Handling guarded assignments.

document_parser.cpp

@@ -218,6 +218,7 @@ namespace Sass {
     Node val(parse_list());
     Node assn(context.new_Node(Node::assignment, path, line, 2));
     assn << var << val;
+    if (lex< default_flag >()) assn << context.new_Node(Node::none, path, line, 0);
     return assn;
   }
   
@@ -609,7 +610,8 @@ namespace Sass {
         peek< exactly<'}'> >(position) ||
         peek< exactly<'{'> >(position) ||
         peek< exactly<')'> >(position) ||
-        peek< exactly<','> >(position))
+        peek< exactly<','> >(position) ||
+        peek< default_flag >(position))
     { return disj1; }
     
     Node space_list(context.new_Node(Node::space_list, path, line, 2));
@@ -620,7 +622,8 @@ namespace Sass {
              peek< exactly<'}'> >(position) ||
              peek< exactly<'{'> >(position) ||
              peek< exactly<')'> >(position) ||
-             peek< exactly<','> >(position)))
+             peek< exactly<','> >(position) ||
+             peek< default_flag >(position)))
     {
       Node disj(parse_disjunction());
       space_list << disj;

eval_apply.cpp

@@ -124,6 +124,7 @@ namespace Sass {
           val = eval(val, prefix, env, f_env, new_Node, ctx);
         }
         Node var(expr[0]);
+        if (expr.is_guarded() && env.query(var.token())) return expr;
         // If a binding exists (possible upframe), then update it.
         // Otherwise, make a new on in the current frame.
         if (env.query(var.token())) {
@@ -657,6 +658,7 @@ namespace Sass {
             val = eval(val, Node(), bindings, ctx.function_env, new_Node, ctx);
           }
           Node var(stm[0]);
+          if (stm.is_guarded() && bindings.query(var.token())) continue;
           // If a binding exists (possible upframe), then update it.
           // Otherwise, make a new on in the current frame.
           if (bindings.query(var.token())) {

node.hpp

@@ -173,6 +173,7 @@ namespace Sass {
     bool& should_eval() const;
     bool& is_unquoted() const;
     bool is_numeric() const;
+    bool is_guarded() const;
 
     string& path() const;
     size_t line() const;
@@ -349,6 +350,7 @@ namespace Sass {
   inline bool& Node::should_eval() const   { return ip_->should_eval; }
   inline bool& Node::is_unquoted() const   { return ip_->is_unquoted; }
   inline bool Node::is_numeric() const     { return ip_->is_numeric(); }
+  inline bool Node::is_guarded() const     { return (type() == assignment) && (size() == 3); }
   
   inline string& Node::path() const  { return ip_->path; }
   inline size_t  Node::line() const  { return ip_->line; }

prelexer.cpp

@@ -271,6 +271,13 @@ namespace Sass {
                        spaces_and_comments,
                        exactly<important_kwd> >(src);
     }
+    // Match Sass "!default" keyword.
+    extern const char default_kwd[] = "default";
+    const char* default_flag(const char* src) {
+      return sequence< exactly<'!'>,
+                       spaces_and_comments,
+                       exactly<default_kwd> >(src);
+    }
     // Match CSS pseudo-class/element prefixes.
     const char* pseudo_prefix(const char* src) {
       return sequence< exactly<':'>, optional< exactly<':'> > >(src);

prelexer.hpp

@@ -351,6 +351,8 @@ namespace Sass {
     const char* uri(const char* src);
     // Match CSS "!important" keyword.
     const char* important(const char* src);
+    // Match Sass "!default" keyword.
+    const char* default_flag(const char* src);
     // Match CSS pseudo-class/element prefixes
     const char* pseudo_prefix(const char* src);
     // Match CSS function call openers.