Replace PushStage-based Filter with GraphStage (part of #19834) (#20269)

akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala

@@ -79,9 +79,9 @@ class InterpreterSpec extends AkkaSpec with GraphInterpreterSpecKit {
       lastEvents() should be(Set(OnComplete))
     }
 
-    "implement one-to-many many-to-one chain correctly" in new OneBoundedSetup[Int](Seq(
-      Doubler(),
-      Filter((x: Int) ⇒ x != 0, stoppingDecider))) {
+    "implement one-to-many many-to-one chain correctly" in new OneBoundedSetup[Int](
+      Doubler().toGS,
+      Filter((x: Int) ⇒ x != 0)) {
 
       lastEvents() should be(Set.empty)
 
@@ -104,9 +104,9 @@ class InterpreterSpec extends AkkaSpec with GraphInterpreterSpecKit {
       lastEvents() should be(Set(OnComplete))
     }
 
-    "implement many-to-one one-to-many chain correctly" in new OneBoundedSetup[Int](Seq(
-      Filter((x: Int) ⇒ x != 0, stoppingDecider),
-      Doubler())) {
+    "implement many-to-one one-to-many chain correctly" in new OneBoundedSetup[Int](
+      Filter((x: Int) ⇒ x != 0),
+      Doubler().toGS) {
 
       lastEvents() should be(Set.empty)
 
@@ -147,7 +147,7 @@ class InterpreterSpec extends AkkaSpec with GraphInterpreterSpecKit {
     }
 
     "implement take inside a chain" in new OneBoundedSetup[Int](
-      Filter((x: Int) ⇒ x != 0, stoppingDecider).toGS,
+      Filter((x: Int) ⇒ x != 0),
       takeTwo,
       Map((x: Int) ⇒ x + 1, stoppingDecider).toGS) {
 

akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSupervisionSpec.scala

@@ -4,7 +4,9 @@
 package akka.stream.impl.fusing
 
 import scala.util.control.NoStackTrace
+import akka.stream.ActorAttributes._
 import akka.stream.Supervision
+import akka.stream.Supervision._
 import akka.stream.stage.Context
 import akka.stream.stage.PushPullStage
 import akka.stream.stage.Stage
@@ -286,22 +288,6 @@ class InterpreterSupervisionSpec extends AkkaSpec with GraphInterpreterSpecKit {
       }
     }
 
-    "resume when Filter throws" in new OneBoundedSetup[Int](Seq(
-      Filter((x: Int) ⇒ if (x == 0) throw TE else true, resumingDecider))) {
-      downstream.requestOne()
-      lastEvents() should be(Set(RequestOne))
-      upstream.onNext(2)
-      lastEvents() should be(Set(OnNext(2)))
-
-      downstream.requestOne()
-      lastEvents() should be(Set(RequestOne))
-      upstream.onNext(0) // boom
-      lastEvents() should be(Set(RequestOne))
-
-      upstream.onNext(3)
-      lastEvents() should be(Set(OnNext(3)))
-    }
-
     "resume when Scan throws" in new OneBoundedSetup[Int](Seq(
       Scan(1, (acc: Int, x: Int) ⇒ if (x == 10) throw TE else acc + x, resumingDecider))) {
       downstream.requestOne()

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

@@ -3,17 +3,26 @@
  */
 package akka.stream.scaladsl
 
+import akka.stream.testkit.scaladsl.TestSink
+
 import scala.concurrent.forkjoin.ThreadLocalRandom.{ current ⇒ random }
+import akka.stream.ActorAttributes._
+import akka.stream.Supervision._
+import akka.stream.testkit.Utils._
 import akka.stream.ActorMaterializer
 import akka.stream.ActorMaterializerSettings
 import akka.stream.testkit._
 import akka.testkit.AkkaSpec
 
+import scala.util.control.NoStackTrace
+
 class FlowFilterSpec extends AkkaSpec with ScriptedTest {
 
   val settings = ActorMaterializerSettings(system)
     .withInputBuffer(initialSize = 2, maxSize = 16)
 
+  implicit val materializer = ActorMaterializer(settings)
+
   "A Filter" must {
 
     "filter" in {
@@ -38,6 +47,18 @@ class FlowFilterSpec extends AkkaSpec with ScriptedTest {
       probe.expectComplete()
     }
 
+    "continue if error" in assertAllStagesStopped {
+      val TE = new Exception("TEST") with NoStackTrace {
+        override def toString = "TE"
+      }
+
+      Source(1 to 3).filter((x: Int) ⇒ if (x == 2) throw TE else true).withAttributes(supervisionStrategy(resumingDecider))
+        .runWith(TestSink.probe[Int])
+        .request(3)
+        .expectNext(1, 3)
+        .expectComplete()
+    }
+
   }
 
   "A FilterNot" must {

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

@@ -153,10 +153,6 @@ private[stream] object Stages {
     override def create(attr: Attributes): Stage[T, T] = fusing.Log(name, extract, loggingAdapter, supervision(attr))
   }
 
-  final case class Filter[T](p: T ⇒ Boolean, attributes: Attributes = filter) extends SymbolicStage[T, T] {
-    override def create(attr: Attributes): Stage[T, T] = fusing.Filter(p, supervision(attr))
-  }
-
   final case class Recover[In, Out >: In](pf: PartialFunction[Throwable, Out], attributes: Attributes = recover) extends SymbolicStage[In, Out] {
     override def create(attr: Attributes): Stage[In, Out] = fusing.Recover(pf)
   }

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

@@ -34,12 +34,37 @@ private[akka] final case class Map[In, Out](f: In ⇒ Out, decider: Supervision.
 /**
  * INTERNAL API
  */
-private[akka] final case class Filter[T](p: T ⇒ Boolean, decider: Supervision.Decider) extends PushStage[T, T] {
-  override def onPush(elem: T, ctx: Context[T]): SyncDirective =
-    if (p(elem)) ctx.push(elem)
-    else ctx.pull()
+private[akka] final case class Filter[T](p: T ⇒ Boolean) extends SimpleLinearGraphStage[T] {
+  override def initialAttributes: Attributes = DefaultAttributes.filter
 
-  override def decide(t: Throwable): Supervision.Directive = decider(t)
+  override def toString: String = "Filter"
+
+  override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
+    new GraphStageLogic(shape) with OutHandler with InHandler {
+      override def toString = "FilterLogic"
+
+      def decider = inheritedAttributes.get[SupervisionStrategy].map(_.decider).getOrElse(Supervision.stoppingDecider)
+
+      override def onPush(): Unit = {
+        try {
+          val elem = grab(in)
+          if (p(elem)) {
+            push(out, elem)
+          } else {
+            pull(in)
+          }
+        } catch {
+          case NonFatal(ex) ⇒ decider(ex) match {
+            case Supervision.Stop ⇒ failStage(ex)
+            case _                ⇒ pull(in)
+          }
+        }
+      }
+
+      override def onPull(): Unit = pull(in)
+
+      setHandlers(in, out, this)
+    }
 }
 
 /**

akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala

@@ -581,7 +581,7 @@ trait FlowOps[+Out, +Mat] {
    *
    * '''Cancels when''' downstream cancels
    */
-  def filter(p: Out ⇒ Boolean): Repr[Out] = andThen(Filter(p))
+  def filter(p: Out ⇒ Boolean): Repr[Out] = via(Filter(p))
 
   /**
    * Only pass on those elements that NOT satisfy the given predicate.