Added Cop to blacklist the use of serialize

This Cop blacklists the use of ActiveRecord's "serialize" method, except
for cases where we already use this.

app/models/application_setting.rb

@@ -13,13 +13,13 @@ class ApplicationSetting < ActiveRecord::Base
                             [\r\n]          # any number of newline characters
                           }x
-  serialize :restricted_visibility_levels
-  serialize :import_sources
-  serialize :disabled_oauth_sign_in_sources, Array
-  serialize :domain_whitelist, Array
-  serialize :domain_blacklist, Array
-  serialize :repository_storages
-  serialize :sidekiq_throttling_queues, Array
+  serialize :restricted_visibility_levels # rubocop:disable Cop/ActiverecordSerialize
+  serialize :import_sources # rubocop:disable Cop/ActiverecordSerialize
+  serialize :disabled_oauth_sign_in_sources, Array # rubocop:disable Cop/ActiverecordSerialize
+  serialize :domain_whitelist, Array # rubocop:disable Cop/ActiverecordSerialize
+  serialize :domain_blacklist, Array # rubocop:disable Cop/ActiverecordSerialize
+  serialize :repository_storages # rubocop:disable Cop/ActiverecordSerialize
+  serialize :sidekiq_throttling_queues, Array # rubocop:disable Cop/ActiverecordSerialize
   cache_markdown_field :sign_in_text
   cache_markdown_field :help_page_text

app/models/audit_event.rb

 class AuditEvent < ActiveRecord::Base
-  serialize :details, Hash
+  serialize :details, Hash # rubocop:disable Cop/ActiverecordSerialize
   belongs_to :user, foreign_key: :author_id

app/models/ci/build.rb

@@ -19,8 +19,8 @@ module Ci
       )
     end
-    serialize :options
-    serialize :yaml_variables, Gitlab::Serializer::Ci::Variables
+    serialize :options # rubocop:disable Cop/ActiverecordSerialize
+    serialize :yaml_variables, Gitlab::Serializer::Ci::Variables # rubocop:disable Cop/ActiverecordSerialize
     delegate :name, to: :project, prefix: true

app/models/ci/trigger_request.rb

@@ -6,7 +6,7 @@ module Ci
     belongs_to :pipeline, foreign_key: :commit_id
     has_many :builds
-    serialize :variables
+    serialize :variables # rubocop:disable Cop/ActiverecordSerialize
     def user_variables
       return [] unless variables

app/models/diff_note.rb

@@ -6,9 +6,9 @@ class DiffNote < Note
   NOTEABLE_TYPES = %w(MergeRequest Commit).freeze
-  serialize :original_position, Gitlab::Diff::Position
-  serialize :position, Gitlab::Diff::Position
-  serialize :change_position, Gitlab::Diff::Position
+  serialize :original_position, Gitlab::Diff::Position # rubocop:disable Cop/ActiverecordSerialize
+  serialize :position, Gitlab::Diff::Position # rubocop:disable Cop/ActiverecordSerialize
+  serialize :change_position, Gitlab::Diff::Position # rubocop:disable Cop/ActiverecordSerialize
   validates :original_position, presence: true
   validates :position, presence: true

app/models/event.rb

@@ -26,7 +26,7 @@ class Event < ActiveRecord::Base
   belongs_to :target, polymorphic: true
   # For Hash only
-  serialize :data
+  serialize :data # rubocop:disable Cop/ActiverecordSerialize
   # Callbacks
   after_create :reset_project_activity

app/models/hooks/web_hook_log.rb

 class WebHookLog < ActiveRecord::Base
   belongs_to :web_hook
-  serialize :request_headers, Hash
-  serialize :request_data, Hash
-  serialize :response_headers, Hash
+  serialize :request_headers, Hash # rubocop:disable Cop/ActiverecordSerialize
+  serialize :request_data, Hash # rubocop:disable Cop/ActiverecordSerialize
+  serialize :response_headers, Hash # rubocop:disable Cop/ActiverecordSerialize
   validates :web_hook, presence: true

app/models/legacy_diff_note.rb

@@ -7,7 +7,7 @@
 class LegacyDiffNote < Note
   include NoteOnDiff
-  serialize :st_diff
+  serialize :st_diff # rubocop:disable Cop/ActiverecordSerialize
   validates :line_code, presence: true, line_code: true

app/models/merge_request.rb

@@ -21,7 +21,7 @@ class MergeRequest < ActiveRecord::Base
   belongs_to :assignee, class_name: "User"
-  serialize :merge_params, Hash
+  serialize :merge_params, Hash # rubocop:disable Cop/ActiverecordSerialize
   after_create :ensure_merge_request_diff, unless: :importing?
   after_update :reload_diff_if_branch_changed

