Enable frozen string in app/controllers/**/*.rbrepo-forks/gitlab-ce-frozen-string-app-controller

Enables frozen string for the following:

* app/controllers/*.rb
* app/controllers/admin/**/*.rb
* app/controllers/boards/**/*.rb
* app/controllers/ci/**/*.rb
* app/controllers/concerns/**/*.rb

Partially addresses #47424.

105 files changed, 221 insertions, 9 deletions

diff --git a/app/controllers/abuse_reports_controller.rb b/app/controllers/abuse_reports_controller.rb
index 51547ed7eaf..68e14f0c2e5 100644
--- a/app/controllers/abuse_reports_controller.rb
+++ b/app/controllers/abuse_reports_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AbuseReportsController < ApplicationController
   before_action :set_user, only: [:new]
 
diff --git a/app/controllers/admin/abuse_reports_controller.rb b/app/controllers/admin/abuse_reports_controller.rb
index 68a49f0749f..d5537023b26 100644
--- a/app/controllers/admin/abuse_reports_controller.rb
+++ b/app/controllers/admin/abuse_reports_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::AbuseReportsController < Admin::ApplicationController
   # rubocop: disable CodeReuse/ActiveRecord
   def index
diff --git a/app/controllers/admin/appearances_controller.rb b/app/controllers/admin/appearances_controller.rb
index 9aaec905734..fdd3b4126ff 100644
--- a/app/controllers/admin/appearances_controller.rb
+++ b/app/controllers/admin/appearances_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::AppearancesController < Admin::ApplicationController
   before_action :set_appearance, except: :create
 
diff --git a/app/controllers/admin/application_controller.rb b/app/controllers/admin/application_controller.rb
index a4648b33cfa..ef182b981f1 100644
--- a/app/controllers/admin/application_controller.rb
+++ b/app/controllers/admin/application_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Provides a base class for Admin controllers to subclass
 #
 # Automatically sets the layout and ensures an administrator is logged in
diff --git a/app/controllers/admin/application_settings_controller.rb b/app/controllers/admin/application_settings_controller.rb
index 869213d61f1..faee2880c67 100644
--- a/app/controllers/admin/application_settings_controller.rb
+++ b/app/controllers/admin/application_settings_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::ApplicationSettingsController < Admin::ApplicationController
   before_action :set_application_setting
 
diff --git a/app/controllers/admin/applications_controller.rb b/app/controllers/admin/applications_controller.rb
index daa21d1be93..00d2cc01192 100644
--- a/app/controllers/admin/applications_controller.rb
+++ b/app/controllers/admin/applications_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::ApplicationsController < Admin::ApplicationController
   include OauthApplications
 
diff --git a/app/controllers/admin/background_jobs_controller.rb b/app/controllers/admin/background_jobs_controller.rb
index 5f90ad7137d..7701f2e645b 100644
--- a/app/controllers/admin/background_jobs_controller.rb
+++ b/app/controllers/admin/background_jobs_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::BackgroundJobsController < Admin::ApplicationController
   def show
     ps_output, _ = Gitlab::Popen.popen(%W(ps ww -U #{Gitlab.config.gitlab.user} -o pid,pcpu,pmem,stat,start,command))
diff --git a/app/controllers/admin/broadcast_messages_controller.rb b/app/controllers/admin/broadcast_messages_controller.rb
index b2fbbfc3e64..a91d9a534cd 100644
--- a/app/controllers/admin/broadcast_messages_controller.rb
+++ b/app/controllers/admin/broadcast_messages_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::BroadcastMessagesController < Admin::ApplicationController
   include BroadcastMessagesHelper
 
diff --git a/app/controllers/admin/dashboard_controller.rb b/app/controllers/admin/dashboard_controller.rb
index 5dc3e6c2990..b5fb5511638 100644
--- a/app/controllers/admin/dashboard_controller.rb
+++ b/app/controllers/admin/dashboard_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::DashboardController < Admin::ApplicationController
   include CountHelper
 
diff --git a/app/controllers/admin/deploy_keys_controller.rb b/app/controllers/admin/deploy_keys_controller.rb
index 5c2025c1988..49ce275ad14 100644
--- a/app/controllers/admin/deploy_keys_controller.rb
+++ b/app/controllers/admin/deploy_keys_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::DeployKeysController < Admin::ApplicationController
   before_action :deploy_keys, only: [:index]
   before_action :deploy_key, only: [:destroy, :edit, :update]
diff --git a/app/controllers/admin/gitaly_servers_controller.rb b/app/controllers/admin/gitaly_servers_controller.rb
index 11c4dfe3d8d..0a5566bfe70 100644
--- a/app/controllers/admin/gitaly_servers_controller.rb
+++ b/app/controllers/admin/gitaly_servers_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::GitalyServersController < Admin::ApplicationController
   def index
     @gitaly_servers = Gitaly::Server.all
diff --git a/app/controllers/admin/groups_controller.rb b/app/controllers/admin/groups_controller.rb
index 2a47f01c6ad..46e85e1424f 100644
--- a/app/controllers/admin/groups_controller.rb
+++ b/app/controllers/admin/groups_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::GroupsController < Admin::ApplicationController
   include MembersPresentation
 
