7 files changed, 38 insertions, 30 deletions
diff --git a/src/library/scala/collection/mutable/DoubleLinkedList.scala b/src/library/scala/collection/mutable/DoubleLinkedList.scala
index f2a732ffd1..4465ebef93 100644
--- a/src/library/scala/collection/mutable/DoubleLinkedList.scala
+++ b/src/library/scala/collection/mutable/DoubleLinkedList.scala
@@ -68,24 +68,22 @@ class DoubleLinkedList[A]() extends LinearSeq[A]
 object DoubleLinkedList extends SeqFactory[DoubleLinkedList] {
   /** $genericCanBuildFrom */
   implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, DoubleLinkedList[A]] = new GenericCanBuildFrom[A]
+
   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 emptyList() = new DoubleLinkedList[A]()
+      var current = emptyList()
 
       def +=(elem: A): this.type = {
-        if (current.nonEmpty)
-          current.insert(new DoubleLinkedList(elem, emptyList))
+        if (current.isEmpty)
+          current = new DoubleLinkedList(elem, emptyList())
         else
-          current = new DoubleLinkedList(elem, emptyList)
+          current append new DoubleLinkedList(elem, emptyList())
+
         this
       }
 
-      def clear() {
-        current = emptyList
-      }
+      def clear(): Unit = current = emptyList()
       def result() = current
     }
 }
diff --git a/src/library/scala/collection/mutable/DoubleLinkedListLike.scala b/src/library/scala/collection/mutable/DoubleLinkedListLike.scala
index 18a0e164a2..7ad2f9558f 100644
--- a/src/library/scala/collection/mutable/DoubleLinkedListLike.scala
+++ b/src/library/scala/collection/mutable/DoubleLinkedListLike.scala
@@ -110,12 +110,9 @@ trait DoubleLinkedListLike[A, This <: Seq[A] with DoubleLinkedListLike[A, This]]
 
   private def outofbounds(n: Int) = throw new IndexOutOfBoundsException(n.toString)
 
-  override def drop(n: Int): This = super[SeqLike].drop(n)
-
-  override def tail = drop(1)
-
-  override def apply(n: Int): A   = atLocation(n)(_.elem)(outofbounds(n))
-  override def update(n: Int, x: A): Unit  = atLocation(n)(_.elem = x)(outofbounds(n))
-  override def get(n: Int): Option[A] = atLocation[Option[A]](n)(x => Some(x.elem))(None)
-
+  override def drop(n: Int): This         = super[SeqLike].drop(n)
+  override def tail                       = drop(1)
+  override def apply(n: Int): A           = atLocation(n)(_.elem)(outofbounds(n))
+  override def update(n: Int, x: A): Unit = atLocation(n)(_.elem = x)(outofbounds(n))
+  override def get(n: Int): Option[A]     = atLocation[Option[A]](n)(x => Some(x.elem))(None)
 }
diff --git a/src/library/scala/collection/mutable/LinkedList.scala b/src/library/scala/collection/mutable/LinkedList.scala
index beee4857b0..6c5bf9ae49 100644
--- a/src/library/scala/collection/mutable/LinkedList.scala
+++ b/src/library/scala/collection/mutable/LinkedList.scala
@@ -60,10 +60,9 @@ class LinkedList[A]() extends LinearSeq[A]
  *  @define coll linked list
  */
 object LinkedList extends SeqFactory[LinkedList] {
-
   override def empty[A]: LinkedList[A] = new LinkedList[A]
-
   implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, LinkedList[A]] = new GenericCanBuildFrom[A]
+
   def newBuilder[A]: Builder[A, LinkedList[A]] =
     (new MutableList) mapResult ((l: MutableList[A]) => l.toLinkedList)
 }
diff --git a/src/library/scala/collection/mutable/LinkedListLike.scala b/src/library/scala/collection/mutable/LinkedListLike.scala
index b24cda946e..a3fd786c2a 100644
--- a/src/library/scala/collection/mutable/LinkedListLike.scala
+++ b/src/library/scala/collection/mutable/LinkedListLike.scala
@@ -60,12 +60,14 @@ trait LinkedListLike[A, This <: Seq[A] with LinkedListLike[A, This]] extends Seq
   var next: This = _
 
   override def isEmpty = next eq this
-
   override def length: Int = length0(repr, 0)
 
-  @tailrec private def length0(elem: This, acc: Int): Int = if (elem.isEmpty) acc else length0(elem.next, acc + 1)
+  @tailrec private def length0(elem: This, acc: Int): Int =
+    if (elem.isEmpty) acc else length0(elem.next, acc + 1)
 
-  override def head: A    = elem
+  override def head: A =
+    if (isEmpty) throw new NoSuchElementException
+    else elem
 
   override def tail: This = {
     require(nonEmpty, "tail of empty list")
@@ -92,7 +94,8 @@ 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) {
-      next = next.append(that)
+      that append next
+      next = that
     }
   }
 
@@ -100,7 +103,7 @@ trait LinkedListLike[A, This <: Seq[A] with LinkedListLike[A, This]] extends Seq
     var i = 0
     var these: This = repr
     while (i < n && !these.isEmpty) {
-      these = these.next.asInstanceOf[This] // !!! concrete overrides abstract problem
+      these = these.next
       i += 1
     }
     these
@@ -108,7 +111,7 @@ trait LinkedListLike[A, This <: Seq[A] with LinkedListLike[A, This]] extends Seq
 
   private def atLocation[T](n: Int)(f: This => T) = {
     val loc = drop(n)
-    if (!loc.isEmpty) f(loc)
+    if (loc.nonEmpty) f(loc)
     else throw new IndexOutOfBoundsException(n.toString)
   }
 
diff --git a/test/files/run/bug4080.check b/test/files/run/bug4080.check
new file mode 100644
index 0000000000..66ce31bb43
--- /dev/null
+++ b/test/files/run/bug4080.check
@@ -0,0 +1 @@
+LinkedList(1, 0, 2, 3)
diff --git a/test/files/run/bug4080.scala b/test/files/run/bug4080.scala
new file mode 100644
index 0000000000..92740ed776
--- /dev/null
+++ b/test/files/run/bug4080.scala
@@ -0,0 +1,12 @@
+import scala.collection.mutable.LinkedList
+
+object Test {
+  def main(args: Array[String]) {
+    val ll = LinkedList(1, 2, 3)
+    ll.insert(LinkedList(0))
+    println(ll)
+    val ll2 = LinkedList[Int]()
+    try println(ll2.head)
+    catch { case _ => () }
+  }
+}
diff --git a/test/files/run/t3361.scala b/test/files/run/t3361.scala
index 17af89a67c..892e36dbd9 100644
--- a/test/files/run/t3361.scala
+++ b/test/files/run/t3361.scala
@@ -39,10 +39,8 @@ object Test extends App {
 
   def insert_1 {
     val ten = DoubleLinkedList(1 to 10: _*)
-    ten.insert(DoubleLinkedList(11)) match {
-      case _: Unit => require(true)
-      case _ => require(false)
-    }
+    ten.append(DoubleLinkedList(11))
+
     // Post-insert size test
     require(11 == ten.size)
     // Post-insert data test