Compiler written in PHP for SCSS files. Compile SASS with leafo/scssphp.

scss-compiler.php

<?php

use Leafo\ScssPhp\Compiler;
require_once('vendor/leafo/scssphp/scss.inc.php');

$theme_root = 'docroot/themes/custom/THEME_NAME';

$scss_source = $theme_root . '/stylesheets';
$scss_contents = file_get_contents($scss_source . '/style.scss');

$css_dist = $theme_root . '/css';

// Make the CSS directory if needed
if ( !file_exists($css_dist) ) {
  mkdir($css_dist, 0755);
}

$scss = new Compiler();
$scss->setLineNumberStyle(Compiler::SOURCE_MAP_INLINE);
$scss->setFormatter('Leafo\ScssPhp\Formatter\Expanded');
$scss->setImportPaths($scss_source . '/scss-imports/');

file_put_contents( $css_dist . '/compiled.css',
  $scss->compile("
    @import 'imports';
    $scss_contents
    ")
);

echo "CSS compiled!\n";
exit;

To get this working, composer require leafo/scssphp, change the name of THEME_NAME to the theme's directory name. Make this executable and then it will compile the style.scss file inside the stylesheets directory and output the results to css/compiled.css (ignore this file in .gitignore). I put this file in a scripts directory in my theme.

Don't forget to have an _imports.scss file in the stylesheets directory to include assets such as custom variables and mixins.

See more at https://github.com/leafo/scssphp