app/models/merge_request_diff.rb

@@ -11,8 +11,8 @@ class MergeRequestDiff < ActiveRecord::Base
   belongs_to :merge_request
-  serialize :st_commits
-  serialize :st_diffs
+  serialize :st_commits # rubocop:disable Cop/ActiverecordSerialize
+  serialize :st_diffs # rubocop:disable Cop/ActiverecordSerialize
   state_machine :state, initial: :empty do
     state :collected

app/models/personal_access_token.rb

@@ -3,7 +3,7 @@ class PersonalAccessToken < ActiveRecord::Base
   include TokenAuthenticatable
   add_authentication_token_field :token
-  serialize :scopes, Array
+  serialize :scopes, Array # rubocop:disable Cop/ActiverecordSerialize
   belongs_to :user

app/models/project_import_data.rb

@@ -10,7 +10,7 @@ class ProjectImportData < ActiveRecord::Base
                  insecure_mode: true,
                  algorithm: 'aes-256-cbc'
-  serialize :data, JSON
+  serialize :data, JSON # rubocop:disable Cop/ActiverecordSerialize
   validates :project, presence: true

app/models/sent_notification.rb

 class SentNotification < ActiveRecord::Base
-  serialize :position, Gitlab::Diff::Position
+  serialize :position, Gitlab::Diff::Position # rubocop:disable Cop/ActiverecordSerialize
   belongs_to :project
   belongs_to :noteable, polymorphic: true

app/models/service.rb

@@ -2,7 +2,7 @@
 # and implement a set of methods
 class Service < ActiveRecord::Base
   include Sortable
-  serialize :properties, JSON
+  serialize :properties, JSON # rubocop:disable Cop/ActiverecordSerialize
   default_value_for :active, false
   default_value_for :push_events, true

app/models/user.rb

@@ -40,7 +40,7 @@ class User < ActiveRecord::Base
          otp_secret_encryption_key: Gitlab::Application.secrets.otp_key_base
   devise :two_factor_backupable, otp_number_of_backup_codes: 10
-  serialize :otp_backup_codes, JSON
+  serialize :otp_backup_codes, JSON # rubocop:disable Cop/ActiverecordSerialize
   devise :lockable, :recoverable, :rememberable, :trackable,
     :validatable, :omniauthable, :confirmable, :registerable

rubocop/cop/activerecord_serialize.rb

+module RuboCop
+  module Cop
+    # Cop that prevents the use of `serialize` in ActiveRecord models.
+    class ActiverecordSerialize < RuboCop::Cop::Cop
+      MSG = 'Do not store serialized data in the database, use separate columns and/or tables instead'.freeze
+
+      def on_send(node)
+        return unless in_models?(node)
+
+        add_offense(node, :selector) if node.children[1] == :serialize
+      end
+
+      def models_path
+        File.join(Dir.pwd, 'app', 'models')
+      end
+
+      def in_models?(node)
+        path = node.location.expression.source_buffer.name
+
+        path.start_with?(models_path)
+      end
+    end
+  end
+end

rubocop/rubocop.rb

 require_relative 'cop/custom_error_class'
 require_relative 'cop/gem_fetcher'
+require_relative 'cop/activerecord_serialize'
 require_relative 'cop/migration/add_column'
 require_relative 'cop/migration/add_column_with_default_to_large_table'
 require_relative 'cop/migration/add_concurrent_foreign_key'

spec/rubocop/cop/activerecord_serialize_spec.rb

+require 'spec_helper'
+require 'rubocop'
+require 'rubocop/rspec/support'
+require_relative '../../../rubocop/cop/activerecord_serialize'
+
+describe RuboCop::Cop::ActiverecordSerialize do
+  include CopHelper
+
+  subject(:cop) { described_class.new }
+
+  context 'inside the app/models directory' do
+    it 'registers an offense when serialize is used' do
+      allow(cop).to receive(:in_models?).and_return(true)
+
+      inspect_source(cop, 'serialize :foo')
+
+      aggregate_failures do
+        expect(cop.offenses.size).to eq(1)
+        expect(cop.offenses.map(&:line)).to eq([1])
+      end
+    end
+  end
+
+  context 'outside the app/models directory' do
+    it 'does nothing' do
+      allow(cop).to receive(:in_models?).and_return(false)
+
+      inspect_source(cop, 'serialize :foo')
+
+      expect(cop.offenses).to be_empty
+    end
+  end
+end