1 files changed, 36 insertions, 12 deletions

diff --git a/src/main/scala/scala/async/AnfTransform.scala b/src/main/scala/scala/async/AnfTransform.scala
index a2d21f6..2fa96c9 100644
--- a/src/main/scala/scala/async/AnfTransform.scala
+++ b/src/main/scala/scala/async/AnfTransform.scala
@@ -81,14 +81,14 @@ private[async] final case class AnfTransform[C <: Context](c: C) {
               treeCopy.ModuleDef(tree, mods, newName, transform(impl).asInstanceOf[Template])
             case x                                   => super.transform(x)
           }
-        case Ident(name)                                            =>
+        case Ident(name)                                       =>
           if (renamed(tree.symbol)) treeCopy.Ident(tree, tree.symbol.name)
           else tree
-        case Select(fun, name)                                      =>
+        case Select(fun, name)                                 =>
           if (renamed(tree.symbol)) {
             treeCopy.Select(tree, transform(fun), tree.symbol.name)
           } else super.transform(tree)
-        case _                                                      => super.transform(tree)
+        case _                                                 => super.transform(tree)
       }
     }
   }
@@ -170,12 +170,12 @@ private[async] final case class AnfTransform[C <: Context](c: C) {
       vd.setPos(pos)
       vd
     }
+  }
 
-    private def defineVal(prefix: String, lhs: Tree, pos: Position): ValDef = {
-      val vd = ValDef(NoMods, name.fresh(prefix), TypeTree(), lhs)
-      vd.setPos(pos)
-      vd
-    }
+  private def defineVal(prefix: String, lhs: Tree, pos: Position): ValDef = {
+    val vd = ValDef(NoMods, name.fresh(prefix), TypeTree(), lhs)
+    vd.setPos(pos)
+    vd
   }
 
   private object anf {
@@ -187,16 +187,26 @@ private[async] final case class AnfTransform[C <: Context](c: C) {
           val stats :+ expr = inline.transformToList(qual)
           stats :+ attachCopy(tree)(Select(expr, sel).setSymbol(tree.symbol))
 
-        case Apply(fun, args) if containsAwait =>
+        case Apply(fun, args) if containsAwait   =>
+          checkForAwaitInNonPrimaryParamSection(fun, args)
+
           // we an assume that no await call appears in a by-name argument position,
           // this has already been checked.
-
+          val isByName: (Int) => Boolean = utils.isByName(fun)
           val funStats :+ simpleFun = inline.transformToList(fun)
-          val argLists = args map inline.transformToList
+          def isAwaitRef(name: Name) = name.toString.startsWith(utils.name.await + "$")
+          val argLists: List[List[Tree]] = args.zipWithIndex map {
+            case (arg, i) if isByName(i) || isSafeToInline(arg) => List(arg)
+            case (arg@Ident(name), _) if isAwaitRef(name)       => List(arg) // not typed, so it eludes the check in `isSafeToInline`
+            case (arg, i)                                       => inline.transformToList(arg) match {
+              case stats :+ expr =>
+                val valDef = defineVal(name.arg(i), expr, arg.pos)
+                stats ::: List(valDef, Ident(valDef.name))
+            }
+          }
           val allArgStats = argLists flatMap (_.init)
           val simpleArgs = argLists map (_.last)
           funStats ++ allArgStats :+ attachCopy(tree)(Apply(simpleFun, simpleArgs).setSymbol(tree.symbol))
-
         case Block(stats, expr) if containsAwait =>
           inline.transformToList(stats :+ expr)
 
@@ -259,4 +269,18 @@ private[async] final case class AnfTransform[C <: Context](c: C) {
     }
   }
 
+  def checkForAwaitInNonPrimaryParamSection(fun: Tree, args: List[Tree]) {
+    // TODO treat the Apply(Apply(.., argsN), ...), args0) holistically, and rewrite
+    // *all* argument lists in the correct order to preserve semantics.
+    fun match {
+      case Apply(fun1, _) =>
+        fun1.tpe match {
+          case MethodType(_, resultType: MethodType) if resultType =:= fun.tpe =>
+            c.error(fun.pos, "implementation restriction: await may only be used in the first parameter list.")
+          case _                                                               =>
+        }
+      case _              =>
+    }
+
+  }
 }