Bump rails to 5.2 and update rubocop

app/admin/admin_users.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveAdmin.register AdminUser do
   permit_params :email, :password, :password_confirmation
 

app/admin/attendees.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveAdmin.register Attendee do
   scope :child?
   scope :diet?

app/admin/dashboard.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveAdmin.register_page 'Dashboard' do
   menu priority: 1, label: proc { I18n.t('active_admin.dashboard') }
 

app/admin/guests.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveAdmin.register Guest do
   permit_params :email, :first_name, :last_name, :attending, :diet, :songs,
                 :notes

app/admin/plus_ones.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveAdmin.register PlusOne do
   permit_params :first_name, :last_name, :diet, :child
 

app/controllers/application_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationController < ActionController::Base
   protect_from_forgery with: :exception
 

app/controllers/guests_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class GuestsController < ApplicationController
   def new
     respond_to :html

app/controllers/plus_ones_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class PlusOnesController < ApplicationController
   before_action do
     @guest = Guest.find_by_id_token(params[:guest_id])
@@ -41,7 +43,7 @@ class PlusOnesController < ApplicationController
   def destroy
     respond_to :html
     @plus_one = @guest.plus_ones.find_by(id: params[:id])
-    @plus_one.destroy if @plus_one
+    @plus_one&.destroy
     redirect_to guest_plus_ones_path(@guest)
   end
 

app/controllers/welcome_controller.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class WelcomeController < ApplicationController
   def index
     @google_maps_url = 'https://goo.gl/maps/nBAxNAsmPSS2'

app/helpers/application_helper.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ApplicationHelper
   def flash_class(key)
     case key
@@ -10,6 +12,7 @@ module ApplicationHelper
 
   def errors_for(object)
     return unless object.errors.any?
+
     content_tag(:div, class: 'mb-3 card border-danger') do
       concat(content_tag(:div, class: 'card-header bg-danger text-white') do
         concat "Oops, #{pluralize(object.errors.count, 'problem')}:"

app/helpers/guests_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module GuestsHelper
 end

app/helpers/plus_ones_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module PlusOnesHelper
 end

app/helpers/welcome_helper.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module WelcomeHelper
 end

app/jobs/application_job.rb

@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class ApplicationJob < ActiveJob::Base
 end

app/mailers/application_mailer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationMailer < ActionMailer::Base
   default from: 'from@example.com'
   layout 'mailer'

app/mailers/guest_mailer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class GuestMailer < ApplicationMailer
   default from: ENV['FROM_EMAIL'], reply_to: ENV['CONTACT_EMAIL']
 

app/models/admin_user.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # ActiveAdmin console user.
 #

app/models/application_record.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationRecord < ActiveRecord::Base
   self.abstract_class = true
 end

app/models/attendee.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # A guest or plus one.
 #

app/models/concerns/findable_with_token.rb

@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 #
 # Make a model findable only when a secure token is provided.
 #
 module FindableWithToken
   extend ActiveSupport::Concern
 
-  ID_TOKEN_RX = /\A(\d+)-(\w+)\z/
+  ID_TOKEN_RX = /\A(\d+)-(\w+)\z/.freeze
 
   included do
     has_secure_token
@@ -15,12 +17,14 @@ module FindableWithToken
 
     def self.find_by_id_token(id_token)
       raise ActiveRecord::RecordNotFound unless id_token =~ ID_TOKEN_RX
+
       id = Regexp.last_match(1)
       token = Regexp.last_match(2)
 
       record = find(id)
       raise ActiveRecord::RecordNotFound unless
         ActiveSupport::SecurityUtils.secure_compare(record.token, token)
+
       record
     end
   end

app/models/guest.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # A primary guest.
 #
@@ -26,6 +28,7 @@ class Guest < ApplicationRecord
   def email_safe_salutation
     return 'Hello,' if
       first_name.blank? || first_name !~ /\A[\p{Word}\s'-]{1,30}\z/i
+
     "Dear #{first_name},"
   end
 

app/models/plus_one.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # An extra guest.
 #