Cleanup TimerSchedulerImpl & TimerInterceptor (#25891)

* Replace TimerMsg hierarchy with a simple mix-in

* Fix a couple of typos

* Remove the need for a cast but just passing a log

* Remove the need for casts by making TimerInterceptor specify it handles Ts

* Prefer a sealed class to a sealed case class

akka-actor-typed/src/main/scala/akka/actor/typed/internal/TimerSchedulerImpl.scala

@@ -18,16 +18,10 @@ import scala.concurrent.duration.FiniteDuration
  * INTERNAL API
  */
 @InternalApi private[akka] object TimerSchedulerImpl {
-  sealed trait TimerMsg {
-    def key: Any
-    def generation: Int
-    def owner: AnyRef
-  }
-
   final case class Timer[T](key: Any, msg: T, repeat: Boolean, generation: Int, task: Cancellable)
-  final case class InfluenceReceiveTimeoutTimerMsg(key: Any, generation: Int, owner: AnyRef) extends TimerMsg
+  sealed class TimerMsg(val key: Any, val generation: Int, val owner: AnyRef) {
-  final case class NotInfluenceReceiveTimeoutTimerMsg(key: Any, generation: Int, owner: AnyRef)
+    override def toString = s"TimerMsg(key=$key, generation=$generation, owner=$owner)"
-    extends TimerMsg with NotInfluenceReceiveTimeout
+  }
 
   def withTimers[T](factory: TimerSchedulerImpl[T] ⇒ Behavior[T]): Behavior[T] = {
     scaladsl.Behaviors.setup[T](wrapWithTimers(factory))
@@ -75,9 +69,9 @@ import scala.concurrent.duration.FiniteDuration
 
     val timerMsg =
       if (msg.isInstanceOf[NotInfluenceReceiveTimeout])
-        NotInfluenceReceiveTimeoutTimerMsg(key, nextGen, this)
+        new TimerMsg(key, nextGen, this) with NotInfluenceReceiveTimeout
       else
-        InfluenceReceiveTimeoutTimerMsg(key, nextGen, this)
+        new TimerMsg(key, nextGen, this)
 
     val task =
       if (repeat)
@@ -118,16 +112,16 @@ import scala.concurrent.duration.FiniteDuration
     timers = Map.empty
   }
 
-  def interceptTimerMsg(ctx: ActorContext[TimerMsg], timerMsg: TimerMsg): T = {
+  def interceptTimerMsg(log: Logger, timerMsg: TimerMsg): T = {
     timers.get(timerMsg.key) match {
       case None ⇒
         // it was from canceled timer that was already enqueued in mailbox
-        ctx.log.debug("Received timer [{}] that has been removed, discarding", timerMsg.key)
+        log.debug("Received timer [{}] that has been removed, discarding", timerMsg.key)
         null.asInstanceOf[T] // message should be ignored
       case Some(t) ⇒
         if (timerMsg.owner ne this) {
           // after restart, it was from an old instance that was enqueued in mailbox before canceled
-          ctx.log.debug("Received timer [{}] from old restarted instance, discarding", timerMsg.key)
+          log.debug("Received timer [{}] from old restarted instance, discarding", timerMsg.key)
           null.asInstanceOf[T] // message should be ignored
         } else if (timerMsg.generation == t.generation) {
           // valid timer
@@ -136,8 +130,8 @@ import scala.concurrent.duration.FiniteDuration
           t.msg
         } else {
           // it was from an old timer that was enqueued in mailbox before canceled
-          ctx.log.debug(
+          log.debug(
-            "Received timer [{}] from from old generation [{}], expected generation [{}], discarding",
+            "Received timer [{}] from old generation [{}], expected generation [{}], discarding",
             timerMsg.key, timerMsg.generation, t.generation)
           null.asInstanceOf[T] // message should be ignored
         }
@@ -147,8 +141,8 @@ import scala.concurrent.duration.FiniteDuration
   def intercept(behavior: Behavior[T]): Behavior[T] = {
     // The scheduled TimerMsg is intercepted to guard against old messages enqueued
     // in mailbox before timer was canceled.
-    // Intercept some signals to cancel timers when when restarting and stopping.
+    // Intercept some signals to cancel timers when restarting and stopping.
-    BehaviorImpl.intercept(new TimerInterceptor(this))(behavior).asInstanceOf[Behavior[T]]
+    BehaviorImpl.intercept(new TimerInterceptor(this))(behavior)
   }
 
 }
@@ -157,14 +151,14 @@ import scala.concurrent.duration.FiniteDuration
  * INTERNAL API
  */
 @InternalApi
-private final class TimerInterceptor[T](timerSchedulerImpl: TimerSchedulerImpl[T]) extends BehaviorInterceptor[AnyRef, T] {
+private final class TimerInterceptor[T](timerSchedulerImpl: TimerSchedulerImpl[T]) extends BehaviorInterceptor[T, T] {
   import TimerSchedulerImpl._
   import BehaviorInterceptor._
 
-  override def aroundReceive(ctx: typed.ActorContext[AnyRef], msg: AnyRef, target: ReceiveTarget[T]): Behavior[T] = {
+  override def aroundReceive(ctx: typed.ActorContext[T], msg: T, target: ReceiveTarget[T]): Behavior[T] = {
     val intercepted = msg match {
-      case msg: TimerMsg ⇒ timerSchedulerImpl.interceptTimerMsg(ctx.asInstanceOf[ActorContext[TimerMsg]], msg)
+      case msg: TimerMsg ⇒ timerSchedulerImpl.interceptTimerMsg(ctx.asScala.log, msg)
-      case msg           ⇒ msg.asInstanceOf[T]
+      case msg           ⇒ msg
     }
 
     // null means not applicable
@@ -172,7 +166,7 @@ private final class TimerInterceptor[T](timerSchedulerImpl: TimerSchedulerImpl[T
     else target(ctx, intercepted)
   }
 
-  override def aroundSignal(ctx: typed.ActorContext[AnyRef], signal: Signal, target: SignalTarget[T]): Behavior[T] = {
+  override def aroundSignal(ctx: typed.ActorContext[T], signal: Signal, target: SignalTarget[T]): Behavior[T] = {
     signal match {
       case PreRestart | PostStop ⇒ timerSchedulerImpl.cancelAll()
       case _                     ⇒ // unhandled