Render mustache templates natively in Rails using a template handler

mustache_template.rb

# ./config/initializers/mustache_template.rb
class MustacheTemplate
  # `call` returns a string which is evaled in the context of the action view
  # This follows the same pattern as other handlers:
  # https://github.com/rails/rails/tree/4-2-stable/actionview/lib/action_view/template/handlers
  def call(template)
    partial_prefix = File.basename(File.dirname(template.identifier))
    <<-cmd
      mustache_template = Mustache.new
      mustache_template.instance_variable_set("@view_paths", view_paths)
      def mustache_template.partial(name)
        partial = @view_paths.find(name, '#{partial_prefix}', true, { formats: [:html], locale: [], handlers: [:mustache] })
        partial.source
      end
      mustache_template.template = '#{template.source.gsub(/'/, "\\\\'")}'
      mustache_template.render(local_assigns).html_safe
    cmd
  end
end
 
ActionView::Template.register_template_handler(:mustache, MustacheTemplate.new)