Enable even more frozen string in lib/**/*.rb

Enables frozen string for the following files:

* lib/generators/**/*.rb
* lib/gitaly/**/*.rb
* lib/google_api/**/*.rb
* lib/haml_lint/**/*.rb
* lib/json_web_token/**/*.rb
* lib/mattermost/**/*.rb
* lib/microsoft_teams/**/*.rb
* lib/object_storage/**/*.rb
* lib/omni_auth/**/*.rb
* lib/peek/**/*.rb
* lib/rouge/**/*.rb
* lib/rspec_flaky/**/*.rb
* lib/system_check/**/*.rb

Partially addresses #47424.

58 files changed, 123 insertions, 4 deletions

diff --git a/.rubocop.yml b/.rubocop.yml
index b7aec5b8b14..b10457995b3 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -48,7 +48,8 @@ Style/FrozenStringLiteralComment:
     - 'danger/**/*'
     - 'db/**/*'
     - 'ee/**/*'
-    - 'lib/**/*'
+    - 'lib/gitlab/**/*'
+    - 'lib/tasks/**/*'
     - 'qa/**/*'
     - 'rubocop/**/*'
     - 'scripts/**/*'
diff --git a/changelogs/unreleased/even-more-frozen-string-lib.yml b/changelogs/unreleased/even-more-frozen-string-lib.yml
new file mode 100644
index 00000000000..3f5fd7710aa
--- /dev/null
+++ b/changelogs/unreleased/even-more-frozen-string-lib.yml
@@ -0,0 +1,5 @@
+---
+title: Enable even more frozen string in lib/**/*.rb
+merge_request:
+author: gfyoung
+type: performance
diff --git a/lib/generators/rails/post_deployment_migration/post_deployment_migration_generator.rb b/lib/generators/rails/post_deployment_migration/post_deployment_migration_generator.rb
index 91175b49c79..15cdd25e711 100644
--- a/lib/generators/rails/post_deployment_migration/post_deployment_migration_generator.rb
+++ b/lib/generators/rails/post_deployment_migration/post_deployment_migration_generator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rails/generators'
 
 module Rails
diff --git a/lib/gitaly/server.rb b/lib/gitaly/server.rb
index f95e423ef22..7b238623418 100644
--- a/lib/gitaly/server.rb
+++ b/lib/gitaly/server.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitaly
   class Server
     def self.all
diff --git a/lib/google_api/auth.rb b/lib/google_api/auth.rb
index 1aeaa387a49..e724e58e9ca 100644
--- a/lib/google_api/auth.rb
+++ b/lib/google_api/auth.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module GoogleApi
   class Auth
     attr_reader :access_token, :redirect_uri, :state
diff --git a/lib/google_api/cloud_platform/client.rb b/lib/google_api/cloud_platform/client.rb
index 77b6610286f..e74ff6a9129 100644
--- a/lib/google_api/cloud_platform/client.rb
+++ b/lib/google_api/cloud_platform/client.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'google/apis/compute_v1'
 require 'google/apis/container_v1'
 require 'google/apis/cloudbilling_v1'
diff --git a/lib/haml_lint/inline_javascript.rb b/lib/haml_lint/inline_javascript.rb
index adbed20f152..5ecd6169ecf 100644
--- a/lib/haml_lint/inline_javascript.rb
+++ b/lib/haml_lint/inline_javascript.rb
@@ -1,4 +1,7 @@
-unless Rails.env.production? # rubocop:disable Naming/FileName
+# rubocop:disable Naming/FileName
+# frozen_string_literal: true
+
+unless Rails.env.production?
   require 'haml_lint/haml_visitor'
   require 'haml_lint/linter'
   require 'haml_lint/linter_registry'
diff --git a/lib/json_web_token/rsa_token.rb b/lib/json_web_token/rsa_token.rb
index d6d6af7089c..160e1e506f1 100644
--- a/lib/json_web_token/rsa_token.rb
+++ b/lib/json_web_token/rsa_token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module JSONWebToken
   class RSAToken < Token
     attr_reader :key_file
diff --git a/lib/json_web_token/token.rb b/lib/json_web_token/token.rb
index 5b67715b0b2..ce5d6f248d0 100644
--- a/lib/json_web_token/token.rb
+++ b/lib/json_web_token/token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module JSONWebToken
   class Token
     attr_accessor :issuer, :subject, :audience, :id
diff --git a/lib/mattermost/client.rb b/lib/mattermost/client.rb
index d80cd7d2a4e..293d0c563c5 100644
--- a/lib/mattermost/client.rb
+++ b/lib/mattermost/client.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mattermost
   ClientError = Class.new(Mattermost::Error)
 
