Fix unreported bug in View.Patched

Fix unreported bug in `View.Patched` where iterator is incorrect due to the patch only being iterable once, and already having been exhausted. Discovered while attempting to optimise `ArrayBuffer` in an earlier version of the previous commit.

Author: NthPortal

library/src/scala/collection/View.scala

@@ -404,8 +404,14 @@ object View extends IterableFactory[View] {
 
  @SerialVersionUID(3L)
  private[collection] class Patched[A](underlying: SomeIterableOps[A], from: Int, other: IterableOnce[A], replaced: Int) extends AbstractView[A] {
- def iterator: Iterator[A] = underlying.iterator.patch(from, other.iterator, replaced)
- override def knownSize: Int = if (underlying.knownSize == 0 && other.knownSize == 0) 0 else super.knownSize
+ // we may be unable to traverse `other` more than once, so we need to cache it if that's the case
+ private val _other: Iterable[A] = other match {
+ case other: Iterable[A] => other
+ case other => LazyList.from(other)
+ }
+
+ def iterator: Iterator[A] = underlying.iterator.patch(from, _other.iterator, replaced)
+ override def knownSize: Int = if (underlying.knownSize == 0 && _other.knownSize == 0) 0 else super.knownSize
  override def isEmpty: Boolean = if (knownSize == 0) true else iterator.isEmpty
  }