diff --git a/app/controllers/admin/health_check_controller.rb b/app/controllers/admin/health_check_controller.rb
index 61247b280b3..44864f9c7d0 100644
--- a/app/controllers/admin/health_check_controller.rb
+++ b/app/controllers/admin/health_check_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::HealthCheckController < Admin::ApplicationController
   def show
     @errors = HealthCheck::Utils.process_checks(['standard'])
diff --git a/app/controllers/admin/hook_logs_controller.rb b/app/controllers/admin/hook_logs_controller.rb
index 3017f96c26f..8301b3aa880 100644
--- a/app/controllers/admin/hook_logs_controller.rb
+++ b/app/controllers/admin/hook_logs_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::HookLogsController < Admin::ApplicationController
   include HooksExecution
 
diff --git a/app/controllers/admin/hooks_controller.rb b/app/controllers/admin/hooks_controller.rb
index a98c355c7ba..d0abdec50ae 100644
--- a/app/controllers/admin/hooks_controller.rb
+++ b/app/controllers/admin/hooks_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::HooksController < Admin::ApplicationController
   include HooksExecution
 
diff --git a/app/controllers/admin/identities_controller.rb b/app/controllers/admin/identities_controller.rb
index 57ad7389a23..b51c2f678ca 100644
--- a/app/controllers/admin/identities_controller.rb
+++ b/app/controllers/admin/identities_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::IdentitiesController < Admin::ApplicationController
   before_action :user
   before_action :identity, except: [:index, :new, :create]
diff --git a/app/controllers/admin/impersonation_tokens_controller.rb b/app/controllers/admin/impersonation_tokens_controller.rb
index 9ebba88ef16..f5825ecb19a 100644
--- a/app/controllers/admin/impersonation_tokens_controller.rb
+++ b/app/controllers/admin/impersonation_tokens_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::ImpersonationTokensController < Admin::ApplicationController
   before_action :user
 
diff --git a/app/controllers/admin/impersonations_controller.rb b/app/controllers/admin/impersonations_controller.rb
index d2f947d2c66..08d7e3b4fa2 100644
--- a/app/controllers/admin/impersonations_controller.rb
+++ b/app/controllers/admin/impersonations_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::ImpersonationsController < Admin::ApplicationController
   skip_before_action :authenticate_admin!
   before_action :authenticate_impersonator!
diff --git a/app/controllers/admin/jobs_controller.rb b/app/controllers/admin/jobs_controller.rb
index 788693c62c4..0c1afdc3d3b 100644
--- a/app/controllers/admin/jobs_controller.rb
+++ b/app/controllers/admin/jobs_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::JobsController < Admin::ApplicationController
   # rubocop: disable CodeReuse/ActiveRecord
   def index
diff --git a/app/controllers/admin/keys_controller.rb b/app/controllers/admin/keys_controller.rb
index 0400a3b2f3b..4e9262ccc96 100644
--- a/app/controllers/admin/keys_controller.rb
+++ b/app/controllers/admin/keys_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::KeysController < Admin::ApplicationController
   before_action :user, only: [:show, :destroy]
 
diff --git a/app/controllers/admin/labels_controller.rb b/app/controllers/admin/labels_controller.rb
index 7eb8f758807..aa5eae7a474 100644
--- a/app/controllers/admin/labels_controller.rb
+++ b/app/controllers/admin/labels_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::LabelsController < Admin::ApplicationController
   before_action :set_label, only: [:show, :edit, :update, :destroy]
 
diff --git a/app/controllers/admin/logs_controller.rb b/app/controllers/admin/logs_controller.rb
index 7248edb64e1..06b0e6a15a3 100644
--- a/app/controllers/admin/logs_controller.rb
+++ b/app/controllers/admin/logs_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::LogsController < Admin::ApplicationController
   before_action :loggers
 
diff --git a/app/controllers/admin/projects_controller.rb b/app/controllers/admin/projects_controller.rb
index 5cb08c9787b..550f29a58d2 100644
--- a/app/controllers/admin/projects_controller.rb
+++ b/app/controllers/admin/projects_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::ProjectsController < Admin::ApplicationController
   include MembersPresentation
 
