Revert "=str #16280 Make flows sharable again" since the problem is solved differently in this branch.

This reverts commit 2af568eb7a0c8d65f3dd2bb04852d05d5cbda416.

akka-stream-tck/src/test/scala/akka/stream/tck/FusableProcessorTest.scala

@@ -22,7 +22,7 @@ class FusableProcessorTest extends AkkaIdentityProcessorVerification[Int] {
     val flowName = getClass.getSimpleName + "-" + processorCounter.incrementAndGet()
 
     val processor = materializer.asInstanceOf[ActorBasedFlowMaterializer].processorForNode(
-      Ast.OpFactory(() ⇒ akka.stream.impl.fusing.Map[Int, Int](identity), "identity"), flowName, 1)
+      Ast.Fusable(Vector(akka.stream.impl.fusing.Map[Int, Int](identity)), "identity"), flowName, 1)
 
     processor.asInstanceOf[Processor[Int, Int]]
   }

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

@@ -14,7 +14,7 @@ import akka.actor.{ Props, ActorRefFactory, ActorRef }
 import akka.stream.{ TransformerLike, MaterializerSettings }
 import akka.stream.FlowMaterializer
 import akka.stream.impl.{ ActorProcessorFactory, TransformProcessorImpl, StreamSupervisor, ActorBasedFlowMaterializer }
-import akka.stream.impl.Ast.{ Transform, OpFactory, AstNode }
+import akka.stream.impl.Ast.{ Transform, Fusable, AstNode }
 import akka.stream.testkit.{ StreamTestKit, AkkaSpec }
 import akka.stream.testkit.ChainSetup
 import akka.testkit._
@@ -73,7 +73,7 @@ object FlowSpec {
     override def processorForNode(op: AstNode, flowName: String, n: Int): Processor[Any, Any] = {
       val props = op match {
         case t: Transform ⇒ Props(new BrokenTransformProcessorImpl(settings, t.mkTransformer(), brokenMessage))
-        case OpFactory(mkOps, _) ⇒ Props(new BrokenActorInterpreter(settings, mkOps.map(_.apply()), brokenMessage)).withDispatcher(settings.dispatcher)
+        case f: Fusable   ⇒ Props(new BrokenActorInterpreter(settings, f.ops, brokenMessage)).withDispatcher(settings.dispatcher)
         case o            ⇒ ActorProcessorFactory.props(this, o)
       }
       val impl = actorOf(props, s"$flowName-$n-${op.name}")

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

@@ -43,12 +43,7 @@ private[akka] object Ast {
 
   case class TimerTransform(name: String, mkTransformer: () ⇒ TimerTransformer[Any, Any]) extends AstNode
 
-  object OpFactory {
-    def apply(mkOp: () ⇒ Op[_, _, _, _, _], name: String): OpFactory =
-      OpFactory(List(mkOp), name)
-  }
-
-  case class OpFactory(mkOps: List[() ⇒ Op[_, _, _, _, _]], name: String) extends AstNode
+  case class Fusable(ops: immutable.Seq[Op[_, _, _, _, _]], name: String) extends AstNode
 
   case class MapAsync(f: Any ⇒ Future[Any]) extends AstNode {
     override def name = "mapAsync"
@@ -331,7 +326,7 @@ private[akka] object ActorProcessorFactory {
   def props(materializer: FlowMaterializer, op: AstNode): Props = {
     val settings = materializer.settings
     (op match {
-      case OpFactory(mkOps, _)  ⇒ Props(new ActorInterpreter(materializer.settings, mkOps.map(_.apply())))
+      case Fusable(ops, _)      ⇒ Props(new ActorInterpreter(materializer.settings, ops))
       case t: Transform         ⇒ Props(new TransformProcessorImpl(settings, t.mkTransformer()))
       case t: TimerTransform    ⇒ Props(new TimerTransformerProcessorsImpl(settings, t.mkTransformer()))
       case m: MapAsync          ⇒ Props(new MapAsyncProcessorImpl(settings, m.f))

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

@@ -108,13 +108,13 @@ trait FlowOps[+Out] {
    * Transform this stream by applying the given function to each of the elements
    * as they pass through this processing step.
    */
-  def map[T](f: Out ⇒ T): Repr[T] = andThen(OpFactory(() ⇒ fusing.Map(f), "map"))
+  def map[T](f: Out ⇒ T): Repr[T] = andThen(Fusable(Vector(fusing.Map(f)), "map"))
 
