Fix ANF transform involving `xs: _*` trees.

We need to unwrap and inline `xs`, then
rewrap the result expression with the wildcard
star.

Addresses the first half of #46.

3 files changed, 54 insertions, 11 deletions

diff --git a/src/main/scala/scala/async/AnfTransform.scala b/src/main/scala/scala/async/AnfTransform.scala
index 2fa96c9..afcf6bd 100644
--- a/src/main/scala/scala/async/AnfTransform.scala
+++ b/src/main/scala/scala/async/AnfTransform.scala
@@ -195,18 +195,18 @@ private[async] final case class AnfTransform[C <: Context](c: C) {
           val isByName: (Int) => Boolean = utils.isByName(fun)
           val funStats :+ simpleFun = inline.transformToList(fun)
           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 (argStats, argExprs): (List[List[Tree]], List[Tree]) =
+            mapArguments[List[Tree]](args) {
+              case (arg, i) if isByName(i) || isSafeToInline(arg) => (Nil, arg)
+              case (arg@Ident(name), _) if isAwaitRef(name)       => (Nil, 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 :+ valDef, Ident(valDef.name))
+                }
             }
-          }
-          val allArgStats = argLists flatMap (_.init)
-          val simpleArgs = argLists map (_.last)
-          funStats ++ allArgStats :+ attachCopy(tree)(Apply(simpleFun, simpleArgs).setSymbol(tree.symbol))
+          funStats ++ argStats.flatten :+ attachCopy(tree)(Apply(simpleFun, argExprs).setSymbol(tree.symbol))
         case Block(stats, expr) if containsAwait =>
           inline.transformToList(stats :+ expr)
 
diff --git a/src/main/scala/scala/async/TransformUtils.scala b/src/main/scala/scala/async/TransformUtils.scala
index 23f39d2..f780799 100644
--- a/src/main/scala/scala/async/TransformUtils.scala
+++ b/src/main/scala/scala/async/TransformUtils.scala
@@ -253,4 +253,25 @@ private[async] final case class TransformUtils[C <: Context](c: C) {
     val castTree = tree.asInstanceOf[symtab.Tree]
     treeInfo.isExprSafeToInline(castTree)
   }
+
+  /** Map a list of arguments to:
+    * - A list of argument Trees
+    * - A list of auxillary results.
+    *
+    * The function unwraps and rewraps the `arg :_*` construct.
+    *
+    * @param args The original argument trees
+    * @param f  A function from argument (with '_*' unwrapped) and argument index to argument.
+    * @tparam A The type of the auxillary result
+    */
+  def mapArguments[A](args: List[Tree])(f: (Tree, Int) => (A, Tree)): (List[A], List[Tree]) = {
+    args match {
+      case args :+ Typed(tree, Ident(tpnme.WILDCARD_STAR)) =>
+        val (a, argExprs :+ lastArgExpr) = (args :+ tree).zipWithIndex.map(f.tupled).unzip
+        val exprs = argExprs :+ Typed(lastArgExpr, Ident(tpnme.WILDCARD_STAR)).setPos(lastArgExpr.pos)
+        (a, exprs)
+      case args                                            =>
+        args.zipWithIndex.map(f.tupled).unzip
+    }
+  }
 }
diff --git a/src/test/scala/scala/async/run/anf/AnfTransformSpec.scala b/src/test/scala/scala/async/run/anf/AnfTransformSpec.scala
index 529386b..41c13e0 100644
--- a/src/test/scala/scala/async/run/anf/AnfTransformSpec.scala
+++ b/src/test/scala/scala/async/run/anf/AnfTransformSpec.scala
@@ -289,4 +289,26 @@ class AnfTransformSpec {
       foo(a = await(next()))
     } mustBe ((1, 2))
   }
+
+  @Test
+  def repeatedParams1() {
+    import scala.async.AsyncId.{async, await}
+    var i = 0
+    def foo(a: Int, b: Int*) = b.toList
+    def id(i: Int) = i
+    async {
+      foo(await(0), id(1), id(2), id(3), await(4))
+    } mustBe (List(1, 2, 3, 4))
+  }
+
+  @Test
+  def repeatedParams2() {
+    import scala.async.AsyncId.{async, await}
+    var i = 0
+    def foo(a: Int, b: Int*) = b.toList
+    def id(i: Int) = i
+    async {
+      foo(await(0), List(id(1), id(2), id(3)): _*)
+    } mustBe (List(1, 2, 3))
+  }
 }