Enable a compiler plugin to use the async transform after patmat

src/main/scala/scala/async/internal/AnfTransform.scala

@@ -16,16 +16,18 @@ private[async] trait AnfTransform {
   import c.internal._
   import decorators._
 
-  def anfTransform(tree: Tree): Block = {
+  def anfTransform(tree: Tree, owner: Symbol): Block = {
     // Must prepend the () for issue #31.
-    val block = c.typecheck(atPos(tree.pos)(Block(List(Literal(Constant(()))), tree))).setType(tree.tpe)
+    val block = c.typecheck(atPos(tree.pos)(newBlock(List(Literal(Constant(()))), tree))).setType(tree.tpe)
 
     sealed abstract class AnfMode
     case object Anf extends AnfMode
     case object Linearizing extends AnfMode
 
+    val tree1 = adjustTypeOfTranslatedPatternMatches(block, owner)
+
     var mode: AnfMode = Anf
-    typingTransform(block)((tree, api) => {
+    typingTransform(tree1, owner)((tree, api) => {
       def blockToList(tree: Tree): List[Tree] = tree match {
         case Block(stats, expr) => stats :+ expr
         case t                  => t :: Nil
@@ -34,7 +36,7 @@ private[async] trait AnfTransform {
       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)
+          newBlock(init, last).setType(last.tpe).setPos(pos)
       }
 
       object linearize {
@@ -66,6 +68,17 @@ private[async] trait AnfTransform {
               stats :+ valDef :+ atPos(tree.pos)(ref1)
 
             case If(cond, thenp, elsep) =>
+              // If we run the ANF transform post patmat, deal with trees like `(if (cond) jump1(){String} else jump2(){String}){String}`
+              // as though it was typed with `Unit`.
+              def isPatMatGeneratedJump(t: Tree): Boolean = t match {
+                case Block(_, expr) => isPatMatGeneratedJump(expr)
+                case If(_, thenp, elsep) => isPatMatGeneratedJump(thenp) && isPatMatGeneratedJump(elsep)
+                case _: Apply if isLabel(t.symbol) => true
+                case _ => false
+              }
+              if (isPatMatGeneratedJump(expr)) {
+                internal.setType(expr, definitions.UnitTpe)
+              }
               // 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) {
@@ -77,7 +90,7 @@ private[async] trait AnfTransform {
                 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 Block(thenStats, thenExpr) => newBlock(thenStats, Assign(Ident(varDef.symbol), cast(thenExpr)))
                     case _                          => Assign(Ident(varDef.symbol), cast(orig))
                   }
                 })
@@ -115,7 +128,7 @@ private[async] trait AnfTransform {
           }
         }
 
-        private def defineVar(prefix: String, tp: Type, pos: Position): ValDef = {
+        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)
         }
@@ -152,8 +165,7 @@ private[async] trait AnfTransform {
         }
 
         def _transformToList(tree: Tree): List[Tree] = trace(tree) {
-          val containsAwait = tree exists isAwait
-          if (!containsAwait) {
+          if (!containsAwait(tree)) {
             tree match {
               case Block(stats, expr) =>
                 // avoids nested block in `while(await(false)) ...`.
@@ -207,10 +219,11 @@ private[async] trait AnfTransform {
               funStats ++ argStatss.flatten.flatten :+ typedNewApply
 
             case Block(stats, expr)                                    =>
-              (stats :+ expr).flatMap(linearize.transformToList)
+              val trees = stats.flatMap(linearize.transformToList).filterNot(isLiteralUnit) ::: linearize.transformToList(expr)
+              eliminateLabelParameters(trees)
 
             case ValDef(mods, name, tpt, rhs) =>
-              if (rhs exists isAwait) {
+              if (containsAwait(rhs)) {
                 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)
@@ -247,7 +260,7 @@ private[async] trait AnfTransform {
               scrutStats :+ treeCopy.Match(tree, scrutExpr, caseDefs)
 
             case LabelDef(name, params, rhs) =>
-              List(LabelDef(name, params, Block(linearize.transformToList(rhs), Literal(Constant(())))).setSymbol(tree.symbol))
+              List(LabelDef(name, params, newBlock(linearize.transformToList(rhs), Literal(Constant(())))).setSymbol(tree.symbol))
 
             case TypeApply(fun, targs) =>
               val funStats :+ simpleFun = linearize.transformToList(fun)
@@ -259,6 +272,44 @@ private[async] trait AnfTransform {
         }
       }
 
