+str #18045 add recoverWith(Source)

akka-stream/src/main/scala/akka/stream/javadsl/SubSource.scala

@@ -602,6 +602,26 @@ class SubSource[+Out, +Mat](delegate: scaladsl.SubFlow[Out, Mat, scaladsl.Source
   def recover[T >: Out](pf: PartialFunction[Throwable, T]): SubSource[T, Mat] =
     new SubSource(delegate.recover(pf))
 
+  /**
+    * RecoverWith allows to switch to alternative Source on flow failure. It will stay in effect after
+    * a failure has been recovered so that each time there is a failure it is fed into the `pf` and a new
+    * Source may be materialized.
+    * Since the underlying failure signal onError arrives out-of-band, it might jump over existing elements.
+    * This stage can recover the failure signal, but not the skipped elements, which will be dropped.
+    *
+    * '''Emits when''' element is available from the upstream or upstream is failed and element is available
+    * from alternative Source
+    *
+    * '''Backpressures when''' downstream backpressures
+    *
+    * '''Completes when''' upstream completes or upstream failed with exception pf can handle
+    *
+    * '''Cancels when''' downstream cancels
+    *
+    */
+  def recoverWith[T >: Out](pf: PartialFunction[Throwable, _ <: Graph[SourceShape[T], NotUsed]]): SubSource[T, Mat @uncheckedVariance] =
+    new SubSource(delegate.recoverWith(pf))
+
   /**
    * Terminate processing (and cancel the upstream publisher) after the given
    * number of elements. Due to input buffering some elements may have been