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.

14 files changed, 28 insertions, 0 deletions

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 =