+      // Replace the label parameters on `matchEnd` with use of a `matchRes` temporary variable
+      def eliminateLabelParameters(statsExpr: List[Tree]): List[Tree] = {
+        import internal.{methodType, setInfo}
+        val caseDefToMatchResult = collection.mutable.Map[Symbol, Symbol]()
+
+        val matchResults = collection.mutable.Buffer[Tree]()
+        val statsExpr0 = statsExpr.reverseMap {
+          case ld @ LabelDef(_, param :: Nil, body) =>
+            val matchResult = linearize.defineVar(name.matchRes, param.tpe, ld.pos)
+            matchResults += matchResult
+            caseDefToMatchResult(ld.symbol) = matchResult.symbol
+            val ld2 = treeCopy.LabelDef(ld, ld.name, Nil, body.substituteSymbols(param.symbol :: Nil, matchResult.symbol :: Nil))
+            setInfo(ld.symbol, methodType(Nil, ld.symbol.info.resultType))
+            ld2
+          case t =>
+            if (caseDefToMatchResult.isEmpty) t
+            else typingTransform(t)((tree, api) =>
+              tree match {
+                case Apply(fun, arg :: Nil) if isLabel(fun.symbol) && caseDefToMatchResult.contains(fun.symbol) =>
+                  api.typecheck(atPos(tree.pos)(newBlock(Assign(Ident(caseDefToMatchResult(fun.symbol)), api.recur(arg)) :: Nil, treeCopy.Apply(tree, fun, Nil))))
+                case Block(stats, expr) =>
+                  api.default(tree) match {
+                    case Block(stats, Block(stats1, expr)) =>
+                      treeCopy.Block(tree, stats ::: stats1, expr)
+                    case t => t
+                  }
+                case _ =>
+                  api.default(tree)
+              }
+            )
+        }
+        matchResults.toList match {
+          case Nil => statsExpr0.reverse
+          case r1 :: Nil => (r1 +: statsExpr0.reverse) :+ atPos(tree.pos)(gen.mkAttributedIdent(r1.symbol))
+          case _ => c.error(macroPos, "Internal error: unexpected tree encountered during ANF transform " + statsExpr); statsExpr
+        }
+      }
+
       def anfLinearize(tree: Tree): Block = {
         val trees: List[Tree] = mode match {
           case Anf         => anf._transformToList(tree)

src/main/scala/scala/async/internal/AsyncBase.scala

@@ -43,9 +43,9 @@ abstract class AsyncBase {
                                  (body: c.Expr[T])
                                  (execContext: c.Expr[futureSystem.ExecContext]): c.Expr[futureSystem.Fut[T]] = {
     import c.universe._, c.internal._, decorators._
-    val asyncMacro = AsyncMacro(c, self)
+    val asyncMacro = AsyncMacro(c, self)(body.tree)
 
-    val code = asyncMacro.asyncTransform[T](body.tree, execContext.tree)(c.weakTypeTag[T])
+    val code = asyncMacro.asyncTransform[T](execContext.tree)(c.weakTypeTag[T])
     AsyncUtils.vprintln(s"async state machine transform expands to:\n ${code}")
 
     // Mark range positions for synthetic code as transparent to allow some wiggle room for overlapping ranges

src/main/scala/scala/async/internal/AsyncId.scala

@@ -41,11 +41,11 @@ object AsyncTestLV extends AsyncBase {
  * A trivial implementation of [[FutureSystem]] that performs computations
  * on the current thread. Useful for testing.
  */
+class Box[A] {
+  var a: A = _
+}
 object IdentityFutureSystem extends FutureSystem {
-
-  class Prom[A] {
-    var a: A = _
-  }
+  type Prom[A] = Box[A]
 
   type Fut[A] = A
   type ExecContext = Unit
@@ -57,7 +57,7 @@ object IdentityFutureSystem extends FutureSystem {
 
     def execContext: Expr[ExecContext] = c.Expr[Unit](Literal(Constant(())))
 
