Prohibit return.

Closes #21

2 files changed, 14 insertions, 0 deletions

diff --git a/src/main/scala/scala/async/AsyncAnalysis.scala b/src/main/scala/scala/async/AsyncAnalysis.scala
index 38fd22f..e319fe8 100644
--- a/src/main/scala/scala/async/AsyncAnalysis.scala
+++ b/src/main/scala/scala/async/AsyncAnalysis.scala
@@ -62,6 +62,8 @@ private[async] final case class AsyncAnalysis[C <: Context](override val c: C) e
       tree match {
         case Try(_, _, _) if containsAwait =>
           reportUnsupportedAwait(tree, "try/catch")
+        case Return(_) =>
+          c.abort(tree.pos, "return is illegal within a async block")
         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 61490e2..229feb6 100644
--- a/src/test/scala/scala/async/neg/NakedAwait.scala
+++ b/src/test/scala/scala/async/neg/NakedAwait.scala
@@ -127,4 +127,16 @@ class NakedAwait {
       """.stripMargin
     }
   }
+
+  @Test
+  def returnIllegal() {
+    expectError("return is illegal") {
+      """
+        | import _root_.scala.async.AsyncId._
+        | def foo(): Any = async { return false }
+        | ()
+        |
+        |""".stripMargin
+    }
+  }
 }