diff --git a/app/controllers/admin/requests_profiles_controller.rb b/app/controllers/admin/requests_profiles_controller.rb
index a478176e138..64d74ae4231 100644
--- a/app/controllers/admin/requests_profiles_controller.rb
+++ b/app/controllers/admin/requests_profiles_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::RequestsProfilesController < Admin::ApplicationController
   def index
     @profile_token = Gitlab::RequestProfiler.profile_token
diff --git a/app/controllers/admin/runner_projects_controller.rb b/app/controllers/admin/runner_projects_controller.rb
index 51d5799cd89..774ce04d079 100644
--- a/app/controllers/admin/runner_projects_controller.rb
+++ b/app/controllers/admin/runner_projects_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::RunnerProjectsController < Admin::ApplicationController
   before_action :project, only: [:create]
 
diff --git a/app/controllers/admin/runners_controller.rb b/app/controllers/admin/runners_controller.rb
index 911603bac17..0b6ff491c66 100644
--- a/app/controllers/admin/runners_controller.rb
+++ b/app/controllers/admin/runners_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::RunnersController < Admin::ApplicationController
   before_action :runner, except: :index
 
diff --git a/app/controllers/admin/spam_logs_controller.rb b/app/controllers/admin/spam_logs_controller.rb
index 8df35d25303..18d22c95b61 100644
--- a/app/controllers/admin/spam_logs_controller.rb
+++ b/app/controllers/admin/spam_logs_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::SpamLogsController < Admin::ApplicationController
   # rubocop: disable CodeReuse/ActiveRecord
   def index
diff --git a/app/controllers/admin/system_info_controller.rb b/app/controllers/admin/system_info_controller.rb
index 99039724521..244fc2b31bb 100644
--- a/app/controllers/admin/system_info_controller.rb
+++ b/app/controllers/admin/system_info_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::SystemInfoController < Admin::ApplicationController
   EXCLUDED_MOUNT_OPTIONS = [
     'nobrowse',
diff --git a/app/controllers/admin/users_controller.rb b/app/controllers/admin/users_controller.rb
index 85bdc85c55b..b783c0e2a6f 100644
--- a/app/controllers/admin/users_controller.rb
+++ b/app/controllers/admin/users_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::UsersController < Admin::ApplicationController
   before_action :user, except: [:index, :new, :create]
 
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 7e2b2cf3ad3..838527aaa41 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'gon'
 require 'fogbugz'
 
diff --git a/app/controllers/autocomplete_controller.rb b/app/controllers/autocomplete_controller.rb
index 9e30b982b06..3766b64a091 100644
--- a/app/controllers/autocomplete_controller.rb
+++ b/app/controllers/autocomplete_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AutocompleteController < ApplicationController
   skip_before_action :authenticate_user!, only: [:users, :award_emojis]
 
diff --git a/app/controllers/boards/application_controller.rb b/app/controllers/boards/application_controller.rb
index b2675025fc0..eab908ba5ed 100644
--- a/app/controllers/boards/application_controller.rb
+++ b/app/controllers/boards/application_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Boards
   class ApplicationController < ::ApplicationController
     respond_to :json
diff --git a/app/controllers/boards/issues_controller.rb b/app/controllers/boards/issues_controller.rb
index 071906f1e91..4f3d737e3ce 100644
--- a/app/controllers/boards/issues_controller.rb
+++ b/app/controllers/boards/issues_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Boards
   class IssuesController < Boards::ApplicationController
     include BoardsResponses
diff --git a/app/controllers/boards/lists_controller.rb b/app/controllers/boards/lists_controller.rb
index e8b5934f2a9..ccd02144671 100644
--- a/app/controllers/boards/lists_controller.rb
+++ b/app/controllers/boards/lists_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Boards
   class ListsController < Boards::ApplicationController
     include BoardsResponses
diff --git a/app/controllers/ci/lints_controller.rb b/app/controllers/ci/lints_controller.rb
index 738a6a5173e..99ce24bd435 100644
--- a/app/controllers/ci/lints_controller.rb
+++ b/app/controllers/ci/lints_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Ci
   class LintsController < ::ApplicationController
     before_action :authenticate_user!
diff --git a/app/controllers/concerns/accepts_pending_invitations.rb b/app/controllers/concerns/accepts_pending_invitations.rb
index 6e8aef52b52..cb66c1a055d 100644
--- a/app/controllers/concerns/accepts_pending_invitations.rb
+++ b/app/controllers/concerns/accepts_pending_invitations.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module AcceptsPendingInvitations
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/authenticates_with_two_factor.rb b/app/controllers/concerns/authenticates_with_two_factor.rb
index 961f121548b..5507328f8ae 100644
--- a/app/controllers/concerns/authenticates_with_two_factor.rb
+++ b/app/controllers/concerns/authenticates_with_two_factor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # == AuthenticatesWithTwoFactor
 #
 # Controller concern to handle two-factor authentication
diff --git a/app/controllers/concerns/boards_responses.rb b/app/controllers/concerns/boards_responses.rb
index da830ec2cb1..b7e4f9b81f1 100644
--- a/app/controllers/concerns/boards_responses.rb
+++ b/app/controllers/concerns/boards_responses.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module BoardsResponses
   include Gitlab::Utils::StrongMemoize
 
