Disallow await in pattern guards (for now)

2 files changed, 13 insertions, 0 deletions

diff --git a/src/main/scala/scala/async/internal/AsyncAnalysis.scala b/src/main/scala/scala/async/internal/AsyncAnalysis.scala
index 62842c9..122109e 100644
--- a/src/main/scala/scala/async/internal/AsyncAnalysis.scala
+++ b/src/main/scala/scala/async/internal/AsyncAnalysis.scala
@@ -63,6 +63,9 @@ trait AsyncAnalysis {
         case ValDef(mods, _, _, _) if mods.hasFlag(Flag.LAZY) =>
           // TODO lift this restriction
           abort(tree.pos, "lazy vals are illegal within an async block")
+        case CaseDef(_, guard, _) if guard exists isAwait     =>
+          // TODO lift this restriction
+          reportUnsupportedAwait(tree, "pattern guard")
         case _                                                =>
           super.traverse(tree)
       }
diff --git a/src/test/scala/scala/async/neg/NakedAwait.scala b/src/test/scala/scala/async/neg/NakedAwait.scala
index aa62d37..ba388c5 100644
--- a/src/test/scala/scala/async/neg/NakedAwait.scala
+++ b/src/test/scala/scala/async/neg/NakedAwait.scala
@@ -133,6 +133,16 @@ class NakedAwait {
   }
 
   @Test
+  def guard() {
+    expectError("await must not be used under a pattern guard.") {
+      """
+        | import _root_.scala.async.internal.AsyncId._
+        | async { 1 match { case _ if await(true) => } }
+      """.stripMargin
+    }
+  }
+
+  @Test
   def nestedMethod() {
     expectError("await must not be used under a nested method.") {
       """