Rails compiles assets both with and without md5 ha

I'm relatively new to RoR and I'm curious about why Rails compiles assets both with and without md5 hash for production?

I run bundle exec rake assets:clean then bundle exec rake assets:precompile

My production.rb file:

MyApp::Application.configure do

  # Code is not reloaded between requests

  config.cache_classes = true

  # Full error reports are disabled and caching is turned on

  config.consider_all_requests_local       = false

  config.action_controller.perform_caching = true

  # Disable Rails's static asset server (Apache or nginx will already do this)

  config.serve_static_assets = false

  # Compress JavaScripts and CSS

  config.assets.compress = true

  # Don't fallback to assets pipeline if a precompiled asset is missed

  config.assets.compile = false

  # Generate digests for assets URLs

  config.assets.digest = true 

  config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for nginx

  config.assets.precompile += %w(tos.js, tos.css)

  config.i18n.fallbacks = true

  config.active_support.deprecation = :notify

end

My application works with files with hashes in their names and it's the way it should be in my case :)

So I have two questions here:

1) Why is it happening when compiled?

Rails compiles assets both with and without md5 hash for production

2) What are these files (without hashes) for?

Maybe I don't get something, so please could someone explain.

The reason it does it is so that you can access the files without knowing the MD5 fingerprint (for example in a non-rails application, or a file within the rails app which isn't compiled or run by the rails stack (e.g. a 500/502 status error page). In this case you would have to compile the assets then change the css/js links in the static HTML files each time you updated the code (thus causing a change in the MD5 hash).

So instead rails produces 2 copies of each asset file, one with the fingerprint in the filename, the other without (e.g. application-731bc240b0e8dbe7f2e6783811d2151a.css, and application.css). The fingerprinted version is obviously preferred (see 'what is fingerprinting and why should I care' in the rails asset pipeline guide). But the non-digested version is there as a fallback.

As a final thought on the matter I'd take a read of the following pull request to the rails git repo: https://github.com/rails/rails/pull/5379 where they are discussing the pros and cons of the non-digested filenames, and the possibility of being able to turn off compilation of them.

HTH