diff --git a/app/controllers/concerns/checks_collaboration.rb b/app/controllers/concerns/checks_collaboration.rb
index 81367663a06..1fa82f7dcd4 100644
--- a/app/controllers/concerns/checks_collaboration.rb
+++ b/app/controllers/concerns/checks_collaboration.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ChecksCollaboration
   def can_collaborate_with_project?(project, ref: nil)
     return true if can?(current_user, :push_code, project)
diff --git a/app/controllers/concerns/continue_params.rb b/app/controllers/concerns/continue_params.rb
index 8b7355974df..f0e6adf4dec 100644
--- a/app/controllers/concerns/continue_params.rb
+++ b/app/controllers/concerns/continue_params.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ContinueParams
   include InternalRedirect
   extend ActiveSupport::Concern
diff --git a/app/controllers/concerns/controller_with_cross_project_access_check.rb b/app/controllers/concerns/controller_with_cross_project_access_check.rb
index a45c3384578..3f72f092683 100644
--- a/app/controllers/concerns/controller_with_cross_project_access_check.rb
+++ b/app/controllers/concerns/controller_with_cross_project_access_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ControllerWithCrossProjectAccessCheck
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/creates_commit.rb b/app/controllers/concerns/creates_commit.rb
index 709c8aaf337..b3777fd2b0f 100644
--- a/app/controllers/concerns/creates_commit.rb
+++ b/app/controllers/concerns/creates_commit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module CreatesCommit
   extend ActiveSupport::Concern
   include Gitlab::Utils::StrongMemoize
@@ -65,7 +67,7 @@ module CreatesCommit
         flash[:notice] = nil
       else
         target = different_project? ? "project" : "branch"
-        flash[:notice] << " You can now submit a merge request to get this change into the original #{target}."
+        flash[:notice] = flash[:notice] + " You can now submit a merge request to get this change into the original #{target}."
       end
     end
   end
diff --git a/app/controllers/concerns/cycle_analytics_params.rb b/app/controllers/concerns/cycle_analytics_params.rb
index 1ab107168c0..c1ef848e1e7 100644
--- a/app/controllers/concerns/cycle_analytics_params.rb
+++ b/app/controllers/concerns/cycle_analytics_params.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module CycleAnalyticsParams
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/diff_for_path.rb b/app/controllers/concerns/diff_for_path.rb
index d5388c4cd20..6be7a2a18a2 100644
--- a/app/controllers/concerns/diff_for_path.rb
+++ b/app/controllers/concerns/diff_for_path.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module DiffForPath
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/enforces_two_factor_authentication.rb b/app/controllers/concerns/enforces_two_factor_authentication.rb
index 69e5cbed343..71bdef8ce03 100644
--- a/app/controllers/concerns/enforces_two_factor_authentication.rb
+++ b/app/controllers/concerns/enforces_two_factor_authentication.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # == EnforcesTwoFactorAuthentication
 #
 # Controller concern to enforce two-factor authentication requirements
diff --git a/app/controllers/concerns/group_tree.rb b/app/controllers/concerns/group_tree.rb
index c363cad0ffa..4f56346832c 100644
--- a/app/controllers/concerns/group_tree.rb
+++ b/app/controllers/concerns/group_tree.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module GroupTree
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   # rubocop: disable CodeReuse/ActiveRecord
diff --git a/app/controllers/concerns/hooks_execution.rb b/app/controllers/concerns/hooks_execution.rb
index a22e46b4860..e8add1f4055 100644
--- a/app/controllers/concerns/hooks_execution.rb
+++ b/app/controllers/concerns/hooks_execution.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module HooksExecution
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/internal_redirect.rb b/app/controllers/concerns/internal_redirect.rb
index 10b9852e329..4d3b5681757 100644
--- a/app/controllers/concerns/internal_redirect.rb
+++ b/app/controllers/concerns/internal_redirect.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module InternalRedirect