diff --git a/lib/mattermost/command.rb b/lib/mattermost/command.rb
index 704813dfdf0..a02745486d6 100644
--- a/lib/mattermost/command.rb
+++ b/lib/mattermost/command.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mattermost
   class Command < Client
     def create(params)
diff --git a/lib/mattermost/error.rb b/lib/mattermost/error.rb
index dee6deb7974..054bd5457bd 100644
--- a/lib/mattermost/error.rb
+++ b/lib/mattermost/error.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mattermost
   Error = Class.new(StandardError)
 end
diff --git a/lib/mattermost/session.rb b/lib/mattermost/session.rb
index 2aa7a2f64d8..e2083848a8d 100644
--- a/lib/mattermost/session.rb
+++ b/lib/mattermost/session.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mattermost
   class NoSessionError < Mattermost::Error
     def message
diff --git a/lib/mattermost/team.rb b/lib/mattermost/team.rb
index 95c2f6f9d6b..58120178f50 100644
--- a/lib/mattermost/team.rb
+++ b/lib/mattermost/team.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mattermost
   class Team < Client
     # Returns all teams that the current user is a member of
diff --git a/lib/microsoft_teams/activity.rb b/lib/microsoft_teams/activity.rb
index d2c420efdaf..207e90d2638 100644
--- a/lib/microsoft_teams/activity.rb
+++ b/lib/microsoft_teams/activity.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MicrosoftTeams
   class Activity
     def initialize(title:, subtitle:, text:, image:)
diff --git a/lib/microsoft_teams/notifier.rb b/lib/microsoft_teams/notifier.rb
index 226ee1373db..c7dec09ba6b 100644
--- a/lib/microsoft_teams/notifier.rb
+++ b/lib/microsoft_teams/notifier.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MicrosoftTeams
   class Notifier
     def initialize(webhook)
diff --git a/lib/object_storage/direct_upload.rb b/lib/object_storage/direct_upload.rb
index 97f56e10ccf..fd26663fef0 100644
--- a/lib/object_storage/direct_upload.rb
+++ b/lib/object_storage/direct_upload.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ObjectStorage
   #
   # The DirectUpload c;ass generates a set of presigned URLs
diff --git a/lib/omni_auth/strategies/bitbucket.rb b/lib/omni_auth/strategies/bitbucket.rb
index ce1bdfe6ee4..6c914b4222a 100644
--- a/lib/omni_auth/strategies/bitbucket.rb
+++ b/lib/omni_auth/strategies/bitbucket.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'omniauth-oauth2'
 
 module OmniAuth
diff --git a/lib/omni_auth/strategies/jwt.rb b/lib/omni_auth/strategies/jwt.rb
index ebdb5c7faf0..a792903fde7 100644
--- a/lib/omni_auth/strategies/jwt.rb
+++ b/lib/omni_auth/strategies/jwt.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'omniauth'
 require 'jwt'
 
diff --git a/lib/peek/rblineprof/custom_controller_helpers.rb b/lib/peek/rblineprof/custom_controller_helpers.rb
index 9beb442bfa3..581cc6a37b4 100644
--- a/lib/peek/rblineprof/custom_controller_helpers.rb
+++ b/lib/peek/rblineprof/custom_controller_helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Peek
   module Rblineprof
     module CustomControllerHelpers
@@ -41,7 +43,7 @@ module Peek
             ]
           end.sort_by{ |a,b,c,d,e,f| -f }
 
-          output = "<div class='modal-dialog modal-xl'><div class='modal-content'>"
+          output = ["<div class='modal-dialog modal-xl'><div class='modal-content'>"]
           output << "<div class='modal-header'>"
           output << "<h4>Line profiling: #{human_description(params[:lineprofiler])}</h4>"
           output << "<button class='close' type='button' data-dismiss='modal' aria-label='close'><span aria-hidden='true'>&times;</span></button>"
@@ -93,7 +95,7 @@ module Peek
 
           output << "</div></div></div>"
 
