Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.0.rc.1)
// Compass (v1.0.0.alpha.20)
// ----

@mixin insert-context($target, $context, $order: before) {
    $new-context: "";
    @if $order == before {
      $new-context: selector-nest($context, $target);  
    }
    @else {
      $new-context: selector-nest($target, $context);  
    }
    foo: $new-context; /* testing selector-nest */
    $new-selector: selector-replace(&, $target, $new-context);
    @at-root #{$new-selector} {
        @content;
    }
}

.tabs {
    .tab {
        background: red;
        &:hover {
            background: white;
        }
    }
    .tab-link {
        color: white;
        @include insert-context('.tab-link', '.tab:hover') {
            color: red;
        }
    }
}

SassMeister-output.css

.tabs .tab {
  background: red;
}
.tabs .tab:hover {
  background: white;
}
.tabs .tab-link {
  color: white;
  foo: .tab:hover .tab-link;
  /* testing selector-nest */
}
.tabs .tab:hover .tab-link, .tab:hover .tabs .tab-link {
  color: red;
}