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/issuable_actions.rb b/app/controllers/concerns/issuable_actions.rb
index e723107bd7f..07e01e903ea 100644
--- a/app/controllers/concerns/issuable_actions.rb
+++ b/app/controllers/concerns/issuable_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module IssuableActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/issuable_collections.rb b/app/controllers/concerns/issuable_collections.rb
index d29154d5c60..5217b4be928 100644
--- a/app/controllers/concerns/issuable_collections.rb
+++ b/app/controllers/concerns/issuable_collections.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module IssuableCollections
   extend ActiveSupport::Concern
   include CookiesHelper
diff --git a/app/controllers/concerns/issues_action.rb b/app/controllers/concerns/issues_action.rb
index 9d58656773d..a75590457d6 100644
--- a/app/controllers/concerns/issues_action.rb
+++ b/app/controllers/concerns/issues_action.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module IssuesAction
   extend ActiveSupport::Concern
   include IssuableCollections
diff --git a/app/controllers/concerns/issues_calendar.rb b/app/controllers/concerns/issues_calendar.rb
index 76e1d1ff4e8..1fdfde4c869 100644
--- a/app/controllers/concerns/issues_calendar.rb
+++ b/app/controllers/concerns/issues_calendar.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module IssuesCalendar
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/lfs_request.rb b/app/controllers/concerns/lfs_request.rb
index 4584ff782a3..9576eb14fdd 100644
--- a/app/controllers/concerns/lfs_request.rb
+++ b/app/controllers/concerns/lfs_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This concern assumes:
 # - a `#project` accessor
 # - a `#user` accessor
diff --git a/app/controllers/concerns/members_presentation.rb b/app/controllers/concerns/members_presentation.rb
index e146e7574aa..c6c3598a976 100644
--- a/app/controllers/concerns/members_presentation.rb
+++ b/app/controllers/concerns/members_presentation.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MembersPresentation
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/membership_actions.rb b/app/controllers/concerns/membership_actions.rb
index 94a352c0bcc..ca713192c9e 100644
--- a/app/controllers/concerns/membership_actions.rb
+++ b/app/controllers/concerns/membership_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MembershipActions
   include MembersPresentation
   extend ActiveSupport::Concern
diff --git a/app/controllers/concerns/merge_requests_action.rb b/app/controllers/concerns/merge_requests_action.rb
index b70db99b157..285f2c3a8a0 100644
--- a/app/controllers/concerns/merge_requests_action.rb
+++ b/app/controllers/concerns/merge_requests_action.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MergeRequestsAction
   extend ActiveSupport::Concern
   include IssuableCollections
diff --git a/app/controllers/concerns/milestone_actions.rb b/app/controllers/concerns/milestone_actions.rb
index d92cf8b4894..eccbe35577b 100644
--- a/app/controllers/concerns/milestone_actions.rb
+++ b/app/controllers/concerns/milestone_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module MilestoneActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/notes_actions.rb b/app/controllers/concerns/notes_actions.rb
index b63f2eb85f0..9422a06387b 100644
--- a/app/controllers/concerns/notes_actions.rb
+++ b/app/controllers/concerns/notes_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module NotesActions
   include RendersNotes
   include Gitlab::Utils::StrongMemoize
diff --git a/app/controllers/concerns/oauth_applications.rb b/app/controllers/concerns/oauth_applications.rb
index f0a68f23566..d97e22df472 100644
--- a/app/controllers/concerns/oauth_applications.rb
+++ b/app/controllers/concerns/oauth_applications.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module OauthApplications
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/params_backward_compatibility.rb b/app/controllers/concerns/params_backward_compatibility.rb
index b0e3d9c7b34..c972d6e3161 100644
--- a/app/controllers/concerns/params_backward_compatibility.rb
+++ b/app/controllers/concerns/params_backward_compatibility.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ParamsBackwardCompatibility
   private
 
