modify parents from within nested selectors

modifier mixin

.vegetables .carrot {
  color: orange;
}
.vegetables.out-of-season .carrot {
  color: brown;
}

.fruits .apple {
  color: red;
}
.fruits .apple.old {
  color: brown;
}

output

// ----
// Sass (v3.4.21)
// Compass (v1.0.3)
// ----

// modifies the first selector with custom content
//
=modifier($modifier, $selector: null)
  $first-selector: $selector or nth(nth(&, 1), 1)
  @at-root #{selector-replace(&, $first-selector, "#{$first-selector}#{$modifier}")}
    @content
  
// by default it modifies the first selector
.vegetables
  .carrot
    color: orange
    +modifier('.out-of-season')
      color: brown
      
// or pass a specific selector
.fruits
  .apple
    color: red
    +modifier('.old', '.apple')
      color: brown