Should error when attempting to output an empty list or map

[xzyfer]

foo {
  foo: foo(());
}

Ruby Sass

Error: () isn't a valid CSS value.
        on line 57 of test.scss

Libsass

foo {
  foo: foo(); }

[KittyGiraudel]

Ruby Sass seems as wrong as LibSass to me.

[mgreter]

This is quite a special case since this is done during Function_Call evaluation. So the List never gets to the Output visitor, which would error in that case. Not sure how to solve this, but we should probably aim to return a function call from the eval step, with evaluated arguments, so output can do it's job. Tried this and it looks promising, but there were some other regressions.

[mgreter]

Just checked and I see I implemented that error in Output, which worked for:

$a: (());
foo {
  foo: $a;
}

But not for the originally reported case, so maybe it's worth creating two issues here ...