path: root/src/main/scala/scala/async/internal/AnfTransform.scala

/*
 * Copyright (C) 2012-2014 Typesafe Inc. <http://www.typesafe.com>
 */

package scala.async.internal

import scala.Predef._
import scala.reflect.internal.util.Collections.map2

private[async] trait AnfTransform {
  self: AsyncMacro =>

  import c.universe._
  import Flag._
  import c.internal._
  import decorators._

  def anfTransform(tree: Tree): Block = {
    // Must prepend the () for issue #31.
    val block = c.typecheck(atPos(tree.pos)(Block(List(Literal(Constant(()))), tree))).setType(tree.tpe)

    sealed abstract class AnfMode
    case object Anf extends AnfMode
    case object Linearizing extends AnfMode

    var mode: AnfMode = Anf
    typingTransform(block)((tree, api) => {
      def blockToList(tree: Tree): List[Tree] = tree match {
        case Block(stats, expr) => stats :+ expr
        case t                  => t :: Nil
      }

      def listToBlock(trees: List[Tree]): Block = trees match {
        case trees @ (init :+ last) =>
          val pos = trees.map(_.pos).reduceLeft(_ union _)
          Block(init, last).setType(last.tpe).setPos(pos)
      }

      object linearize {
        def transformToList(tree: Tree): List[Tree] = {
          mode = Linearizing; blockToList(api.recur(tree))
        }

        def transformToBlock(tree: Tree): Block = listToBlock(transformToList(tree))

        def _transformToList(tree: Tree): List[Tree] = trace(tree) {
          val stats :+ expr = anf.transformToList(tree)
          def statsExprUnit =
            stats :+ expr :+ api.typecheck(atPos(expr.pos)(Literal(Constant(()))))
          expr match {
            case Apply(fun, args) if isAwait(fun) =>
              val valDef = defineVal(name.await, expr, tree.pos)
              val ref = gen.mkAttributedStableRef(valDef.symbol).setType(tree.tpe)
              val ref1 = if (ref.tpe =:= definitions.UnitTpe)
                // https://github.com/scala/async/issues/74
                // Use a cast to hide from "pure expression does nothing" error
                //
                // TODO avoid creating a ValDef for the result of this await to avoid this tree shape altogether.
                // This will require some deeper changes to the later parts of the macro which currently assume regular
                // tree structure around `await` calls.
                gen.mkCast(ref, definitions.UnitTpe)
              else ref
              stats :+ valDef :+ atPos(tree.pos)(ref1)

            case If(cond, thenp, elsep) =>
              // if type of if-else is Unit don't introduce assignment,
              // but add Unit value to bring it into form expected by async transform
              if (expr.tpe =:= definitions.UnitTpe) {
                statsExprUnit
              } else {
                val varDef = defineVar(name.ifRes, expr.tpe, tree.pos)
                def branchWithAssign(orig: Tree) = api.typecheck(atPos(orig.pos) {
                  def cast(t: Tree) = mkAttributedCastPreservingAnnotations(t, tpe(varDef.symbol))
                  orig match {
                    case Block(thenStats, thenExpr) => Block(thenStats, Assign(Ident(varDef.symbol), cast(thenExpr)))
                    case _                          => Assign(Ident(varDef.symbol), cast(orig))
                  }
                })
                val ifWithAssign = treeCopy.If(tree, cond, branchWithAssign(thenp), branchWithAssign(elsep)).setType(definitions.UnitTpe)
                stats :+ varDef :+ ifWithAssign :+ atPos(tree.pos)(gen.mkAttributedStableRef(varDef.symbol)).setType(tree.tpe)
              }
            case LabelDef(name, params, rhs) =>
              statsExprUnit