diff --git a/app/controllers/concerns/preview_markdown.rb b/app/controllers/concerns/preview_markdown.rb
index 99123fcb3b0..c61b9fabe9e 100644
--- a/app/controllers/concerns/preview_markdown.rb
+++ b/app/controllers/concerns/preview_markdown.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module PreviewMarkdown
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/renders_blob.rb b/app/controllers/concerns/renders_blob.rb
index ba7adcfea86..b8026c7a01d 100644
--- a/app/controllers/concerns/renders_blob.rb
+++ b/app/controllers/concerns/renders_blob.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RendersBlob
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/renders_commits.rb b/app/controllers/concerns/renders_commits.rb
index b1c9b1e532f..f48e0586211 100644
--- a/app/controllers/concerns/renders_commits.rb
+++ b/app/controllers/concerns/renders_commits.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RendersCommits
   def limited_commits(commits)
     if commits.size > MergeRequestDiff::COMMITS_SAFE_SIZE
diff --git a/app/controllers/concerns/renders_member_access.rb b/app/controllers/concerns/renders_member_access.rb
index c5b77dacb26..955ac1a1bc8 100644
--- a/app/controllers/concerns/renders_member_access.rb
+++ b/app/controllers/concerns/renders_member_access.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RendersMemberAccess
   def prepare_groups_for_rendering(groups)
     preload_max_member_access_for_collection(Group, groups)
diff --git a/app/controllers/concerns/renders_notes.rb b/app/controllers/concerns/renders_notes.rb
index c5f23e33424..ce36da6b715 100644
--- a/app/controllers/concerns/renders_notes.rb
+++ b/app/controllers/concerns/renders_notes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RendersNotes
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def prepare_notes_for_rendering(notes, noteable = nil)
diff --git a/app/controllers/concerns/repository_settings_redirect.rb b/app/controllers/concerns/repository_settings_redirect.rb
index f3db3cd563b..0f18735c29e 100644
--- a/app/controllers/concerns/repository_settings_redirect.rb
+++ b/app/controllers/concerns/repository_settings_redirect.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RepositorySettingsRedirect
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/requires_whitelisted_monitoring_client.rb b/app/controllers/concerns/requires_whitelisted_monitoring_client.rb
index 88d1b34bb06..426f224d26b 100644
--- a/app/controllers/concerns/requires_whitelisted_monitoring_client.rb
+++ b/app/controllers/concerns/requires_whitelisted_monitoring_client.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RequiresWhitelistedMonitoringClient
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/routable_actions.rb b/app/controllers/concerns/routable_actions.rb
index 0931bdf4c04..88939b002b2 100644
--- a/app/controllers/concerns/routable_actions.rb
+++ b/app/controllers/concerns/routable_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module RoutableActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/send_file_upload.rb b/app/controllers/concerns/send_file_upload.rb
index 382ec91f771..0bb7b7efed0 100644
--- a/app/controllers/concerns/send_file_upload.rb
+++ b/app/controllers/concerns/send_file_upload.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SendFileUpload
   def send_upload(file_upload, send_params: {}, redirect_params: {}, attachment: nil, disposition: 'attachment')
     if attachment
diff --git a/app/controllers/concerns/service_params.rb b/app/controllers/concerns/service_params.rb
index c1acb50b76c..8bd93a349ef 100644
--- a/app/controllers/concerns/service_params.rb
+++ b/app/controllers/concerns/service_params.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ServiceParams
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/snippets_actions.rb b/app/controllers/concerns/snippets_actions.rb
index 120614739aa..8c22490700c 100644
--- a/app/controllers/concerns/snippets_actions.rb
+++ b/app/controllers/concerns/snippets_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SnippetsActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/spammable_actions.rb b/app/controllers/concerns/spammable_actions.rb
index 922aa58a00f..c3a1b12af84 100644
--- a/app/controllers/concerns/spammable_actions.rb
+++ b/app/controllers/concerns/spammable_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module SpammableActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/todos_actions.rb b/app/controllers/concerns/todos_actions.rb
index c0acdb3498d..78b65f7961b 100644
--- a/app/controllers/concerns/todos_actions.rb
+++ b/app/controllers/concerns/todos_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module TodosActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/toggle_award_emoji.rb b/app/controllers/concerns/toggle_award_emoji.rb
index ae0b815f85e..97b343f8b1a 100644
--- a/app/controllers/concerns/toggle_award_emoji.rb
+++ b/app/controllers/concerns/toggle_award_emoji.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ToggleAwardEmoji
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/toggle_subscription_action.rb b/app/controllers/concerns/toggle_subscription_action.rb
index 776583579e8..e613bfaeef2 100644
--- a/app/controllers/concerns/toggle_subscription_action.rb
+++ b/app/controllers/concerns/toggle_subscription_action.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ToggleSubscriptionAction
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/uploads_actions.rb b/app/controllers/concerns/uploads_actions.rb
index 56772df21d7..7a1c7abfb8f 100644
--- a/app/controllers/concerns/uploads_actions.rb
+++ b/app/controllers/concerns/uploads_actions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module UploadsActions
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/with_performance_bar.rb b/app/controllers/concerns/with_performance_bar.rb
index 6a8b1a4de7b..c12839c7bbd 100644
--- a/app/controllers/concerns/with_performance_bar.rb
+++ b/app/controllers/concerns/with_performance_bar.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module WithPerformanceBar
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/concerns/workhorse_request.rb b/app/controllers/concerns/workhorse_request.rb
index 43c0f1b173c..028f10e866a 100644
--- a/app/controllers/concerns/workhorse_request.rb
+++ b/app/controllers/concerns/workhorse_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module WorkhorseRequest
   extend ActiveSupport::Concern
 
