Improved operator string represenation #29935

* New attribute with source location information introduced and added to stages that takes lambdas
* Better default toString for GraphStageLogic including source location where possible
  and used that for debugging, errors and stream snapshots

akka-stream-tests/src/test/scala/akka/stream/impl/GraphStageLogicSpec.scala

@@ -282,7 +282,7 @@ class GraphStageLogicSpec extends StreamSpec with GraphInterpreterSpecKit with S
           })
           .runWith(Sink.ignore)
       }
-      ex.getMessage should startWith("No handler defined in stage [stage-name] for in port [in")
+      ex.getMessage should startWith("No handler defined in stage [").and(include("] for in port [in"))
     }
 
     "give a good error message if out handler missing" in {
@@ -308,7 +308,7 @@ class GraphStageLogicSpec extends StreamSpec with GraphInterpreterSpecKit with S
           .map(_ => "whatever")
           .runWith(Sink.ignore)
       }
-      ex.getMessage should startWith("No handler defined in stage [stage-name] for out port [out")
+      ex.getMessage should startWith("No handler defined in stage [").and(include("] for out port [out"))
     }
 
     "give a good error message if out handler missing with downstream boundary" in {
@@ -332,7 +332,7 @@ class GraphStageLogicSpec extends StreamSpec with GraphInterpreterSpecKit with S
           })
           .runWith(Sink.ignore.async)
       }
-      ex.getMessage should startWith("No handler defined in stage [stage-name] for out port [out")
+      ex.getMessage should startWith("No handler defined in stage [").and(include("] for out port [out"))
     }
 
     "give a good error message if handler missing with downstream publisher" in {
@@ -357,7 +357,7 @@ class GraphStageLogicSpec extends StreamSpec with GraphInterpreterSpecKit with S
           })
           .runWith(Sink.ignore)
       }
-      ex.getMessage should startWith("No handler defined in stage [stage-name] for out port [out")
+      ex.getMessage should startWith("No handler defined in stage [").and(include("] for out port [out"))
     }
 
     "give a good error message if handler missing when stage is an island" in {
@@ -382,7 +382,7 @@ class GraphStageLogicSpec extends StreamSpec with GraphInterpreterSpecKit with S
           .async
           .runWith(Sink.ignore)
       }
-      ex.getMessage should startWith("No handler defined in stage [stage-name] for out port [out")
+      ex.getMessage should startWith("No handler defined in stage [").and(include("] for out port [out"))
     }
 
     "give a good error message if sub source is pushed twice" in {

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

@@ -46,7 +46,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      source.runWith(Sink.head).futureValue shouldBe Some("my-name")
+      source.runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -58,7 +58,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      source.runWith(Sink.head).futureValue shouldBe Some("my-name")
+      source.runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {
@@ -120,7 +120,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("my-name")
+      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -132,7 +132,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("my-name")
+      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {
@@ -192,7 +192,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.runWith(sink).flatMap(identity).futureValue shouldBe Some("my-name")
+      Source.empty.runWith(sink).flatMap(identity).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -204,7 +204,7 @@ class FromMaterializerSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.runWith(sink).flatMap(identity).flatMap(identity).futureValue shouldBe Some("my-name")
+      Source.empty.runWith(sink).flatMap(identity).flatMap(identity).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {

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

@@ -49,7 +49,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      source.runWith(Sink.head).futureValue shouldBe Some("my-name")
+      source.runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -61,7 +61,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      source.runWith(Sink.head).futureValue shouldBe Some("my-name")
+      source.runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {
@@ -123,7 +123,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("my-name")
+      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -135,7 +135,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("my-name")
+      Source.empty.via(flow).runWith(Sink.head).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {
@@ -195,7 +195,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.runWith(sink).flatMap(identity).futureValue shouldBe Some("my-name")
+      Source.empty.runWith(sink).flatMap(identity).futureValue shouldBe Some("setup-my-name")
     }
 
     "propagate attributes when nested" in {
@@ -207,7 +207,7 @@ class SetupSpec extends StreamSpec {
         }
         .named("my-name")
 
-      Source.empty.runWith(sink).flatMap(identity).flatMap(identity).futureValue shouldBe Some("my-name")
+      Source.empty.runWith(sink).flatMap(identity).flatMap(identity).futureValue shouldBe Some("setup-my-name")
     }
 
