
        case tree: Block if (expr.tpe eq tree.expr.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, stats, expr)
      }
    }

    override def If(tree: Tree)(cond: Tree, thenp: Tree, elsep: Tree)(implicit ctx: Context): If = {
      val tree1 = untpd.cpy.If(tree)(cond, thenp, elsep)
      tree match {
        case tree: If if (thenp.tpe eq tree.thenp.tpe) && (elsep.tpe eq tree.elsep.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, thenp, elsep)
      }
    }

    override def Closure(tree: Tree)(env: List[Tree], meth: Tree, tpt: Tree)(implicit ctx: Context): Closure =
      ta.assignType(untpd.cpy.Closure(tree)(env, meth, tpt), meth, tpt)
      // Same remark as for Apply

    override def Match(tree: Tree)(selector: Tree, cases: List[CaseDef])(implicit ctx: Context): Match = {
      val tree1 = untpd.cpy.Match(tree)(selector, cases)
      tree match {
        case tree: Match if sameTypes(cases, tree.cases) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, cases)
      }
    }

    override def CaseDef(tree: Tree)(pat: Tree, guard: Tree, body: Tree)(implicit ctx: Context): CaseDef = {
      val tree1 = untpd.cpy.CaseDef(tree)(pat, guard, body)
      tree match {
        case tree: CaseDef if (body.tpe eq tree.body.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, body)
      }
    }

    override def Return(tree: Tree)(expr: Tree, from: Tree)(implicit ctx: Context): Return =
      ta.assignType(untpd.cpy.Return(tree)(expr, from))

    override def Try(tree: Tree)(expr: Tree, handler: Tree, finalizer: Tree)(implicit ctx: Context): Try = {
      val tree1 = untpd.cpy.Try(tree)(expr, handler, finalizer)
      tree match {
        case tree: Try if (expr.tpe eq tree.expr.tpe) && (handler.tpe eq tree.handler.tpe) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, expr, handler)
      }
    }

    override def Throw(tree: Tree)(expr: Tree)(implicit ctx: Context): Throw =
      ta.assignType(untpd.cpy.Throw(tree)(expr))

    override def SeqLiteral(tree: Tree)(elems: List[Tree])(implicit ctx: Context): SeqLiteral = {
      val tree1 = untpd.cpy.SeqLiteral(tree)(elems)
      tree match {
        case tree: SeqLiteral if sameTypes(elems, tree.elems) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, elems)
      }
    }

    override def Annotated(tree: Tree)(annot: Tree, arg: Tree)(implicit ctx: Context): Annotated = {
      val tree1 = untpd.cpy.Annotated(tree)(annot, arg)
      tree match {
        case tree: Annotated if (arg.tpe eq tree.arg.tpe) && (annot eq tree.annot) => tree1.withTypeUnchecked(tree.tpe)
        case _ => ta.assignType(tree1, annot, arg)
      }
    }

    override def If(tree: If)(cond: Tree = tree.cond, thenp: Tree = tree.thenp, elsep: Tree = tree.elsep)(implicit ctx: Context): If =
      If(tree: Tree)(cond, thenp, elsep)
    override def Closure(tree: Closure)(env: List[Tree] = tree.env, meth: Tree = tree.meth, tpt: Tree = tree.tpt)(implicit ctx: Context): Closure =
      Closure(tree: Tree)(env, meth, tpt)
    override def CaseDef(tree: CaseDef)(pat: Tree = tree.pat, guard: Tree = tree.guard, body: Tree = tree.body)(implicit ctx: Context): CaseDef =
      CaseDef(tree: Tree)(pat, guard, body)
    override def Try(tree: Try)(expr: Tree = tree.expr, handler: Tree = tree.handler, finalizer: Tree = tree.finalizer)(implicit ctx: Context): Try =
      Try(tree: Tree)(expr, handler, finalizer)
  }

  implicit class TreeOps[ThisTree <: tpd.Tree](val tree: ThisTree)/* extends AnyVal*/ {

    def isValue(implicit ctx: Context): Boolean =
      tree.isTerm && tree.tpe.widen.isValueType

    def isValueOrPattern(implicit ctx: Context) =
      tree.isValue || tree.isPattern

    def isValueType: Boolean =
      tree.isType && tree.tpe.isValueType

    def isInstantiation: Boolean = tree match {
      case Apply(Select(New(_), nme.CONSTRUCTOR), _) => true
      case _ => false
    }

    def shallowFold[T](z: T)(op: (T, tpd.Tree) => T) =
      new ShallowFolder(op).apply(z, tree)

    def deepFold[T](z: T)(op: (T, tpd.Tree) => T) =
      new DeepFolder(op).apply(z, tree)

    def find[T](pred: (tpd.Tree) => Boolean): Option[tpd.Tree] =
      shallowFold[Option[tpd.Tree]](None)((accum, tree) => if (pred(tree)) Some(tree) else accum)

    def subst(from: List[Symbol], to: List[Symbol])(implicit ctx: Context): ThisTree =
      new TreeTypeMap(substFrom = from, substTo = to).apply(tree)