-          response.body += "<div class='modal' id='modal-peek-line-profile' tabindex=-1>#{output}</div>".html_safe
+          response.body += "<div class='modal' id='modal-peek-line-profile' tabindex=-1>#{output.join}</div>".html_safe
         end
 
         ret
diff --git a/lib/peek/views/gitaly.rb b/lib/peek/views/gitaly.rb
index ab35f7a2258..860963ef94f 100644
--- a/lib/peek/views/gitaly.rb
+++ b/lib/peek/views/gitaly.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Peek
   module Views
     class Gitaly < View
diff --git a/lib/peek/views/host.rb b/lib/peek/views/host.rb
index 43c8a35c7ea..da0816b364c 100644
--- a/lib/peek/views/host.rb
+++ b/lib/peek/views/host.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Peek
   module Views
     class Host < View
diff --git a/lib/rouge/formatters/html_gitlab.rb b/lib/rouge/formatters/html_gitlab.rb
index e877ab10248..e2a7d3ef5ba 100644
--- a/lib/rouge/formatters/html_gitlab.rb
+++ b/lib/rouge/formatters/html_gitlab.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Rouge
   module Formatters
     class HTMLGitlab < Rouge::Formatters::HTML
diff --git a/lib/rouge/plugins/common_mark.rb b/lib/rouge/plugins/common_mark.rb
index 8f9de061124..d240df5a0e0 100644
--- a/lib/rouge/plugins/common_mark.rb
+++ b/lib/rouge/plugins/common_mark.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # A rouge plugin for CommonMark markdown engine.
 # Used to highlight code generated by CommonMark.
 
diff --git a/lib/rspec_flaky/config.rb b/lib/rspec_flaky/config.rb
index 06e96f969f1..55c1d4747b4 100644
--- a/lib/rspec_flaky/config.rb
+++ b/lib/rspec_flaky/config.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RspecFlaky
   class Config
     def self.generate_report?
diff --git a/lib/rspec_flaky/example.rb b/lib/rspec_flaky/example.rb
index b6e790cbbab..3c1b05257a0 100644
--- a/lib/rspec_flaky/example.rb
+++ b/lib/rspec_flaky/example.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RspecFlaky
   # This is a wrapper class for RSpec::Core::Example
   class Example
diff --git a/lib/rspec_flaky/flaky_example.rb b/lib/rspec_flaky/flaky_example.rb
index 6be24014d89..da5dbf06bc9 100644
--- a/lib/rspec_flaky/flaky_example.rb
+++ b/lib/rspec_flaky/flaky_example.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RspecFlaky
   # This represents a flaky RSpec example and is mainly meant to be saved in a JSON file
   class FlakyExample < OpenStruct
diff --git a/lib/rspec_flaky/flaky_examples_collection.rb b/lib/rspec_flaky/flaky_examples_collection.rb
index dea23c325be..290a51766e9 100644
--- a/lib/rspec_flaky/flaky_examples_collection.rb
+++ b/lib/rspec_flaky/flaky_examples_collection.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'active_support/hash_with_indifferent_access'
 
 require_relative 'flaky_example'
diff --git a/lib/rspec_flaky/listener.rb b/lib/rspec_flaky/listener.rb
index 9cd0c38cb55..19cc0baa2d3 100644
--- a/lib/rspec_flaky/listener.rb
+++ b/lib/rspec_flaky/listener.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'json'
 
 require_dependency 'rspec_flaky/config'
diff --git a/lib/rspec_flaky/report.rb b/lib/rspec_flaky/report.rb
index 1c362fdd20d..9a0fb88c424 100644
--- a/lib/rspec_flaky/report.rb
+++ b/lib/rspec_flaky/report.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'json'
 require 'time'
 