     "handle factory failure" in {

akka-stream/src/main/scala/akka/stream/Attributes.scala

@@ -7,12 +7,10 @@ package akka.stream
 import java.net.URLEncoder
 import java.time.Duration
 import java.util.Optional
-
 import scala.annotation.tailrec
 import scala.compat.java8.OptionConverters._
 import scala.concurrent.duration.FiniteDuration
 import scala.reflect.{ classTag, ClassTag }
-
 import akka.annotation.ApiMayChange
 import akka.annotation.DoNotInherit
 import akka.annotation.InternalApi
@@ -21,6 +19,7 @@ import akka.japi.function
 import akka.stream.impl.TraversalBuilder
 import akka.util.{ ByteString, OptionVal }
 import akka.util.JavaDurationConverters._
+import akka.util.LineNumbers
 
 /**
  * Holds attributes which can be used to alter [[akka.stream.scaladsl.Flow]] / [[akka.stream.javadsl.Flow]]
@@ -304,6 +303,32 @@ object Attributes {
 
   final case class Name(n: String) extends Attribute
 
+  /**
+   * Attribute that contains the source location of for example a lambda passed to an operator, useful for example
+   * for debugging. Included in the default toString of GraphStageLogic if present
+   */
+  final class SourceLocation(lambda: AnyRef) extends Attribute {
+    lazy val locationName: String = {
+      val locationName = LineNumbers(lambda) match {
+        case LineNumbers.NoSourceInfo           => "unknown"
+        case LineNumbers.UnknownSourceFormat(_) => "unknown"
+        case LineNumbers.SourceFile(filename)   => filename
+        case LineNumbers.SourceFileLines(filename, from, _) =>
+          s"$filename:$from"
+      }
+      s"${lambda.getClass.getPackage.getName}-$locationName"
+    }
+
+    override def toString: String = locationName
+  }
+
+  object SourceLocation {
+    def forLambda(lambda: AnyRef): SourceLocation = new SourceLocation(lambda)
+
+    def stringFrom(attributes: Attributes): String =
+      attributes.get[SourceLocation].map(_.locationName).getOrElse("unknown")
+  }
+
   /**
    * Each asynchronous piece of a materialized stream topology is executed by one Actor
    * that manages an input buffer for all inlets of its shape. This attribute configures

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

@@ -6,8 +6,8 @@ package akka.stream.impl
 
 import scala.concurrent.{ Future, Promise }
 import scala.util.control.NonFatal
-
 import akka.annotation.InternalApi
+import akka.stream.Attributes.SourceLocation
 import akka.stream._
 import akka.stream.impl.Stages.DefaultAttributes
 import akka.stream.scaladsl.{ Keep, Source }
@@ -28,7 +28,7 @@ import akka.stream.stage._
   val out = Outlet[T]("LazySource.out")
   override val shape = SourceShape(out)
 
-  override protected def initialAttributes = DefaultAttributes.lazySource
+  override protected def initialAttributes = DefaultAttributes.lazySource and SourceLocation.forLambda(sourceFactory)
 
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, Future[M]) = {
     val matPromise = Promise[M]()

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

@@ -834,8 +834,7 @@ private final case class SavedIslandData(
         if (isIn) s"in port id [$missingHandlerIdx]"
         else s"out port id [$missingHandlerIdx]"
     }
-    throw new IllegalStateException(
+    throw new IllegalStateException(s"No handler defined in stage [${logic.toString}] for $portLabel." +
-      s"No handler defined in stage [${logic.originalStage.getOrElse(logic).toString}] for $portLabel." +
     " All inlets and outlets must be assigned a handler with setHandler in the constructor of your graph stage logic.")
   }
 

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

@@ -7,8 +7,8 @@ package akka.stream.impl
 import scala.concurrent.Future
 import scala.concurrent.Promise
 import scala.util.control.NonFatal
-
 import akka.annotation.InternalApi
+import akka.stream.Attributes.SourceLocation
 import akka.stream._
 import akka.stream.scaladsl.Flow
 import akka.stream.scaladsl.Keep
@@ -26,6 +26,8 @@ import akka.stream.stage.OutHandler
   private val in = Inlet[T]("SetupSinkStage.in")
   override val shape = SinkShape(in)
 
