Fixed a bug SI-5377 (https://issues.scala-lang.org/browse/SI-5377).

Added test cases for SI-5377.

src/library/scala/collection/SeqLike.scala

@@ -152,7 +152,7 @@ trait SeqLike[+A, +Repr] extends IterableLike[A, Repr] with GenSeqLike[A, Repr]
       if (!hasNext)
         Iterator.empty.next
 
-      val result = (self.newBuilder ++= elms).result
+      val result = (self.newBuilder ++= elms.toList).result
       var i = idxs.length - 2
       while(i >= 0 && idxs(i) >= idxs(i+1))
         i -= 1

test/files/run/t5377.check

@@ -0,0 +1,18 @@
+1 List(1)
+1 List(1)
+2 List(1, 2) List(2, 1)
+2 List(1, 2) List(2, 1)
+2 List(2, 1) List(1, 2)
+2 List(2, 1) List(1, 2)
+3 List(1, 2, 3) List(1, 3, 2) List(2, 1, 3) List(2, 3, 1) List(3, 1, 2) List(3, 2, 1)
+3 List(1, 2, 3) List(1, 3, 2) List(2, 1, 3) List(2, 3, 1) List(3, 1, 2) List(3, 2, 1)
+3 List(1, 3, 2) List(1, 2, 3) List(3, 1, 2) List(3, 2, 1) List(2, 1, 3) List(2, 3, 1)
+3 List(1, 3, 2) List(1, 2, 3) List(3, 1, 2) List(3, 2, 1) List(2, 1, 3) List(2, 3, 1)
+3 List(2, 1, 3) List(2, 3, 1) List(1, 2, 3) List(1, 3, 2) List(3, 2, 1) List(3, 1, 2)
+3 List(2, 1, 3) List(2, 3, 1) List(1, 2, 3) List(1, 3, 2) List(3, 2, 1) List(3, 1, 2)
+3 List(2, 3, 1) List(2, 1, 3) List(3, 2, 1) List(3, 1, 2) List(1, 2, 3) List(1, 3, 2)
+3 List(2, 3, 1) List(2, 1, 3) List(3, 2, 1) List(3, 1, 2) List(1, 2, 3) List(1, 3, 2)
+3 List(3, 1, 2) List(3, 2, 1) List(1, 3, 2) List(1, 2, 3) List(2, 3, 1) List(2, 1, 3)
+3 List(3, 1, 2) List(3, 2, 1) List(1, 3, 2) List(1, 2, 3) List(2, 3, 1) List(2, 1, 3)
+3 List(3, 2, 1) List(3, 1, 2) List(2, 3, 1) List(2, 1, 3) List(1, 3, 2) List(1, 2, 3)
+3 List(3, 2, 1) List(3, 1, 2) List(2, 3, 1) List(2, 1, 3) List(1, 3, 2) List(1, 2, 3)

test/files/run/t5377.scala

@@ -0,0 +1,47 @@
+object Test {
+  def testPermutations1(num: Int, stream: Stream[Int]): Unit = {
+    val perm = stream.permutations
+    print(num)
+    while(perm.hasNext) {
+      print(" " + perm.next().toList)
+    }
+    println()
+  }
+  def testPermutations2(num: Int, stream: List[Int]): Unit = {
+    val perm = stream.permutations
+    print(num)
+    while(perm.hasNext) {
+      print(" " + perm.next().toList)
+    }
+    println()
+  }
+
+  def main(args: Array[String]): Unit = {
+    testPermutations1(1, Stream(1))
+    testPermutations2(1, List(1))
+
+    testPermutations1(2, Stream(1, 2))
+    testPermutations2(2, List(1, 2))
+
+    testPermutations1(2, Stream(2, 1))
+    testPermutations2(2, List(2, 1))
+
+    testPermutations1(3, Stream(1, 2, 3))
+    testPermutations2(3, List(1, 2, 3))
+
+    testPermutations1(3, Stream(1, 3, 2))
+    testPermutations2(3, List(1, 3, 2))
+
+    testPermutations1(3, Stream(2, 1, 3))
+    testPermutations2(3, List(2, 1, 3))
+
+    testPermutations1(3, Stream(2, 3, 1))
+    testPermutations2(3, List(2, 3, 1))
+
+    testPermutations1(3, Stream(3, 1, 2))
+    testPermutations2(3, List(3, 1, 2))
+
+    testPermutations1(3, Stream(3, 2, 1))
+    testPermutations2(3, List(3, 2, 1))
+  }
+}