Ruby Sass deprecated in March 2019

[dtrunk90]

Ruby Sass is deprecated and will be unmaintained as of 26 March 2019.

• If you use Sass as a command-line tool, we recommend using Dart Sass, the new
  primary implementation: https://sass-lang.com/install
• If you use Sass as a plug-in for a Ruby web framework, we recommend using the
  sassc gem: https://github.com/sass/sassc-ruby#readme

For more details, please refer to the Sass blog:
http://sass.logdown.com/posts/7081811

I suggest to annotate the current SassRubyGenerator as @Deprecated with a note to use a new generator which needs to be implemented. Either by copying the old one and using the new sassc-ruby or (which I think is better as jruby is a mess) by creating a new generator using jsass.

[dtrunk90]

I tried adding a generator which seems to work theoretically. But I can't get my Bootstrap 4 files compiled.

The only mapping is /static/scss/main.scss and its content is as simple as:

@import '../vendor/bootstrap-scss/bootstrap';

I'm getting tons of exceptions like: io.bit3.jsass.CompilationException: Error: Undefined variable: "$font-family-monospace".

So maybe switching to sassc-ruby is a better option.

You can see the new jsass generator in the referenced commit. Feel free to copy into your project if you want.