+  override protected def initialAttributes: Attributes = Attributes.name("setup") and SourceLocation.forLambda(factory)
+
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, Future[M]) = {
     val matPromise = Promise[M]()
     (createStageLogic(matPromise), matPromise.future)
@@ -62,6 +64,8 @@ import akka.stream.stage.OutHandler
   private val out = Outlet[U]("SetupFlowStage.out")
   override val shape = FlowShape(in, out)
 
+  override protected def initialAttributes: Attributes = Attributes.name("setup") and SourceLocation.forLambda(factory)
+
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, Future[M]) = {
     val matPromise = Promise[M]()
     (createStageLogic(matPromise), matPromise.future)
@@ -105,6 +109,8 @@ import akka.stream.stage.OutHandler
   private val out = Outlet[T]("SetupSourceStage.out")
   override val shape = SourceShape(out)
 
+  override protected def initialAttributes: Attributes = Attributes.name("setup") and SourceLocation.forLambda(factory)
+
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, Future[M]) = {
     val matPromise = Promise[M]()
     (createStageLogic(matPromise), matPromise.future)

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

@@ -5,7 +5,6 @@
 package akka.stream.impl
 
 import java.util.function.BinaryOperator
-
 import scala.annotation.unchecked.uncheckedVariance
 import scala.collection.immutable
 import scala.collection.mutable
@@ -15,10 +14,8 @@ import scala.util.Failure
 import scala.util.Success
 import scala.util.Try
 import scala.util.control.NonFatal
-
 import org.reactivestreams.Publisher
 import org.reactivestreams.Subscriber
-
 import akka.NotUsed
 import akka.annotation.DoNotInherit
 import akka.annotation.InternalApi
@@ -27,6 +24,7 @@ import akka.event.Logging
 import akka.stream._
 import akka.stream.ActorAttributes.StreamSubscriptionTimeout
 import akka.stream.Attributes.InputBuffer
+import akka.stream.Attributes.SourceLocation
 import akka.stream.impl.QueueSink.Output
 import akka.stream.impl.QueueSink.Pull
 import akka.stream.impl.Stages.DefaultAttributes
@@ -537,7 +535,7 @@ import akka.util.ccompat._
 @InternalApi final private[stream] class LazySink[T, M](sinkFactory: T => Future[Sink[T, M]])
     extends GraphStageWithMaterializedValue[SinkShape[T], Future[M]] {
   val in = Inlet[T]("lazySink.in")
-  override def initialAttributes = DefaultAttributes.lazySink
+  override def initialAttributes = DefaultAttributes.lazySink and SourceLocation.forLambda(sinkFactory)
   override val shape: SinkShape[T] = SinkShape.of(in)
 
   override def toString: String = "LazySink"

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

@@ -27,6 +27,7 @@ import akka.stream.Attributes._
     val filterNot = name("filterNot")
     val collect = name("collect")
     val recover = name("recover")
+    val mapError = name("mapError")
     val mapAsync = name("mapAsync")
     val mapAsyncUnordered = name("mapAsyncUnordered")
     val ask = name("ask")

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

@@ -679,7 +679,7 @@ import akka.util.OptionVal
     if (!isInitialized)
       UninitializedInterpreterImpl(logics.zipWithIndex.map {
         case (logic, idx) =>
-          LogicSnapshotImpl(idx, logic.originalStage.getOrElse(logic).toString, logic.attributes)
+          LogicSnapshotImpl(idx, logic.toString, logic.attributes)
       }.toVector)
     else interpreter.toSnapshot
   }

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

@@ -306,7 +306,7 @@ import akka.stream.stage._
         logic.preStart()
       } catch {
         case NonFatal(e) =>
-          log.error(e, "Error during preStart in [{}]: {}", logic.originalStage.getOrElse(logic), e.getMessage)
+          log.error(e, "Error during preStart in [{}]: {}", logic.toString, e.getMessage)
           logic.failStage(e)
       }
       afterStageHasRun(logic)
@@ -366,7 +366,7 @@ import akka.stream.stage._
               case None         => true
             }
             if (loggingEnabled)
-              log.error(e, "Error in stage [{}]: {}", activeStage.originalStage.getOrElse(activeStage), e.getMessage)
+              log.error(e, "Error in stage [{}]: {}", activeStage.toString, e.getMessage)
             activeStage.failStage(e)
 
