Fix a false positive for Rails/NotNullColumn when adding a :virtual column

Author: fatkodima

changelog/fix_not_null_column_to_accept_virtual_columns.md

@@ -0,0 +1 @@
+* [#887](https://github.com/rubocop/rubocop-rails/issues/887): Fix a false positive for `Rails/NotNullColumn` when adding a `:virtual` column. ([@fatkodima][])

lib/rubocop/cop/rails/not_null_column.rb

@@ -21,7 +21,7 @@ class NotNullColumn < Base
         RESTRICT_ON_SEND = %i[add_column add_reference].freeze
 
         def_node_matcher :add_not_null_column?, <<~PATTERN
-          (send nil? :add_column _ _ _ (hash $...))
+          (send nil? :add_column _ _ $_ (hash $...))
         PATTERN
 
         def_node_matcher :add_not_null_reference?, <<~PATTERN
@@ -44,17 +44,20 @@ def on_send(node)
         private
 
         def check_add_column(node)
-          pairs = add_not_null_column?(node)
-          check_pairs(pairs)
+          add_not_null_column?(node) do |type, pairs|
+            return if type.value == :virtual || type.value == 'virtual'
+
+            check_pairs(pairs)
+          end
         end
 
         def check_add_reference(node)
-          pairs = add_not_null_reference?(node)
-          check_pairs(pairs)
+          add_not_null_reference?(node) do |pairs|
+            check_pairs(pairs)
+          end
         end
 
         def check_pairs(pairs)
-          return unless pairs
           return if pairs.any? { |pair| default_option?(pair) }
 
           null_false = pairs.find { |pair| null_false?(pair) }

spec/rubocop/cop/rails/not_null_column_spec.rb

@@ -28,6 +28,13 @@
                                              ^^^^^^^^^^^ Do not add a NOT NULL column without a default value.
         RUBY
       end
+
+      it 'does not register an offense for virtual columns' do
+        expect_no_offenses(<<~RUBY)
+          add_column :users, :height_in, :virtual, as: "height_cm / 2.54", null: false, default: nil
+          add_column :users, :height_in, 'virtual', as: "height_cm / 2.54", null: false, default: nil
+        RUBY
+      end
     end
 
     context 'with null: true' do