Fix and test case for broken linked lists, cont...

Fix and test case for broken linked lists, contributed by Lucien
Pereira. Closes #3361, no review.

2 files changed, 12 insertions, 7 deletions

diff --git a/src/library/scala/collection/mutable/DoubleLinkedList.scala b/src/library/scala/collection/mutable/DoubleLinkedList.scala
index e702301703..d3c86953c8 100644
--- a/src/library/scala/collection/mutable/DoubleLinkedList.scala
+++ b/src/library/scala/collection/mutable/DoubleLinkedList.scala
@@ -69,15 +69,21 @@ object DoubleLinkedList extends SeqFactory[DoubleLinkedList] {
   def newBuilder[A]: Builder[A, DoubleLinkedList[A]] =
     new Builder[A, DoubleLinkedList[A]] {
       var current: DoubleLinkedList[A] = _
+      val emptyList = new DoubleLinkedList[A]()
+      if(null == current)
+        current = emptyList
+
       def +=(elem: A): this.type = {
-        val tmp = new DoubleLinkedList(elem, null)
-        if (current != null)
-          current.insert(tmp)
+        if (current.nonEmpty)
+          current.insert(new DoubleLinkedList(elem, emptyList))
         else
-          current = tmp
+          current = new DoubleLinkedList(elem, emptyList)
         this
       }
-      def clear() { current = null }
+
+      def clear() {
+        current = emptyList
+      }
       def result() = current
     }
 }
diff --git a/src/library/scala/collection/mutable/LinkedListLike.scala b/src/library/scala/collection/mutable/LinkedListLike.scala
index ca904e0a24..6fb516d566 100644
--- a/src/library/scala/collection/mutable/LinkedListLike.scala
+++ b/src/library/scala/collection/mutable/LinkedListLike.scala
@@ -66,8 +66,7 @@ trait LinkedListLike[A, This <: Seq[A] with LinkedListLike[A, This]] extends Seq
   def insert(that: This): Unit = {
     require(nonEmpty, "insert into empty list")
     if (that.nonEmpty) {
-      that.append(next)
-      next = that
+      next = next.append(that)
     }
   }