Enable even more frozen string in lib/gitlab

Enables frozens string for the following:

* lib/gitlab/conflict/**/*.rb
* lib/gitlab/cross_project_access/**/*.rb
* lib/gitlab/cycle_analytics/**/*.rb
* lib/gitlab/data_builder/**/*.rb
* lib/gitlab/database/**/*.rb
* lib/gitlab/dependency_linker/**/*.rb
* lib/gitlab/diff/**/*.rb
* lib/gitlab/downtime_check/**/*.rb
* lib/gitlab/email/**/*.rb
* lib/gitlab/etag_caching/**/*.rb

Partially addresses gitlab-org/gitlab-ce#47424.

102 files changed, 214 insertions, 5 deletions

diff --git a/changelogs/unreleased/frozen-string-lib-gitlab-more.yml b/changelogs/unreleased/frozen-string-lib-gitlab-more.yml
new file mode 100644
index 00000000000..cfbc4ced635
--- /dev/null
+++ b/changelogs/unreleased/frozen-string-lib-gitlab-more.yml
@@ -0,0 +1,5 @@
+---
+title: Enable even more frozen string in lib/gitlab/**/*.rb
+merge_request:
+author: gfyoung
+type: performance
diff --git a/lib/gitlab/conflict/file.rb b/lib/gitlab/conflict/file.rb
index 501c2111530..0ca99506311 100644
--- a/lib/gitlab/conflict/file.rb
+++ b/lib/gitlab/conflict/file.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Conflict
     class File
diff --git a/lib/gitlab/conflict/file_collection.rb b/lib/gitlab/conflict/file_collection.rb
index 65a65b67975..53406af2c4e 100644
--- a/lib/gitlab/conflict/file_collection.rb
+++ b/lib/gitlab/conflict/file_collection.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Conflict
     class FileCollection
diff --git a/lib/gitlab/cross_project_access/check_collection.rb b/lib/gitlab/cross_project_access/check_collection.rb
index 88376232065..55527ba5e87 100644
--- a/lib/gitlab/cross_project_access/check_collection.rb
+++ b/lib/gitlab/cross_project_access/check_collection.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   class CrossProjectAccess
     class CheckCollection
diff --git a/lib/gitlab/cross_project_access/check_info.rb b/lib/gitlab/cross_project_access/check_info.rb
index e8a845c7f1e..2a9eacad680 100644
--- a/lib/gitlab/cross_project_access/check_info.rb
+++ b/lib/gitlab/cross_project_access/check_info.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   class CrossProjectAccess
     class CheckInfo
diff --git a/lib/gitlab/cross_project_access/class_methods.rb b/lib/gitlab/cross_project_access/class_methods.rb
index 90eac94800c..64ad30794d3 100644
--- a/lib/gitlab/cross_project_access/class_methods.rb
+++ b/lib/gitlab/cross_project_access/class_methods.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   class CrossProjectAccess
     module ClassMethods
diff --git a/lib/gitlab/cycle_analytics/base_event_fetcher.rb b/lib/gitlab/cycle_analytics/base_event_fetcher.rb
index e3e3767cc75..304d60996a6 100644
--- a/lib/gitlab/cycle_analytics/base_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/base_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/base_query.rb b/lib/gitlab/cycle_analytics/base_query.rb
index 86d708be0d6..36231b187cd 100644
--- a/lib/gitlab/cycle_analytics/base_query.rb
+++ b/lib/gitlab/cycle_analytics/base_query.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module BaseQuery
diff --git a/lib/gitlab/cycle_analytics/base_stage.rb b/lib/gitlab/cycle_analytics/base_stage.rb
index 038d5a19bc4..e2d6a301734 100644
--- a/lib/gitlab/cycle_analytics/base_stage.rb
+++ b/lib/gitlab/cycle_analytics/base_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class BaseStage
diff --git a/lib/gitlab/cycle_analytics/code_event_fetcher.rb b/lib/gitlab/cycle_analytics/code_event_fetcher.rb
index 06357c9b377..591db3c35e6 100644
--- a/lib/gitlab/cycle_analytics/code_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/code_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class CodeEventFetcher < BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/code_stage.rb b/lib/gitlab/cycle_analytics/code_stage.rb
index 5f9dc9a4303..2e5f9ef5a40 100644
--- a/lib/gitlab/cycle_analytics/code_stage.rb
+++ b/lib/gitlab/cycle_analytics/code_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class CodeStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/event_fetcher.rb b/lib/gitlab/cycle_analytics/event_fetcher.rb
index 50e126cf00b..98a30a8fc97 100644
--- a/lib/gitlab/cycle_analytics/event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module EventFetcher
diff --git a/lib/gitlab/cycle_analytics/issue_event_fetcher.rb b/lib/gitlab/cycle_analytics/issue_event_fetcher.rb
index 1754f91dccb..30c6ead8968 100644
--- a/lib/gitlab/cycle_analytics/issue_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/issue_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class IssueEventFetcher < BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/issue_stage.rb b/lib/gitlab/cycle_analytics/issue_stage.rb
