adds serializer for akka.Done. #23854

(cherry picked from commit 53a543788494d7b6457f129b1ad4ff57ff530584)

akka-actor/src/main/scala/akka/Done.scala

@@ -3,12 +3,15 @@
  */
 package akka
 
+import java.io.Serializable
+import akka.annotation.DoNotInherit
+
 /**
  * Typically used together with `Future` to signal completion
  * but there is no actual value completed. More clearly signals intent
  * than `Unit` and is available both from Scala and Java (which `Unit` is not).
  */
-sealed abstract class Done
+@DoNotInherit sealed abstract class Done extends Serializable
 
 case object Done extends Done {
   /**

akka-docs/src/main/paradox/serialization.md

@@ -41,11 +41,16 @@ depending on the akka-remote module), so normally you don't need to add
 configuration for that; since `com.google.protobuf.GeneratedMessage`
 implements `java.io.Serializable`, protobuf messages will always be
 serialized using the protobuf protocol unless specifically overridden. In order
-to disable a default serializer, map its marker type to “none”:
+to disable a default serializer, see @ref:[Disabling the Java Serializer](remoting.md#disable-java-serializer)
+
+### Enable additional bindings
+
+`akka.Done` is by default serialized by the Java serializer, add the following binding to avoid that.
+It's not enabled by default for compatibility reasons. 
 
 ```
 akka.actor.serialization-bindings {
-  "java.io.Serializable" = none
+  "akka.Done" = akka-misc
 }
 ```
 
@@ -251,4 +256,4 @@ incompatibility as Java serialization does.
 
 [Akka-kryo by Roman Levenstein](https://github.com/romix/akka-kryo-serialization)
 
-[Twitter Chill Scala extensions for Kryo (based on Akka Version 2.3.x but due to backwards compatibility of the Serializer Interface this extension also works with 2.4.x)](https://github.com/twitter/chill)
+[Twitter Chill Scala extensions for Kryo (based on Akka Version 2.3.x but due to backwards compatibility of the Serializer Interface this extension also works with 2.4.x)](https://github.com/twitter/chill)

akka-remote/src/main/resources/reference.conf

@@ -49,6 +49,12 @@ akka {
       "com.google.protobuf.GeneratedMessage" = proto
       
       "java.util.Optional" = akka-misc
+
+      # akka.Done is handled by the MiscMessageSerializer, but it is not enabled for
+      # compatibility reasons (it was added in Akka 2.5.8). Enable by adding
+      # akka.actor.serialization-bindings {
+      #   "akka.Done" = akka-misc
+      # }
     }
 
     # Additional serialization-bindings that are replacing Java serialization are

akka-remote/src/main/scala/akka/remote/serialization/MiscMessageSerializer.scala

@@ -8,6 +8,7 @@ import java.nio.charset.StandardCharsets
 import java.util.Optional
 import java.util.concurrent.TimeUnit
 
+import akka.Done
 import akka.actor._
 import akka.dispatch.Dispatchers
 import akka.remote.routing.RemoteRouterConfig
@@ -43,6 +44,7 @@ class MiscMessageSerializer(val system: ExtendedActorSystem) extends SerializerW
     case PoisonPill                           ⇒ ParameterlessSerializedMessage
     case Kill                                 ⇒ ParameterlessSerializedMessage
     case RemoteWatcher.Heartbeat              ⇒ ParameterlessSerializedMessage
+    case Done                                 ⇒ ParameterlessSerializedMessage
     case hbrsp: RemoteWatcher.HeartbeatRsp    ⇒ serializeHeartbeatRsp(hbrsp)
     case rs: RemoteScope                      ⇒ serializeRemoteScope(rs)
     case LocalScope                           ⇒ ParameterlessSerializedMessage
@@ -253,6 +255,7 @@ class MiscMessageSerializer(val system: ExtendedActorSystem) extends SerializerW
   private val PoisonPillManifest = "P"
   private val KillManifest = "K"
   private val RemoteWatcherHBManifest = "RWHB"
+  private val DoneManifest = "DONE"
   private val RemoteWatcherHBRespManifest = "RWHR"
   private val ActorInitializationExceptionManifest = "AIEX"
   private val LocalScopeManifest = "LS"
@@ -281,6 +284,7 @@ class MiscMessageSerializer(val system: ExtendedActorSystem) extends SerializerW
     PoisonPillManifest → ((_) ⇒ PoisonPill),
     KillManifest → ((_) ⇒ Kill),
     RemoteWatcherHBManifest → ((_) ⇒ RemoteWatcher.Heartbeat),
+    DoneManifest → ((_) ⇒ Done),
     RemoteWatcherHBRespManifest → deserializeHeartbeatRsp,
     ActorInitializationExceptionManifest → deserializeActorInitializationException,
     LocalScopeManifest → ((_) ⇒ LocalScope),
@@ -311,6 +315,7 @@ class MiscMessageSerializer(val system: ExtendedActorSystem) extends SerializerW
       case PoisonPill                         ⇒ PoisonPillManifest
       case Kill                               ⇒ KillManifest
       case RemoteWatcher.Heartbeat            ⇒ RemoteWatcherHBManifest
+      case Done                               ⇒ DoneManifest
       case _: RemoteWatcher.HeartbeatRsp      ⇒ RemoteWatcherHBRespManifest
       case LocalScope                         ⇒ LocalScopeManifest
       case _: RemoteScope                     ⇒ RemoteScopeManifest

akka-remote/src/test/scala/akka/remote/serialization/MiscMessageSerializerSpec.scala

@@ -15,6 +15,7 @@ import scala.concurrent.duration._
 import java.util.Optional
 import java.io.NotSerializableException
 
+import akka.Done
 import akka.remote.routing.RemoteRouterConfig
 import akka.routing._
 
@@ -23,6 +24,8 @@ object MiscMessageSerializerSpec {
     """
     akka.actor.serialization-bindings {
       "akka.remote.serialization.MiscMessageSerializerSpec$TestException" = akka-misc
+      # not enabled by default
+      "akka.Done" = akka-misc
     }
     """
 
@@ -85,6 +88,7 @@ class MiscMessageSerializerSpec extends AkkaSpec(MiscMessageSerializerSpec.testC
       "PoisonPill" → PoisonPill,
       "RemoteWatcher.Heartbeat" → RemoteWatcher.Heartbeat,
       "RemoteWatcher.HertbeatRsp" → RemoteWatcher.HeartbeatRsp(65537),
+      "Done" → Done,
       "LocalScope" → LocalScope,
       "RemoteScope" → RemoteScope(Address("akka", "system", "localhost", 2525)),
       "Config" → system.settings.config,