Whoops! Ruby just Crashed in Rails

This is more of a PSA than anything.

I have a legacy app I'm not ready to upgrade to Rails 7 yet. Ruby 2.7.5 and Rails 6. Suddenly it started to crash on the first request to the server. Like the Ruby callstack crash, the big one.

If this happens to you, make the coffee-rails gem the first thing you look at. I removed the gem from Gemfile, re-ran bundler, commented out the references to coffeescript files in application.js, and started the Rails server.

After two days of head-scratching, Bingo! It worked. (Minus the missing JavaScript, of course.)

Then I used decaffeinate to quickly convert those coffeescript files into vanilla JavaScript and uncommented their references in application.js.

I hope this helps someone.