nth() doesn't take & as an argument

[cristianl]

Libsass fails to compile a stylesheet if you try to use the nth() function with & as the first argument; it works if you assign & to a variable first. This is inconsistent with Ruby Sass.

Rationale:
According to the docs (http://sass-lang.com/documentation/Sass/Script/Functions.html#selector_parse-instance_method), & returns a Sass::Script::Value::List. nth() takes a list as its first argument.

Example:

.container {
  .box {
    $_last-selector: nth(&, -1);
    $_targeted-element: nth($_last-selector, -1);
    content: "#{$_targeted-element}";
  }
}

Expected output (from Ruby Sass 3.4.13):

.container .box {
  content: ".box";
}

Result in Libsass 3.2.4: Error — "invalid selector after & on line 3 at column 43"

---

When I use nth() with a list that was declared manually, Libsass and Sass behave consistently. For instance, if I save the value of & in a variable:

.container {
  .box {
    $_ampersand-list: &;
    $_last-selector: nth($_ampersand-list, -1);
    $_targeted-element: nth($_last-selector, -1);
    content: "#{$_targeted-element}";
  }
}

Output (same in Libsass 3.2.4 and Ruby Sass 3.4.13):

.container .box {
  content: ".box";
}

---

This also works on Libsass 3.2.4, as expected:

$selector-list: ('.foo' '.bar', '.baz' '.qux');

$_last-selector: nth($selector-list, -1);
$_targeted-element: nth($_last-selector, -1);

#{$_targeted-element} {
  color: whitesmoke;
}

Output (same in Libsass 3.2.4 and Ruby Sass 3.4.13):

.qux {
  color: whitesmoke;
}

---

This might be related to the issue with @at-root and interpolation (#1043, #1210), though it's closer to how Libsass behaved until 3.2.2 (when interpolated in @at-root, the value of & would simply be ignored), not the current behavior, from 3.2.3 (the value of & is output, but the selector is nested inside its parent, not the root of the stylesheet).

UPDATE: This seems to be another instance of the issue in #1260 and #1122, i.e. & fails in the context of function arguments.

[xzyfer]

You're correct this is due to & not being evaluated as a function parameter. As a work around you can use #{&}.

[xzyfer]

Closing as this is a duplicate of #1260.