diff --git a/lib/system_check/app/active_users_check.rb b/lib/system_check/app/active_users_check.rb
index 1d72c8d6903..8446c2fc2c8 100644
--- a/lib/system_check/app/active_users_check.rb
+++ b/lib/system_check/app/active_users_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class ActiveUsersCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/database_config_exists_check.rb b/lib/system_check/app/database_config_exists_check.rb
index d1fae192350..1769145ed63 100644
--- a/lib/system_check/app/database_config_exists_check.rb
+++ b/lib/system_check/app/database_config_exists_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class DatabaseConfigExistsCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/git_config_check.rb b/lib/system_check/app/git_config_check.rb
index d08a81639e3..4e8d607096c 100644
--- a/lib/system_check/app/git_config_check.rb
+++ b/lib/system_check/app/git_config_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class GitConfigCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/git_user_default_ssh_config_check.rb b/lib/system_check/app/git_user_default_ssh_config_check.rb
index ad41760dff2..6cd53779bfd 100644
--- a/lib/system_check/app/git_user_default_ssh_config_check.rb
+++ b/lib/system_check/app/git_user_default_ssh_config_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class GitUserDefaultSSHConfigCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/git_version_check.rb b/lib/system_check/app/git_version_check.rb
index 44ec888c197..994af3ab53e 100644
--- a/lib/system_check/app/git_version_check.rb
+++ b/lib/system_check/app/git_version_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class GitVersionCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/gitlab_config_exists_check.rb b/lib/system_check/app/gitlab_config_exists_check.rb
index 247aa0994e4..1cc5ead0d89 100644
--- a/lib/system_check/app/gitlab_config_exists_check.rb
+++ b/lib/system_check/app/gitlab_config_exists_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class GitlabConfigExistsCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/gitlab_config_up_to_date_check.rb b/lib/system_check/app/gitlab_config_up_to_date_check.rb
index c609e48e133..58c7e3039c8 100644
--- a/lib/system_check/app/gitlab_config_up_to_date_check.rb
+++ b/lib/system_check/app/gitlab_config_up_to_date_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class GitlabConfigUpToDateCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/init_script_exists_check.rb b/lib/system_check/app/init_script_exists_check.rb
index d246e058e86..d36dbe7d67d 100644
--- a/lib/system_check/app/init_script_exists_check.rb
+++ b/lib/system_check/app/init_script_exists_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class InitScriptExistsCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/init_script_up_to_date_check.rb b/lib/system_check/app/init_script_up_to_date_check.rb
index 53a47eb0f42..569c41df6e4 100644
--- a/lib/system_check/app/init_script_up_to_date_check.rb
+++ b/lib/system_check/app/init_script_up_to_date_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class InitScriptUpToDateCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/log_writable_check.rb b/lib/system_check/app/log_writable_check.rb
index 3e0c436d6ee..e26ad143eb8 100644
--- a/lib/system_check/app/log_writable_check.rb
+++ b/lib/system_check/app/log_writable_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class LogWritableCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/migrations_are_up_check.rb b/lib/system_check/app/migrations_are_up_check.rb
index 5eedbacce77..b12e9ac6bba 100644
--- a/lib/system_check/app/migrations_are_up_check.rb
+++ b/lib/system_check/app/migrations_are_up_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class MigrationsAreUpCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/orphaned_group_members_check.rb b/lib/system_check/app/orphaned_group_members_check.rb
index 2b46d36fe51..3e6ffb8190b 100644
--- a/lib/system_check/app/orphaned_group_members_check.rb
+++ b/lib/system_check/app/orphaned_group_members_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class OrphanedGroupMembersCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/projects_have_namespace_check.rb b/lib/system_check/app/projects_have_namespace_check.rb
index a6ec9f7665c..2bf2529acf1 100644
--- a/lib/system_check/app/projects_have_namespace_check.rb
+++ b/lib/system_check/app/projects_have_namespace_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class ProjectsHaveNamespaceCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/redis_version_check.rb b/lib/system_check/app/redis_version_check.rb
index a0610e73576..890f8b44d13 100644
--- a/lib/system_check/app/redis_version_check.rb
+++ b/lib/system_check/app/redis_version_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class RedisVersionCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/ruby_version_check.rb b/lib/system_check/app/ruby_version_check.rb
index 57bbabece1f..d73c39f2c3f 100644
