Question

I’m trying to create a Rails app template I have this block of code in there

file 'config/sass.rb', <<-RUBY

  Sass::Engine::DEFAULT_OPTIONS[:load_paths].tap do |load_paths|
    load_paths << "#{Rails.root}/app/assets/stylesheets"
    load_paths << "#{Gem.loaded_specs['compass'].full_gem_path}/frameworks/compass/stylesheets"
  end

RUBY

When I run ‘rails new’ with this template I get the following error:

undefined method `root' for Rails:Module (NoMethodError)

I’m new to app templates as well as this code block syntax. (What do you even call that <<-RUBY block? It’s really hard to search for on google). It was my impression that it wouldn’t be running any of the code inside the block so it shouldn’t be causing errors. What gives?

UPDATE: Let me add some more context:

I’m trying to modify the app template here: https://github.com/leshill/rails3-app/blob/master/app.rb I want add the code from this blog post: http://metaskills.net/2011/05/18/use-compass-sass-framework-files-with-the-rails-3.1-asset-pipeline/ so that I can have compass support in rails3.1

Answer 1

You are asking the “rails new” command to create a file and passing a block of content using a “heredoc” (signaled by the <<-SOMESTRING syntax). More about heredoc:

http://en.wikipedia.org/wiki/Here_document#Ruby

The parser will treat the content just like a Ruby string surrounded by doublequotes and attempt to substitute any string enclosed by #{}. It fails because it can’t find a variable named Rails.root.

You can avoid the substitution behavior (have the content treated like a Ruby string surrounded by singlequotes) by using single-quote-style-heredoc. Surround the heredoc signal with singlequotes:

file ‘config/sass.rb’, <<-‘RUBY’

Sass::Engine::DEFAULT_OPTIONS[:load_paths].tap do |load_paths|
load_paths << “#{Rails.root}/app/assets/stylesheets”
load_paths << “#{Gem.loaded_specs[‘compass’].full_gem_path}/frameworks/compass/stylesheets”
end

RUBY

Since you’re creating Rails app template for a starter app, it might be helpful to look at the

Rails 3.1 Application Templates
from the Rails Apps project on GitHub.

The project provides good examples of app templates plus documentation (be sure to take a look at Thor::Actions and Rails::Generators::Actions).