Merge pull request scala#3213 from Ichoran/issue/8014

Fixes SI-8014, regression in Vector ++ TraversableOnce.

Author: adriaanm

src/library/scala/collection/immutable/Vector.scala

@@ -227,7 +227,7 @@ override def companion: GenericCompanion[Vector] = Vector
             val ri = this.reverseIterator
             while (ri.hasNext) v = ri.next +: v
             v.asInstanceOf[That]
-          case _ => super.++(that)
+          case _ => super.++(again)
         }
       }
     }

test/junit/scala/collection/VectorTest.scala

@@ -0,0 +1,51 @@
+package scala.collection.mutable
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Test
+import scala.collection.mutable
+
+@RunWith(classOf[JUnit4])
+/* Test for SI-8014 and ++ in general  */
+class VectorTest {
+  val noVec = Vector.empty[Int]
+  val smallVec = Vector.range(0,3)
+  val bigVec = Vector.range(0,64)
+  val smsm = Vector.tabulate(2 * smallVec.length)(i => (i % smallVec.length))
+  val smbig = Vector.tabulate(smallVec.length + bigVec.length)(i => 
+    if (i < smallVec.length) i else i - smallVec.length
+  )
+  val bigsm = Vector.tabulate(smallVec.length + bigVec.length)(i => 
+    if (i < bigVec.length) i else i - bigVec.length
+  )
+  val bigbig = Vector.tabulate(2 * bigVec.length)(i => (i % bigVec.length))
+
+
+  val vecs = List(noVec, smallVec, bigVec)
+  val ans = List(
+    vecs,
+    List(smallVec, smsm, smbig),
+    List(bigVec, bigsm, bigbig)
+  )
+
+  @Test
+  def vectorCat() {
+    val cats = vecs.map(a => vecs.map(a ++ _))
+    assert( cats == ans )
+  }
+
+  @Test
+  def iteratorCat() {
+    def its = vecs.map(_.toList.toIterator)
+    val cats = vecs.map(a => its.map(a ++ _))
+    println(cats)
+    assert( cats == ans )
+  }
+
+  @Test
+  def arrayCat() {
+    val ars = vecs.map(_.toArray)
+    val cats = vecs.map(a => ars.map(a ++ _))
+    assert( cats == ans )
+  }
+}