From 0b6476e4ce78a8baa537370b5fad7b8aed707912 Mon Sep 17 00:00:00 2001
From: SengMing Tan <tansengming@gmail.com>
Date: Sat, 24 Nov 2018 17:41:09 -0500
Subject: [PATCH] add rubocop cop to prevent the safe navigation operator

Close #596
---
 .rubocop.yml                                  |  1 +
 app/helpers/users_helper.rb                   | 10 +++++--
 .../cop/style/disallow_safe_navigation.rb     | 27 +++++++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 extras/rubocop/cop/style/disallow_safe_navigation.rb

diff --git a/.rubocop.yml b/.rubocop.yml
index cbc2d0fc..a6f3fdae 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,4 +1,5 @@
 # Project setup:
+require: ./extras/rubocop/cop/style/disallow_safe_navigation
 Rails:
   Enabled: true
 AllCops:
diff --git a/app/helpers/users_helper.rb b/app/helpers/users_helper.rb
index 71542711..34dba763 100644
--- a/app/helpers/users_helper.rb
+++ b/app/helpers/users_helper.rb
@@ -9,7 +9,7 @@ module UsersHelper
     capture do
       concat link_to(stories_displayed, "/newest/#{showing_user.username}")
 
-      concat(" (+#{stories_deleted} deleted)") if @user&.is_moderator? && stories_deleted > 0
+      concat(" (+#{stories_deleted} deleted)") if user_is_moderator? && stories_deleted > 0
 
       if tag
         concat ", most commonly tagged "
@@ -24,9 +24,15 @@ module UsersHelper
     capture do
       concat link_to(showing_user.comments_posted_count, "/threads/#{showing_user.username}")
 
-      if @user&.is_moderator? && comments_deleted > 0
+      if user_is_moderator? && comments_deleted > 0
         concat " (+#{comments_deleted} deleted)"
       end
     end
   end
+
+private
+
+  def user_is_moderator?
+    @user && @user.is_moderator?
+  end
 end
diff --git a/extras/rubocop/cop/style/disallow_safe_navigation.rb b/extras/rubocop/cop/style/disallow_safe_navigation.rb
new file mode 100644
index 00000000..c7b9aaf5
--- /dev/null
+++ b/extras/rubocop/cop/style/disallow_safe_navigation.rb
@@ -0,0 +1,27 @@
+module RuboCop
+  module Cop
+    module Style
+      # The "safe navigation" operator &. makes it easier to work with and
+      # propagate nil values. This will disallow the use of the safe navigation
+      # operator
+      #
+      # @example
+      # 
+      #   # bad
+      #   foo&.bar
+      #   a.foo&.bar
+      #
+      class DisallowSafeNavigation < Cop
+        extend TargetRubyVersion
+
+        MSG = 'Do not use &.'.freeze
+
+        minimum_target_ruby_version 2.3
+
+        def on_csend(node)
+          add_offense(node)
+        end
+      end
+    end
+  end
+end