Merge pull request scala#7582 from rpmcdougall/ticket/11328

incorrect endsWith implementation on Range #11328

Author: szeiger

src/library/scala/collection/immutable/Range.scala

@@ -609,15 +609,17 @@ private class RangeIterator(
   }
 
   override def drop(n: Int): Iterator[Int] = {
-    val longPos = _next.toLong + step * n
-    if (step > 0) {
-      _next = Math.min(lastElement, longPos).toInt
-      _hasNext = longPos <= lastElement
-    }
-    else if (step < 0) {
-      _next = Math.max(lastElement, longPos).toInt
-      _hasNext = longPos >= lastElement
+    if (n > 0) {
+      val longPos = _next.toLong + step * n
+      if (step > 0) {
+        _next = Math.min(lastElement, longPos).toInt
+        _hasNext = longPos <= lastElement
+      }
+      else if (step < 0) {
+        _next = Math.max(lastElement, longPos).toInt
+        _hasNext = longPos >= lastElement
+      }
     }
-    this
+      this
   }
 }

test/junit/scala/collection/immutable/RangeTest.scala

@@ -89,4 +89,19 @@ class RangeTest {
     assertEquals(20, (20 to 1 by -1).min(Ordering.Int.reverse))
     assertEquals(1, (20 to 1 by -1).max(Ordering.Int.reverse))
   }
+
+  @Test
+  def testRangeEndsWith(): Unit = {
+    assertFalse((0 until 0).endsWith(List(-4, -3, -2, -1)))
+    assertTrue((-8 until -1).endsWith((-8 until -1).takeRight(1)))
+    assertTrue((0 until 0).endsWith(0 until 0))
+  }
+
+  @Test
+  def testRangeDrop(): Unit = {
+    assertTrue((0 until 0).iterator.drop(-4).toList.isEmpty)
+    assertEquals(4, (1 to 4).iterator.drop(-4).toList.size)
+  }
+
+
 }