Merge pull request #28833 from akka/wip-28786-stash-clear-patriknw

clear StashBuffer, #28786

akka-actor-typed-tests/src/test/scala/akka/actor/typed/scaladsl/StashBufferSpec.scala

@@ -195,6 +195,46 @@ class StashBufferSpec extends AnyWordSpec with Matchers with LogCapturing {
       buffer.size should ===(0)
     }
 
+    "clear" in {
+      val buffer = StashBuffer[String](context, 10)
+      buffer.stash("m1")
+      buffer.stash("m2")
+      buffer.clear()
+      buffer.size should ===(0)
+      buffer.stash("m3")
+      buffer.size should ===(1)
+    }
+
+    "be able to clear while unstashing" in {
+      val buffer = StashBuffer[String](context, 10)
+      buffer.stash("m1")
+      buffer.stash("m2")
+      buffer.stash("clear")
+      buffer.stash("m3")
+
+      val valueInbox = TestInbox[String]()
+      def behavior(state: String): Behavior[String] =
+        Behaviors.receive[String] { (_, message) =>
+          if (message == "get") {
+            valueInbox.ref ! state
+            Behaviors.same
+          } else if (message == "clear") {
+            buffer.clear()
+            Behaviors.same
+          } else {
+            behavior(state + message)
+          }
+        }
+
+      val b2 = buffer.unstashAll(behavior(""))
+      buffer.size should ===(0)
+
+      buffer.stash("get")
+      buffer.unstashAll(b2)
+      // clear called before processing m3 so not included
+      valueInbox.expectMessage("m1m2")
+    }
+
     "fail quick on invalid start behavior" in {
       val stash = StashBuffer[String](context, 10)
       stash.stash("one")

akka-actor-typed/src/main/mima-filters/2.6.4.backwards.excludes/issue-28786-stash-clear.excludes

@@ -0,0 +1,3 @@
+# #28786 add clear to StashBuffer, ok because of DoNotInherit
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.actor.typed.javadsl.StashBuffer.clear")
+ProblemFilters.exclude[ReversedMissingMethodProblem]("akka.actor.typed.scaladsl.StashBuffer.clear")

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

@@ -78,6 +78,13 @@ import akka.util.{ unused, ConstantFun }
     this
   }
 
+  override def clear(): Unit = {
+    _first = null
+    _last = null
+    _size = 0
+    stashCleared(ctx)
+  }
+
   @InternalStableApi
   private def createNode(message: T, @unused ctx: scaladsl.ActorContext[T]): Node[T] = {
     new Node(null, message)

akka-actor-typed/src/main/scala/akka/actor/typed/javadsl/StashBuffer.scala

@@ -74,6 +74,11 @@ import akka.japi.function.Procedure
    */
   def forEach(f: Procedure[T]): Unit
 
+  /**
+   * Removes all messages from the buffer.
+   */
+  def clear(): Unit
+
   /**
    * Process all stashed messages with the `behavior` and the returned
    * [[Behavior]] from each processed message. The `StashBuffer` will be

akka-actor-typed/src/main/scala/akka/actor/typed/scaladsl/StashBuffer.scala

@@ -85,6 +85,11 @@ import akka.annotation.{ DoNotInherit, InternalApi }
    */
   def foreach(f: T => Unit): Unit
 
+  /**
+   * Removes all messages from the buffer.
+   */
+  def clear(): Unit
+
   /**
    * Process all stashed messages with the `behavior` and the returned
    * [[Behavior]] from each processed message. The `StashBuffer` will be