Decouple config.asset_host assignment from rails:

[Edouard-chin]

Decouple config.asset_host assignment from rails:

• There is two way to set the asset_host in rails: config.action_controller.asset_host= and config.asset_host= (the latter being usefull to both set action_mailer/action_controller asset_host)
• Opening this PR for two reasons:
  1. Getting the asset_host from config.action_controller currently works when the asset_host is defined using config.asset_host but I feel like this might be by chance:
     • When rails initialization process kicks in, the action_controller.set_configs initializer runs. A variable options is assigned and reference config.action_controller. The options variable get modified and by doing so modify the refernce to config.action_controller https://github.com/rails/rails/blob/1bee2fb600c07625b830afd33b43ead3364c9715/actionpack/lib/action_controller/railtie.rb#L50
  2. If a gem decide to set the asset_host automatically for any apps, the gem can do so inside an initializer.

       initializer :set_asset_host do |app|
         app.config.asset_host = 'https://example.com'
       end

     This code won't have any effect in sprockets-rails and as a result any assets referenced inside css, i.e. (.div { background-image: url('/assets/rails.png') }) will not be prefixed by the asset_host

[rails-bot]

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[rafaelfranca]

This is actually coupling more sprockets-rails to rails. I think the real problem is that the config used to configure the sprockets environment is the config at the block definition time https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L135, not the config in the after_initialize. Try to pass the config a second argument when executing the block here https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L179