index 7b03811efb2..4eae2da512c 100644
--- a/lib/gitlab/cycle_analytics/issue_stage.rb
+++ b/lib/gitlab/cycle_analytics/issue_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class IssueStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/metrics_tables.rb b/lib/gitlab/cycle_analytics/metrics_tables.rb
index f5d08c0b658..3e0302d308d 100644
--- a/lib/gitlab/cycle_analytics/metrics_tables.rb
+++ b/lib/gitlab/cycle_analytics/metrics_tables.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module MetricsTables
diff --git a/lib/gitlab/cycle_analytics/permissions.rb b/lib/gitlab/cycle_analytics/permissions.rb
index 1e11e84a9cb..afefd09b614 100644
--- a/lib/gitlab/cycle_analytics/permissions.rb
+++ b/lib/gitlab/cycle_analytics/permissions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class Permissions
diff --git a/lib/gitlab/cycle_analytics/plan_event_fetcher.rb b/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
index 086203b9ccc..db8ac3becea 100644
--- a/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/plan_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class PlanEventFetcher < BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/plan_stage.rb b/lib/gitlab/cycle_analytics/plan_stage.rb
index 1a0afb56b4f..513e4575be0 100644
--- a/lib/gitlab/cycle_analytics/plan_stage.rb
+++ b/lib/gitlab/cycle_analytics/plan_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class PlanStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/production_event_fetcher.rb b/lib/gitlab/cycle_analytics/production_event_fetcher.rb
index 0fa2e87f673..6681cb42c90 100644
--- a/lib/gitlab/cycle_analytics/production_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/production_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class ProductionEventFetcher < IssueEventFetcher
diff --git a/lib/gitlab/cycle_analytics/production_helper.rb b/lib/gitlab/cycle_analytics/production_helper.rb
index d0ca62e46e4..aff65b150fb 100644
--- a/lib/gitlab/cycle_analytics/production_helper.rb
+++ b/lib/gitlab/cycle_analytics/production_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module ProductionHelper
diff --git a/lib/gitlab/cycle_analytics/production_stage.rb b/lib/gitlab/cycle_analytics/production_stage.rb
index 0fa8a65cb99..6fd7214dce7 100644
--- a/lib/gitlab/cycle_analytics/production_stage.rb
+++ b/lib/gitlab/cycle_analytics/production_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class ProductionStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/review_event_fetcher.rb b/lib/gitlab/cycle_analytics/review_event_fetcher.rb
index dada819a2a8..de100295281 100644
--- a/lib/gitlab/cycle_analytics/review_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/review_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class ReviewEventFetcher < BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/review_stage.rb b/lib/gitlab/cycle_analytics/review_stage.rb
index cfbbdc43fd9..294b656bc55 100644
--- a/lib/gitlab/cycle_analytics/review_stage.rb
+++ b/lib/gitlab/cycle_analytics/review_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class ReviewStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/stage.rb b/lib/gitlab/cycle_analytics/stage.rb
index 28e0455df59..1bd40a7aa18 100644
--- a/lib/gitlab/cycle_analytics/stage.rb
+++ b/lib/gitlab/cycle_analytics/stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module Stage
diff --git a/lib/gitlab/cycle_analytics/stage_summary.rb b/lib/gitlab/cycle_analytics/stage_summary.rb
index fc77bd86097..5198dd5b4eb 100644
--- a/lib/gitlab/cycle_analytics/stage_summary.rb
+++ b/lib/gitlab/cycle_analytics/stage_summary.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class StageSummary
diff --git a/lib/gitlab/cycle_analytics/staging_event_fetcher.rb b/lib/gitlab/cycle_analytics/staging_event_fetcher.rb
index 2f014153ca5..70ce82383b3 100644
--- a/lib/gitlab/cycle_analytics/staging_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/staging_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class StagingEventFetcher < BaseEventFetcher
diff --git a/lib/gitlab/cycle_analytics/staging_stage.rb b/lib/gitlab/cycle_analytics/staging_stage.rb
index d5684bb9201..dbc2414ff66 100644
--- a/lib/gitlab/cycle_analytics/staging_stage.rb
+++ b/lib/gitlab/cycle_analytics/staging_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class StagingStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/summary/base.rb b/lib/gitlab/cycle_analytics/summary/base.rb
