Even after fixing #11, it's clear that source maps aren't being generated correctly.

Given:

@def BG_COLOR red;

.test {
  font-family: Helvetica, Tahoma;
  background-color: BG_COLOR;
}

The compiler produces:

.a{font-family:Helvetica,Tahoma;background-color:red}

and the sourcemap:

{
"version":3,
"file":"test.source.map",
"lineCount":1,
"mappings":"AAEqB,CAAD,CAGwE,aAFjD,QAAA,CAAA,CAAW,KAAX,CAEiD,kBAL9E;",
"sources":["/tmp/test.gss"],
"names":[]
}

A visualization of the sourcemap shows that the @def is correctly linked, but none of the other parts make much sense.