Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// ----

@mixin desc($name) {
  @at-root &-#{$name} { @content; }
}

@mixin tdesc($name, $parent) {
  @at-root #{$name} #{$parent} { @content; }
}

@mixin mod($name) {
  @at-root &--#{$name} { @content; }
}

@function with-parent($name, $parent) {
  @return #{$parent}-#{$name};
}

.Component {
  height: 10rem;
  $parent: &;
  
  // .Component-header
  @include desc(header) { 
    height: 20rem;
  }
  // .Component--small
  @include mod(small) { 
    height: 5rem;
    @include tdesc(&, with-parent(header, $parent)) {
      height: 10rem;
    }
  }
}

SassMeister-output.css

.Component {
  height: 10rem;
}
.Component-header {
  height: 20rem;
}
.Component--small {
  height: 5rem;
}
.Component--small .Component-header {
  height: 10rem;
}