Enable frozen in app/mailers/**/*.rb

app/mailers/abuse_report_mailer.rb

+# frozen_string_literal: true
+
 class AbuseReportMailer < BaseMailer
   def notify(abuse_report_id)
     return unless deliverable?

app/mailers/base_mailer.rb

+# frozen_string_literal: true
+
 class BaseMailer < ActionMailer::Base
   around_action :render_with_default_locale
 

app/mailers/devise_mailer.rb

+# frozen_string_literal: true
+
 class DeviseMailer < Devise::Mailer
   default from: "#{Gitlab.config.gitlab.email_display_name} <#{Gitlab.config.gitlab.email_from}>"
   default reply_to: Gitlab.config.gitlab.email_reply_to
@@ -9,8 +11,9 @@ class DeviseMailer < Devise::Mailer
   protected
 
   def subject_for(key)
-    subject = super
-    subject << " | #{Gitlab.config.gitlab.email_subject_suffix}" if Gitlab.config.gitlab.email_subject_suffix.present?
-    subject
+    subject = [super]
+    subject << Gitlab.config.gitlab.email_subject_suffix if Gitlab.config.gitlab.email_subject_suffix.present?
+
+    subject.join(' | ')
   end
 end

app/mailers/email_rejection_mailer.rb

+# frozen_string_literal: true
+
 class EmailRejectionMailer < BaseMailer
   def rejection(reason, original_raw, can_retry = false)
     @reason = reason

app/mailers/emails/issues.rb

+# frozen_string_literal: true
+
 module Emails
   module Issues
     def new_issue_email(recipient_id, issue_id, reason = nil)

app/mailers/emails/members.rb

+# frozen_string_literal: true
+
 module Emails
   module Members
     extend ActiveSupport::Concern

app/mailers/emails/merge_requests.rb

+# frozen_string_literal: true
+
 module Emails
   module MergeRequests
     def new_merge_request_email(recipient_id, merge_request_id, reason = nil)

app/mailers/emails/notes.rb

+# frozen_string_literal: true
+
 module Emails
   module Notes
     def note_commit_email(recipient_id, note_id)

app/mailers/emails/pages_domains.rb

+# frozen_string_literal: true
+
 module Emails
   module PagesDomains
     def pages_domain_enabled_email(domain, recipient)

app/mailers/emails/pipelines.rb

+# frozen_string_literal: true
+
 module Emails
   module Pipelines
     def pipeline_success_email(pipeline, recipients)
@@ -39,10 +41,10 @@ module Emails
     end
 
     def pipeline_subject(status)
-      commit = @pipeline.short_sha
-      commit << " in #{@merge_request.to_reference}" if @merge_request
+      commit = [@pipeline.short_sha]
+      commit << "in #{@merge_request.to_reference}" if @merge_request
 
-      subject("Pipeline ##{@pipeline.id} has #{status} for #{@pipeline.ref}", commit)
+      subject("Pipeline ##{@pipeline.id} has #{status} for #{@pipeline.ref}", commit.join(' '))
     end
   end
 end

app/mailers/emails/profile.rb

+# frozen_string_literal: true
+
 module Emails
   module Profile
     def new_user_email(user_id, token = nil)

app/mailers/emails/projects.rb

+# frozen_string_literal: true
+
 module Emails
   module Projects
     def project_was_moved_email(project_id, user_id, old_path_with_namespace)

app/mailers/notify.rb

+# frozen_string_literal: true
+
 class Notify < BaseMailer
   include ActionDispatch::Routing::PolymorphicRoutes
   include GitlabRoutingHelper
@@ -92,12 +94,14 @@ class Notify < BaseMailer
   #   >> subject('Lorem ipsum', 'Dolor sit amet')
   #   => "Lorem ipsum | Dolor sit amet"
   def subject(*extra)
-    subject = ""
-    subject << "#{@project.name} | " if @project
-    subject << "#{@group.name} | " if @group
-    subject << extra.join(' | ') if extra.present?
-    subject << " | #{Gitlab.config.gitlab.email_subject_suffix}" if Gitlab.config.gitlab.email_subject_suffix.present?
-    subject
+    subject = []
+
+    subject << @project.name if @project
+    subject << @group.name if @group
+    subject.concat(extra) if extra.present?
+    subject << Gitlab.config.gitlab.email_subject_suffix if Gitlab.config.gitlab.email_subject_suffix.present?
+
+    subject.join(' | ')
   end
 
   # Return a string suitable for inclusion in the 'Message-Id' mail header.

app/mailers/previews/devise_mailer_preview.rb

+# frozen_string_literal: true
+
 class DeviseMailerPreview < ActionMailer::Preview
   def confirmation_instructions_for_signup
     DeviseMailer.confirmation_instructions(unsaved_user, 'faketoken', {})

app/mailers/previews/email_rejection_mailer_preview.rb

+# frozen_string_literal: true
+
 class EmailRejectionMailerPreview < ActionMailer::Preview
   def rejection
     EmailRejectionMailer.rejection("some rejection reason", "From: someone@example.com\nraw email here").message

app/mailers/previews/notify_preview.rb

+# frozen_string_literal: true
+
 class NotifyPreview < ActionMailer::Preview
   def note_merge_request_email_for_individual_note
     note_email(:note_merge_request_email) do

app/mailers/previews/repository_check_mailer_preview.rb

+# frozen_string_literal: true
+
 class RepositoryCheckMailerPreview < ActionMailer::Preview
   def notify
     RepositoryCheckMailer.notify(3).message

app/mailers/repository_check_mailer.rb

+# frozen_string_literal: true
+
 class RepositoryCheckMailer < BaseMailer
   def notify(failed_count)
     @message =

changelogs/unreleased/frozen-string-enable-app-mailers.yml

+---
+title: Enable frozen in app/mailers/**/*.rb
+merge_request: 21147
+author: gfyoung
+type: performance