Unexpected behaviour with @at-root

[KittyGiraudel]

Bug found by Jaime Caballero: https://twitter.com/jaicab_/status/602583391515574273.

Test case

@mixin test {
  $selector-list: &;                 // (.a .b,)
  $selector: nth($selector-list, 1); // (.a .b)
  $first: nth($selector, 1);         // .a
  $second: nth($selector, 2);        // .b
  $add: 'dummy';

  @at-root #{$first} #{$add} #{$second} {
    @content;
  }
}


.a .b {
  @include test {
    color: red;
  }
}

Expected result

.a dummy .b {
  color: red;
}

Actual result (LibSass 3.2.4)

.a .b .a dummy .b {
  color: red;
}

[jaicab]

Thanks @hugogiraudel for setting up this issue!
It's interesting that when you add some actual text around it (like an html tag or something) it does work. Check out my original example on SassMeister.

[xzyfer]

I've assigned this to 3.3. A spec would be appreciated. Possibly related to #1210

[KittyGiraudel]

There you have it.

[mgreter]

This issue is also covered by my latest WIP branch, which seems to fix most if not all @at-root related bugs (ETA unknown, targeted 3.3): #1249

[xzyfer]

Looking at this closer it's actually just an @at-root problem. The selector functions have nothing to do with.

This is a duplicate of #1210.