feat: support the flattening syntax for supervising

actor-typed-tests/src/test/java/jdocs/org/apache/pekko/typed/supervision/SupervisionCompileOnlyTest.java

@@ -86,9 +86,8 @@ public void supervision() {
     // #restart-limit
 
     // #multiple
-    Behaviors.supervise(
-            Behaviors.supervise(behavior)
-                .onFailure(IllegalStateException.class, SupervisorStrategy.restart()))
+    Behaviors.supervise(behavior)
+        .onFailure(IllegalStateException.class, SupervisorStrategy.restart())
         .onFailure(IllegalArgumentException.class, SupervisorStrategy.stop());
     // #multiple
 

actor-typed-tests/src/test/java/org/apache/pekko/actor/typed/javadsl/ActorCompile.java

@@ -183,9 +183,8 @@ public Behavior<MyMsg> receive(TypedActorContext<MyMsg> context, MyMsg message)
     SupervisorStrategy strategy7 = strategy6.withResetBackoffAfter(Duration.ofSeconds(2));
 
     Behavior<MyMsg> behv =
-        Behaviors.supervise(
-                Behaviors.supervise(Behaviors.<MyMsg>ignore())
-                    .onFailure(IllegalStateException.class, strategy6))
+        Behaviors.supervise(Behaviors.<MyMsg>ignore())
+            .onFailure(IllegalStateException.class, strategy6)
             .onFailure(RuntimeException.class, strategy1);
   }
 

actor-typed-tests/src/test/scala/docs/org/apache/pekko/typed/supervision/SupervisionCompileOnly.scala

@@ -44,7 +44,8 @@ object SupervisionCompileOnly {
 
   // #multiple
   Behaviors
-    .supervise(Behaviors.supervise(behavior).onFailure[IllegalStateException](SupervisorStrategy.restart))
+    .supervise(behavior)
+    .onFailure[IllegalStateException](SupervisorStrategy.restart)
     .onFailure[IllegalArgumentException](SupervisorStrategy.stop)
   // #multiple
 

actor-typed-tests/src/test/scala/org/apache/pekko/actor/typed/SupervisionSpec.scala

@@ -844,7 +844,8 @@ class SupervisionSpec extends ScalaTestWithActorTestKit("""
     "support nesting to handle different exceptions" in {
       val probe = TestProbe[Event]("evt")
       val behv = Behaviors
-        .supervise(Behaviors.supervise(targetBehavior(probe.ref)).onFailure[Exc2](SupervisorStrategy.resume))
+        .supervise(targetBehavior(probe.ref))
+        .onFailure[Exc2](SupervisorStrategy.resume)
         .onFailure[Exc3](SupervisorStrategy.restart)
       val ref = spawn(behv)
       ref ! IncrementState

actor-typed/src/main/mima-filters/1.0.x.backwards.excludes/issue-3413.excludes

@@ -0,0 +1,21 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# Change the return type of `Behaviors.supervise` to support flattened supervision
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("org.apache.pekko.actor.typed.javadsl.Behaviors#Supervise.onFailure")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("org.apache.pekko.actor.typed.scaladsl.Behaviors#Supervise.onFailure")
+ProblemFilters.exclude[IncompatibleResultTypeProblem]("org.apache.pekko.actor.typed.scaladsl.Behaviors#Supervise.onFailure$extension")

actor-typed/src/main/scala/org/apache/pekko/actor/typed/Behavior.scala

@@ -19,11 +19,9 @@ import scala.reflect.ClassTag
 
 import org.apache.pekko
 import pekko.actor.InvalidMessageException
-import pekko.actor.typed.internal.BehaviorImpl
+import pekko.actor.typed.internal.{ BehaviorImpl, BehaviorTags, InterceptorImpl, Supervisor }
 import pekko.actor.typed.internal.BehaviorImpl.DeferredBehavior
 import pekko.actor.typed.internal.BehaviorImpl.StoppedBehavior
-import pekko.actor.typed.internal.BehaviorTags
-import pekko.actor.typed.internal.InterceptorImpl
 import pekko.annotation.DoNotInherit
 import pekko.annotation.InternalApi
 
@@ -71,6 +69,33 @@ abstract class Behavior[T](private[pekko] val _tag: Int) { behavior =>
 
