Extra catch-ignore for source attributes in case not possible #30138

akka-stream-tests/src/test/scala/akka/stream/SourceLocationAttributeSpec.scala

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2009-2021 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.stream
+
+import akka.stream.scaladsl.Flow
+import akka.stream.testkit.StreamSpec
+
+class SourceLocationAttributeSpec extends StreamSpec {
+
+  "The SourceLocation attribute" must {
+    "not throw NPE" in {
+      // #30138
+      val f1 = Flow[Int].fold(0)(_ + _)
+      val f2 = Flow[Int].fold(0)(_ + _)
+      f1.join(f2).toString
+    }
+  }
+
+}

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

@@ -21,6 +21,8 @@ import akka.util.{ ByteString, OptionVal }
 import akka.util.JavaDurationConverters._
 import akka.util.LineNumbers
 
+import scala.util.control.NonFatal
+
 /**
  * Holds attributes which can be used to alter [[akka.stream.scaladsl.Flow]] / [[akka.stream.javadsl.Flow]]
  * or [[akka.stream.scaladsl.GraphDSL]] / [[akka.stream.javadsl.GraphDSL]] materialization.
@@ -308,7 +310,7 @@ object Attributes {
    * for debugging. Included in the default toString of GraphStageLogic if present
    */
   final class SourceLocation(lambda: AnyRef) extends Attribute {
-    lazy val locationName: String = {
+    lazy val locationName: String = try {
       val locationName = LineNumbers(lambda) match {
         case LineNumbers.NoSourceInfo           => "unknown"
         case LineNumbers.UnknownSourceFormat(_) => "unknown"
@@ -317,6 +319,8 @@ object Attributes {
           s"$filename:$from"
       }
       s"${lambda.getClass.getPackage.getName}-$locationName"
+    } catch {
+      case NonFatal(_) => "unknown" // location is not critical so give up without failing
     }
 
     override def toString: String = locationName