Build the reverse_order on its proper method.

The reverse_order method was using a flag to control if the order should
be reversed or not. Instead of using this variable just build the reverse order
inside its proper method.

This implementation was leading to an unexpected behavior when using
reverse_order and then applying reorder(nil).

Example:
  Before
    Post.order(:name).reverse_order.reorder(nil)
    # => SELECT "posts".* FROM "posts"   ORDER BY "posts"."id" DESC

  After
    Post.order(:name).reverse_order.reorder(nil)
   # => SELECT "posts".* FROM "posts"

1 files changed, 11 insertions, 3 deletions

diff --git a/activerecord/test/cases/relation/mutation_test.rb b/activerecord/test/cases/relation/mutation_test.rb
index 4fafa668fb..c81a3002d6 100644
--- a/activerecord/test/cases/relation/mutation_test.rb
+++ b/activerecord/test/cases/relation/mutation_test.rb
@@ -107,10 +107,18 @@ module ActiveRecord
     end
 
     test 'reverse_order!' do
-      assert relation.reverse_order!.equal?(relation)
-      assert relation.reverse_order_value
+      relation = Post.order('title ASC, comments_count DESC')
+
+      relation.reverse_order!
+
+      assert_equal 'title DESC', relation.order_values.first
+      assert_equal 'comments_count ASC', relation.order_values.last
+
+
       relation.reverse_order!
-      assert !relation.reverse_order_value
+
+      assert_equal 'title ASC', relation.order_values.first
+      assert_equal 'comments_count DESC', relation.order_values.last
     end
 
     test 'create_with!' do