Lint for unused SCSS variables
Created by: cvrebert
See:
- http://blog.gospodarets.com/finding_unused_scss_variables/
- https://gist.github.com/badsyntax/6193491
v4 currently (as of d756e12f) has several unused variables:
$enable-gradients
$font-family-serif
$font-size-xs
$line-height-computed
$nav-link-hover-bg
$nav-pills-active-link-hover-bg
$nav-pills-active-link-hover-color
$nav-tabs-justified-active-link-border-color
$nav-tabs-justified-link-border-color
$navbar-dark-disabled-color
$navbar-light-disabled-color
$pre-bg
$pre-border-color
$progress-bar-bg
$progress-border-radius
Also, we'll need some sort of exemption system (e.g. magic comments) for variables which we don't use out of the box but are exposed for the benefit of downstream users (e.g. the many color palette vars in #18462).