3 files changed, 27 insertions, 3 deletions
diff --git a/src/main/scala/scala/async/internal/AnfTransform.scala b/src/main/scala/scala/async/internal/AnfTransform.scala
index f19a87a..8518cf5 100644
--- a/src/main/scala/scala/async/internal/AnfTransform.scala
+++ b/src/main/scala/scala/async/internal/AnfTransform.scala
@@ -162,7 +162,14 @@ private[async] trait AnfTransform {
       def _transformToList(tree: Tree): List[Tree] = trace(tree) {
         val containsAwait = tree exists isAwait
         if (!containsAwait) {
-          List(tree)
+          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)
diff --git a/src/main/scala/scala/async/internal/ExprBuilder.scala b/src/main/scala/scala/async/internal/ExprBuilder.scala
index 85e0953..b0cd914 100644
--- a/src/main/scala/scala/async/internal/ExprBuilder.scala
+++ b/src/main/scala/scala/async/internal/ExprBuilder.scala
@@ -127,7 +127,11 @@ trait ExprBuilder {
     private var nextJumpState: Option[Int] = None
 
     def +=(stat: Tree): this.type = {
-      assert(nextJumpState.isEmpty, s"statement appeared after a label jump: $stat")
+      stat match {
+        case Literal(Constant(())) => // This case occurs in do/while
+        case _ =>
+          assert(nextJumpState.isEmpty, s"statement appeared after a label jump: $stat")
+      }
       def addStat() = stats += stat
       stat match {
         case Apply(fun, Nil) =>
@@ -228,7 +232,7 @@ trait ExprBuilder {
         currState = afterAwaitState
         stateBuilder = new AsyncStateBuilder(currState, symLookup)
 
-      case If(cond, thenp, elsep) if stat exists isAwait =>
+      case If(cond, thenp, elsep) if (stat exists isAwait) || containsForiegnLabelJump(stat) =>
         checkForUnsupportedAwait(cond)
 
         val thenStartState = nextState()
diff --git a/src/main/scala/scala/async/internal/TransformUtils.scala b/src/main/scala/scala/async/internal/TransformUtils.scala
index 71fddaa..e382c62 100644
--- a/src/main/scala/scala/async/internal/TransformUtils.scala
+++ b/src/main/scala/scala/async/internal/TransformUtils.scala
@@ -96,6 +96,19 @@ private[async] trait TransformUtils {
     treeInfo.isExprSafeToInline(tree)
   }
 
+  // `while(await(x))` ... or `do { await(x); ... } while(...)` contain an `If` that loops;
+  // we must break that `If` into states so that it convert the label jump into a state machine
+  // transition
+  final def containsForiegnLabelJump(t: Tree): Boolean = {
+    val labelDefs = t.collect {
+      case ld: LabelDef => ld.symbol
+    }.toSet
+    t.exists {
+      case rt: RefTree => !(labelDefs contains rt.symbol)
+      case _ => false
+    }
+  }
+
   /** Map a list of arguments to:
     * - A list of argument Trees
     * - A list of auxillary results.