chore(rubocop): fix Style/TrivialAccessors issues

.rubocop_todo.yml

@@ -686,17 +686,6 @@ Style/TrailingUnderscoreVariable:
     - 'spec/lib/gitlab/etag_caching/middleware_spec.rb'
     - 'spec/services/quick_actions/interpret_service_spec.rb'
 
-# Offense count: 5
-# Cop supports --auto-correct.
-# Configuration parameters: ExactNameMatch, AllowPredicates, AllowDSLWriters, IgnoreClassMethods, Whitelist.
-# Whitelist: to_ary, to_a, to_c, to_enum, to_h, to_hash, to_i, to_int, to_io, to_open, to_path, to_proc, to_r, to_regexp, to_str, to_s, to_sym
-Style/TrivialAccessors:
-  Exclude:
-    - 'app/models/external_issue.rb'
-    - 'app/serializers/base_serializer.rb'
-    - 'lib/gitlab/auth/ldap/person.rb'
-    - 'lib/system_check/base_check.rb'
-
 # Offense count: 4
 # Cop supports --auto-correct.
 Style/UnlessElse:

app/models/external_issue.rb

@@ -3,6 +3,8 @@
 class ExternalIssue
   include Referable
 
+  attr_reader :project
+
   def initialize(issue_identifier, project)
     @issue_identifier, @project = issue_identifier, project
   end
@@ -32,12 +34,8 @@ class ExternalIssue
     [self.class, to_s].hash
   end
 
-  def project
-    @project
-  end
-
   def project_id
-    @project.id
+    project.id
   end
 
   def to_reference(_from = nil, full: nil)

app/serializers/base_serializer.rb

@@ -16,11 +16,11 @@ class BaseSerializer
       .as_json
   end
 
-  def self.entity(entity_class)
+  class << self
+    attr_reader :entity_class
+
+    def entity(entity_class)
       @entity_class ||= entity_class
     end
-
-  def self.entity_class
-    @entity_class
   end
 end

lib/gitlab/auth/ldap/person.rb

@@ -98,9 +98,7 @@ module Gitlab
 
         private
 
-        def entry
-          @entry
-        end
+        attr_reader :entry
 
         def config
           @config ||= Gitlab::Auth::LDAP::Config.new(provider)

lib/system_check/base_check.rb

@@ -70,18 +70,14 @@ module SystemCheck
     # multiple reasons why a check can fail
     #
     # @param [String] reason to be displayed
-    def skip_reason=(reason)
-      @skip_reason = reason
-    end
+    attr_writer :skip_reason
 
     # Skip reason defined during runtime
     #
     # This value have precedence over the one defined in the subclass
     #
     # @return [String] the reason
-    def skip_reason
-      @skip_reason
-    end
+    attr_reader :skip_reason
 
     # Does the check support automatically repair routine?
     #