Autodetect Loaded Markups

[Jeremy]

I'm working on a gem for for a rails app. If the user has the relevant gems loaded up, I'd like to use the Tilt::Template for sprockets, if they don't have it, meh.

source:

    # try loading common markups
    %w(erb haml liquid md radius slim str textile wiki).
    each do |ext|
      begin
        config.angular_templates.markups << ext if Tilt[ext]
      rescue LoadError
        # They don't have the required library required. Oh well.
      end
    end

It seems to work exactly as I hoped, however when I tested with Rails 4.1 + Spring, when I start the rails console for the first time I get the autoloading ... in a non thread-safe way warning. It doesn't seem to happen with rails server, or if spring is disabled.

WARN: tilt autoloading 'liquid' in a non thread-safe way; explicit require 'liquid' suggested.
WARN: tilt autoloading 'redcarpet' in a non thread-safe way; explicit require 'redcarpet' suggested.
WARN: tilt autoloading 'rdiscount' in a non thread-safe way; explicit require 'rdiscount' suggested.
WARN: tilt autoloading 'rdiscount' in a non thread-safe way; explicit require 'rdiscount' suggested.
WARN: tilt autoloading 'bluecloth' in a non thread-safe way; explicit require 'bluecloth' suggested.
WARN: tilt autoloading 'kramdown' in a non thread-safe way; explicit require 'kramdown' suggested.
WARN: tilt autoloading 'maruku' in a non thread-safe way; explicit require 'maruku' suggested.
WARN: tilt autoloading 'radius' in a non thread-safe way; explicit require 'radius' suggested.
WARN: tilt autoloading 'redcloth' in a non thread-safe way; explicit require 'redcloth' suggested.
WARN: tilt autoloading 'wikicloth' in a non thread-safe way; explicit require 'wikicloth' suggested.
WARN: tilt autoloading 'creole' in a non thread-safe way; explicit require 'creole' suggested.

I'm a little confused, because I expected the require to cause the LoadError exception, so I'm not sure why it's even getting to the warn block -- I definitely don't have libraries for liquid or radius installed. Rails is pulling Tilt 1.4, and after reading that source, I'm not confused.

Should I just silence the output from this block and move on, or is there a better way to check if there is a library loaded for an extension?

With HAML or SLIM there is a 1:1 extension to library ratio, and I could check for defined constants, but with markdown there are dozens, and six months from now there could be a new markdown library. I'd like, "if Tilt supports it, we support it" simplicity.

[Magnus Holm]

At the moment there is no better way to check if a template engine is available. The only way to check for lazily loaded template engine is to invoke require which is indeed not thread-safe.

Why do you need a list of available template engines?

[Jeremy]

We're setting up sprockets to process html-ish things on the asset pipeline for use with AngularJS:

app.config.angular_templates.markups.each do |ext|
  Sprockets.register_engine ".#{ext}", Tilt[ext]
end

Sprockets.register_engine '.html', AngularRailsTemplates::Template

You can put a foo.html.haml in the rails assets folder, and it will render the haml into html and turn that html into a javascript blob that directly inserts the template into Angular's template cache.

We also print the markups array in a javascript comment to let the user know what extensions have been registered and will be processed.

[Magnus Holm]

I'm closing this in favor of keeping the discussion in #228. In 2.1 I will implement two methods: one for attempting to lazy load all available template classes, and another for detecting what templates/extensions are available.