index a917ddccac7..709221c648e 100644
--- a/lib/gitlab/cycle_analytics/summary/base.rb
+++ b/lib/gitlab/cycle_analytics/summary/base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module Summary
diff --git a/lib/gitlab/cycle_analytics/summary/commit.rb b/lib/gitlab/cycle_analytics/summary/commit.rb
index 550c1755a71..f0019b26fa2 100644
--- a/lib/gitlab/cycle_analytics/summary/commit.rb
+++ b/lib/gitlab/cycle_analytics/summary/commit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module Summary
diff --git a/lib/gitlab/cycle_analytics/summary/deploy.rb b/lib/gitlab/cycle_analytics/summary/deploy.rb
index 099d798aac6..3b56dc2a7bc 100644
--- a/lib/gitlab/cycle_analytics/summary/deploy.rb
+++ b/lib/gitlab/cycle_analytics/summary/deploy.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module Summary
diff --git a/lib/gitlab/cycle_analytics/summary/issue.rb b/lib/gitlab/cycle_analytics/summary/issue.rb
index 9bbf7a2685f..51695c86192 100644
--- a/lib/gitlab/cycle_analytics/summary/issue.rb
+++ b/lib/gitlab/cycle_analytics/summary/issue.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     module Summary
diff --git a/lib/gitlab/cycle_analytics/test_event_fetcher.rb b/lib/gitlab/cycle_analytics/test_event_fetcher.rb
index a2589c6601a..4d5ea5b7c34 100644
--- a/lib/gitlab/cycle_analytics/test_event_fetcher.rb
+++ b/lib/gitlab/cycle_analytics/test_event_fetcher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class TestEventFetcher < StagingEventFetcher
diff --git a/lib/gitlab/cycle_analytics/test_stage.rb b/lib/gitlab/cycle_analytics/test_stage.rb
index 0e9d235ca79..c31b664148b 100644
--- a/lib/gitlab/cycle_analytics/test_stage.rb
+++ b/lib/gitlab/cycle_analytics/test_stage.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class TestStage < BaseStage
diff --git a/lib/gitlab/cycle_analytics/updater.rb b/lib/gitlab/cycle_analytics/updater.rb
index 953268ebd46..c642809a792 100644
--- a/lib/gitlab/cycle_analytics/updater.rb
+++ b/lib/gitlab/cycle_analytics/updater.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class Updater
diff --git a/lib/gitlab/cycle_analytics/usage_data.rb b/lib/gitlab/cycle_analytics/usage_data.rb
index 5122e3417ca..913ee373f54 100644
--- a/lib/gitlab/cycle_analytics/usage_data.rb
+++ b/lib/gitlab/cycle_analytics/usage_data.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module CycleAnalytics
     class UsageData
diff --git a/lib/gitlab/data_builder/build.rb b/lib/gitlab/data_builder/build.rb
index 0b71b31a476..3407380127e 100644
--- a/lib/gitlab/data_builder/build.rb
+++ b/lib/gitlab/data_builder/build.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module Build
diff --git a/lib/gitlab/data_builder/note.rb b/lib/gitlab/data_builder/note.rb
index f573368e572..65601dcdf31 100644
--- a/lib/gitlab/data_builder/note.rb
+++ b/lib/gitlab/data_builder/note.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module Note
diff --git a/lib/gitlab/data_builder/pipeline.rb b/lib/gitlab/data_builder/pipeline.rb
index f382992cb0a..76c8b4ec5c2 100644
--- a/lib/gitlab/data_builder/pipeline.rb
+++ b/lib/gitlab/data_builder/pipeline.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module Pipeline
diff --git a/lib/gitlab/data_builder/push.rb b/lib/gitlab/data_builder/push.rb
index b498f113859..9bf2f9291a8 100644
--- a/lib/gitlab/data_builder/push.rb
+++ b/lib/gitlab/data_builder/push.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module Push
diff --git a/lib/gitlab/data_builder/repository.rb b/lib/gitlab/data_builder/repository.rb
index c9c13ec6487..0e627fd623e 100644
--- a/lib/gitlab/data_builder/repository.rb
+++ b/lib/gitlab/data_builder/repository.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module Repository
diff --git a/lib/gitlab/data_builder/wiki_page.rb b/lib/gitlab/data_builder/wiki_page.rb
index 226974b698c..9368446fa59 100644
--- a/lib/gitlab/data_builder/wiki_page.rb
+++ b/lib/gitlab/data_builder/wiki_page.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DataBuilder
     module WikiPage
diff --git a/lib/gitlab/database/arel_methods.rb b/lib/gitlab/database/arel_methods.rb
index d7e3ce08b32..991e4152dcb 100644
--- a/lib/gitlab/database/arel_methods.rb
+++ b/lib/gitlab/database/arel_methods.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module ArelMethods
diff --git a/lib/gitlab/database/count.rb b/lib/gitlab/database/count.rb
index 5f549ed2b3c..ea6529e2dc4 100644
--- a/lib/gitlab/database/count.rb
+++ b/lib/gitlab/database/count.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # For large tables, PostgreSQL can take a long time to count rows due to MVCC.
