Parser should catch error on duplicate keys in maps

[lunelson]

So, ruby-sass throws an error when a map is declared that has any duplicate keys, including any at nested levels. i.e. maps that are values or keys within other maps:

$map: (
  alpha: 1,
  beta: 2,
  gamma: 3,
  delta: (
    eta: 5,
    eta: 6,
  ),
);

Duplicate key "eta" in map (eta: 5, eta: 6).

Libsass currently does not run this check, and should; however, libsass can also do better than ruby-sass here. Note that ruby-sass fails to pick up duplicate-key maps that result from other operations. Example:

$map1: (
  alpha: 1,
  beta: 2,
  gamma: 3,
);

$map2: (
  alpha: 2
);

$map3: join($map1, $map2);

.test {
  out: inspect($map3);
}

.test {
  out: alpha 1, beta 2, gamma 3, alpha 2;
}

So imo libsass should have a map-validity check routine that runs on anything that involves SassScript maps or lists (as the latter may contain a map) as outputs or assignments.

[xzyfer]

I thought this had been addressed previously. My bad. Good catch.

however, libsass can also do better than ruby-sass

I like the idea, but as far as Libsass is concerned Ruby sass is the "right way". Our goal is to act exactly as they do. If you want this feature in Libsass I would the suggestion on the Ruby sass repo.

[lunelson]

Right. Good idea, I will put up an issue on ruby-sass about it too.

[xzyfer]

We can't currently test this case. See sass/sass-spec#136