SI-8554 Two-arg remove throws exception on large count

ListBuffer now throws exceptions like other buffers do when trying to index out of range.

Also harmonized the order of testing (`count < 0` tested before `n` in range).

Test in scala-collection-laws (gated by SI8554 flag).  Also modified test in run/t6634.scala

1 files changed, 8 insertions, 5 deletions

diff --git a/src/library/scala/collection/mutable/ArrayBuffer.scala b/src/library/scala/collection/mutable/ArrayBuffer.scala
index 011fd415ee..167e04ccbd 100644
--- a/src/library/scala/collection/mutable/ArrayBuffer.scala
+++ b/src/library/scala/collection/mutable/ArrayBuffer.scala
@@ -149,13 +149,16 @@ class ArrayBuffer[A](override protected val initialSize: Int)
   /** Removes the element on a given index position. It takes time linear in
    *  the buffer size.
    *
-   *  @param n       the index which refers to the first element to delete.
-   *  @param count   the number of elements to delete
-   *  @throws IndexOutOfBoundsException if `n` is out of bounds.
+   *  @param n       the index which refers to the first element to remove.
+   *  @param count   the number of elements to remove.
+   *  @throws   IndexOutOfBoundsException if the index `n` is not in the valid range
+   *            `0 <= n <= length - count` (with `count > 0`).
+   *  @throws   IllegalArgumentException if `count < 0`.
    */
   override def remove(n: Int, count: Int) {
-    require(count >= 0, "removing negative number of elements")
-    if (n < 0 || n > size0 - count) throw new IndexOutOfBoundsException(n.toString)
+    if (count < 0) throw new IllegalArgumentException("removing negative number of elements: " + count.toString)
+    else if (count == 0) return  // Did nothing
+    if (n < 0 || n > size0 - count) throw new IndexOutOfBoundsException("at " + n.toString + " deleting " + count.toString)
     copy(n + count, n, size0 - (n + count))
     reduceToSize(size0 - count)
   }