 # We can optimize this by using the reltuples count as described in https://wiki.postgresql.org/wiki/Slow_Counting.
 module Gitlab
diff --git a/lib/gitlab/database/date_time.rb b/lib/gitlab/database/date_time.rb
index 25e56998038..79d2caff151 100644
--- a/lib/gitlab/database/date_time.rb
+++ b/lib/gitlab/database/date_time.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module DateTime
diff --git a/lib/gitlab/database/grant.rb b/lib/gitlab/database/grant.rb
index 7d334a79009..862ab96c887 100644
--- a/lib/gitlab/database/grant.rb
+++ b/lib/gitlab/database/grant.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     # Model that can be used for querying permissions of a SQL user.
diff --git a/lib/gitlab/database/median.rb b/lib/gitlab/database/median.rb
index f64e3d53138..0da5119a3ed 100644
--- a/lib/gitlab/database/median.rb
+++ b/lib/gitlab/database/median.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # https://www.periscopedata.com/blog/medians-in-sql.html
 module Gitlab
   module Database
diff --git a/lib/gitlab/database/migration_helpers.rb b/lib/gitlab/database/migration_helpers.rb
index f98d6dbd46f..134d1e7a724 100644
--- a/lib/gitlab/database/migration_helpers.rb
+++ b/lib/gitlab/database/migration_helpers.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module MigrationHelpers
diff --git a/lib/gitlab/database/multi_threaded_migration.rb b/lib/gitlab/database/multi_threaded_migration.rb
index 7ae5a4c17c8..1d39a3d0b57 100644
--- a/lib/gitlab/database/multi_threaded_migration.rb
+++ b/lib/gitlab/database/multi_threaded_migration.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module MultiThreadedMigration
diff --git a/lib/gitlab/database/read_only_relation.rb b/lib/gitlab/database/read_only_relation.rb
index 4571ad122ce..2362208e5dd 100644
--- a/lib/gitlab/database/read_only_relation.rb
+++ b/lib/gitlab/database/read_only_relation.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     # Module that can be injected into a ActiveRecord::Relation to make it
diff --git a/lib/gitlab/database/rename_reserved_paths_migration/v1.rb b/lib/gitlab/database/rename_reserved_paths_migration/v1.rb
index f333ff22300..2314246da55 100644
--- a/lib/gitlab/database/rename_reserved_paths_migration/v1.rb
+++ b/lib/gitlab/database/rename_reserved_paths_migration/v1.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This module can be included in migrations to make it easier to rename paths
