How to get warnings about invalid css values

I am migrating from sass to postcss. To make it easier, I am using postcss-simple-vars, which supports similar variables like sass does.

My problem is:

$size: 100px;

.class {
    width: $size * 2;
}

Sass result:

.class {
    width: 200px;
}

Postcss with simple vars result:

.class {
    width: 100px * 2;
}

The latter seems to be invalid css code. In order to fix it, I need to use the calc() function. The problem is to find all the occurances of those calculations in my code. I have ~ 1 MB of scss...

Is there any tool (linter, compiler, etc) which would analyze my css and warn me of all the places where this needs to be taken care of?