             // Abort chasing
@@ -600,7 +600,7 @@ import akka.stream.stage._
       logic.afterPostStop()
     } catch {
       case NonFatal(e) =>
-        log.error(e, s"Error during postStop in [{}]: {}", logic.originalStage.getOrElse(logic), e.getMessage)
+        log.error(e, s"Error during postStop in [{}]: {}", logic.toString, e.getMessage)
     }
   }
 
@@ -680,8 +680,7 @@ import akka.stream.stage._
 
     val logicSnapshots = logics.zipWithIndex.map {
       case (logic, idx) =>
-        val label = logic.originalStage.getOrElse(logic).toString
+        LogicSnapshotImpl(idx, logic.toString, logic.attributes)
-        LogicSnapshotImpl(idx, label, logic.attributes)
     }
     val logicIndexes = logics.zipWithIndex.map { case (stage, idx) => stage -> idx }.toMap
     val connectionSnapshots = connections.filter(_ != null).map { connection =>

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

@@ -5,12 +5,12 @@
 package akka.stream.impl.fusing
 
 import java.util.concurrent.TimeUnit.NANOSECONDS
-
 import akka.actor.{ ActorRef, Terminated }
 import akka.annotation.{ DoNotInherit, InternalApi }
 import akka.event.Logging.LogLevel
 import akka.event._
 import akka.stream.ActorAttributes.SupervisionStrategy
+import akka.stream.Attributes.SourceLocation
 import akka.stream.Attributes.{ InputBuffer, LogLevels }
 import akka.stream.OverflowStrategies._
 import akka.stream.impl.Stages.DefaultAttributes
@@ -40,7 +40,7 @@ import akka.util.ccompat._
   val out = Outlet[Out]("Map.out")
   override val shape = FlowShape(in, out)
 
-  override def initialAttributes: Attributes = DefaultAttributes.map
+  override def initialAttributes: Attributes = DefaultAttributes.map and SourceLocation.forLambda(f)
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -69,7 +69,7 @@ import akka.util.ccompat._
  * INTERNAL API
  */
 @InternalApi private[akka] final case class Filter[T](p: T => Boolean) extends SimpleLinearGraphStage[T] {
-  override def initialAttributes: Attributes = DefaultAttributes.filter
+  override def initialAttributes: Attributes = DefaultAttributes.filter and SourceLocation.forLambda(p)
 
   override def toString: String = "Filter"
 
@@ -121,7 +121,7 @@ import akka.util.ccompat._
  */
 @InternalApi private[akka] final case class TakeWhile[T](p: T => Boolean, inclusive: Boolean = false)
     extends SimpleLinearGraphStage[T] {
-  override def initialAttributes: Attributes = DefaultAttributes.takeWhile
+  override def initialAttributes: Attributes = DefaultAttributes.takeWhile and SourceLocation.forLambda(p)
 
   override def toString: String = "TakeWhile"
 
@@ -159,7 +159,7 @@ import akka.util.ccompat._
  * INTERNAL API
  */
 @InternalApi private[akka] final case class DropWhile[T](p: T => Boolean) extends SimpleLinearGraphStage[T] {
-  override def initialAttributes: Attributes = DefaultAttributes.dropWhile
+  override def initialAttributes: Attributes = DefaultAttributes.dropWhile and SourceLocation.forLambda(p)
 
   def createLogic(inheritedAttributes: Attributes) =
     new SupervisedGraphStageLogic(inheritedAttributes, shape) with InHandler with OutHandler {
@@ -231,7 +231,7 @@ private[stream] object Collect {
   val out = Outlet[Out]("Collect.out")
   override val shape = FlowShape(in, out)
 
-  override def initialAttributes: Attributes = DefaultAttributes.collect
+  override def initialAttributes: Attributes = DefaultAttributes.collect and SourceLocation.forLambda(pf)
 