 # of `Namespace` & `Project` models certain paths would become `reserved`.
 #
diff --git a/lib/gitlab/database/rename_reserved_paths_migration/v1/migration_classes.rb b/lib/gitlab/database/rename_reserved_paths_migration/v1/migration_classes.rb
index 26ae6966746..f1dc3ed74fe 100644
--- a/lib/gitlab/database/rename_reserved_paths_migration/v1/migration_classes.rb
+++ b/lib/gitlab/database/rename_reserved_paths_migration/v1/migration_classes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module RenameReservedPathsMigration
diff --git a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb
index 14de28a1d08..a5b42bbfdd9 100644
--- a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb
+++ b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module RenameReservedPathsMigration
diff --git a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_namespaces.rb b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_namespaces.rb
index 73971af6a74..6bbad707f0f 100644
--- a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_namespaces.rb
+++ b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_namespaces.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module RenameReservedPathsMigration
diff --git a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_projects.rb b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_projects.rb
index 827aeb12a02..580be9fe267 100644
--- a/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_projects.rb
+++ b/lib/gitlab/database/rename_reserved_paths_migration/v1/rename_projects.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     module RenameReservedPathsMigration
diff --git a/lib/gitlab/database/sha_attribute.rb b/lib/gitlab/database/sha_attribute.rb
index b2d8ee81977..6516d6e648d 100644
--- a/lib/gitlab/database/sha_attribute.rb
+++ b/lib/gitlab/database/sha_attribute.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Database
     BINARY_TYPE =
diff --git a/lib/gitlab/dependency_linker/base_linker.rb b/lib/gitlab/dependency_linker/base_linker.rb
index d2360583741..ac2efe598b4 100644
--- a/lib/gitlab/dependency_linker/base_linker.rb
+++ b/lib/gitlab/dependency_linker/base_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class BaseLinker
diff --git a/lib/gitlab/dependency_linker/cartfile_linker.rb b/lib/gitlab/dependency_linker/cartfile_linker.rb
index 4f69f2c4ab2..0e33f0956dd 100644
--- a/lib/gitlab/dependency_linker/cartfile_linker.rb
+++ b/lib/gitlab/dependency_linker/cartfile_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class CartfileLinker < MethodLinker
diff --git a/lib/gitlab/dependency_linker/cocoapods.rb b/lib/gitlab/dependency_linker/cocoapods.rb
index 2fbde7da1b4..38eabe303de 100644
--- a/lib/gitlab/dependency_linker/cocoapods.rb
+++ b/lib/gitlab/dependency_linker/cocoapods.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     module Cocoapods
diff --git a/lib/gitlab/dependency_linker/composer_json_linker.rb b/lib/gitlab/dependency_linker/composer_json_linker.rb
index cfd4ec15125..22d2bead891 100644
--- a/lib/gitlab/dependency_linker/composer_json_linker.rb
+++ b/lib/gitlab/dependency_linker/composer_json_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class ComposerJsonLinker < PackageJsonLinker
diff --git a/lib/gitlab/dependency_linker/gemfile_linker.rb b/lib/gitlab/dependency_linker/gemfile_linker.rb
index bfea836bcb2..8ab219c4962 100644
--- a/lib/gitlab/dependency_linker/gemfile_linker.rb
+++ b/lib/gitlab/dependency_linker/gemfile_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class GemfileLinker < MethodLinker
diff --git a/lib/gitlab/dependency_linker/gemspec_linker.rb b/lib/gitlab/dependency_linker/gemspec_linker.rb
index f1783ee2ab4..b924ea86d89 100644
--- a/lib/gitlab/dependency_linker/gemspec_linker.rb
+++ b/lib/gitlab/dependency_linker/gemspec_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class GemspecLinker < MethodLinker
diff --git a/lib/gitlab/dependency_linker/godeps_json_linker.rb b/lib/gitlab/dependency_linker/godeps_json_linker.rb
index fe091baee6d..d24c137793e 100644
--- a/lib/gitlab/dependency_linker/godeps_json_linker.rb
+++ b/lib/gitlab/dependency_linker/godeps_json_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class GodepsJsonLinker < JsonLinker
diff --git a/lib/gitlab/dependency_linker/json_linker.rb b/lib/gitlab/dependency_linker/json_linker.rb
index a8ef25233d8..298d214df61 100644
--- a/lib/gitlab/dependency_linker/json_linker.rb
+++ b/lib/gitlab/dependency_linker/json_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class JsonLinker < BaseLinker
