Install Compass in Rails 3.1/3.2

application.rb

# Precompile *all* assets, except those that start with underscore
config.assets.precompile << /(^[^_\/]|\/[^_])[^\/]*$/

application.scss

/*
 * application.scss
 *
 * Important! Do *not* use Sprockets "require" syntax.
 * Use @import to include other stylesheets and Compass mixins.
 */

// Include some nice mixins
@import "compass/css3";
@import "sassy-buttons";

// Example: import partial stylesheet named "_users.scss"
@import "users";

compass.rb

# config/compass.rb
additional_import_paths = ["app/assets/stylesheets/basics", "app/assets/stylesheets/shared"]

digest_for-error

A ActionView::Template::Error occurred in sessions#new:

1024.css isn't precompiled
.bundle/bundle/gems/actionpack-3.2.0/lib/sprockets/helpers/rails_helper.rb:142:in `digest_for'

example.scss

.logo
{
  background: image-url("logo-small.png") no-repeat;
}

Gemfile

group :assets do
  gem 'compass-rails','~> 1.0.0.rc.2'
  gem 'compass-colors'
  gem 'sassy-buttons'
  gem 'sass-rails', '~> 3.2.3'
  # non-compass gems omitted for brevity
end

rake-output

$ bundle exec rake assets:precompile
/Users/mbrictson/.rbenv/versions/1.9.3-p0/bin/ruby script/rake assets:precompile:all RAILS_ENV=production RAILS_GROUPS=assets
rake aborted!
Undefined variable: "$body-text-line-height".
  (in /Users/mbrictson/Work/rails-project/app/assets/stylesheets/basics/_grid.scss)

Tasks: TOP => assets:precompile:primary
(See full trace by running task with --trace)
rake aborted!
Command failed with status (1): [/Users/mbrictson/.rbenv/versions/1.9.3-p0/...]

Tasks: TOP => assets:precompile
(See full trace by running task with --trace)

tree

.
├── Gemfile
├── app
│   └── assets
│       ├── images
│       │   └── logo-small.png
│       ├── javascripts
│       │   └── application.js
│       └── stylesheets
│           ├── _users.scss
│           └── application.scss
└── config
    ├── application.rb
    └── compass.rb

I have a problem with running Compass according to the instructions on
http://blog.55minutes.com/2012/01/getting-compass-to-work-with-rails-31-and-32/

EDIT: The problem is caused by setting:

config.assets.compile = true

in config/environments/production.rb

When it is set to true then Rails tries to compile missing assets on demand when running in production mode. To achieve that it needs Compass and other stuff, that is only available in development and test environments (as set in Gemfile).

The problematic part of the mentioned entry is a note that one should avoid directly requiring compass in the Gemfile.
In my case putting only compass-rails in Gemfile causes Compass global constant to be invisible and causes errors to be thrown when in production mode. That's because the compass gem is not loaded. Here is the example error I got:

ActionView::Template::Error (File to import not found or unreadable: blueprint/reset.
Load path: Sass::Rails::Importer(/myapp/assets/stylesheets/print.css.scss)
  (in /myapp/assets/stylesheets/print.css.scss)): […]

That's just the effect of my initializers/sass.rb being unable to set proper paths.
My code for setting the paths for SASS is:

if Rails.application.config.respond_to?(:sass)
  Rails.application.config.sass.tap do |sass|

    sass.load_paths.tap do |load_paths|
      load_paths << File.join(Rails.root, 'app', 'assets', 'stylesheets')
      if Kernel.const_defined?( :Compass )
        ['compass','blueprint'].each do |compass_framework|
          load_paths << Compass::Frameworks[compass_framework].stylesheets_directory
        end
      end
    end

    sass.line_comments    = Rails.env.production? ? false : true
    sass.preferred_syntax = :scss
  end
end

Conclusion: either put compass-rails out of assets group in Gemfile or disable config.assets.compile in config/environment/production.rb.

@siefca, yes, the config.assets.compile=true setting is problematic in production. Usually you will not want to do this. If you have good reason to set config.assets.compile=true, then you will need to ensure the asset pipeline gems are loaded.

I actually describe this in detail in the following blog post (see the config.assets.compile section):

http://blog.55minutes.com/2012/02/untangling-the-rails-asset-pipeline-part-3-configuration/

@mbrictson: That;s true. I'm just using it as a workaround, since rake assets:precompile takes sometimes up to 10 minutes with Sprockets and Compass.

Just a note, but in 'application.scss', @import "sassybuttons" should be @import "sassy-buttons" as per jhardy/Sassy-Buttons#14