Fix Range#sum optimized version

At 1bd4d1c67459a91415ee73a8f55d2309c0d62a87 was added Range#sum
optimized version for arithmetic progressions. This improvment injected
a defect with not integer range boundaries. The defect was fixed by
e0adfa82c05f9c975005f102b4bcaebfcd17d241. The second commit really
disabled optimization at all because in Ruby integer-valued numbers are
instances of Fixnum and Bignum classes. We should #use is_a?
(#kind_of?) method instead #instance_of? to check if value is numerical:

    1.class                 # => Fixnum
    1.instance_of?(Integer) # => false
    1.is_a?(Integer)        # => true

    -100_000_000_000.class                 # => Bignum
    -100_000_000_000.instance_of?(Integer) # => false
    -100_000_000_000.is_a?(Integer)        # => true

Moreover original implementation of Range#sum has a defect with reverse
range boundaries. If the first boundary is less than the second range is
empty. Current commit fixes and tests this case too.

1 files changed, 5 insertions, 0 deletions

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