Merge pull request #6487 from avakhov/range-sum-optimization

Fix Range#sum optimized version

2 files changed, 11 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index 02d5a7080f..03efe6a19a 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -65,11 +65,15 @@ class Range #:nodoc:
   # Optimize range sum to use arithmetic progression if a block is not given and
   # we have a range of numeric values.
   def sum(identity = 0)
-    if block_given? || !(first.instance_of?(Integer) && last.instance_of?(Integer))
+    if block_given? || !(first.is_a?(Integer) && last.is_a?(Integer))
       super
     else
       actual_last = exclude_end? ? (last - 1) : last
-      (actual_last - first + 1) * (actual_last + first) / 2
+      if actual_last >= first
+        (actual_last - first + 1) * (actual_last + first) / 2
+      else
+        identity
+      end
     end
   end
 end
diff --git a/activesupport/test/core_ext/enumerable_test.rb b/activesupport/test/core_ext/enumerable_test.rb
index 0bf48dd378..0a1abac767 100644
--- a/activesupport/test/core_ext/enumerable_test.rb
+++ b/activesupport/test/core_ext/enumerable_test.rb
@@ -84,6 +84,11 @@ class EnumerableTests < ActiveSupport::TestCase
     assert_equal 10, (1..4.5).sum
     assert_equal 6, (1...4).sum
     assert_equal 'abc', ('a'..'c').sum
+    assert_equal 50_000_005_000_000, (0..10_000_000).sum
+    assert_equal 0, (10..0).sum
+    assert_equal 5, (10..0).sum(5)
+    assert_equal 10, (10..10).sum
+    assert_equal 42, (10...10).sum(42)
   end
 
   def test_index_by