Dynamic division with interpolation not compatible with libsass

[atomicpages]

Found this problem with playing with node-sass the other day with this code snippet:

@function _calcRU($px, $base, $unit) {
    $unit: quote($unit);

    @if not $unit == "em" or not $unit == "rem" or not $unit == "%" {
        @debug "Invalid unit, choose 'em' or 'rem'";
        @return null;
    }

    @if not unitless($px) {
        $px: strip-units($px);
    }

    @if not unitless($base) {
        $base: strip-units($base);
    }

    @if($unit == "%") {
        @return percentage($px / $base);
    }

    @return ($px / $base) * 1#{$unit};
}

This test with Sass 3.2.19 and above

body {
    font-size: _calcRU(12, 10, "%");
    font-size: _calcRU(16, 10, "rem");
    font-size: _calcRU(20, 10, "em");
    font-size: _calcRU(24, 10, "rem");
}

yields

body {
    font-size: 120%;
    font-size: 1.6rem;
    font-size: 2em;
    font-size: 2.4rem;
}

Testing with the current libsass master I get "invalid operands for multiplication".

[mgreter]

I can confirm that this bug exists on latest master.
Test case can probably be shortened to:

foo { bar: 10 * 5#{px}; }

[mgreter]

@xzyfer I gave it a try, but it is a bit more complicated than expected. Actually with my first approach it started to accept stuff like this (which I found quite neat, but is not what ruby sass does):

10f#{o}o + 20foo -> 30foo

It also correctly complained when units where off for calculations. Not sure what the reasons are for ruby sass to not evaluate interpolated stuff into numbers again (there was actuall only one failing spec test with function type returning number instead of string). IMO ruby aborts the Binary_Expression parsing when it sees some interpolated stuff, which seems not that easy to implement currently (I suspect this has also something to do with our "everything is a space list" issue).

[xzyfer]

I'm not surprised this is difficult. My initial impression was that this is related to #442.

[KittyGiraudel]

Not sure what the reasons are for ruby sass to not evaluate interpolated stuff into numbers again (there was actuall only one failing spec test with function type returning number instead of string).

Because I believe Sass designers do not want units to be thought as a random string living at the end of a number. While there seem to be an issue with LibSass on this case, the initial problem could be solved by correctly using numbers with units, rather than dealing with strings all along.

[xzyfer]

This fix was a false positive due to sass/sass-spec#380. The spec still fails.

[mgreter]

We now have a passing spec test since #1249 was merged 🎈