Merge pull request #25542 from akka/wip-25034-abs-patriknw

fix negative math.abs in Sharding Typed, #25034

akka-cluster-sharding-typed/src/main/scala/akka/cluster/sharding/typed/ShardingMessageExtractor.scala

@@ -81,7 +81,7 @@ final class HashCodeMessageExtractor[A](
   extends ShardingMessageExtractor[ShardingEnvelope[A], A] {
 
   override def entityId(envelope: ShardingEnvelope[A]): String = envelope.entityId
-  override def shardId(entityId: String): String = (math.abs(entityId.hashCode) % maxNumberOfShards).toString
+  override def shardId(entityId: String): String = math.abs(entityId.hashCode % maxNumberOfShards).toString
   override def unwrapMessage(envelope: ShardingEnvelope[A]): A = envelope.message
 }
 
@@ -98,7 +98,7 @@ abstract class HashCodeNoEnvelopeMessageExtractor[A](
   override val handOffStopMessage: A)
   extends ShardingMessageExtractor[A, A] {
 
-  override def shardId(entityId: String): String = (math.abs(entityId.hashCode) % maxNumberOfShards).toString
+  override def shardId(entityId: String): String = math.abs(entityId.hashCode % maxNumberOfShards).toString
   override final def unwrapMessage(message: A): A = message
 
   override def toString = s"HashCodeNoEnvelopeMessageExtractor($maxNumberOfShards)"

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ShardRegion.scala

@@ -134,6 +134,9 @@ object ShardRegion {
         case ShardRegion.StartEntity(id) ⇒ id
         case _                           ⇒ entityId(message)
       }
+      // It would be better to have abs(id.hashCode % maxNumberOfShards), see issue #25034
+      // but to avoid getting different values when rolling upgrade we keep the old way,
+      // and it doesn't have any serious consequences
       (math.abs(id.hashCode) % maxNumberOfShards).toString
     }
   }