How can I get the Rails asset pipeline to produce source maps?

Question

I\'d like to have Rails produce source maps alongside the compiled coffeescript/minified JS, for better error logging. There doesn\'t seem to be comprehensive documentation on t

Answer 1

Rails supports source maps for minified JavaScript! Rails relies on Sprockets for asset compilation, and source maps support was added to Sprockets in this pull request.

Answer 2

This looks like it should work: http://alexspeller.com/2012/09/15/Source_maps_for_coffeescript_in_rails.html

Though, keep in mind the warning at the end:

Important Note: this rather brutal hack replaces the normal coffeescript compiler by shelling out to the CoffeeScriptRedux compiler, which is not in fact finished. This is just a proof of concept, you probably shouldn’t use it.

So I wouldn't recommend running this in production, but if you have a staging environment (also on Heroku, also with minified Javascript) it might be useful.

Answer 3

If you don't really want source-maps, but instead just want line numbers in coffee-script compile exceptions try this:

It used to be that just having coffee-rails in your Gemfile would produce exceptions with line numbers in the original coffeescript source. Then, they disappeared with a line-number-less exception. I did some digging, and I found that coffee-script-source 1.5.x gave line numbers in the compilation exceptions, while coffee-script-source 1.6.x did not. I believe is a bug, and I wouldn't be surprised if this was "fixed" in the future.

# Gemfile
gem 'coffee-rails', '~> 4.0.0'
  gem 'coffee-script-source', '~> 1.5.0' # 1.6 doesn't include line numbers in exceptions

Then you'll get exceptions like ('coffee-script-source', '~> 1.5.0')

Showing /Users/.../app/views/layouts/application.html.erb where line #12 raised:

SyntaxError: missing } on line 15
  (in /Users/.../app/assets/javascripts/app.js.coffee)

Instead of ('coffee-script-source', '~> 1.6.3')

Showing /Users/.../app/views/layouts/application.html.erb where line #12 raised:

SyntaxError: missing }
  (in /Users/.../app/assets/javascripts/app.js.coffee)

Answer 4

Tested this. It works. https://github.com/markbates/coffee-rails-source-maps. However it makes your asset rendering much slower.