Fix and test for Iterator corner case.

3 files changed, 16 insertions, 2 deletions

diff --git a/src/library/scala/collection/Iterator.scala b/src/library/scala/collection/Iterator.scala
index 701b24f300..2ee4e8056e 100644
--- a/src/library/scala/collection/Iterator.scala
+++ b/src/library/scala/collection/Iterator.scala
@@ -374,9 +374,12 @@ trait Iterator[+A] extends TraversableOnce[A] {
   def ++[B >: A](that: => Iterator[B]): Iterator[B] = new Iterator[B] {
     // optimize a little bit to prevent n log n behavior.
     private var cur : Iterator[B] = self
-    // this was unnecessarily looping forever on x ++ x
+    // since that is by-name, make sure it's only referenced once -
+    // if "val it = that" is inside the block, then hasNext on an empty
+    // iterator will continually reevaluate it.  (ticket #3269)
+    lazy val it = that
+    // the eq check is to avoid an infinite loop on "x ++ x"
     def hasNext = cur.hasNext || ((cur eq self) && {
-      val it = that
       it.hasNext && {
         cur = it
         true
diff --git a/test/files/run/bug3269.check b/test/files/run/bug3269.check
new file mode 100644
index 0000000000..c25611c15c
--- /dev/null
+++ b/test/files/run/bug3269.check
@@ -0,0 +1,2 @@
+1
+Hello
diff --git a/test/files/run/bug3269.scala b/test/files/run/bug3269.scala
new file mode 100644
index 0000000000..17e42cdb0e
--- /dev/null
+++ b/test/files/run/bug3269.scala
@@ -0,0 +1,9 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val it = List(1).iterator ++ { println("Hello"); Iterator.empty }
+    println(it.next)
+    it.hasNext
+    it.hasNext
+    it.hasNext
+  }
+}