akka-stream compiler warnings as fatal errors (#26673)

akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala

@@ -18,19 +18,21 @@ import akka.stream.impl.{ ReactiveStreamsCompliance, Buffer => BufferImpl }
 import akka.stream.scaladsl.{ Flow, Keep, Source }
 import akka.stream.stage._
 import akka.stream.{ Supervision, _ }
+
 import scala.annotation.tailrec
 import scala.collection.immutable
 import scala.collection.immutable.VectorBuilder
 import scala.concurrent.{ Future, Promise }
 import scala.util.control.{ NoStackTrace, NonFatal }
 import scala.util.{ Failure, Success, Try }
-
 import akka.stream.ActorAttributes.SupervisionStrategy
+
 import scala.concurrent.duration.{ FiniteDuration, _ }
 import scala.util.control.Exception.Catcher
-
 import akka.stream.impl.Stages.DefaultAttributes
 import akka.util.OptionVal
+import akka.util.unused
+import com.github.ghik.silencer.silent
 
 /**
  * INTERNAL API
@@ -473,7 +475,7 @@ private[stream] object Collect {
           })
       }
 
-      private def onRestart(t: Throwable): Unit = {
+      private def onRestart(): Unit = {
         current = zero
         elementHandled = false
       }
@@ -498,7 +500,7 @@ private[stream] object Collect {
           case Supervision.Stop   => failStage(t)
           case Supervision.Resume => safePull()
           case Supervision.Restart =>
-            onRestart(t)
+            onRestart()
             safePull()
         }
         elementHandled = true
@@ -531,7 +533,7 @@ private[stream] object Collect {
           case NonFatal(ex) =>
             decider(ex) match {
               case Supervision.Stop    => failStage(ex)
-              case Supervision.Restart => onRestart(ex)
+              case Supervision.Restart => onRestart()
               case Supervision.Resume  => ()
             }
             tryPull(in)
@@ -629,7 +631,7 @@ private[stream] object Collect {
       private var aggregator: Out = zero
       private var aggregating: Future[Out] = Future.successful(aggregator)
 
-      private def onRestart(t: Throwable): Unit = {
+      private def onRestart(@unused t: Throwable): Unit = {
         aggregator = zero
       }
 
@@ -1407,6 +1409,7 @@ private[stream] object Collect {
       private lazy val self = getStageActor {
         case (_, Terminated(`targetRef`)) =>
           failStage(new WatchedActorTerminatedException("Watch", targetRef))
+        case (_, _) => // keep the compiler happy (stage actor receive is total)
       }
 
       override def preStart(): Unit = {
@@ -1886,7 +1889,7 @@ private[stream] object Collect {
     new GraphStageLogic(shape) with InHandler with OutHandler { self =>
       override def toString = s"Reduce.Logic(aggregator=$aggregator)"
 
-      var aggregator: T = _
+      private var aggregator: T = _
 
       private def decider =
         inheritedAttributes.mandatoryAttribute[SupervisionStrategy].decider
@@ -1905,6 +1908,7 @@ private[stream] object Collect {
         })
       }
 
+      @silent // compiler complaining about aggregator = _: T
       override def onPush(): Unit = {
         val elem = grab(in)
         try {