title: How to have auto-complete for SASS classes generated with a mixin
body: <p>I have a mixin that generates the classes for the directions of flex.</p>
  
  <p>This is the snippet:</p>
  
  <pre><code>// Generated class
  $flex-directions: 'row', 'row-reverse', 'column', 'column-reverse', 'normal';
  @each $direction in $flex-directions {
    .flex-#{$direction} {
      @include flex-direction(#{$direction});
    }
  }
  </code></pre>
  
  <p>But in my HTML code, WebStorm does not suggest the classes created with mixins.</p>
  
  <p>How I can create an interface of a mixin or another way to have the class auto-complete in WebStorm?</p>