   def createLogic(inheritedAttributes: Attributes) =
     new SupervisedGraphStageLogic(inheritedAttributes, shape) with InHandler with OutHandler {
@@ -264,7 +264,7 @@ private[stream] object Collect {
  */
 @InternalApi private[akka] final case class Recover[T](pf: PartialFunction[Throwable, T])
     extends SimpleLinearGraphStage[T] {
-  override protected def initialAttributes: Attributes = DefaultAttributes.recover
+  override protected def initialAttributes: Attributes = DefaultAttributes.recover and SourceLocation.forLambda(pf)
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -315,6 +315,9 @@ private[stream] object Collect {
  */
 @InternalApi private[akka] final case class MapError[T](f: PartialFunction[Throwable, Throwable])
     extends SimpleLinearGraphStage[T] {
+
+  override protected def initialAttributes: Attributes = DefaultAttributes.mapError
+
   override def createLogic(attr: Attributes) =
     new GraphStageLogic(shape) with InHandler with OutHandler {
       override def onPush(): Unit = push(out, grab(in))
@@ -390,7 +393,7 @@ private[stream] object Collect {
     extends GraphStage[FlowShape[In, Out]] {
   override val shape = FlowShape[In, Out](Inlet("Scan.in"), Outlet("Scan.out"))
 
-  override def initialAttributes: Attributes = DefaultAttributes.scan
+  override def initialAttributes: Attributes = DefaultAttributes.scan and SourceLocation.forLambda(f)
 
   override def toString: String = "Scan"
 
@@ -457,7 +460,7 @@ private[stream] object Collect {
   val out = Outlet[Out]("ScanAsync.out")
   override val shape: FlowShape[In, Out] = FlowShape[In, Out](in, out)
 
-  override val initialAttributes: Attributes = Attributes.name("scanAsync")
+  override val initialAttributes: Attributes = Attributes.name("scanAsync") and SourceLocation.forLambda(f)
 
   override val toString: String = "ScanAsync"
 
@@ -576,7 +579,7 @@ private[stream] object Collect {
 
   override def toString: String = "Fold"
 
-  override val initialAttributes = DefaultAttributes.fold
+  override val initialAttributes = DefaultAttributes.fold and SourceLocation.forLambda(f)
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -635,7 +638,7 @@ private[stream] object Collect {
 
   override def toString: String = "FoldAsync"
 
-  override val initialAttributes = DefaultAttributes.foldAsync
+  override val initialAttributes = DefaultAttributes.foldAsync and SourceLocation.forLambda(f)
 
   def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -816,7 +819,7 @@ private[stream] object Collect {
  */
 @InternalApi private[akka] final case class LimitWeighted[T](val n: Long, val costFn: T => Long)
     extends SimpleLinearGraphStage[T] {
-  override def initialAttributes: Attributes = DefaultAttributes.limitWeighted
+  override def initialAttributes: Attributes = DefaultAttributes.limitWeighted and SourceLocation.forLambda(costFn)
 
   def createLogic(inheritedAttributes: Attributes) =
     new SupervisedGraphStageLogic(inheritedAttributes, shape) with InHandler with OutHandler {
@@ -1161,7 +1164,7 @@ private[stream] object Collect {
   private val in = Inlet[In]("expand.in")
   private val out = Outlet[Out]("expand.out")
 
-  override def initialAttributes = DefaultAttributes.expand
+  override def initialAttributes = DefaultAttributes.expand and SourceLocation.forLambda(extrapolate)
 
   override val shape = FlowShape(in, out)
 
@@ -1253,7 +1256,7 @@ private[stream] object Collect {
   private val in = Inlet[In]("MapAsync.in")
   private val out = Outlet[Out]("MapAsync.out")
 
-  override def initialAttributes = DefaultAttributes.mapAsync
+  override def initialAttributes = DefaultAttributes.mapAsync and SourceLocation.forLambda(f)
 
   override val shape = FlowShape(in, out)
 
@@ -1353,7 +1356,7 @@ private[stream] object Collect {
   private val in = Inlet[In]("MapAsyncUnordered.in")
   private val out = Outlet[Out]("MapAsyncUnordered.out")
 
-  override def initialAttributes = DefaultAttributes.mapAsyncUnordered
+  override def initialAttributes = DefaultAttributes.mapAsyncUnordered and SourceLocation.forLambda(f)
 
   override val shape = FlowShape(in, out)
 
@@ -1718,7 +1721,7 @@ private[stream] object Collect {
   val in = Inlet[T]("in")
   val out = Outlet[immutable.Seq[T]]("out")
 
-  override def initialAttributes = DefaultAttributes.groupedWeightedWithin
+  override def initialAttributes = DefaultAttributes.groupedWeightedWithin and SourceLocation.forLambda(costFn)
 
   val shape = FlowShape(in, out)
 
