Fix "last equality wins" logic in relation merge

This is a real fix (as compared to the band-aid in b127d86c), which uses
the recently-added equality methods for ARel nodes. It has the side
benefit of simplifying the merge code a bit.

1 files changed, 7 insertions, 4 deletions

diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 4ef11590a9..684538940a 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -675,11 +675,14 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal [developers(:poor_jamis)], devs.to_a
   end
 
-  def test_relation_merging_with_arel_equalities_with_a_non_attribute_left_hand_ignores_non_attributes_when_discarding_equalities
+  def test_relation_merging_with_arel_equalities_keeps_last_equality_with_non_attribute_left_hand
     salary_attr = Developer.arel_table[:salary]
-    devs = Developer.where(salary_attr.eq(80000)).merge(
-      Developer.where(salary_attr.eq(9000)).
-        where(Arel::Nodes::NamedFunction.new('abs', [salary_attr]).eq(9000))
+    devs = Developer.where(
+      Arel::Nodes::NamedFunction.new('abs', [salary_attr]).eq(80000)
+    ).merge(
+      Developer.where(
+        Arel::Nodes::NamedFunction.new('abs', [salary_attr]).eq(9000)
+      )
     )
     assert_equal [developers(:poor_jamis)], devs.to_a
   end