"Expected to find a manifest file" error with assets disabled

[delner]

With the release of Sprockets 4.0 and the requirement of a manifest.js file, we're seeing an error similar to #443 with sprockets-rails 3.2.1 where our test suite is producing this error:

/usr/local/bundle/gems/sprockets-rails-3.2.1/lib/sprockets/railtie.rb:105:in `block in <class:Railtie>': Expected to find a manifest file in `app/assets/config/manifest.js` (Sprockets::Railtie::ManifestNeededError)
But did not, please create this file and use it to link any assets that need
to be rendered by your app:

Example:
  //= link_tree ../images
  //= link_directory ../javascripts .js
  //= link_directory ../stylesheets .css
and restart your server

We load the standard require 'rails/all' in our test suite (which loads sprockets 4.0 by default), but we have no interest in using Sprockets or the asset pipeline within it.

If we disable Sprockets with config.assets.enabled = false in our application, we expect that we shouldn't need to have a manifest.js file. However, merely having require 'sprockets/railtie' anywhere in your application will force this check to occur unconditionally, regardless of if you've disabled the the application pipeline:

https://github.com/rails/sprockets-rails/blob/v3.2.1/lib/sprockets/railtie.rb#L103-L110

initializer :set_default_precompile do |app|
  if using_sprockets4?
    raise ManifestNeededError unless ::Rails.root.join("app/assets/config/manifest.js").exist?
    app.config.assets.precompile += %w( manifest.js )
  else
    app.config.assets.precompile += [LOOSE_APP_ASSETS, /(?:\/|\\|\A)application\.(css|js)$/]
  end
end

I would suggest changing this check to be based conditionally on whether assets are enabled or not, so users are not forced to completely remove sprocket-rails to disable it.

[rafaelfranca]

The proper way to fix this is stop using require 'rails/all' and not load sprockets/rails in your application.

[delner]

This is not a good option for us; we need all the default Rails components other than Sprockets, and to have to update our require '*/railtie' statements every time Rails adds new components (e.g. ActionText, ActionMailbox) because sprockets-rails doesn't check whether its actually enabled or not seems like a bad experience for Rails users who gem 'rails'.

[rafaelfranca]

The way Rails let you opt-out components is by requiring individual railties. Railties are added once a year, you don't need a lot of work to add require statements once a year. There is no other option, sorry.

[delner]

If preventing require 'sprockets/railtie' (from being loaded as a part of require 'rails/all') is the only way to disable Sprockets, then what is the purpose of config.assets.enabled = false?

[rafaelfranca]

That is for disabling compilation of assets. That doesn't disable the sprockets-rails to be loaded or executed.

[matthewmath]

Just curious, the path is sprockets 3.2.1, why is using_sprockets4? now returning true and dropping into the required manifest code?

[rafaelfranca]

sprockets is different of sprockets-rails. The path is sprockets-rails-3.2.1

[denys-husiev]

I have this error just because I need to require 'sprockets/railtie' for using graphiql-rails gem. And to fix it, I should add manifest.js file to my rails api project. Seems a little weird :)