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

This commit changes stream flatten to avoid allocating a
stack frame for every stream item. Previously, flattening
a stream whose elements are mostly empty would result in
a StackOverflowException.

This commit also adds a test demonstrating the problem.

1 files changed, 8 insertions, 0 deletions

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))
+  }
+}