# The dynamic stylesheet language for the Rails 4+ asset pipeline.
This gem provides integration for Rails projects using the Less stylesheet language in the asset pipeline.
[](http://travis-ci.org/metaskills/less-rails)
## Installing
Just bundle up less-rails in your Gemfile. This will pull in less as a runtime dependency too.
```ruby
gem 'less-rails', '~> 2.7.0'
```
But be warned, less.rb relies on a JavaScript runtime gem too. Just like ExecJS, it will look for a gem that is appropriate to your system. Typically, this means you will need one of the following.
```ruby
gem 'therubyracer' # Ruby
gem 'therubyrhino' # JRuby
```
## Configuration
This gem was made for other gems to properly hook into one place to provide paths to the Less::Parser. For example, the less-rails-bootstrap project at http://github.com/metaskills/less-rails-bootstrap and each project should do the path configuration for you. If you need to, you can configure less-rails with additional paths. These paths have higher priority than those from your applications assets load paths.
```ruby
MyProject::Application.configure do
config.less.paths << "#{Rails.root}/lib/less/protractor/stylesheets"
config.less.compress = true
end
```
#### About Compression
If `config.assets.compress` is set to true, we will set the `config.less.compress` to true as well. Less has real basic compression and it is recommended that you set the rails `config.assets.css_compressor` to something more stronger like `:yui` in your `config/environments/production.rb` file. Note, this requires the [yui-compressor](https://rubygems.org/gems/yui-compressor) gem but does an excellent job of compressing assets.
## Import Hooks
Any `@import` to a `.less` file will automatically declare that file as a sprockets dependency to the file importing it. This means that you can edit imported framework files and see changes reflected in the parent during development. So this:
```css
@import "frameworks/bootstrap/mixins";
#leftnav { .border-radius(5px); }
```
Will end up acting as if you had done this below:
```css
/*
*= depend_on "frameworks/bootstrap/mixins.less"
*/
@import "frameworks/bootstrap/mixins";
#leftnav { .border-radius(5px); }
```
## Helpers
When referencing assets use the following helpers in LESS.
```css
asset-path(@relative-asset-path) /* Returns a string to the asset. */
asset-path("rails.png") /* Becomes: "/assets/rails.png" */
asset-url(@relative-asset-path) /* Returns url reference to the asset. */
asset-url("rails.png") /* Becomes: url(/assets/rails.png) */
```
As a convenience, for each of the following asset classes there are corresponding `-path` and `-url` helpers image, font, video, audio, javascript and stylesheet. The following examples only show the `-url` variants since you get the idea of the `-path` ones above.
```css
image-url("rails.png") /* Becomes: url(/assets/rails.png) */
font-url("rails.ttf") /* Becomes: url(/assets/rails.ttf) */
video-url("rails.mp4") /* Becomes: url(/videos/rails.mp4) */
audio-url("rails.mp3") /* Becomes: url(/audios/rails.mp3) */
javascript-url("rails.js") /* Becomes: url(/assets/rails.js) */
stylesheet-url("rails.css") /* Becomes: url(/assets/rails.css) */
```
Lastly, we provide a data url method for base64 encoding assets.
```css
asset-data-url("rails.png") /* Becomes: url(data:image/png;base64,iVBORw0K...) */
```
Please note that these helpers are only available server-side, and something like ERB templates should be used if client-side rendering is desired.
## Generators
Installation of the gem will set your applications stylesheet engine to use Less. It is possible to have many gems that set the stylesheet engine, for instance the sass-rails and/or stylus gems. In this case, you can resolve the ambiguity by setting the stylesheet engine in your `config/application.rb` file like so. Doing so would mean all generated assets will be in the a fresh `css.less` template.
```ruby
config.app_generators.stylesheet_engine :less
```
We have generators for both assets and scaffold in the `less` namespace. For instance the following would generate a blank `app/assets/stylesheets/posts.css.less` template.
```
$ rails generate less:assets posts
```
We also have a generator for rails scaffold CSS. Just like the Sass gem, we simply parse the scaffold.css in the default rails generator and save it as a scaffolds.css.less file. This is done automatically during other scaffold generator actions.
## Contributing
This gem is fully tested from Rails 4.0 to Rails 4.2. We run our tests on [Travis CI](http://travis-ci.org/metaskills/less-rails) in both Ruby 1.9, 2.0, and jRuby 1.9 mode. If you detect a problem, open up a github issue or fork the repo and help out. After you fork or clone the repository, the following commands will get you up and running on the test suite.
```shell
$ bundle install
$ bundle exec rake appraisal:setup
$ bundle exec rake appraisal test
```
We use the [appraisal](https://github.com/thoughtbot/appraisal) gem from Thoughtbot to help us generate the individual gemfiles for each Rails version and to run the tests locally against each generated Gemfile. The `rake appraisal test` command actually runs our test suite against all Rails versions in our `Appraisal` file. If you want to run the tests for a specific Rails version, use `rake -T` for a list. For example, the following command will run the tests for Rails 4.0 only.
```shell
$ bundle exec rake appraisal:rails40 test
```
Our current build status is:
[](http://travis-ci.org/metaskills/less-rails)
## License
Less::Rails is Copyright (c) 2011-2013 Ken Collins, <ken@metaskills.net> and is distributed under the MIT license.