@@ -2038,7 +2041,7 @@ private[stream] object Collect {
  * INTERNAL API
  */
 @InternalApi private[akka] final class Reduce[T](val f: (T, T) => T) extends SimpleLinearGraphStage[T] {
-  override def initialAttributes: Attributes = DefaultAttributes.reduce
+  override def initialAttributes: Attributes = DefaultAttributes.reduce and SourceLocation.forLambda(f)
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
     new GraphStageLogic(shape) with InHandler with OutHandler { self =>
@@ -2166,7 +2169,7 @@ private[akka] final class StatefulMapConcat[In, Out](val f: () => In => Iterable
   val out = Outlet[Out]("StatefulMapConcat.out")
   override val shape = FlowShape(in, out)
 
-  override def initialAttributes: Attributes = DefaultAttributes.statefulMapConcat
+  override def initialAttributes: Attributes = DefaultAttributes.statefulMapConcat and SourceLocation.forLambda(f)
 
   def createLogic(inheritedAttributes: Attributes) = new GraphStageLogic(shape) with InHandler with OutHandler {
     lazy val decider = inheritedAttributes.mandatoryAttribute[SupervisionStrategy].decider

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

@@ -6,7 +6,6 @@ package akka.stream.impl.fusing
 
 import java.util.Collections
 import java.util.concurrent.atomic.AtomicReference
-
 import scala.annotation.tailrec
 import scala.collection.immutable
 import scala.concurrent.duration.FiniteDuration
@@ -16,6 +15,7 @@ import akka.annotation.InternalApi
 import akka.stream._
 import akka.stream.ActorAttributes.StreamSubscriptionTimeout
 import akka.stream.ActorAttributes.SupervisionStrategy
+import akka.stream.Attributes.SourceLocation
 import akka.stream.impl.{ Buffer => BufferImpl }
 import akka.stream.impl.ActorSubscriberMessage
 import akka.stream.impl.ActorSubscriberMessage.OnError
@@ -473,8 +473,10 @@ import akka.util.ccompat.JavaConverters._
     val p: T => Boolean,
     val substreamCancelStrategy: SubstreamCancelStrategy)
     extends GraphStage[FlowShape[T, Source[T, NotUsed]]] {
+
   val in: Inlet[T] = Inlet("Split.in")
   val out: Outlet[Source[T, NotUsed]] = Outlet("Split.out")
+
   override val shape: FlowShape[T, Source[T, NotUsed]] = FlowShape(in, out)
 
   private val propagateSubstreamCancel = substreamCancelStrategy match {
@@ -482,6 +484,8 @@ import akka.util.ccompat.JavaConverters._
     case SubstreamCancelStrategies.Drain     => false
   }
 
+  override protected def initialAttributes: Attributes = DefaultAttributes.split and SourceLocation.forLambda(p)
+
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new TimerGraphStageLogic(shape) {
     import Split._
 

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

@@ -10,14 +10,13 @@ import scala.collection.immutable
 import scala.concurrent.Future
 import scala.concurrent.duration.FiniteDuration
 import scala.reflect.ClassTag
-
 import org.reactivestreams.{ Processor, Publisher, Subscriber, Subscription }
-
 import akka.Done
 import akka.NotUsed
 import akka.actor.ActorRef
 import akka.annotation.DoNotInherit
 import akka.event.{ LogMarker, LoggingAdapter, MarkerLoggingAdapter }
+import akka.stream.Attributes.SourceLocation
 import akka.stream._
 import akka.stream.impl.{
   fusing,
@@ -663,7 +662,7 @@ object Flow {
    * this will delay downstream cancellation until nested flow's materialization which is then immediately cancelled (with the original cancellation cause).
    */
   def lazyFlow[I, O, M](create: () => Flow[I, O, M]): Flow[I, O, Future[M]] =
-    lazyFutureFlow(() => Future.successful(create()))
+    lazyFutureFlow(() => Future.successful(create())).addAttributes(Attributes(SourceLocation.forLambda(create)))
 
   /**
    * Defers invoking the `create` function to create a future flow until there downstream demand has caused upstream
@@ -704,6 +703,7 @@ object Flow {
             .mapMaterializedValue(_ => Future.failed[M](new NeverMaterializedException()))
           f
       }(Keep.right)
+      .addAttributes(Attributes(SourceLocation.forLambda(create)))
       .mapMaterializedValue(_.flatten)
 
