diff --git a/changelogs/unreleased/enable-frozen-string-lib-gitlab.yml b/changelogs/unreleased/enable-frozen-string-lib-gitlab.yml
new file mode 100644
index 00000000000..4a216c46d38
--- /dev/null
+++ b/changelogs/unreleased/enable-frozen-string-lib-gitlab.yml
@@ -0,0 +1,5 @@
+---
+title: Enable some frozen string in lib/gitlab
+merge_request:
+author: gfyoung
+type: performance
diff --git a/lib/gitlab/auth/activity.rb b/lib/gitlab/auth/activity.rb
index 761f0819c60..558628b5422 100644
--- a/lib/gitlab/auth/activity.rb
+++ b/lib/gitlab/auth/activity.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     ##
diff --git a/lib/gitlab/auth/database/authentication.rb b/lib/gitlab/auth/database/authentication.rb
index 1234ace0334..c0dc2b0875f 100644
--- a/lib/gitlab/auth/database/authentication.rb
+++ b/lib/gitlab/auth/database/authentication.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # These calls help to authenticate to OAuth provider by providing username and password
 #
 
diff --git a/lib/gitlab/auth/ip_rate_limiter.rb b/lib/gitlab/auth/ip_rate_limiter.rb
index e6173d45af3..81e616fa20a 100644
--- a/lib/gitlab/auth/ip_rate_limiter.rb
+++ b/lib/gitlab/auth/ip_rate_limiter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     class IpRateLimiter
diff --git a/lib/gitlab/auth/ldap/access.rb b/lib/gitlab/auth/ldap/access.rb
index f323d2e0f7a..c875bba4bcb 100644
--- a/lib/gitlab/auth/ldap/access.rb
+++ b/lib/gitlab/auth/ldap/access.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # LDAP authorization model
 #
 # * Check if we are allowed access (not blocked)
diff --git a/lib/gitlab/auth/ldap/adapter.rb b/lib/gitlab/auth/ldap/adapter.rb
index 82ff1e77e5c..42c657afe6a 100644
--- a/lib/gitlab/auth/ldap/adapter.rb
+++ b/lib/gitlab/auth/ldap/adapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module LDAP
diff --git a/lib/gitlab/auth/ldap/auth_hash.rb b/lib/gitlab/auth/ldap/auth_hash.rb
index ac5c14d374d..83fdc8a8c76 100644
--- a/lib/gitlab/auth/ldap/auth_hash.rb
+++ b/lib/gitlab/auth/ldap/auth_hash.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Class to parse and transform the info provided by omniauth
 #
 module Gitlab
diff --git a/lib/gitlab/auth/ldap/authentication.rb b/lib/gitlab/auth/ldap/authentication.rb
index 7c134fb6438..174e81dd603 100644
--- a/lib/gitlab/auth/ldap/authentication.rb
+++ b/lib/gitlab/auth/ldap/authentication.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # These calls help to authenticate to LDAP by providing username and password
 #
 # Since multiple LDAP servers are supported, it will loop through all of them
diff --git a/lib/gitlab/auth/ldap/config.rb b/lib/gitlab/auth/ldap/config.rb
index d4415eaa6dc..7ceb96f502b 100644
--- a/lib/gitlab/auth/ldap/config.rb
+++ b/lib/gitlab/auth/ldap/config.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Load a specific server configuration
 module Gitlab
   module Auth
diff --git a/lib/gitlab/auth/ldap/dn.rb b/lib/gitlab/auth/ldap/dn.rb
index 1fa5338f5a6..5df914aa367 100644
--- a/lib/gitlab/auth/ldap/dn.rb
+++ b/lib/gitlab/auth/ldap/dn.rb
@@ -1,4 +1,5 @@
 # -*- ruby encoding: utf-8 -*-
+# frozen_string_literal: true
 
 # Based on the `ruby-net-ldap` gem's `Net::LDAP::DN`
 #
diff --git a/lib/gitlab/auth/ldap/ldap_connection_error.rb b/lib/gitlab/auth/ldap/ldap_connection_error.rb
