Restore support for Model.pluck('sql fragment')

activerecord/lib/active_record/relation/calculations.rb

@@ -130,7 +130,8 @@ def pluck(column_name)
       column = types[key]
 
       result.map do |attributes|
-        value = klass.initialize_attributes(attributes)[key]
+        raise ArgumentError, "Pluck expects to select just one attribute: #{attributes.inspect}" unless attributes.one?
+        value = klass.initialize_attributes(attributes).first[1]
         if column
           column.type_cast value
         else

activerecord/test/cases/calculations_test.rb

@@ -466,6 +466,14 @@ def test_pluck_not_auto_table_name_prefix_if_column_joined
     assert_equal [7], Company.joins(:contracts).pluck(:developer_id)
   end
 
+  def test_pluck_with_selection_clause
+    assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT credit_limit').sort
+  end
+
+  def test_pluck_expects_a_single_selection
+    assert_raise(ArgumentError) { Account.pluck 'id, credit_limit' }
+  end
+
   def test_plucks_with_ids
     assert_equal Company.all.map(&:id).sort, Company.ids.sort
   end