    /** Change owner from `from` to `to`. If `from` is a weak owner, also change its
     *  owner to `to`, and continue until a non-weak owner is reached.
     */
    def changeOwner(from: Symbol, to: Symbol)(implicit ctx: Context): ThisTree = {
      def loop(from: Symbol, froms: List[Symbol], tos: List[Symbol]): ThisTree = {
        if (from.isWeakOwner) loop(from.owner, from :: froms, to :: tos)
        else {
          //println(i"change owner ${from :: froms}%, % ==> $tos of $tree")
          new TreeTypeMap(oldOwners = from :: froms, newOwners = tos).apply(tree)
        }
      }
      loop(from, Nil, to :: Nil)
    }

    def select(name: Name)(implicit ctx: Context): Select =
      Select(tree, name)

    def select(tp: NamedType)(implicit ctx: Context): Select =
      untpd.Select(tree, tp.name).withType(tp)

    def select(sym: Symbol)(implicit ctx: Context): Select =
      untpd.Select(tree, sym.name).withType(
        TermRef.withSigAndDenot(tree.tpe, sym.name.asTermName, sym.signature, sym.denot.asSeenFrom(tree.tpe)))

    def selectWithSig(name: Name, sig: Signature)(implicit ctx: Context) =
      untpd.SelectWithSig(tree, name, sig)
        .withType(TermRef.withSig(tree.tpe, name.asTermName, sig))

    def appliedTo(arg: Tree)(implicit ctx: Context): Tree =
      appliedToArgs(arg :: Nil)

    def appliedTo(arg: Tree, args: Tree*)(implicit ctx: Context): Tree =
      appliedToArgs(arg :: args.toList)

    def appliedToArgs(args: List[Tree])(implicit ctx: Context): Apply =
      Apply(tree, args)

    def appliedToArgss(argss: List[List[Tree]])(implicit ctx: Context): Tree =
      ((tree: Tree) /: argss)(Apply(_, _))

    def appliedToNone(implicit ctx: Context): Tree = {
     tree.tpe.widen match {
        case fntpe: MethodType => appliedToArgs(Nil)
        case _ => tree
      }
    }


    def appliedToType(targ: Type)(implicit ctx: Context): Tree =
      appliedToTypes(targ :: Nil)

    def appliedToTypes(targs: List[Type])(implicit ctx: Context): Tree =
      appliedToTypeTrees(targs map (TypeTree(_)))

    def appliedToTypeTrees(targs: List[Tree])(implicit ctx: Context): Tree =
      if (targs.isEmpty) tree else TypeApply(tree, targs)

    def isInstance(tp: Type)(implicit ctx: Context): Tree =
      tree.select(defn.Any_isInstanceOf).appliedToType(tp)

    def asInstance(tp: Type)(implicit ctx: Context): Tree = {
      assert(tp.isValueType, i"bad cast: $tree.asInstanceOf[$tp]")
      tree.select(defn.Any_asInstanceOf).appliedToType(tp)
    }

    def ensureConforms(tp: Type)(implicit ctx: Context): Tree =
      if (tree.tpe <:< tp) tree else asInstance(tp)

    def and(that: Tree)(implicit ctx: Context): Tree =
      tree.select(defn.Boolean_&&).appliedTo(that)

    def or(that: Tree)(implicit ctx: Context): Tree =
      tree.select(defn.Boolean_||).appliedTo(that)

    // --- Higher order traversal methods -------------------------------

    def foreachSubTree(f: Tree => Unit): Unit = { //TODO should go in tpd.
      val traverser = new TreeTraverser {
        def traverse(tree: Tree) = foldOver(f(tree), tree)
      }
      traverser.traverse(tree)
    }

    def existsSubTree(p: Tree => Boolean): Boolean = {
      val acc = new TreeAccumulator[Boolean] {
        def apply(x: Boolean, t: Tree) = x || p(t) || foldOver(x, t)
      }
      acc(false, tree)
    }
  }

  implicit class ListOfTreeDecorator(val xs: List[tpd.Tree]) extends AnyVal {
    def tpes: List[Type] = xs map (_.tpe)
  }

  // convert a numeric with a toXXX method
  def primitiveConversion(tree: Tree, numericCls: Symbol)(implicit ctx: Context): Tree = {
    val mname      = ("to" + numericCls.name).toTermName
    val conversion = tree.tpe member mname
    if (conversion.symbol.exists)
      ensureApplied(tree.select(conversion.symbol.termRef))
    else if (tree.tpe.widen isRef numericCls)
      tree
    else {
      ctx.warning(i"conversion from ${tree.tpe.widen} to ${numericCls.typeRef} will always fail at runtime.")
      Throw(New(defn.ClassCastExceptionClass.typeRef, Nil)) withPos tree.pos
    }
  }

  @tailrec
  def sameTypes(trees: List[tpd.Tree], trees1: List[tpd.Tree]): Boolean = {
    if (trees.isEmpty) trees.isEmpty
    else if (trees1.isEmpty) trees.isEmpty
    else (trees.head.tpe eq trees1.head.tpe) && sameTypes(trees.tail, trees1.tail)
  }

  def evalOnce(tree: Tree)(within: Tree => Tree)(implicit ctx: Context) = {
    if (isIdempotentExpr(tree)) within(tree)
    else {
      val vdef = SyntheticValDef(ctx.freshName("ev$").toTermName, tree)
      Block(vdef :: Nil, within(Ident(vdef.namedType)))
    }
  }

  def runtimeCall(name: TermName, args: List[Tree])(implicit ctx: Context): Tree = {
    Ident(defn.ScalaRuntimeModule.requiredMethod(name).termRef).appliedToArgs(args)
  }

  // ensure that constructors are fully applied?
  // ensure that normal methods are fully applied?

}