How to use SASS and Compass in Drupal 7 using Sassy

I've recently started using SASS rather than LESS to do my CSS preprocessing - namely due to its integration with Compass and it's built-in CSS3 mixins. Here are three modules that provide the ability to use SASS within Drupal.

Sassy

Prepro

Libraries API

Alternatively, you could use a base theme like Sasson that includes a SASS compiler.

Download the PHPSass Library

The first thing to do is download the PHPSass library from GitHub, as this is a requirement of the Sassy module and we can't enable it without the library. So, in a Terminal window:

$ mkdir -p sites/all/libraries;
$ cd sites/all/libraries;
$ wget https://github.com/richthegeek/phpsass/archive/master.tar.gz;
$ tar zxf master.tar.gz;
$ rm master.tar.gz;
$ mv phpsass-master/ phpsass

Or, if you're using Drush Make files:

libraries[phpsass][download][type] = "get"
libraries[phpsass][download][url] = "https://github.com/richthegeek/phpsass/archive/master.tar.gz"

The PHPSass library should now be located at sites/all/libraries/phpsass.

Download and enable the Drupal modules

This is easy if you use Drush:

$ drush dl libraries prepro sassy
$ drush en -y libraries prepro sassy sassy_compass

Otherwise, download the each module from it's respective project page and place it within your sites/all/modules or sites/all/modules/contrib directory.

Configuring the Prepro module

The Prepro module provides various settings that can be changed for each preprocessor. Go to admin/config/media/prepro to configure the module as required.

Personally, in development, I'd set caching to 'uncached' and the error reporting method to 'show on page'. In production, I'd change these to "cached" and "watchdog" respectively. I'd also set the output style to "compressed",

Adding SASS files into your theme

With this done, you can now add SASS and SCSS files by adding a line like stylesheets[all][] = css/base.scss in your theme's .info file.