            case Match(scrut, cases) =>
              // if type of match is Unit don't introduce assignment,
              // but add Unit value to bring it into form expected by async transform
              if (expr.tpe =:= definitions.UnitTpe) {
                statsExprUnit
              }
              else {
                val varDef = defineVar(name.matchRes, expr.tpe, tree.pos)
                def typedAssign(lhs: Tree) =
                  api.typecheck(atPos(lhs.pos)(Assign(Ident(varDef.symbol), mkAttributedCastPreservingAnnotations(lhs, tpe(varDef.symbol)))))
                val casesWithAssign = cases map {
                  case cd@CaseDef(pat, guard, body) =>
                    val newBody = body match {
                      case b@Block(caseStats, caseExpr) => treeCopy.Block(b, caseStats, typedAssign(caseExpr)).setType(definitions.UnitTpe)
                      case _                            => typedAssign(body)
                    }
                    treeCopy.CaseDef(cd, pat, guard, newBody).setType(definitions.UnitTpe)
                }
                val matchWithAssign = treeCopy.Match(tree, scrut, casesWithAssign).setType(definitions.UnitTpe)
                require(matchWithAssign.tpe != null, matchWithAssign)
                stats :+ varDef :+ matchWithAssign :+ atPos(tree.pos)(gen.mkAttributedStableRef(varDef.symbol)).setType(tree.tpe)
              }
            case _                   =>
              stats :+ expr
          }
        }

        private def defineVar(prefix: String, tp: Type, pos: Position): ValDef = {
          val sym = api.currentOwner.newTermSymbol(name.fresh(prefix), pos, MUTABLE | SYNTHETIC).setInfo(uncheckedBounds(tp))
          valDef(sym, mkZero(uncheckedBounds(tp))).setType(NoType).setPos(pos)
        }
      }

      object trace {
        private var indent = -1

        private def indentString = "  " * indent

        def apply[T](args: Any)(t: => T): T = {
          def prefix = mode.toString.toLowerCase
          indent += 1
          def oneLine(s: Any) = s.toString.replaceAll("""\n""", "\\\\n").take(127)
          try {
            AsyncUtils.trace(s"${indentString}$prefix(${oneLine(args)})")
            val result = t
            AsyncUtils.trace(s"${indentString}= ${oneLine(result)}")
            result
          } finally {
            indent -= 1
          }
        }
      }

      def defineVal(prefix: String, lhs: Tree, pos: Position): ValDef = {
        val sym = api.currentOwner.newTermSymbol(name.fresh(prefix), pos, SYNTHETIC).setInfo(uncheckedBounds(lhs.tpe))
        internal.valDef(sym, internal.changeOwner(lhs, api.currentOwner, sym)).setType(NoType).setPos(pos)
      }

      object anf {
        def transformToList(tree: Tree): List[Tree] = {
          mode = Anf; blockToList(api.recur(tree))
        }

        def _transformToList(tree: Tree): List[Tree] = trace(tree) {
          val containsAwait = tree exists isAwait
          if (!containsAwait) {
            tree match {
              case Block(stats, expr) =>
                // avoids nested block in `while(await(false)) ...`.
                // TODO I think `containsAwait` really should return true if the code contains a label jump to an enclosing
                // while/doWhile and there is an await *anywhere* inside that construct.
                stats :+ expr
              case _ => List(tree)
            }
          } else tree match {
            case Select(qual, sel) =>
              val stats :+ expr = linearize.transformToList(qual)
              stats :+ treeCopy.Select(tree, expr, sel)

            case Throw(expr) =>
              val stats :+ expr1 = linearize.transformToList(expr)
              stats :+ treeCopy.Throw(tree, expr1)

            case Typed(expr, tpt) =>
              val stats :+ expr1 = linearize.transformToList(expr)
              stats :+ treeCopy.Typed(tree, expr1, tpt)

            case Applied(fun, targs, argss) if argss.nonEmpty =>
              // we can assume that no await call appears in a by-name argument position,
              // this has already been checked.
              val funStats :+ simpleFun = linearize.transformToList(fun)
              val (argStatss, argExprss): (List[List[List[Tree]]], List[List[Tree]]) =
                mapArgumentss[List[Tree]](fun, argss) {
                  case Arg(expr, byName, _) if byName /*|| isPure(expr) TODO */ => (Nil, expr)
                  case Arg(expr, _, argName)                                    =>
                    linearize.transformToList(expr) match {
                      case stats :+ expr1 =>
                        val valDef = defineVal(argName, expr1, expr1.pos)
                        require(valDef.tpe != null, valDef)
                        val stats1 = stats :+ valDef
                        (stats1, atPos(tree.pos.makeTransparent)(gen.stabilize(gen.mkAttributedIdent(valDef.symbol))))
                    }
                }

