<===> options.yml
---
:ignore_for:
- dart-sass

<===> input.scss
.selector1{ foo: bar; }
.selector2{ zapf: dings; }

.selector3{ @extend .selector1, .selector2; }
<===> output.css
.selector1, .selector3 {
  foo: bar;
}

.selector2, .selector3 {
  zapf: dings;
}