But I was having trouble getting it to work right, not sure why, but it appeared to be related to the compass dependency.
The compass dependency is actually in the original chosen.js source too — chosen.js is originally written in SASS. And chosen-rails is trying to use the original chosen.js source.
I made a fork which instead uses the post-compiled pure JS and CSS from the chosen.js release, rather than it’s source. (Well, it has to customize the CSS a bit to change referenced url()s to Rails asset pipeline asset-url() calls.)