Merge pull request scala#4415 from Ichoran/issue/9254

SI-9254  UnrolledBuffer appends in wrong position

Author: adriaanm

src/library/scala/collection/mutable/UnrolledBuffer.scala

@@ -208,7 +208,7 @@ object UnrolledBuffer extends ClassTagTraversableFactory[UnrolledBuffer] {
   def newBuilder[T](implicit t: ClassTag[T]): Builder[T, UnrolledBuffer[T]] = new UnrolledBuffer[T]
 
   val waterline = 50
-  val waterlineDelim = 100
+  val waterlineDelim = 100    // TODO -- fix this name!  It's a denominator, not a delimiter.  (But it's part of the API so we can't just change it.)
   private[collection] val unrolledlength = 32
 
   /** Unrolled buffer node.
@@ -319,13 +319,15 @@ object UnrolledBuffer extends ClassTagTraversableFactory[UnrolledBuffer] {
 	for (elem <- t) curr = curr append elem
 	curr.next = newnextnode
 
-	// try to merge the last node of this with the newnextnode
+	// try to merge the last node of this with the newnextnode and fix tail pointer if needed
 	if (curr.tryMergeWithNext()) buffer.lastPtr = curr
+	else if (newnextnode.next eq null) buffer.lastPtr = newnextnode
       }
-      else if (idx == size) {
+      else if (idx == size || (next eq null)) {
 	var curr = this
 	for (elem <- t) curr = curr append elem
-      } else insertAll(idx - size, t, buffer)
+      }
+      else next.insertAll(idx - size, t, buffer)
     }
     private def nullout(from: Int, until: Int) {
       var idx = from
@@ -344,7 +346,7 @@ object UnrolledBuffer extends ClassTagTraversableFactory[UnrolledBuffer] {
       tryMergeWithNext()
     }
 
-    override def toString = array.take(size).mkString("Unrolled[" + array.length + "](", ", ", ")") + " -> " + (if (next ne null) next.toString else "")
+    override def toString = array.take(size).mkString("Unrolled@%08x".format(System.identityHashCode(this)) + "[" + size + "/" + array.length + "](", ", ", ")") + " -> " + (if (next ne null) next.toString else "")
   }
 
 }

test/junit/scala/collection/mutable/UnrolledBufferTest.scala

@@ -0,0 +1,25 @@
+package scala.collection.mutable
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Test
+
+@RunWith(classOf[JUnit4])
+class UnrolledBufferTestTest {
+  @Test
+  def test_SI9254_original() {
+    val b = new UnrolledBuffer[Int]()
+    (1 to 16).foreach(i => b append i)
+    b.insert(0,-1)
+    b append 17
+    assert(b sameElements (Seq(-1) ++ (1 to 16) ++ Seq(17)))
+  }
+
+  @Test
+  def test_SI9254_additional() {
+    val b = new UnrolledBuffer[Int]()
+    (1 to 100).foreach(i => b append i)
+    b.insert(40, -1)
+    assert(b sameElements((1 to 40) ++ Seq(-1) ++ (41 to 100)))
+  }
+}