--- a/lib/system_check/app/ruby_version_check.rb
+++ b/lib/system_check/app/ruby_version_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class RubyVersionCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/tmp_writable_check.rb b/lib/system_check/app/tmp_writable_check.rb
index 99a75e57abf..6687df091d3 100644
--- a/lib/system_check/app/tmp_writable_check.rb
+++ b/lib/system_check/app/tmp_writable_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class TmpWritableCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/uploads_directory_exists_check.rb b/lib/system_check/app/uploads_directory_exists_check.rb
index 7026d0ba075..940eff9d4cf 100644
--- a/lib/system_check/app/uploads_directory_exists_check.rb
+++ b/lib/system_check/app/uploads_directory_exists_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class UploadsDirectoryExistsCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/uploads_path_permission_check.rb b/lib/system_check/app/uploads_path_permission_check.rb
index 7df6c060254..4a49f3bc2bb 100644
--- a/lib/system_check/app/uploads_path_permission_check.rb
+++ b/lib/system_check/app/uploads_path_permission_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class UploadsPathPermissionCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/app/uploads_path_tmp_permission_check.rb b/lib/system_check/app/uploads_path_tmp_permission_check.rb
index b276a81eac1..ae374f4707c 100644
--- a/lib/system_check/app/uploads_path_tmp_permission_check.rb
+++ b/lib/system_check/app/uploads_path_tmp_permission_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module App
     class UploadsPathTmpPermissionCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/base_check.rb b/lib/system_check/base_check.rb
index 0f5742dd67f..e06245294c4 100644
--- a/lib/system_check/base_check.rb
+++ b/lib/system_check/base_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   # Base class for Checks. You must inherit from here
   # and implement the methods below when necessary
diff --git a/lib/system_check/helpers.rb b/lib/system_check/helpers.rb
index 6227e461d24..07d479848fe 100644
--- a/lib/system_check/helpers.rb
+++ b/lib/system_check/helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module Helpers
     include ::Gitlab::TaskHelpers
diff --git a/lib/system_check/incoming_email/foreman_configured_check.rb b/lib/system_check/incoming_email/foreman_configured_check.rb
index 1db7bf2b782..944913087da 100644
--- a/lib/system_check/incoming_email/foreman_configured_check.rb
+++ b/lib/system_check/incoming_email/foreman_configured_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module IncomingEmail
     class ForemanConfiguredCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/incoming_email/imap_authentication_check.rb b/lib/system_check/incoming_email/imap_authentication_check.rb
index 3550c5796b0..613c2296375 100644
--- a/lib/system_check/incoming_email/imap_authentication_check.rb
+++ b/lib/system_check/incoming_email/imap_authentication_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module IncomingEmail
     class ImapAuthenticationCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/incoming_email/initd_configured_check.rb b/lib/system_check/incoming_email/initd_configured_check.rb
index ea23b8ef49c..acb4b5a9e74 100644
--- a/lib/system_check/incoming_email/initd_configured_check.rb
+++ b/lib/system_check/incoming_email/initd_configured_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module IncomingEmail
     class InitdConfiguredCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/incoming_email/mail_room_running_check.rb b/lib/system_check/incoming_email/mail_room_running_check.rb
index c1807501829..b7aead4624e 100644
--- a/lib/system_check/incoming_email/mail_room_running_check.rb
+++ b/lib/system_check/incoming_email/mail_room_running_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module IncomingEmail
     class MailRoomRunningCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/orphans/namespace_check.rb b/lib/system_check/orphans/namespace_check.rb
index 09b57c7b408..53b2d8fd5b3 100644
--- a/lib/system_check/orphans/namespace_check.rb
+++ b/lib/system_check/orphans/namespace_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module Orphans
     class NamespaceCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/orphans/repository_check.rb b/lib/system_check/orphans/repository_check.rb
index 2695c658874..ef8fe945f61 100644
--- a/lib/system_check/orphans/repository_check.rb
+++ b/lib/system_check/orphans/repository_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   module Orphans
     class RepositoryCheck < SystemCheck::BaseCheck
diff --git a/lib/system_check/simple_executor.rb b/lib/system_check/simple_executor.rb
index 99c9e984107..11818ae54f8 100644
--- a/lib/system_check/simple_executor.rb
+++ b/lib/system_check/simple_executor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SystemCheck
   # Simple Executor is current default executor for GitLab
   # It is a simple port from display logic in the old check.rake