diff --git a/lib/gitlab/dependency_linker/method_linker.rb b/lib/gitlab/dependency_linker/method_linker.rb
index 0ffa2a83c93..d4d85bb3390 100644
--- a/lib/gitlab/dependency_linker/method_linker.rb
+++ b/lib/gitlab/dependency_linker/method_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class MethodLinker < BaseLinker
diff --git a/lib/gitlab/dependency_linker/package_json_linker.rb b/lib/gitlab/dependency_linker/package_json_linker.rb
index 330c95f0880..578e25f806a 100644
--- a/lib/gitlab/dependency_linker/package_json_linker.rb
+++ b/lib/gitlab/dependency_linker/package_json_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class PackageJsonLinker < JsonLinker
diff --git a/lib/gitlab/dependency_linker/podfile_linker.rb b/lib/gitlab/dependency_linker/podfile_linker.rb
index 60ad166ea17..def9b04cca9 100644
--- a/lib/gitlab/dependency_linker/podfile_linker.rb
+++ b/lib/gitlab/dependency_linker/podfile_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class PodfileLinker < GemfileLinker
diff --git a/lib/gitlab/dependency_linker/podspec_json_linker.rb b/lib/gitlab/dependency_linker/podspec_json_linker.rb
index d82237ed3f1..1a2493e7cc0 100644
--- a/lib/gitlab/dependency_linker/podspec_json_linker.rb
+++ b/lib/gitlab/dependency_linker/podspec_json_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class PodspecJsonLinker < JsonLinker
diff --git a/lib/gitlab/dependency_linker/podspec_linker.rb b/lib/gitlab/dependency_linker/podspec_linker.rb
index 924e55e9820..6b1758c5a43 100644
--- a/lib/gitlab/dependency_linker/podspec_linker.rb
+++ b/lib/gitlab/dependency_linker/podspec_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class PodspecLinker < MethodLinker
diff --git a/lib/gitlab/dependency_linker/requirements_txt_linker.rb b/lib/gitlab/dependency_linker/requirements_txt_linker.rb
index 9c9620bc36a..f630c13b760 100644
--- a/lib/gitlab/dependency_linker/requirements_txt_linker.rb
+++ b/lib/gitlab/dependency_linker/requirements_txt_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module DependencyLinker
     class RequirementsTxtLinker < BaseLinker
diff --git a/lib/gitlab/diff/diff_refs.rb b/lib/gitlab/diff/diff_refs.rb
index 81df47964be..d4823f60826 100644
--- a/lib/gitlab/diff/diff_refs.rb
+++ b/lib/gitlab/diff/diff_refs.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class DiffRefs
diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index fb117baca9e..f3bd8b69869 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class File
diff --git a/lib/gitlab/diff/file_collection/base.rb b/lib/gitlab/diff/file_collection/base.rb
index 2ad6fe8449d..10df037a0dd 100644
--- a/lib/gitlab/diff/file_collection/base.rb
+++ b/lib/gitlab/diff/file_collection/base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module FileCollection
diff --git a/lib/gitlab/diff/file_collection/commit.rb b/lib/gitlab/diff/file_collection/commit.rb
index 4dc297ec036..7b1d6171e82 100644
--- a/lib/gitlab/diff/file_collection/commit.rb
+++ b/lib/gitlab/diff/file_collection/commit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module FileCollection
diff --git a/lib/gitlab/diff/file_collection/compare.rb b/lib/gitlab/diff/file_collection/compare.rb
index 20d8f891cc3..586c5cf87af 100644
--- a/lib/gitlab/diff/file_collection/compare.rb
+++ b/lib/gitlab/diff/file_collection/compare.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module FileCollection
diff --git a/lib/gitlab/diff/file_collection/merge_request_diff.rb b/lib/gitlab/diff/file_collection/merge_request_diff.rb
index 0dd073a3a8e..e29bf75f341 100644
--- a/lib/gitlab/diff/file_collection/merge_request_diff.rb
+++ b/lib/gitlab/diff/file_collection/merge_request_diff.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module FileCollection
diff --git a/lib/gitlab/diff/formatters/base_formatter.rb b/lib/gitlab/diff/formatters/base_formatter.rb
index 5e923b9e602..9704aed82c1 100644
--- a/lib/gitlab/diff/formatters/base_formatter.rb
+++ b/lib/gitlab/diff/formatters/base_formatter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module Formatters
diff --git a/lib/gitlab/diff/formatters/image_formatter.rb b/lib/gitlab/diff/formatters/image_formatter.rb
index ccd0d309972..5bc9f0c337f 100644
--- a/lib/gitlab/diff/formatters/image_formatter.rb
+++ b/lib/gitlab/diff/formatters/image_formatter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module Formatters
diff --git a/lib/gitlab/diff/formatters/text_formatter.rb b/lib/gitlab/diff/formatters/text_formatter.rb
index 01c7e9f51ab..f6e247ef665 100644