index ef0a695742b..d0e5f24d203 100644
--- a/lib/gitlab/auth/ldap/ldap_connection_error.rb
+++ b/lib/gitlab/auth/ldap/ldap_connection_error.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module LDAP
diff --git a/lib/gitlab/auth/ldap/person.rb b/lib/gitlab/auth/ldap/person.rb
index 8dfae3ee541..a0244a3cea1 100644
--- a/lib/gitlab/auth/ldap/person.rb
+++ b/lib/gitlab/auth/ldap/person.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module LDAP
diff --git a/lib/gitlab/auth/ldap/user.rb b/lib/gitlab/auth/ldap/user.rb
index 3c21ddf3241..9c71671f409 100644
--- a/lib/gitlab/auth/ldap/user.rb
+++ b/lib/gitlab/auth/ldap/user.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # LDAP extension for User model
 #
 # * Find or create user from omniauth.auth data
diff --git a/lib/gitlab/auth/o_auth/auth_hash.rb b/lib/gitlab/auth/o_auth/auth_hash.rb
index ed8fba94305..4a5f9d2839d 100644
--- a/lib/gitlab/auth/o_auth/auth_hash.rb
+++ b/lib/gitlab/auth/o_auth/auth_hash.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Class to parse and transform the info provided by omniauth
 #
 module Gitlab
diff --git a/lib/gitlab/auth/o_auth/authentication.rb b/lib/gitlab/auth/o_auth/authentication.rb
index d4e7f35c857..5f008678bd1 100644
--- a/lib/gitlab/auth/o_auth/authentication.rb
+++ b/lib/gitlab/auth/o_auth/authentication.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # These calls help to authenticate to OAuth provider by providing username and password
 #
 
diff --git a/lib/gitlab/auth/o_auth/identity_linker.rb b/lib/gitlab/auth/o_auth/identity_linker.rb
index de92d7a214d..e69c2bb54dc 100644
--- a/lib/gitlab/auth/o_auth/identity_linker.rb
+++ b/lib/gitlab/auth/o_auth/identity_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module OAuth
diff --git a/lib/gitlab/auth/o_auth/provider.rb b/lib/gitlab/auth/o_auth/provider.rb
index 26da9d09ccc..9fdf3324db3 100644
--- a/lib/gitlab/auth/o_auth/provider.rb
+++ b/lib/gitlab/auth/o_auth/provider.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module OAuth
diff --git a/lib/gitlab/auth/o_auth/session.rb b/lib/gitlab/auth/o_auth/session.rb
index 8f2b4d58552..4925b107042 100644
--- a/lib/gitlab/auth/o_auth/session.rb
+++ b/lib/gitlab/auth/o_auth/session.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # :nocov:
 module Gitlab
   module Auth
diff --git a/lib/gitlab/auth/o_auth/user.rb b/lib/gitlab/auth/o_auth/user.rb
index 2b4f6ed75e5..a4e8a41b246 100644
--- a/lib/gitlab/auth/o_auth/user.rb
+++ b/lib/gitlab/auth/o_auth/user.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # OAuth extension for User model
 #
 # * Find GitLab user based on omniauth uid and provider
diff --git a/lib/gitlab/auth/omniauth_identity_linker_base.rb b/lib/gitlab/auth/omniauth_identity_linker_base.rb
index 8ae29a02a13..253445570f2 100644
--- a/lib/gitlab/auth/omniauth_identity_linker_base.rb
+++ b/lib/gitlab/auth/omniauth_identity_linker_base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     class OmniauthIdentityLinkerBase
diff --git a/lib/gitlab/auth/request_authenticator.rb b/lib/gitlab/auth/request_authenticator.rb
index 66de52506ce..cb9f2582936 100644
--- a/lib/gitlab/auth/request_authenticator.rb
+++ b/lib/gitlab/auth/request_authenticator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Use for authentication only, in particular for Rack::Attack.
