-str Remove deprecated onDownstreamFinish() in GraphStage.

Author: He-Pin

akka-stream/src/main/scala/akka/stream/stage/GraphStage.scala

@@ -683,13 +683,6 @@ abstract class GraphStageLogic private[stream] (val inCount: Int, val outCount:
   final def completeStage(): Unit =
     internalCompleteStage(SubscriptionWithCancelException.StageWasCompleted, OptionVal.None)
 
-  // Variable used from `OutHandler.onDownstreamFinish` to carry over cancellation cause in cases where
-  // `OutHandler` implementations call `super.onDownstreamFinished()`.
-  /**
-   * INTERNAL API
-   */
-  @InternalApi private[stream] var lastCancellationCause: Throwable = _
-
   /**
    * Automatically invokes [[cancel]] or [[complete]] on all the input or output ports that have been called,
    * then marks the stage as stopped.
@@ -1893,34 +1886,14 @@ trait OutHandler {
   @throws(classOf[Exception])
   def onPull(): Unit
 
-  /**
-   * Called when the output port will no longer accept any new elements. After this callback no other callbacks will
-   * be called for this port.
-   */
-  @throws(classOf[Exception])
-  @deprecatedOverriding("Override `def onDownstreamFinish(cause: Throwable)`, instead.", since = "2.6.0") // warns when overriding
-  @deprecated("Call onDownstreamFinish with a cancellation cause.", since = "2.6.0") // warns when calling
-  def onDownstreamFinish(): Unit = {
-    val thisStage = GraphInterpreter.currentInterpreter.activeStage
-    require(
-      thisStage.lastCancellationCause ne null,
-      "onDownstreamFinish() must not be called without a cancellation cause")
-    thisStage.cancelStage(thisStage.lastCancellationCause)
-  }
-
   /**
    * Called when the output port will no longer accept any new elements. After this callback no other callbacks will
    * be called for this port.
    */
   @throws(classOf[Exception])
   def onDownstreamFinish(cause: Throwable): Unit = {
     val thisStage = GraphInterpreter.currentInterpreter.activeStage
-    try {
-      require(cause ne null, "Cancellation cause must not be null")
-      require(thisStage.lastCancellationCause eq null, "onDownstreamFinish(cause) must not be called recursively")
-      thisStage.lastCancellationCause = cause
-      (onDownstreamFinish(): @nowarn("msg=deprecated")) // if not overridden, call old deprecated variant
-    } finally thisStage.lastCancellationCause = null
+    thisStage.cancelStage(cause)
   }
 }