 }
@@ -1204,7 +1204,7 @@ trait FlowOps[+Out, +Mat] {
    * '''Cancels when''' downstream cancels
    */
   def filterNot(p: Out => Boolean): Repr[Out] =
-    via(Flow[Out].filter(!p(_)).withAttributes(DefaultAttributes.filterNot))
+    via(Flow[Out].filter(!p(_)).withAttributes(DefaultAttributes.filterNot and SourceLocation.forLambda(p)))
 
   /**
    * Terminate processing (and cancel the upstream publisher) after predicate
@@ -1776,7 +1776,9 @@ trait FlowOps[+Out, +Mat] {
    * See also [[FlowOps.conflate]], [[FlowOps.limit]], [[FlowOps.limitWeighted]] [[FlowOps.batch]] [[FlowOps.batchWeighted]]
    */
   def conflateWithSeed[S](seed: Out => S)(aggregate: (S, Out) => S): Repr[S] =
-    via(Batch(1L, ConstantFun.zeroLong, seed, aggregate).withAttributes(DefaultAttributes.conflate))
+    via(
+      Batch(1L, ConstantFun.zeroLong, seed, aggregate)
+        .withAttributes(DefaultAttributes.conflate and SourceLocation.forLambda(aggregate)))
 
   /**
    * Allows a faster upstream to progress independently of a slower subscriber by conflating elements into a summary
@@ -1831,7 +1833,9 @@ trait FlowOps[+Out, +Mat] {
    * @param aggregate Takes the currently batched value and the current pending element to produce a new aggregate
    */
   def batch[S](max: Long, seed: Out => S)(aggregate: (S, Out) => S): Repr[S] =
-    via(Batch(max, ConstantFun.oneLong, seed, aggregate).withAttributes(DefaultAttributes.batch))
+    via(
+      Batch(max, ConstantFun.oneLong, seed, aggregate)
+        .withAttributes(DefaultAttributes.batch and SourceLocation.forLambda(aggregate)))
 
   /**
    * Allows a faster upstream to progress independently of a slower subscriber by aggregating elements into batches
@@ -1862,7 +1866,9 @@ trait FlowOps[+Out, +Mat] {
    * @param aggregate Takes the currently batched value and the current pending element to produce a new batch
    */
   def batchWeighted[S](max: Long, costFn: Out => Long, seed: Out => S)(aggregate: (S, Out) => S): Repr[S] =
-    via(Batch(max, costFn, seed, aggregate).withAttributes(DefaultAttributes.batchWeighted))
+    via(
+      Batch(max, costFn, seed, aggregate).withAttributes(
+        DefaultAttributes.batchWeighted and SourceLocation.forLambda(aggregate)))
 
   /**
    * Allows a faster downstream to progress independently of a slower upstream by extrapolating elements from an older

akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala

@@ -5,18 +5,16 @@
 package akka.stream.stage
 
 import java.util.concurrent.atomic.AtomicReference
-
 import scala.annotation.tailrec
 import scala.collection.{ immutable, mutable }
 import scala.concurrent.{ Future, Promise }
 import scala.concurrent.duration.FiniteDuration
-
 import com.github.ghik.silencer.silent
-
 import akka.{ Done, NotUsed }
 import akka.actor._
 import akka.annotation.InternalApi
 import akka.japi.function.{ Effect, Procedure }
+import akka.stream.Attributes.SourceLocation
 import akka.stream._
 import akka.stream.impl.{ ReactiveStreamsCompliance, TraversalBuilder }
 import akka.stream.impl.ActorSubscriberMessage
@@ -1584,7 +1582,15 @@ abstract class GraphStageLogic private[stream] (val inCount: Int, val outCount:
   }
 
   override def toString: String =
-    attributes.get[Attributes.Name].map(attr => s"${getClass.toString}-${attr.n}").getOrElse(getClass.toString)
+    attributes.get[Attributes.Name] match {
+      case Some(name) =>
+        attributes.get[SourceLocation] match {
+          case Some(location) => s"${getClass.getName}-${name.n}(${location.locationName})"
+          case None           => s"${getClass.getName}-${name.n}"
+        }
+
+      case None => getClass.getName
+    }
 
 }