 # Does not perform authorization of scopes, etc.
 module Gitlab
diff --git a/lib/gitlab/auth/result.rb b/lib/gitlab/auth/result.rb
index 00cdc94a9ef..78fa25c5516 100644
--- a/lib/gitlab/auth/result.rb
+++ b/lib/gitlab/auth/result.rb
@@ -1,4 +1,7 @@
-module Gitlab # rubocop:disable Naming/FileName
+# rubocop:disable Naming/FileName
+# frozen_string_literal: true
+
+module Gitlab
   module Auth
     Result = Struct.new(:actor, :project, :type, :authentication_abilities) do
       def ci?(for_project)
diff --git a/lib/gitlab/auth/saml/auth_hash.rb b/lib/gitlab/auth/saml/auth_hash.rb
index 3bc5e2864df..316354fd50c 100644
--- a/lib/gitlab/auth/saml/auth_hash.rb
+++ b/lib/gitlab/auth/saml/auth_hash.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module Saml
diff --git a/lib/gitlab/auth/saml/config.rb b/lib/gitlab/auth/saml/config.rb
index 625dab7c6f4..8cb999f50d4 100644
--- a/lib/gitlab/auth/saml/config.rb
+++ b/lib/gitlab/auth/saml/config.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module Saml
diff --git a/lib/gitlab/auth/saml/identity_linker.rb b/lib/gitlab/auth/saml/identity_linker.rb
index 7e4b191d512..ae0d6dded4e 100644
--- a/lib/gitlab/auth/saml/identity_linker.rb
+++ b/lib/gitlab/auth/saml/identity_linker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     module Saml
diff --git a/lib/gitlab/auth/saml/user.rb b/lib/gitlab/auth/saml/user.rb
index 6c3b75f3eb0..ec95bc46791 100644
--- a/lib/gitlab/auth/saml/user.rb
+++ b/lib/gitlab/auth/saml/user.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # SAML extension for User model
 #
 # * Find GitLab user based on SAML uid and provider
diff --git a/lib/gitlab/auth/too_many_ips.rb b/lib/gitlab/auth/too_many_ips.rb
index ed862791551..ee4d80e6b89 100644
--- a/lib/gitlab/auth/too_many_ips.rb
+++ b/lib/gitlab/auth/too_many_ips.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     class TooManyIps < StandardError
diff --git a/lib/gitlab/auth/unique_ips_limiter.rb b/lib/gitlab/auth/unique_ips_limiter.rb
index baa1f802d8a..31dd61ae6cf 100644
--- a/lib/gitlab/auth/unique_ips_limiter.rb
+++ b/lib/gitlab/auth/unique_ips_limiter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     class UniqueIpsLimiter
diff --git a/lib/gitlab/auth/user_access_denied_reason.rb b/lib/gitlab/auth/user_access_denied_reason.rb
index 1893cb001b2..fd09fe76c02 100644
--- a/lib/gitlab/auth/user_access_denied_reason.rb
+++ b/lib/gitlab/auth/user_access_denied_reason.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     class UserAccessDeniedReason
diff --git a/lib/gitlab/auth/user_auth_finders.rb b/lib/gitlab/auth/user_auth_finders.rb
index 064cba43278..5df6db6f366 100644
--- a/lib/gitlab/auth/user_auth_finders.rb
+++ b/lib/gitlab/auth/user_auth_finders.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Auth
     AuthenticationError = Class.new(StandardError)
diff --git a/lib/gitlab/badge/base.rb b/lib/gitlab/badge/base.rb
index 909fa24fa90..fb55b9e2f1f 100644
--- a/lib/gitlab/badge/base.rb
+++ b/lib/gitlab/badge/base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     class Base
diff --git a/lib/gitlab/badge/coverage/metadata.rb b/lib/gitlab/badge/coverage/metadata.rb
index e898f5d790e..9181ba2d4b0 100644
--- a/lib/gitlab/badge/coverage/metadata.rb
+++ b/lib/gitlab/badge/coverage/metadata.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Coverage
