Improving argument parsing to match the new restrictions in canonical Sass.

document.hpp

@@ -133,7 +133,7 @@ namespace Sass {
     Node parse_parameter();
     Node parse_mixin_call();
     Node parse_arguments();
-    Node parse_argument();
+    Node parse_argument(Node::Type);
     Node parse_assignment();
     Node parse_propset();
     Node parse_ruleset(Selector_Lookahead lookahead, Node::Type inside_of = Node::none);

document_parser.cpp

@@ -192,15 +192,18 @@ namespace Sass {
   {
     Token name(lexed);
     Node args(context.new_Node(Node::arguments, path, line, 0));
+    Node::Type arg_type = Node::none;
     if (lex< exactly<'('> >()) {
       if (!peek< exactly<')'> >(position)) {
-        Node arg(parse_argument());
+        Node arg(parse_argument(Node::none));
         arg.should_eval() = true;
         args << arg;
+        if (arg.type() == Node::assignment) arg_type = Node::assignment;
         while (lex< exactly<','> >()) {
-          Node arg(parse_argument());
+          Node arg(parse_argument(arg_type));
           arg.should_eval() = true;
           args << arg;
+          if (arg.type() == Node::assignment) arg_type = Node::assignment;
         }
       }
       if (!lex< exactly<')'> >()) throw_syntax_error("improperly terminated argument list for " + name.to_string());
@@ -208,8 +211,10 @@ namespace Sass {
     return args;
   }
   
-  Node Document::parse_argument()
+  Node Document::parse_argument(Node::Type arg_type)
   {
+    // if arg_type is assignment, only accept keyword args from here onwards
+    if (arg_type == Node::assignment) {
       if (peek< sequence < variable, spaces_and_comments, exactly<':'> > >()) {
         lex< variable >();
         Node var(context.new_Node(Node::variable, path, line, lexed));
@@ -220,8 +225,33 @@ namespace Sass {
         return assn;
       }
       else {
-      return parse_space_list();
+        throw_syntax_error("ordinal arguments must precede keyword arguments");
+      }
     }
+    // otherwise accept either, and let the caller set the arg_type flag
+    if (arg_type == Node::none &&
+        peek< sequence < variable, spaces_and_comments, exactly<':'> > >()) {
+      lex< variable >();
+      Node var(context.new_Node(Node::variable, path, line, lexed));
+      lex< exactly<':'> >();
+      Node val(parse_space_list());
+      Node assn(context.new_Node(Node::assignment, path, line, 2));
+      assn << var << val;
+      return assn;
+    }
+    return parse_space_list();
+    // if (peek< sequence < variable, spaces_and_comments, exactly<':'> > >()) {
+    //   lex< variable >();
+    //   Node var(context.new_Node(Node::variable, path, line, lexed));
+    //   lex< exactly<':'> >();
+    //   Node val(parse_space_list());
+    //   Node assn(context.new_Node(Node::assignment, path, line, 2));
+    //   assn << var << val;
+    //   return assn;
+    // }
+    // else {
+    //   return parse_space_list();
+    // }
   }
 
   Node Document::parse_assignment()