LESS CSS Preprocessor

This module allows for automatic compilation of LESS style sheets.

Requirements

LESS requires at least one of two possible engines available:

oyejorge/less.php archived

This is a pure PHP implementation, which is good for shared hosting, or if you don't feel comfortable installing or configuring software on your server.

It lacks the ability to execute javascript embedded in .less files, so some LESS libraries might not work.

Requirements:
1. Libraries
2. oyejorge/less.php installed such that Less.php is located at sites/all/libraries/less.php/Less.php
This project has been archived by the author and is extremely out of date. It does not include support for LESS features released since v2, and will break when they are encountered. Use of this engine is highly discouraged.
less.js

You can read about how to install here: less.js

Please read Command Line Requirements to ensure that less.js is installed properly.

Once installed, you must select your engine on 'admin/config/development/less'.

Less engines written in PHP do not support embedded JavaScript evaluation.

Optional

Autoprefixer

postcss/autoprefixer

Write your CSS rules without vendor prefixes (in fact, forget about them entirely)

Autoprefixer will use the data based on current browser popularity and property support to apply prefixes for you.

Please read Command Line Requirements to ensure that autoprefixer is installed properly.

Command Line Requirements

Both less.js and postcss/autoprefixer require that PHP can call these programs directly from the command line.

It is up to the installer (you) to ensure that the lessc and/or autoprefixer are able to be called by PHP without a full path to the binary.

Thus is it required that you configure your PATH for the user that your PHP installation runs under to ensure that these programs can be run by name without the full path.

LESS Development:

Syntax: http://lesscss.org/features/

File placement:
If your source file was sites/all/modules/test/test.css.less
Then your compiled file will be sites/[yoursite]/files/less/[random.string]/sites/all/modules/test/test.css

Usage

Include less files in your module.library.yml just as you would with regular css files

[module.library.yml]:

source:
  version: 1.x
  css:
    theme:
      less/source.css.less: {}

Compatibility

Should work with most themes and caching mechanisms.

CSS Aggregation

Fully compatible with "Optimize CSS files" setting on "Admin->Site configuration->Performance" (admin/settings/performance).

RTL Support

RTL support will work as long as your file names end with ".css.less".

Assuming your file is named "somename.css.less", Drupal automatically looks for a file name "somename-rtl.css.less"

Variables

Variable defaults can be defined in .theme and .module files using hook_less_variables_alter()

.theme file:

function hook_theme_less_variables_alter( array &$less_variables, $system_name )
{
  	$less_variables['@defaults'] = '~"theme/less/defaults.less"';
$less_variables['@styles'] = '~"theme/less"';
$less_variables['@theme_images'] = '~"/img"';
}

Aetheron/Less-CSS-Preprocessor