-    def promType[A: WeakTypeTag]: Type = weakTypeOf[Prom[A]]
+    def promType[A: WeakTypeTag]: Type = weakTypeOf[Box[A]]
     def tryType[A: WeakTypeTag]: Type = weakTypeOf[scala.util.Try[A]]
     def execContextType: Type = weakTypeOf[Unit]
 

src/main/scala/scala/async/internal/AsyncMacro.scala

@@ -1,15 +1,17 @@
 package scala.async.internal
 
 object AsyncMacro {
-  def apply(c0: reflect.macros.Context, base: AsyncBase): AsyncMacro { val c: c0.type } = {
+  def apply(c0: reflect.macros.Context, base: AsyncBase)(body0: c0.Tree): AsyncMacro { val c: c0.type } = {
     import language.reflectiveCalls
     new AsyncMacro { self =>
       val c: c0.type                                             = c0
+      val body: c.Tree = body0
       // This member is required by `AsyncTransform`:
       val asyncBase: AsyncBase                                   = base
       // These members are required by `ExprBuilder`:
       val futureSystem: FutureSystem                             = base.futureSystem
       val futureSystemOps: futureSystem.Ops {val c: self.c.type} = futureSystem.mkOps(c)
+      val containsAwait: c.Tree => Boolean = containsAwaitCached(body0)
     }
   }
 }
@@ -19,7 +21,10 @@ private[async] trait AsyncMacro
   with ExprBuilder with AsyncTransform with AsyncAnalysis with LiveVariables {
 
   val c: scala.reflect.macros.Context
+  val body: c.Tree
+  val containsAwait: c.Tree => Boolean
 
   lazy val macroPos = c.macroApplication.pos.makeTransparent
   def atMacroPos(t: c.Tree) = c.universe.atPos(macroPos)(t)
+
 }

src/main/scala/scala/async/internal/AsyncTransform.scala

@@ -9,7 +9,7 @@ trait AsyncTransform {
 
   val asyncBase: AsyncBase
 
-  def asyncTransform[T](body: Tree, execContext: Tree)
+  def asyncTransform[T](execContext: Tree)
                        (resultType: WeakTypeTag[T]): Tree = {
 
     // We annotate the type of the whole expression as `T @uncheckedBounds` so as not to introduce
@@ -22,7 +22,7 @@ trait AsyncTransform {
     // Transform to A-normal form:
     //  - no await calls in qualifiers or arguments,
     //  - if/match only used in statement position.
-    val anfTree0: Block = anfTransform(body)
+    val anfTree0: Block = anfTransform(body, c.internal.enclosingOwner)
 
     val anfTree = futureSystemOps.postAnfTransform(anfTree0)
 
@@ -35,15 +35,15 @@ trait AsyncTransform {
     val stateMachine: ClassDef = {
       val body: List[Tree] = {
         val stateVar = ValDef(Modifiers(Flag.MUTABLE | Flag.PRIVATE | Flag.LOCAL), name.state, TypeTree(definitions.IntTpe), Literal(Constant(StateAssigner.Initial)))
-        val result = ValDef(NoMods, name.result, TypeTree(futureSystemOps.promType[T](uncheckedBoundsResultTag)), futureSystemOps.createProm[T](uncheckedBoundsResultTag).tree)
+        val resultAndAccessors = mkMutableField(futureSystemOps.promType[T](uncheckedBoundsResultTag), name.result, futureSystemOps.createProm[T](uncheckedBoundsResultTag).tree)
         val execContextValDef = ValDef(NoMods, name.execContext, TypeTree(), execContext)
 
         val apply0DefDef: DefDef = {
           // We extend () => Unit so we can pass this class as the by-name argument to `Future.apply`.
           // See SI-1247 for the the optimization that avoids creation.
           DefDef(NoMods, name.apply, Nil, Nil, TypeTree(definitions.UnitTpe), Apply(Ident(name.apply), literalNull :: Nil))
         }
-        List(emptyConstructor, stateVar, result, execContextValDef) ++ List(applyDefDefDummyBody, apply0DefDef)
+        List(emptyConstructor, stateVar) ++ resultAndAccessors ++ List(execContextValDef) ++ List(applyDefDefDummyBody, apply0DefDef)
       }
 
       val tryToUnit = appliedType(definitions.FunctionClass(1), futureSystemOps.tryType[Any], typeOf[Unit])