Import errors when using CSSBundling + 3rd Party Gem assets

[rapito]

Given a rails application that uses a gem like rails-assets-jstree.
After trying to execute rails css:install:sass, I get a "Can't find stylesheet to import." error per each css asset that is inside a gem. I can perfectly follow the @import statement to the gem's asset.

Is there a necessary extra step to set cssbundling to be able to lookup inside included gems?

• Command Executed: rails css:install:sass
• Output:

Error: Can't find stylesheet to import.
   ╷
29 │ @import 'jstree';
   │         ^^^^^^^^
   ╵
  app/assets/stylesheets/application.sass.scss 29:9  root stylesheet
error Command failed with exit code 65.

• application.sass.scss:

// something something
@import 'jstree';
// something more

• Gemfile

source 'https://rails-assets.org' do
  gem 'rails-assets-jstree'
end

• jstree gem structure
  

[dhh]

You have to manually change your Sass configuration to include the gem assets in the load path. Not something that happens automatically.