Checking for unbound variable references.

eval_apply.cpp

@@ -205,6 +205,7 @@ namespace Sass {
       } break;
       
       case Node::variable: {
+        if (!env.query(expr.content.token)) eval_error("reference to unbound variable " + expr.content.token.to_string(), expr.line_number, expr.file_name);
         return env[expr.content.token];
       } break;
       

exceptional.scss

@@ -30,12 +30,12 @@ div[hux ~= "hello"] {
   
 }
 
-$y: hey;
+//$y: hey;
 
 @mixin foo($x) {
   foofoo: $x $y;
 }
 
 div {
-  @include foo(blah, $x: ho, goo);
+  @include foo();
 }
\ No newline at end of file