--- a/lib/gitlab/diff/formatters/text_formatter.rb
+++ b/lib/gitlab/diff/formatters/text_formatter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     module Formatters
diff --git a/lib/gitlab/diff/highlight.rb b/lib/gitlab/diff/highlight.rb
index 1d833183ec3..d2484217ab9 100644
--- a/lib/gitlab/diff/highlight.rb
+++ b/lib/gitlab/diff/highlight.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class Highlight
diff --git a/lib/gitlab/diff/image_point.rb b/lib/gitlab/diff/image_point.rb
index 1f157354ea4..a3ce032f8e2 100644
--- a/lib/gitlab/diff/image_point.rb
+++ b/lib/gitlab/diff/image_point.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class ImagePoint
diff --git a/lib/gitlab/diff/inline_diff.rb b/lib/gitlab/diff/inline_diff.rb
index 72d5ec547da..5815d1bae4a 100644
--- a/lib/gitlab/diff/inline_diff.rb
+++ b/lib/gitlab/diff/inline_diff.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class InlineDiff
@@ -71,7 +73,7 @@ module Gitlab
         def find_changed_line_pairs(lines)
           # Prefixes of all diff lines, indicating their types
           # For example: `" - +  -+  ---+++ --+  -++"`
-          line_prefixes = lines.each_with_object("") { |line, s| s << (line[0] || ' ') }.gsub(/[^ +-]/, ' ')
+          line_prefixes = lines.each_with_object(+"") { |line, s| s << (line[0] || ' ') }.gsub(/[^ +-]/, ' ')
 
           changed_line_pairs = []
           line_prefixes.scan(LINE_PAIRS_PATTERN) do
diff --git a/lib/gitlab/diff/inline_diff_markdown_marker.rb b/lib/gitlab/diff/inline_diff_markdown_marker.rb
index c2a2eb15931..3c536c43a9e 100644
--- a/lib/gitlab/diff/inline_diff_markdown_marker.rb
+++ b/lib/gitlab/diff/inline_diff_markdown_marker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class InlineDiffMarkdownMarker < Gitlab::StringRangeMarker
diff --git a/lib/gitlab/diff/inline_diff_marker.rb b/lib/gitlab/diff/inline_diff_marker.rb
index 81e91ea0ab7..1bbde1ffd2a 100644
--- a/lib/gitlab/diff/inline_diff_marker.rb
+++ b/lib/gitlab/diff/inline_diff_marker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class InlineDiffMarker < Gitlab::StringRangeMarker
diff --git a/lib/gitlab/diff/line.rb b/lib/gitlab/diff/line.rb
index 5b67cd46c48..74fed7c4b1b 100644
--- a/lib/gitlab/diff/line.rb
+++ b/lib/gitlab/diff/line.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class Line
diff --git a/lib/gitlab/diff/line_mapper.rb b/lib/gitlab/diff/line_mapper.rb
index cf71d47df8e..fba7bff4781 100644
--- a/lib/gitlab/diff/line_mapper.rb
+++ b/lib/gitlab/diff/line_mapper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # When provided a diff for a specific file, maps old line numbers to new line
 # numbers and back, to find out where a specific line in a file was moved by the
 # changes.
diff --git a/lib/gitlab/diff/parallel_diff.rb b/lib/gitlab/diff/parallel_diff.rb
index 0cb26fa45c8..77b65fea726 100644
--- a/lib/gitlab/diff/parallel_diff.rb
+++ b/lib/gitlab/diff/parallel_diff.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class ParallelDiff
diff --git a/lib/gitlab/diff/parser.rb b/lib/gitlab/diff/parser.rb
index 7ae7ed286ed..4a47e4b80b6 100644
--- a/lib/gitlab/diff/parser.rb
+++ b/lib/gitlab/diff/parser.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Diff
     class Parser
diff --git a/lib/gitlab/diff/position.rb b/lib/gitlab/diff/position.rb
index f967494199e..9c4d9377593 100644
--- a/lib/gitlab/diff/position.rb
+++ b/lib/gitlab/diff/position.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Defines a specific location, identified by paths line numbers and image coordinates,
 # within a specific diff, identified by start, head and base commit ids.
 module Gitlab
diff --git a/lib/gitlab/diff/position_tracer.rb b/lib/gitlab/diff/position_tracer.rb
index 8457e0c4cb6..af3df820422 100644
--- a/lib/gitlab/diff/position_tracer.rb
+++ b/lib/gitlab/diff/position_tracer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Finds the diff position in the new diff that corresponds to the same location
 # specified by the provided position in the old diff.
 module Gitlab
diff --git a/lib/gitlab/downtime_check/message.rb b/lib/gitlab/downtime_check/message.rb
index 543e62794c5..ec38bd769a3 100644
--- a/lib/gitlab/downtime_check/message.rb
+++ b/lib/gitlab/downtime_check/message.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   class DowntimeCheck
     class Message
@@ -18,13 +20,13 @@ module Gitlab
       def to_s
         label = offline ? OFFLINE : ONLINE
 
-        message = "[#{label}]: #{path}"
+        message = ["[#{label}]: #{path}"]
 
         if reason?
