Add Gitlab/ModelsInheritApplicationRecordCop.dd-rails5-applicationrecord-cop

New models after rails 5 upgrade should inherit from ApplicationRecord,
not ActiveRecord::Base

Signed-off-by: ddavison <ddavison@gitlab.com>

4 files changed, 55 insertions, 0 deletions

diff --git a/.rubocop.yml b/.rubocop.yml
index a95ded8af1c..ffa77799a91 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -163,6 +163,9 @@ Gitlab/ModuleWithInstanceVariables:
 Gitlab/HTTParty:
   Enabled: true
 
+Gitlab/ModelsInheritApplicationRecord:
+  Enabled: true
+
 GitlabSecurity/PublicSend:
   Enabled: true
   Exclude:
diff --git a/rubocop/cop/gitlab/models_inherit_application_record.rb b/rubocop/cop/gitlab/models_inherit_application_record.rb
new file mode 100644
index 00000000000..1172930d1a2
--- /dev/null
+++ b/rubocop/cop/gitlab/models_inherit_application_record.rb
@@ -0,0 +1,41 @@
+require_relative '../../model_helpers'
+
+module RuboCop
+  module Cop
+    module Models
+      # This cop checks for models that extend from ActiveRecord::Base
+      #
+      # @example
+      #   # bad
+      #   class MyModel < ActiveRecord::Base
+      #
+      #   # good
+      #   class MyModel < ApplicationRecord
+      class ModelsInheritApplicationRecord < RuboCop::Cop::Cop
+        include ModelHelpers
+
+        MESSAGE = <<~EOL.freeze
+          Models should not inherit from ActiveRecord::Base anymore. Please inherit ApplicationRecord instead
+
+          Rails 5 upgrade item 5.2 dictates all Models inherit from ApplicationRecord
+
+          https://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html#active-record-models-now-inherit-from-applicationrecord-by-default
+        EOL
+
+
+        def_node_matcher :extends_activerecord_base?, <<~PATTERN
+          (class
+            (const nil ...)
+            (const
+              (const nil :ActiveRecord) :Base) nil)
+        PATTERN
+
+        def on_send(node)
+          return unless model?(node)
+
+          add_offense(node, location: :expression, message: MESSAGE) if extends_activerecord_base?(node)
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/model_helpers.rb b/rubocop/model_helpers.rb
new file mode 100644
index 00000000000..177dc5cd923
--- /dev/null
+++ b/rubocop/model_helpers.rb
@@ -0,0 +1,10 @@
+module RuboCop
+  # Module containing helper methods for writing Model cops.
+  module ModelHelpers
+    def model?(node)
+      path = node.location.expression.source_buffer.name
+
+      path.start_with?(File.join(Dir.pwd, 'models'))
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index 6c9b8753c1a..bad746234ff 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -2,6 +2,7 @@
 require_relative 'cop/gitlab/module_with_instance_variables'
 require_relative 'cop/gitlab/predicate_memoization'
 require_relative 'cop/gitlab/httparty'
+require_relative 'cop/gitlab/models_inherit_application_record'
 require_relative 'cop/gitlab/finder_with_find_by'
 require_relative 'cop/gitlab/union'
 require_relative 'cop/include_sidekiq_worker'