<===> input.scss
@mixin foo() {
  @media (mix-width: 100px) {
    @extend %bar;
  }
}

foo {
  @media (mix-width: 100px) {
    %bar {
      foo: bar;
    }
  }

  @include foo;
}

<===> output.css
@media (mix-width: 100px) {
  foo foo {
    foo: bar;
  }
}