diff --git a/lib/gitlab/badge/coverage/report.rb b/lib/gitlab/badge/coverage/report.rb
index 16fd6f01495..a7fcb6b0fca 100644
--- a/lib/gitlab/badge/coverage/report.rb
+++ b/lib/gitlab/badge/coverage/report.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Coverage
diff --git a/lib/gitlab/badge/coverage/template.rb b/lib/gitlab/badge/coverage/template.rb
index afbf9dd17e3..817dc28f84a 100644
--- a/lib/gitlab/badge/coverage/template.rb
+++ b/lib/gitlab/badge/coverage/template.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Coverage
diff --git a/lib/gitlab/badge/metadata.rb b/lib/gitlab/badge/metadata.rb
index 8ad6f3cb986..b9ae68134b0 100644
--- a/lib/gitlab/badge/metadata.rb
+++ b/lib/gitlab/badge/metadata.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     ##
diff --git a/lib/gitlab/badge/pipeline/metadata.rb b/lib/gitlab/badge/pipeline/metadata.rb
index db1e9f8cfb8..d4d789558c9 100644
--- a/lib/gitlab/badge/pipeline/metadata.rb
+++ b/lib/gitlab/badge/pipeline/metadata.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Pipeline
diff --git a/lib/gitlab/badge/pipeline/status.rb b/lib/gitlab/badge/pipeline/status.rb
index d1d9b7949f5..37e61f07e5b 100644
--- a/lib/gitlab/badge/pipeline/status.rb
+++ b/lib/gitlab/badge/pipeline/status.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Pipeline
diff --git a/lib/gitlab/badge/pipeline/template.rb b/lib/gitlab/badge/pipeline/template.rb
index e09db32262d..64c3dfcd10b 100644
--- a/lib/gitlab/badge/pipeline/template.rb
+++ b/lib/gitlab/badge/pipeline/template.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     module Pipeline
diff --git a/lib/gitlab/badge/template.rb b/lib/gitlab/badge/template.rb
index bfeb0052642..ed2ec50b197 100644
--- a/lib/gitlab/badge/template.rb
+++ b/lib/gitlab/badge/template.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Badge
     ##
diff --git a/lib/gitlab/bare_repository_import/importer.rb b/lib/gitlab/bare_repository_import/importer.rb
index 04aa6aab771..3cd327f5109 100644
--- a/lib/gitlab/bare_repository_import/importer.rb
+++ b/lib/gitlab/bare_repository_import/importer.rb
@@ -1,10 +1,15 @@
+# frozen_string_literal: true
+
 module Gitlab
   module BareRepositoryImport
     class Importer
       NoAdminError = Class.new(StandardError)
 
       def self.execute(import_path)
-        import_path << '/' unless import_path.ends_with?('/')
+        unless import_path.ends_with?('/')
+          import_path = "#{import_path}/"
+        end
+
         repos_to_import = Dir.glob(import_path + '**/*.git')
 
         unless user = User.admins.order_id_asc.first
diff --git a/lib/gitlab/bare_repository_import/repository.rb b/lib/gitlab/bare_repository_import/repository.rb
index c0c666dfb7b..b903c581aac 100644
--- a/lib/gitlab/bare_repository_import/repository.rb
+++ b/lib/gitlab/bare_repository_import/repository.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module BareRepositoryImport
     class Repository
@@ -6,9 +8,12 @@ module Gitlab
       attr_reader :group_path, :project_name, :repo_path
 
       def initialize(root_path, repo_path)
+        unless root_path.ends_with?('/')
+          root_path = "#{root_path}/"
+        end
+
         @root_path = root_path
         @repo_path = repo_path
-        @root_path << '/' unless root_path.ends_with?('/')
 
         full_path =
           if hashed? && !wiki?
