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

3 files changed, 19 insertions, 12 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)
   }
diff --git a/src/library/scala/collection/mutable/BufferLike.scala b/src/library/scala/collection/mutable/BufferLike.scala
index 8d24538620..bd9c61ae6a 100644
--- a/src/library/scala/collection/mutable/BufferLike.scala
+++ b/src/library/scala/collection/mutable/BufferLike.scala
@@ -105,15 +105,18 @@ trait BufferLike[A, +This <: BufferLike[A, This] with Buffer[A]]
     */
   def remove(n: Int): A
 
-  /** Removes a number of elements from a given index position.
+  /** Removes a number of elements from a given index position.  Subclasses of `BufferLike`
+   *  will typically override this method to provide better performance than `count`
+   *  successive calls to single-element `remove`.
    *
    *  @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`.
+   *            `0 <= n <= length - count` (with `count > 0`).
    *  @throws   IllegalArgumentException if `count < 0`.
    */
   def remove(n: Int, count: Int) {
+    if (count < 0) throw new IllegalArgumentException("removing negative number of elements: " + count.toString)
     for (i <- 0 until count) remove(n)
   }
 
diff --git a/src/library/scala/collection/mutable/ListBuffer.scala b/src/library/scala/collection/mutable/ListBuffer.scala
index 2bc6738e53..eece557fe8 100644
--- a/src/library/scala/collection/mutable/ListBuffer.scala
+++ b/src/library/scala/collection/mutable/ListBuffer.scala
@@ -262,13 +262,14 @@ final class ListBuffer[A]
    *
    *  @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`.
    */
-  @migration("Invalid input values will be rejected in future releases.", "2.11")
   override def remove(n: Int, count: Int) {
-    if (n >= len)
-      return
-    if (count < 0)
-      throw new IllegalArgumentException(s"removing negative number ($count) of elements")
+    if (count < 0) throw new IllegalArgumentException("removing negative number of elements: " + count.toString)
+    else if (count == 0) return  // Nothing to do
+    if (n < 0 || n > len - count) throw new IndexOutOfBoundsException("at " + n.toString + " deleting " + count.toString)
     if (exported) copy()
     val n1 = n max 0
     val count1 = count min (len - n1)