[Fix rubocop#451] Fix a false negative for Rails/RelativeDateConstant

Fixes rubocop#451.

This commit fixes a false negative for `Rails/RelativeDateConstant` when
a method is chained after a relative date method.

CHANGELOG.md

@@ -11,6 +11,7 @@
 * [#421](https://github.com/rubocop/rubocop-rails/issues/421): Fix incorrect auto-correct for `Rails/LinkToBlank` when using `target: '_blank'` with hash brackets for the option. ([@koic][])
 * [#436](https://github.com/rubocop/rubocop-rails/issues/436): Fix a false positive for `Rails/ContentTag` when the first argument is a splat argument. ([@koic][])
 * [#435](https://github.com/rubocop/rubocop-rails/issues/435): Fix a false negative for `Rails/BelongsTo` when using `belongs_to` lambda block with `required` option. ([@koic][])
+* [#451](https://github.com/rubocop/rubocop-rails/issues/451): Fix a false negative for `Rails/RelativeDateConstant` when a method is chained after a relative date method. ([@koic][])
 
 ### Changes
 

lib/rubocop/cop/rails/relative_date_constant.rb

@@ -33,11 +33,16 @@ class RelativeDateConstant < Base
 
         MSG = 'Do not assign %<method_name>s to constants as it ' \
               'will be evaluated only once.'
+        RELATIVE_DATE_METHODS = %i[since from_now after ago until before].freeze
 
         def on_casgn(node)
-          relative_date_assignment?(node) do |method_name|
-            add_offense(node, message: message(method_name)) do |corrector|
-              autocorrect(corrector, node)
+          return if node.children[2]&.block_type?
+
+          node.each_descendant(:send) do |send_node|
+            relative_date?(send_node) do |method_name|
+              add_offense(node, message: message(method_name)) do |corrector|
+                autocorrect(corrector, node)
+              end
             end
           end
         end
@@ -88,23 +93,19 @@ def offense_range(name, value)
           range_between(name.loc.expression.begin_pos, value.loc.expression.end_pos)
         end
 
-        def_node_matcher :relative_date_assignment?, <<~PATTERN
-          {
-            (casgn _ _ (send _ ${:since :from_now :after :ago :until :before}))
-            (casgn _ _ ({erange irange} _ (send _ ${:since :from_now :after :ago :until :before})))
-            (casgn _ _ ({erange irange} (send _ ${:since :from_now :after :ago :until :before}) _))
-          }
-        PATTERN
+        def relative_date_method?(method_name)
+          RELATIVE_DATE_METHODS.include?(method_name)
+        end
 
         def_node_matcher :relative_date_or_assignment?, <<~PATTERN
-          (:or_asgn (casgn _ _) (send _ ${:since :from_now :after :ago :until :before}))
+          (:or_asgn (casgn _ _) (send _ $#relative_date_method?))
         PATTERN
 
         def_node_matcher :relative_date?, <<~PATTERN
           {
-            ({erange irange} _ (send _ ${:since :from_now :after :ago :until :before}))
-            ({erange irange} (send _ ${:since :from_now :after :ago :until :before}) _)
-            (send _ ${:since :from_now :after :ago :until :before})
+            ({erange irange} _ (send _ $#relative_date_method?))
+            ({erange irange} (send _ $#relative_date_method?) _)
+            (send _ $#relative_date_method?)
           }
         PATTERN
       end

spec/rubocop/cop/rails/relative_date_constant_spec.rb

@@ -43,6 +43,23 @@ def self.expired_at
       RUBY
     end
 
+    it 'registers and corrects an offense when a method is chained after a relative date method' do
+      expect_offense(<<~RUBY)
+        class SomeClass
+          START_DATE = 2.weeks.ago.to_date
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Do not assign ago to constants as it will be evaluated only once.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        class SomeClass
+          def self.start_date
+            2.weeks.ago.to_date
+          end
+        end
+      RUBY
+    end
+
     it 'registers an offense for exclusive end range' do
       expect_offense(<<~RUBY)
         class SomeClass