Merge pull request #40097 from Shopify/ar-reorder-uniq

Call uniq! on the `reorder` arguments.

activerecord/lib/active_record/relation/query_methods.rb

@@ -405,6 +405,7 @@ def reorder(*args)
     # Same as #reorder but operates on relation in-place instead of copying.
     def reorder!(*args) # :nodoc:
       preprocess_order_args(args) unless args.all?(&:blank?)
+      args.uniq!
       self.reordering_value = true
       self.order_values = args
       self

activerecord/test/cases/relations_test.rb

@@ -425,6 +425,11 @@ def test_finding_with_reorder
     assert_equal ["The First Topic", "The Second Topic of the day", "The Third Topic of the day", "The Fourth Topic of the day", "The Fifth Topic of the day"], topics_titles
   end
 
+  def test_reorder_deduplication
+    topics = Topic.reorder("id desc", "id desc")
+    assert_equal ["id desc"], topics.order_values
+  end
+
   def test_finding_with_reorder_by_aliased_attributes
     topics = Topic.order("author_name").reorder(:heading)
     assert_equal 5, topics.to_a.size