Secure path logic against any other directory with ee in it

The logic was breaking for a path that included ee in its name other
than the ee/ directory, e.g. employee/ or gitlab-ee/. This is fixed
with a better detection of a file within the ee directory.

rubocop/cop/ignored_columns.rb

@@ -2,7 +2,7 @@
 
 module RuboCop
   module Cop
-    # Cop that blacklists the usage of Group.public_or_visible_to_user
+    # Cop that blacklists the usage of `ActiveRecord::Base.ignored_columns=` directly
     class IgnoredColumns < RuboCop::Cop::Cop
       USE_CONCERN_MSG = 'Use `IgnoredColumns` concern instead of adding to `self.ignored_columns`.'
       WRONG_MODEL_MSG = 'If the model exists in CE and EE, the column has to be ignored ' \
@@ -43,11 +43,19 @@ def used_in_wrong_model?
       end
 
       def ee_model?(path)
-        path.include?('ee/')
+        path.include?(ee_directory)
+      end
+
+      def ee_directory
+        File.join(rails_root, 'ee')
+      end
+
+      def rails_root
+        File.expand_path('../..', __dir__)
       end
 
       def ce_model_exists?(path)
-        File.exist?(path.gsub(%r{ee/}, ''))
+        File.exist?(path.gsub(%r{/ee/}, '/'))
       end
     end
   end

spec/rubocop/cop/ignored_columns_spec.rb

@@ -43,8 +43,6 @@ class Baz < ApplicationRecord
     end
 
     it 'flags ignore_columns usage in EE model' do
-      file_path = full_path('ee/app/models/ee/bar.rb')
-
       expect_no_offenses(<<~RUBY, file_path)
         class Bar < ApplicationRecord
           ignore_columns :foo, remove_with: '14.3', remove_after: '2021-09-22'
@@ -90,7 +88,7 @@ class Bar < ApplicationRecord
   private
 
   def full_path(path)
-    rails_root = '../../../../'
+    rails_root = '../../../'
 
     File.expand_path(File.join(rails_root, path), __dir__)
   end