              def copyApplied(tree: Tree, depth: Int): Tree = {
                tree match {
                  case TypeApply(_, targs) => treeCopy.TypeApply(tree, simpleFun, targs)
                  case _ if depth == 0     => simpleFun
                  case Apply(fun, args)    =>
                    val newTypedArgs = map2(args.map(_.pos), argExprss(depth - 1))((pos, arg) => api.typecheck(atPos(pos)(arg)))
                    treeCopy.Apply(tree, copyApplied(fun, depth - 1), newTypedArgs)
                }
              }

              val typedNewApply = copyApplied(tree, argss.length)

              funStats ++ argStatss.flatten.flatten :+ typedNewApply

            case Block(stats, expr)                                    =>
              (stats :+ expr).flatMap(linearize.transformToList)

            case ValDef(mods, name, tpt, rhs) =>
              if (rhs exists isAwait) {
                val stats :+ expr = api.atOwner(api.currentOwner.owner)(linearize.transformToList(rhs))
                stats.foreach(_.changeOwner(api.currentOwner, api.currentOwner.owner))
                stats :+ treeCopy.ValDef(tree, mods, name, tpt, expr)
              } else List(tree)

            case Assign(lhs, rhs) =>
              val stats :+ expr = linearize.transformToList(rhs)
              stats :+ treeCopy.Assign(tree, lhs, expr)

            case If(cond, thenp, elsep) =>
              val condStats :+ condExpr = linearize.transformToList(cond)
              val thenBlock = linearize.transformToBlock(thenp)
              val elseBlock = linearize.transformToBlock(elsep)
              condStats :+ treeCopy.If(tree, condExpr, thenBlock, elseBlock)

            case Match(scrut, cases) =>
              val scrutStats :+ scrutExpr = linearize.transformToList(scrut)
              val caseDefs = cases map {
                case CaseDef(pat, guard, body) =>
                  // extract local variables for all names bound in `pat`, and rewrite `body`
                  // to refer to these.
                  // TODO we can move this into ExprBuilder once we get rid of `AsyncDefinitionUseAnalyzer`.
                  val block = linearize.transformToBlock(body)
                  val (valDefs, mappings) = (pat collect {
                    case b@Bind(name, _) =>
                      val vd = defineVal(name.toTermName + AnfTransform.this.name.bindSuffix, gen.mkAttributedStableRef(b.symbol).setPos(b.pos), b.pos)
                      (vd, (b.symbol, vd.symbol))
                  }).unzip
                  val (from, to) = mappings.unzip
                  val b@Block(stats1, expr1) = block.substituteSymbols(from, to).asInstanceOf[Block]
                  val newBlock = treeCopy.Block(b, valDefs ++ stats1, expr1)
                  treeCopy.CaseDef(tree, pat, guard, newBlock)
              }
              scrutStats :+ treeCopy.Match(tree, scrutExpr, caseDefs)

            case LabelDef(name, params, rhs) =>
              List(LabelDef(name, params, Block(linearize.transformToList(rhs), Literal(Constant(())))).setSymbol(tree.symbol))

            case TypeApply(fun, targs) =>
              val funStats :+ simpleFun = linearize.transformToList(fun)
              funStats :+ treeCopy.TypeApply(tree, simpleFun, targs)

            case _ =>
              List(tree)
          }
        }
      }

      def anfLinearize(tree: Tree): Block = {
        val trees: List[Tree] = mode match {
          case Anf         => anf._transformToList(tree)
          case Linearizing => linearize._transformToList(tree)
        }
        listToBlock(trees)
      }

      tree match {
        case _: ValDef | _: DefDef | _: Function | _: ClassDef | _: TypeDef =>
          api.atOwner(tree.symbol)(anfLinearize(tree))
        case _: ModuleDef                                                   =>
          api.atOwner(tree.symbol.asModule.moduleClass orElse tree.symbol)(anfLinearize(tree))
        case _                                                              =>
          anfLinearize(tree)
      }
    }).asInstanceOf[Block]
  }
}