diff --git a/lib/gitlab/bitbucket_import/importer.rb b/lib/gitlab/bitbucket_import/importer.rb
index a7dfccea2f6..45e550b3450 100644
--- a/lib/gitlab/bitbucket_import/importer.rb
+++ b/lib/gitlab/bitbucket_import/importer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module BitbucketImport
     class Importer
diff --git a/lib/gitlab/bitbucket_import/project_creator.rb b/lib/gitlab/bitbucket_import/project_creator.rb
index d94f70fd1fb..11070a68e02 100644
--- a/lib/gitlab/bitbucket_import/project_creator.rb
+++ b/lib/gitlab/bitbucket_import/project_creator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module BitbucketImport
     class ProjectCreator
diff --git a/lib/gitlab/bitbucket_server_import/project_creator.rb b/lib/gitlab/bitbucket_server_import/project_creator.rb
index 35e8cd7e0ab..48ca4951957 100644
--- a/lib/gitlab/bitbucket_server_import/project_creator.rb
+++ b/lib/gitlab/bitbucket_server_import/project_creator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module BitbucketServerImport
     class ProjectCreator
diff --git a/lib/gitlab/cache/ci/project_pipeline_status.rb b/lib/gitlab/cache/ci/project_pipeline_status.rb
index add048d671e..b369b9e7600 100644
--- a/lib/gitlab/cache/ci/project_pipeline_status.rb
+++ b/lib/gitlab/cache/ci/project_pipeline_status.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This class is not backed by a table in the main database.
 # It loads the latest Pipeline for the HEAD of a repository, and caches that
 # in Redis.
diff --git a/lib/gitlab/cache/request_cache.rb b/lib/gitlab/cache/request_cache.rb
index b96e161a5b6..4c658dc0b8d 100644
--- a/lib/gitlab/cache/request_cache.rb
+++ b/lib/gitlab/cache/request_cache.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Cache
     # See https://docs.gitlab.com/ee/development/utilities.html#requestcache
diff --git a/lib/gitlab/checks/change_access.rb b/lib/gitlab/checks/change_access.rb
index 7a4224e5bbe..49e7f7e1fd7 100644
--- a/lib/gitlab/checks/change_access.rb
+++ b/lib/gitlab/checks/change_access.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class ChangeAccess
diff --git a/lib/gitlab/checks/commit_check.rb b/lib/gitlab/checks/commit_check.rb
index 7e0c34aada3..6dd74e8fb74 100644
--- a/lib/gitlab/checks/commit_check.rb
+++ b/lib/gitlab/checks/commit_check.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class CommitCheck
diff --git a/lib/gitlab/checks/force_push.rb b/lib/gitlab/checks/force_push.rb
index 87af4a90572..263972923ed 100644
--- a/lib/gitlab/checks/force_push.rb
+++ b/lib/gitlab/checks/force_push.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class ForcePush
diff --git a/lib/gitlab/checks/lfs_integrity.rb b/lib/gitlab/checks/lfs_integrity.rb
index 3f7adecc621..fa3dc1808df 100644
--- a/lib/gitlab/checks/lfs_integrity.rb
+++ b/lib/gitlab/checks/lfs_integrity.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class LfsIntegrity
diff --git a/lib/gitlab/checks/matching_merge_request.rb b/lib/gitlab/checks/matching_merge_request.rb
index 86f4aaeb4d3..71361b12d07 100644
--- a/lib/gitlab/checks/matching_merge_request.rb
+++ b/lib/gitlab/checks/matching_merge_request.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class MatchingMergeRequest
diff --git a/lib/gitlab/checks/post_push_message.rb b/lib/gitlab/checks/post_push_message.rb
index 473c0385b34..492dbb5a596 100644
--- a/lib/gitlab/checks/post_push_message.rb
+++ b/lib/gitlab/checks/post_push_message.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class PostPushMessage
diff --git a/lib/gitlab/checks/project_created.rb b/lib/gitlab/checks/project_created.rb
index cec270d6a58..0058a402a62 100644
--- a/lib/gitlab/checks/project_created.rb
+++ b/lib/gitlab/checks/project_created.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class ProjectCreated < PostPushMessage
diff --git a/lib/gitlab/checks/project_moved.rb b/lib/gitlab/checks/project_moved.rb
index 3a197078d08..cb3b7acaaad 100644
--- a/lib/gitlab/checks/project_moved.rb
+++ b/lib/gitlab/checks/project_moved.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Gitlab
   module Checks
     class ProjectMoved < PostPushMessage