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.

3 files changed, 112 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)
     }
   }
 
diff --git a/test/files/run/t3361.scala b/test/files/run/t3361.scala
new file mode 100644
index 0000000000..3e6fc30c8f
--- /dev/null
+++ b/test/files/run/t3361.scala
@@ -0,0 +1,100 @@
+object Test extends Application {
+  import scala.collection.mutable.DoubleLinkedList
+
+  empty
+  builder_1
+  builder_2
+  chaining_1
+  chaining_2
+  insert_1
+  insert_2
+  append_1
+  append_2
+
+  def empty {
+    val none = DoubleLinkedList()
+    require(none.size == 0)
+    none.foreach( _ => require(false))
+  }
+
+  def builder_1 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    require(10 == ten.size)
+  }
+
+  def builder_2 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    require((ten.size*(ten.size+1))/2 == ten.reduceLeft(_ + _))
+  }
+
+  def chaining_1 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    require(ten.reverse == DoubleLinkedList((1 to 10).reverse: _*))
+  }
+
+  def chaining_2 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    require(ten == ten.reverse.reverse)
+  }
+
+  def insert_1 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    ten.insert(DoubleLinkedList(11)) match {
+      case _: Unit => require(true)
+      case _ => require(false)
+    }
+    // Post-insert size test
+    require(11 == ten.size)
+    // Post-insert data test
+    require((ten.size*(ten.size+1))/2 == ten.reduceLeft(_ + _))
+    // Post-insert chaining test
+    require(ten == ten.reverse.reverse)
+    // Post-insert position test
+    require(ten.last == 11)
+  }
+
+  def insert_2 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    try {
+      DoubleLinkedList().insert(ten)
+    } catch {
+      case _: IllegalArgumentException => require(true)
+      case _ => require(false)
+    }
+    val zero = DoubleLinkedList(0)
+    zero.insert(ten)
+    require(zero.size == 11)
+    require(zero.head == 0)
+    require(zero.last == 10)
+  }
+
+  def append_1 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    val eleven = ten.append(DoubleLinkedList(11))
+    // Post-append equality test
+    require(ten == eleven)
+    // Post-append size test
+    require(11 == ten.size)
+    // Post-append data test
+    require((ten.size*(ten.size+1))/2 == ten.reduceLeft(_ + _))
+    // Post-append chaining test
+    require(ten == ten.reverse.reverse)
+    // Post-append position test
+    require(ten.last == 11)
+  }
+
+  def append_2 {
+    val ten = DoubleLinkedList(1 to 10: _*)
+    try {
+      DoubleLinkedList().append(ten)
+    } catch {
+      case _: IllegalArgumentException => require(true)
+      case _ => require(false)
+    }
+    val zero = DoubleLinkedList(0)
+    zero.append(ten)
+    require(zero.size == 11)
+    require(zero.head == 0)
+    require(zero.last == 10)
+  }
+}