rails/rails#32808 — demonstrate that mail is not eager loaded correctly during application initialization

application.rb

gem "railties", "5.2.0"
gem "actionmailer", "5.2.0"

require "rails/application"
require "action_mailer/railtie"

class Application < Rails::Application
  config.eager_load = true
end

$LOADED_FEATURES.size
# => 440

Application.initialize!

$LOADED_FEATURES.size
# => 887

Mail.autoload? :ContentTypeElement
# => "mail/elements/content_type_element" # i.e. true

$LOADED_FEATURES.grep /content_type_element/
# => [] # empty, so mail/elements/content_type_element is not loaded

Mail::ContentTypeElement

Mail.autoload? :ContentTypeElement
# => nil # i.e. false

$LOADED_FEATURES.size
# => 901

$LOADED_FEATURES.grep /content_type_element/
# => [".../mail-2.7.0/lib/mail/elements/content_type_element.rb"]

Mail.eager_autoload!

$LOADED_FEATURES.size
# => 921