Merge pull request scala/scala#7153 from xuwei-k/Vector-prependedAll

fix scala/scala#11122 Vector#prependedAll

Author: lrytz

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

@@ -204,18 +204,23 @@ final class Vector[+A] private[immutable] (private[collection] val startIndex: I
     import Vector.{Log2ConcatFaster, TinyAppendFaster}
     if (prefix.iterator.isEmpty) this
     else {
-      prefix.size match {
-        case n if n <= TinyAppendFaster || n < (this.size >>> Log2ConcatFaster) =>
-          var v: Vector[B] = this
-          val it = prefix.toIndexedSeq.reverseIterator
-          while (it.hasNext) v = it.next() +: v
-          v
-        case n if this.size < (n >>> Log2ConcatFaster) && prefix.isInstanceOf[Vector[_]] =>
-          var v = prefix.asInstanceOf[Vector[B]]
-          val it = this.iterator
-          while (it.hasNext) v = v :+ it.next()
-          v
-        case _ => super.prependedAll(prefix)
+      prefix match {
+        case prefix: collection.Iterable[B] =>
+          prefix.size match {
+            case n if n <= TinyAppendFaster || n < (this.size >>> Log2ConcatFaster) =>
+              var v: Vector[B] = this
+              val it = prefix.toIndexedSeq.reverseIterator
+              while (it.hasNext) v = it.next() +: v
+              v
+            case n if this.size < (n >>> Log2ConcatFaster) && prefix.isInstanceOf[Vector[_]] =>
+              var v = prefix.asInstanceOf[Vector[B]]
+              val it = this.iterator
+              while (it.hasNext) v = v :+ it.next()
+              v
+            case _ => super.prependedAll(prefix)
+          }
+        case _ =>
+          super.prependedAll(prefix)
       }
     }
   }