diff --git a/app/controllers/confirmations_controller.rb b/app/controllers/confirmations_controller.rb
index 7bc46a6ccc0..2c4aab67448 100644
--- a/app/controllers/confirmations_controller.rb
+++ b/app/controllers/confirmations_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ConfirmationsController < Devise::ConfirmationsController
   include AcceptsPendingInvitations
 
@@ -20,7 +22,7 @@ class ConfirmationsController < Devise::ConfirmationsController
       after_sign_in(resource)
     else
       Gitlab::AppLogger.info("Email Confirmed: username=#{resource.username} email=#{resource.email} ip=#{request.remote_ip}")
-      flash[:notice] += " Please sign in."
+      flash[:notice] = flash[:notice] + " Please sign in."
       new_session_path(:user, anchor: 'login-pane')
     end
   end
diff --git a/app/controllers/dashboard_controller.rb b/app/controllers/dashboard_controller.rb
index ff133001b84..241753a505a 100644
--- a/app/controllers/dashboard_controller.rb
+++ b/app/controllers/dashboard_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class DashboardController < Dashboard::ApplicationController
   include IssuesAction
   include MergeRequestsAction
diff --git a/app/controllers/graphql_controller.rb b/app/controllers/graphql_controller.rb
index 0a1cf169aca..a1ec144410b 100644
--- a/app/controllers/graphql_controller.rb
+++ b/app/controllers/graphql_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class GraphqlController < ApplicationController
   # Unauthenticated users have access to the API for public data
   skip_before_action :authenticate_user!
diff --git a/app/controllers/groups_controller.rb b/app/controllers/groups_controller.rb
index 8b46eedae79..062c8c4e9e1 100644
--- a/app/controllers/groups_controller.rb
+++ b/app/controllers/groups_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class GroupsController < Groups::ApplicationController
   include API::Helpers::RelatedResourcesHelpers
   include IssuesAction
diff --git a/app/controllers/health_check_controller.rb b/app/controllers/health_check_controller.rb
index c3d18991fd4..a2abed7ba4e 100644
--- a/app/controllers/health_check_controller.rb
+++ b/app/controllers/health_check_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class HealthCheckController < HealthCheck::HealthCheckController
   include RequiresWhitelistedMonitoringClient
 end
diff --git a/app/controllers/health_controller.rb b/app/controllers/health_controller.rb
index 3fedd5bfb29..ab4bc911e17 100644
--- a/app/controllers/health_controller.rb
+++ b/app/controllers/health_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class HealthController < ActionController::Base
   protect_from_forgery with: :exception, except: :storage_check, prepend: true
   include RequiresWhitelistedMonitoringClient
diff --git a/app/controllers/help_controller.rb b/app/controllers/help_controller.rb
index a394521698c..e5a1fc9d6ff 100644
--- a/app/controllers/help_controller.rb
+++ b/app/controllers/help_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class HelpController < ApplicationController
   skip_before_action :authenticate_user!
 
diff --git a/app/controllers/ide_controller.rb b/app/controllers/ide_controller.rb
index 96bb2237d90..eeeebe430a7 100644
--- a/app/controllers/ide_controller.rb
+++ b/app/controllers/ide_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class IdeController < ApplicationController
   layout 'fullscreen'
 
diff --git a/app/controllers/invites_controller.rb b/app/controllers/invites_controller.rb
index 025d8270b7c..315d1375e02 100644
--- a/app/controllers/invites_controller.rb
+++ b/app/controllers/invites_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class InvitesController < ApplicationController
   before_action :member
   skip_before_action :authenticate_user!, only: :decline
@@ -50,9 +52,9 @@ class InvitesController < ApplicationController
   def authenticate_user!
     return if current_user
 
-    notice = "To accept this invitation, sign in"
-    notice << " or create an account" if Gitlab::CurrentSettings.allow_signup?
-    notice << "."
+    notice = ["To accept this invitation, sign in"]
+    notice << "or create an account" if Gitlab::CurrentSettings.allow_signup?
+    notice = notice.join(' ') + "."
 
     store_location_for :user, request.fullpath
     redirect_to new_user_session_path, notice: notice
diff --git a/app/controllers/jwt_controller.rb b/app/controllers/jwt_controller.rb
index d172aee5436..f9008a5b67e 100644
--- a/app/controllers/jwt_controller.rb
+++ b/app/controllers/jwt_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class JwtController < ApplicationController
   skip_before_action :authenticate_user!
   skip_before_action :verify_authenticity_token
diff --git a/app/controllers/koding_controller.rb b/app/controllers/koding_controller.rb
index 745abf3c0f5..72aa9d4f17f 100644
--- a/app/controllers/koding_controller.rb
+++ b/app/controllers/koding_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class KodingController < ApplicationController
   before_action :check_integration!
   layout 'koding'
diff --git a/app/controllers/metrics_controller.rb b/app/controllers/metrics_controller.rb
index 0400ffcfee5..7353be478e1 100644
--- a/app/controllers/metrics_controller.rb
+++ b/app/controllers/metrics_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class MetricsController < ActionController::Base
   include RequiresWhitelistedMonitoringClient
 
diff --git a/app/controllers/notification_settings_controller.rb b/app/controllers/notification_settings_controller.rb
index 461f26561f1..84dce74ace8 100644
--- a/app/controllers/notification_settings_controller.rb
+++ b/app/controllers/notification_settings_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class NotificationSettingsController < ApplicationController
   before_action :authenticate_user!
 
diff --git a/app/controllers/omniauth_callbacks_controller.rb b/app/controllers/omniauth_callbacks_controller.rb
index 1547d4b5972..30be50d4595 100644
--- a/app/controllers/omniauth_callbacks_controller.rb
+++ b/app/controllers/omniauth_callbacks_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class OmniauthCallbacksController < Devise::OmniauthCallbacksController
   include AuthenticatesWithTwoFactor
   include Devise::Controllers::Rememberable
@@ -135,14 +137,13 @@ class OmniauthCallbacksController < Devise::OmniauthCallbacksController
 
   def handle_signup_error
     label = Gitlab::Auth::OAuth::Provider.label_for(oauth['provider'])
-    message = "Signing in using your #{label} account without a pre-existing GitLab account is not allowed."
+    message = ["Signing in using your #{label} account without a pre-existing GitLab account is not allowed."]
 
