Move config.assets out into sprockets-rails plugin

[josh]

Alright @rafaelfranca, got another thing.

It seems to work pretty good if the Sprockets Railtie just defines its own config.assets as an options set.

https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L48-55

[josh]

But I really hate doing this. How can we move this out too?

[guilleiguaran]

/cc @drogus @josevalim any ideas?

[drogus]

Can't we just add railtie to sprockets-rails and create an initializer there?

[rafaelfranca]

@drogus in this case not. This is a initializer that have to run in every engine. I think we can move this to sprockets-rails, reopen Rails::Engine there and add this initializer, since the sprockets/railtie is loaded before the engines.

[josevalim]

I don't think we should completely remove the config.assets from Rails. For example, config.assets.paths can be consumed by other applications (I believe rake-pipeline does it). So I would rather leave the basic options around and sprockets can extend it further with its own.

[josh]

@josevalim the annoying issue is that assets is attr_accessor instead of a property on the ordered options object. Inorder to define my own options, I need to undef that accessor.

I think rake-pipeline should just bring its own options that it cares about.

[josh]

Alright, don't really care now, I'm going to have to wipe the current config.assets anyway for old rails. So whatever config.assets are initialized by rails will just be ignored by the plugin.