Okay, doing it correctly this time.

eval_apply.cpp

@@ -323,7 +323,7 @@ namespace Sass {
             if (!f_env.count(resolved_name)) throw_eval_error("wrong number of arguments to " + name, expr.path(), expr.line());
             f = f_env[resolved_name];
           }
-          return apply_function(f, expr[1], prefix, env, f_env, new_Node, ctx);
+          return apply_function(f, expr[1], prefix, env, f_env, new_Node, ctx, expr.path(), expr.line());
         }
       } break;
       

eval_apply.hpp

@@ -19,7 +19,7 @@ namespace Sass {
   double operate(Node::Type op, double lhs, double rhs);
   
   Node apply_mixin(Node mixin, const Node args, Node prefix, Environment& env, map<string, Function>& f_env, Node_Factory& new_Node, Context& ctx, bool dynamic_scope = false);
-  Node apply_function(const Function& f, const Node args, Node prefix, Environment& env, map<string, Function>& f_env, Node_Factory& new_Node, Context& ctx, string& path = "", size_t line = 0);
+  Node apply_function(const Function& f, const Node args, Node prefix, Environment& env, map<string, Function>& f_env, Node_Factory& new_Node, Context& ctx, string& path, size_t line);
   Node expand_selector(Node sel, Node pre, Node_Factory& new_Node);
   Node expand_backref(Node sel, Node pre);
   void extend_selectors(vector<pair<Node, Node> >&, multimap<Node, Node>&, Node_Factory&);