"Expected to find a manifest file"...but I don't have any asset

[coorasse]

This error is raised when the manifest file is not present. See also #444 .
Our use case is different: our app doesn't contain any sprockets assets, and uses webpacker to manage everything, but an engine that is mounted needs Sprockets. So basically:

• I don't want to create a manifest.js. I don't need it. I don't have any resource.
• I cannot disable sprockets. Is needed by the engine
• My only solution is to rollback sprockets to < 4.

Proposed solution: remove this check.
I am willing to hear alternative solution and/or open a PR to fix this.

[rafaelfranca]

How is your engine using sprockets? Without a manifest the engine should not be working with sprockets 4.

[coorasse]

https://github.com/sferik/rails_admin

apparently it doesn't have one. does this mean the engine should lock onto sprockets < 4 or add a manifest.js ?

[rafaelfranca]

It seems Rails admin is configuring sprcokets using the precompile list, so it should work if your application don't have a manifest https://github.com/sferik/rails_admin/blob/master/lib/rails_admin/engine.rb#L17.

I'm torn about removing this check. If we remove, people upgrading to sprockets 4 will silently have their apps not compiling the assets they were expecting, but in case like yours, you really don't need a manifest.

I wonder if it would be sufficient if we had a configuration to disable this check.

[jonathanhefner]

(Preface: I use Sprockets in all of my Rails apps, and I greatly appreciate all the work that has gone into it.)

I recently encountered two use cases for disabling this check.

1. Adding an extremely minimal dummy Rails app to a gem test suite. For example, adding the following:

   ## test/test_helper.rb
   
   require 'rails/all'
   
   module Dummy
     class Application < Rails::Application
       config.root = File.join(__dir__, "dummy")
       config.load_defaults Rails::VERSION::STRING.to_f
       config.eager_load = false
     end
   end
   
   Rails.application.initialize!

   With Sprockets 4, requires a test/dummy/app/assets/config/manifest.js file.

2. Testing a generator that calls out to other generators. When a generator invokes another generator, Rails requires certain files to already exist in #{destination}/bin and #{destination}/config. With Sprockets 4, a #{destination}/app/assets/config/manifest.js file is also required.

[coorasse]

I think a configuration to disable this check would be sufficient.

[rafaelfranca]

1. Adding an extremely minimal dummy Rails app to a gem test suite. For example, adding the following:

That is not an minimal dummy Rails app. This is and would not have that problem

## test/test_helper.rb

require "rails"
require "active_model/railtie"
require "active_job/railtie"
require "action_controller/railtie"
require "action_view/railtie"

module Dummy
  class Application < Rails::Application
    config.root = File.join(__dir__, "dummy")
    config.load_defaults Rails::VERSION::STRING.to_f
    config.eager_load = false
  end
end

Rails.application.initialize!

[denys-husiev]

@rafaelfranca are you going to add configuration to disable this check? If yes, could you please provide an issue number so I can follow when it's done.

Thanks in advance

[mjankowski]

That is not an minimal dummy Rails app. This is and would not have that problem.

Thanks for this suggestion! I had a similar problem (spec suite in gem which should not have a manifest.js file, but does set up a dummy rails app). Changing away from the full rails/all to just including the piece s I needed solved this for me.

I think a config option might still make sense, but until then, this might help gem authors with dummy apps sort it out.

[kennyadsl]

I think #446 would fix this issue, since it allows to specify a custom path for the Dummy app manifest, as we would do in Solidus if it gets merged.

[estiens]

Still no way to disable this?

[jmoon90]

https://github.com/sferik/rails_admin

apparently it doesn't have one. does this mean the engine should lock onto sprockets < 4 or add a manifest.js ?

This fixed my issue. For an API only heroku app I removed all my assets and

1. added gem "sprockets", "<4"
2. ran bundle update sprockets
3. Able to deploy to heroku