Merge pull request #3304 from non/bug/stream-flatten2-8100

SI-8100 - prevent possible SOE during Stream#flatten.

3 files changed, 19 insertions, 8 deletions

diff --git a/src/library/scala/collection/immutable/Stream.scala b/src/library/scala/collection/immutable/Stream.scala
index a82e31f5da..49c3b4c3cd 100644
--- a/src/library/scala/collection/immutable/Stream.scala
+++ b/src/library/scala/collection/immutable/Stream.scala
@@ -960,14 +960,16 @@ self =>
    * }}}
    */
   override def flatten[B](implicit asTraversable: A => /*<:<!!!*/ GenTraversableOnce[B]): Stream[B] = {
-    def flatten1(t: Traversable[B]): Stream[B] =
-      if (!t.isEmpty)
-        cons(t.head, flatten1(t.tail))
-      else
-        tail.flatten
-
-    if (isEmpty) Stream.empty
-    else flatten1(asTraversable(head).seq.toTraversable)
+    var st: Stream[A] = this
+    while (st.nonEmpty) {
+      val h = asTraversable(st.head)
+      if (h.isEmpty) {
+        st = st.tail
+      } else {
+        return h.toStream #::: st.tail.flatten
+      }
+    }
+    Stream.empty
   }
 
   override def view = new StreamView[A, Stream[A]] {
diff --git a/test/files/run/t8100.check b/test/files/run/t8100.check
new file mode 100644
index 0000000000..cdd927fd88
--- /dev/null
+++ b/test/files/run/t8100.check
@@ -0,0 +1 @@
+Success(0)
diff --git a/test/files/run/t8100.scala b/test/files/run/t8100.scala
new file mode 100644
index 0000000000..b9d0fe5003
--- /dev/null
+++ b/test/files/run/t8100.scala
@@ -0,0 +1,8 @@
+object Test {
+  import scala.util.Try
+
+  def main(args: Array[String]): Unit = {
+    def stream = Stream.from(0).take(100000).map(n => None)
+    println(Try(stream.flatten.length))
+  }
+}