1<===> input.scss
2@mixin foo() {
3    @if false {
4      a { b: c }
5    } @else {
6      @content;
7    }
8}
9
10@include foo() {
11  .foo {
12    bar: baz;
13  }
14}
15
16<===> output.css
17.foo {
18  bar: baz;
19}
20