   /**
    * Transform each input element into a sequence of output elements that is
    * then flattened into the output stream.
    */
-  def mapConcat[T](f: Out ⇒ immutable.Seq[T]): Repr[T] = andThen(OpFactory(() ⇒ fusing.MapConcat(f), "mapConcat"))
+  def mapConcat[T](f: Out ⇒ immutable.Seq[T]): Repr[T] = andThen(Fusable(Vector(fusing.MapConcat(f)), "mapConcat"))
 
   /**
    * Transform this stream by applying the given function to each of the elements
@@ -144,16 +144,16 @@ trait FlowOps[+Out] {
   /**
    * Only pass on those elements that satisfy the given predicate.
    */
-  def filter(p: Out ⇒ Boolean): Repr[Out] = andThen(OpFactory(() ⇒ fusing.Filter(p), "filter"))
+  def filter(p: Out ⇒ Boolean): Repr[Out] = andThen(Fusable(Vector(fusing.Filter(p)), "filter"))
 
   /**
    * Transform this stream by applying the given partial function to each of the elements
    * on which the function is defined as they pass through this processing step.
    * Non-matching elements are filtered out.
    */
-  def collect[T](pf: PartialFunction[Out, T]): Repr[T] = andThen(OpFactory(List(
-    () ⇒ fusing.Filter(pf.isDefinedAt),
-    () ⇒ fusing.Map(pf.apply)), "filter"))
+  def collect[T](pf: PartialFunction[Out, T]): Repr[T] = andThen(Fusable(Vector(
+    fusing.Filter(pf.isDefinedAt),
+    fusing.Map(pf.apply)), "filter"))
 
   /**
    * Chunk up this stream into groups of the given size, with the last group
@@ -163,7 +163,7 @@ trait FlowOps[+Out] {
    */
   def grouped(n: Int): Repr[immutable.Seq[Out]] = {
     require(n > 0, "n must be greater than 0")
-    andThen(OpFactory(() ⇒ fusing.Grouped(n), "grouped"))
+    andThen(Fusable(Vector(fusing.Grouped(n)), "grouped"))
   }
 
   /**
@@ -208,8 +208,8 @@ trait FlowOps[+Out] {
    * No elements will be dropped if `n` is zero or negative.
    */
   def drop(n: Int): Repr[Out] =
-    if (n <= 0) andThen(OpFactory(Nil, "drop"))
-    else andThen(OpFactory(() ⇒ fusing.Drop(n), "drop"))
+    if (n <= 0) andThen(Fusable(Vector.empty, "drop"))
+    else andThen(Fusable(Vector(fusing.Drop(n)), "drop"))
 
   /**
    * Discard the elements received within the given duration at beginning of the stream.
@@ -240,8 +240,8 @@ trait FlowOps[+Out] {
    * or negative.
    */
   def take(n: Int): Repr[Out] =
-    if (n <= 0) andThen(OpFactory(() ⇒ fusing.Completed(), "take"))
-    else andThen(OpFactory(() ⇒ fusing.Take(n), "take"))
+    if (n <= 0) andThen(Fusable(Vector(fusing.Completed()), "take"))
+    else andThen(Fusable(Vector(fusing.Take(n)), "take"))
 
   /**
    * Terminate processing (and cancel the upstream publisher) after the given
@@ -278,7 +278,7 @@ trait FlowOps[+Out] {
    * @param aggregate Takes the currently aggregated value and the current pending element to produce a new aggregate
    */
   def conflate[S](seed: Out ⇒ S)(aggregate: (S, Out) ⇒ S): Repr[S] =
-    andThen(OpFactory(() ⇒ fusing.Conflate(seed, aggregate), "conflate"))
+    andThen(Fusable(Vector(fusing.Conflate(seed, aggregate)), "conflate"))
 
   /**
    * Allows a faster downstream to progress independently of a slower publisher by extrapolating elements from an older
@@ -294,7 +294,7 @@ trait FlowOps[+Out] {
    *                    state.
    */
   def expand[S, U](seed: Out ⇒ S)(extrapolate: S ⇒ (U, S)): Repr[U] =
-    andThen(OpFactory(() ⇒ fusing.Expand(seed, extrapolate), "expand"))
+    andThen(Fusable(Vector(fusing.Expand(seed, extrapolate)), "expand"))
 
   /**
    * Adds a fixed size buffer in the flow that allows to store elements from a faster upstream until it becomes full.
@@ -306,7 +306,7 @@ trait FlowOps[+Out] {
    */
   def buffer(size: Int, overflowStrategy: OverflowStrategy): Repr[Out] = {
     require(size > 0, s"Buffer size must be larger than zero but was [$size]")
-    andThen(OpFactory(() ⇒ fusing.Buffer(size, overflowStrategy), "buffer"))
+    andThen(Fusable(Vector(fusing.Buffer(size, overflowStrategy)), "buffer"))
   }
 
   /**