 }
 
+/**
+ * INTERNAL API
+ * A behavior type that could be supervised, Not for user extension.
+ */
+@InternalApi
+class SuperviseBehavior[T] private[pekko] (
+    val wrapped: Behavior[T]) extends Behavior[T](BehaviorTags.SuperviseBehavior) {
+  private final val ThrowableClassTag = ClassTag(classOf[Throwable])
+
+  /** Specify the [[SupervisorStrategy]] to be invoked when the wrapped behavior throws. */
+  def onFailure[Thr <: Throwable](strategy: SupervisorStrategy)(
+      implicit tag: ClassTag[Thr] = ThrowableClassTag): SuperviseBehavior[T] = {
+    val effectiveTag = if (tag == ClassTag.Nothing) ThrowableClassTag else tag
+    new SuperviseBehavior[T](Supervisor(Behavior.validateAsInitial(wrapped), strategy)(effectiveTag))
+  }
+
+  /**
+   * Specify the [[SupervisorStrategy]] to be invoked when the wrapped behavior throws.
+   *
+   * Only exceptions of the given type (and their subclasses) will be handled by this supervision behavior.
+   */
+  def onFailure[Thr <: Throwable](clazz: Class[Thr], strategy: SupervisorStrategy): SuperviseBehavior[T] =
+    onFailure(strategy)(ClassTag(clazz))
+
+  private[pekko] def unwrap: Behavior[T] = wrapped
+}
+
 /**
  * Extension point for implementing custom behaviors in addition to the existing
  * set of behaviors available through the DSLs in [[pekko.actor.typed.scaladsl.Behaviors]] and [[pekko.actor.typed.javadsl.Behaviors]]
@@ -180,7 +205,8 @@ object Behavior {
         val startedInner = start(wrapped.nestedBehavior, ctx.asInstanceOf[TypedActorContext[Any]])
         if (startedInner eq wrapped.nestedBehavior) wrapped
         else wrapped.replaceNested(startedInner)
-      case _ => behavior
+      case supervise: SuperviseBehavior[T] => start(supervise.unwrap, ctx)
+      case _                               => behavior
     }
   }
 
@@ -266,6 +292,8 @@ object Behavior {
         throw new IllegalArgumentException(s"cannot execute with [$behavior] as behavior")
       case BehaviorTags.DeferredBehavior =>
         throw new IllegalArgumentException(s"deferred [$behavior] should not be passed to interpreter")
+      case BehaviorTags.SuperviseBehavior =>
+        throw new IllegalArgumentException(s"supervise [$behavior] should not be passed to interpreter")
       case BehaviorTags.IgnoreBehavior =>
         BehaviorImpl.same[T]
       case BehaviorTags.StoppedBehavior =>

actor-typed/src/main/scala/org/apache/pekko/actor/typed/internal/BehaviorImpl.scala

@@ -39,6 +39,7 @@ private[pekko] object BehaviorTags {
   final val SameBehavior = 6
   final val FailedBehavior = 7
   final val StoppedBehavior = 8
+  final val SuperviseBehavior = 9
 
 }
 

actor-typed/src/main/scala/org/apache/pekko/actor/typed/javadsl/Behaviors.scala

@@ -20,13 +20,7 @@ import scala.reflect.ClassTag
 
 import org.apache.pekko
 import pekko.actor.typed._
-import pekko.actor.typed.internal.{
-  BehaviorImpl,
-  StashBufferImpl,
-  Supervisor,
-  TimerSchedulerImpl,
-  WithMdcBehaviorInterceptor
-}
+import pekko.actor.typed.internal.{ BehaviorImpl, StashBufferImpl, TimerSchedulerImpl, WithMdcBehaviorInterceptor }
 import pekko.japi.function.{ Effect, Function2 => JapiFunction2 }
 import pekko.japi.pf.PFBuilder
 import pekko.util.ccompat.JavaConverters._
@@ -271,16 +265,16 @@ object Behaviors {
      *
      * Only exceptions of the given type (and their subclasses) will be handled by this supervision behavior.
      */
-    def onFailure[Thr <: Throwable](clazz: Class[Thr], strategy: SupervisorStrategy): Behavior[T] =
-      Supervisor(Behavior.validateAsInitial(wrapped), strategy)(ClassTag(clazz))
+    def onFailure[Thr <: Throwable](clazz: Class[Thr], strategy: SupervisorStrategy): SuperviseBehavior[T] =
+      new SuperviseBehavior[T](wrapped).onFailure(clazz, strategy)
 
     /**
      * Specify the [[SupervisorStrategy]] to be invoked when the wrapped behavior throws.
      *
      * All non-fatal (see [[scala.util.control.NonFatal]]) exceptions types will be handled using the given strategy.
      */
     def onFailure(strategy: SupervisorStrategy): Behavior[T] =
-      onFailure(classOf[Exception], strategy)
+      new SuperviseBehavior[T](wrapped).onFailure(strategy)
   }
 
   /**

actor-typed/src/main/scala/org/apache/pekko/actor/typed/scaladsl/Behaviors.scala

@@ -15,8 +15,8 @@ package org.apache.pekko.actor.typed
 package scaladsl
 
 import scala.reflect.ClassTag
-
 import org.apache.pekko
+import org.apache.pekko.actor.typed.SuperviseBehavior
 import pekko.actor.typed.internal._
 import pekko.annotation.{ DoNotInherit, InternalApi }
 
@@ -233,9 +233,8 @@ object Behaviors {
 
     /** Specify the [[SupervisorStrategy]] to be invoked when the wrapped behavior throws. */
     def onFailure[Thr <: Throwable](strategy: SupervisorStrategy)(
-        implicit tag: ClassTag[Thr] = ThrowableClassTag): Behavior[T] = {
-      val effectiveTag = if (tag == ClassTag.Nothing) ThrowableClassTag else tag
-      Supervisor(Behavior.validateAsInitial(wrapped), strategy)(effectiveTag)
+        implicit tag: ClassTag[Thr] = ThrowableClassTag): SuperviseBehavior[T] = {
+      new SuperviseBehavior[T](wrapped).onFailure(strategy)(tag)
     }
   }