-          message += ":\n\n#{reason}\n\n"
+          message << ":\n\n#{reason}\n\n"
         end
 
-        message
+        message.join
       end
 
       def reason?
diff --git a/lib/gitlab/email/attachment_uploader.rb b/lib/gitlab/email/attachment_uploader.rb
index 83440ae227d..a826519b2dd 100644
--- a/lib/gitlab/email/attachment_uploader.rb
+++ b/lib/gitlab/email/attachment_uploader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     class AttachmentUploader
diff --git a/lib/gitlab/email/hook/additional_headers_interceptor.rb b/lib/gitlab/email/hook/additional_headers_interceptor.rb
index 064cb5e659a..aa2ef76069b 100644
--- a/lib/gitlab/email/hook/additional_headers_interceptor.rb
+++ b/lib/gitlab/email/hook/additional_headers_interceptor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Hook
diff --git a/lib/gitlab/email/hook/delivery_metrics_observer.rb b/lib/gitlab/email/hook/delivery_metrics_observer.rb
index 1c2985f6045..c7af485fcc5 100644
--- a/lib/gitlab/email/hook/delivery_metrics_observer.rb
+++ b/lib/gitlab/email/hook/delivery_metrics_observer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Hook
diff --git a/lib/gitlab/email/hook/disable_email_interceptor.rb b/lib/gitlab/email/hook/disable_email_interceptor.rb
index 7bb8b53f0c8..6b6b1d85109 100644
--- a/lib/gitlab/email/hook/disable_email_interceptor.rb
+++ b/lib/gitlab/email/hook/disable_email_interceptor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Hook
diff --git a/lib/gitlab/email/hook/email_template_interceptor.rb b/lib/gitlab/email/hook/email_template_interceptor.rb
index be0c4dd862e..13f8db2051d 100644
--- a/lib/gitlab/email/hook/email_template_interceptor.rb
+++ b/lib/gitlab/email/hook/email_template_interceptor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Hook
diff --git a/lib/gitlab/email/html_parser.rb b/lib/gitlab/email/html_parser.rb
index 50559a48973..77f299bcade 100644
--- a/lib/gitlab/email/html_parser.rb
+++ b/lib/gitlab/email/html_parser.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     class HTMLParser
diff --git a/lib/gitlab/email/message/repository_push.rb b/lib/gitlab/email/message/repository_push.rb
index cd9d3a6483f..ec412e7a8b1 100644
--- a/lib/gitlab/email/message/repository_push.rb
+++ b/lib/gitlab/email/message/repository_push.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Message
@@ -116,7 +118,7 @@ module Gitlab
         end
 
         def subject
-          subject_text = '[Git]'
+          subject_text = ['[Git]']
           subject_text << "[#{project.full_path}]"
           subject_text << "[#{ref_name}]" if @action == :push
           subject_text << ' '
@@ -134,6 +136,8 @@ module Gitlab
             subject_action[0] = subject_action[0].capitalize
             subject_text << "#{subject_action} #{ref_type} #{ref_name}"
           end
+
+          subject_text.join
         end
       end
     end
diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index d8c594ad0e7..ec4a936e073 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_dependency 'gitlab/email/handler'
 
 # Inspired in great part by Discourse's Email::Receiver
diff --git a/lib/gitlab/email/reply_parser.rb b/lib/gitlab/email/reply_parser.rb
index ae6b84607d6..2743f011ca6 100644
--- a/lib/gitlab/email/reply_parser.rb
+++ b/lib/gitlab/email/reply_parser.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Inspired in great part by Discourse's Email::Receiver
 module Gitlab
   module Email
diff --git a/lib/gitlab/etag_caching/middleware.rb b/lib/gitlab/etag_caching/middleware.rb
index d5d35dbd97f..0341f930b9c 100644
--- a/lib/gitlab/etag_caching/middleware.rb
+++ b/lib/gitlab/etag_caching/middleware.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module EtagCaching
     class Middleware
diff --git a/lib/gitlab/etag_caching/router.rb b/lib/gitlab/etag_caching/router.rb
index 75167a6b088..08e30214b46 100644
--- a/lib/gitlab/etag_caching/router.rb
+++ b/lib/gitlab/etag_caching/router.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module EtagCaching
     class Router
diff --git a/lib/gitlab/etag_caching/store.rb b/lib/gitlab/etag_caching/store.rb
index 21172ff8d93..2395e7be026 100644
--- a/lib/gitlab/etag_caching/store.rb
+++ b/lib/gitlab/etag_caching/store.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module EtagCaching
     class Store