     if Gitlab::CurrentSettings.allow_signup?
-      message << " Create a GitLab account first, and then connect it to your #{label} account."
+      message << "Create a GitLab account first, and then connect it to your #{label} account."
     end
 
-    flash[:notice] = message
-
+    flash[:notice] = message.join(' ')
     redirect_to new_user_session_path
   end
 
diff --git a/app/controllers/passwords_controller.rb b/app/controllers/passwords_controller.rb
index a1bcf206b65..2912a22411e 100644
--- a/app/controllers/passwords_controller.rb
+++ b/app/controllers/passwords_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class PasswordsController < Devise::PasswordsController
   skip_before_action :require_no_authentication, only: [:edit, :update]
 
diff --git a/app/controllers/profiles_controller.rb b/app/controllers/profiles_controller.rb
index a43d47797f1..15248d2d08f 100644
--- a/app/controllers/profiles_controller.rb
+++ b/app/controllers/profiles_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ProfilesController < Profiles::ApplicationController
   include ActionView::Helpers::SanitizeHelper
 
diff --git a/app/controllers/projects_controller.rb b/app/controllers/projects_controller.rb
index 64d9b16a041..7352c5e9bec 100644
--- a/app/controllers/projects_controller.rb
+++ b/app/controllers/projects_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ProjectsController < Projects::ApplicationController
   include API::Helpers::RelatedResourcesHelpers
   include IssuableCollections
diff --git a/app/controllers/registrations_controller.rb b/app/controllers/registrations_controller.rb
index e6d6965036e..8b8d87524a8 100644
--- a/app/controllers/registrations_controller.rb
+++ b/app/controllers/registrations_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class RegistrationsController < Devise::RegistrationsController
   include Recaptcha::Verify
   include AcceptsPendingInvitations
diff --git a/app/controllers/root_controller.rb b/app/controllers/root_controller.rb
index 651b82f04f4..ebf70f25bda 100644
--- a/app/controllers/root_controller.rb
+++ b/app/controllers/root_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # RootController
 #
 # This controller exists solely to handle requests to `root_url`. When a user is
diff --git a/app/controllers/search_controller.rb b/app/controllers/search_controller.rb
index a928758f325..1b22907c10f 100644
--- a/app/controllers/search_controller.rb
+++ b/app/controllers/search_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class SearchController < ApplicationController
   include ControllerWithCrossProjectAccessCheck
   include SearchHelper
diff --git a/app/controllers/sent_notifications_controller.rb b/app/controllers/sent_notifications_controller.rb
index 93a71103a09..2b76921ebd8 100644
--- a/app/controllers/sent_notifications_controller.rb
+++ b/app/controllers/sent_notifications_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class SentNotificationsController < ApplicationController
   skip_before_action :authenticate_user!
 
diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index 9f2e66dea90..643eb75c83c 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class SessionsController < Devise::SessionsController
   include InternalRedirect
   include AuthenticatesWithTwoFactor
diff --git a/app/controllers/snippets_controller.rb b/app/controllers/snippets_controller.rb
index 19d865900e9..694c3a59e2b 100644
--- a/app/controllers/snippets_controller.rb
+++ b/app/controllers/snippets_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class SnippetsController < ApplicationController
   include RendersNotes
   include ToggleAwardEmoji
diff --git a/app/controllers/uploads_controller.rb b/app/controllers/uploads_controller.rb
index 3d227b0a955..fa5d84633b5 100644
--- a/app/controllers/uploads_controller.rb
+++ b/app/controllers/uploads_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UploadsController < ApplicationController
   include UploadsActions
 
diff --git a/app/controllers/user_callouts_controller.rb b/app/controllers/user_callouts_controller.rb
index b8d2deba93b..ebf1dd8ca02 100644
--- a/app/controllers/user_callouts_controller.rb
+++ b/app/controllers/user_callouts_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UserCalloutsController < ApplicationController
   def create
     if ensure_callout.persisted?
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 2f65f4a7403..e509098d778 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UsersController < ApplicationController
   include RoutableActions
   include RendersMemberAccess
diff --git a/changelogs/unreleased/frozen-string-app-controller.yml b/changelogs/unreleased/frozen-string-app-controller.yml
new file mode 100644
index 00000000000..95fea4eae63
--- /dev/null
+++ b/changelogs/unreleased/frozen-string-app-controller.yml
@@ -0,0 +1,5 @@
+---
+title: Enable frozen string in app/controllers/**/*.rb
+merge_request: gfyoung
+author:
+type: performance