=str #16349 fix map + map optimization

akka-stream-tests/src/test/scala/akka/stream/scaladsl/OptimizingActorBasedFlowMaterializerSpec.scala

@@ -39,5 +39,14 @@ class OptimizingActorBasedFlowMaterializerSpec extends AkkaSpec with ImplicitSen
 
       Await.result(f, 5.seconds) should be(expected)
     }
+
+    "optimize map + map" in {
+      implicit val mat = FlowMaterializer().asInstanceOf[ActorBasedFlowMaterializer].copy(optimizations = Optimizations.all)
+
+      val fl = Source(1 to 100).map(_ + 2).map(_ * 2).fold(0)(_ + _)
+      val expected = (1 to 100).map(_ + 2).map(_ * 2).fold(0)(_ + _)
+
+      Await.result(fl, 5.seconds) should be(expected)
+    }
   }
-}
+}

akka-stream/src/main/scala/akka/stream/impl/ActorBasedFlowMaterializer.scala

@@ -228,7 +228,7 @@ case class ActorBasedFlowMaterializer(override val settings: MaterializerSetting
           case noMatch if !optimizations.simplification || (noMatch ne orig) ⇒ orig
 
           // Two consecutive maps is equivalent to one pipelined map
-          case Ast.Map(second) :: Ast.Map(first) :: rest ⇒ Ast.Map(first compose second) :: rest
+          case Ast.Map(second) :: Ast.Map(first) :: rest ⇒ Ast.Map(first andThen second) :: rest
 
           case noMatch ⇒ noMatch
         }