Improve arg binding when arglist contains expressions

It seems that arglist should always be a list of `Argument`
objects. This is not always true and this commit makes the
`value_at_index` method more robust to avoid the segfault.

Author: mgreter

src/ast.cpp

@@ -1952,5 +1952,20 @@ namespace Sass {
     return message();
   }
 
+  //////////////////////////////////////////////////////////////////////////////////////////
+  // Additional method on Lists to retrieve values directly or from an encompassed Argument.
+  //////////////////////////////////////////////////////////////////////////////////////////
+  Expression* List::value_at_index(size_t i) {
+    if (is_arglist_) {
+      if (Argument* arg = dynamic_cast<Argument*>((*this)[i])) {
+        return arg->value();
+      } else {
+        return (*this)[i];
+      }
+    } else {
+      return (*this)[i];
+    }
+  }
+
 }
 

src/ast.hpp

@@ -1707,11 +1707,6 @@ namespace Sass {
     ATTACH_OPERATIONS()
   };
 
-  //////////////////////////////////////////////////////////////////////////////////////////
-  // Additional method on Lists to retrieve values directly or from an encompassed Argument.
-  //////////////////////////////////////////////////////////////////////////////////////////
-  inline Expression* List::value_at_index(size_t i) { return is_arglist_ ? ((Argument*)(*this)[i])->value() : (*this)[i]; }
-
   /////////////////////////////////////////
   // Abstract base class for CSS selectors.
   /////////////////////////////////////////

src/functions.cpp

@@ -1562,16 +1562,24 @@ namespace Sass {
       List* arglist = SASS_MEMORY_NEW(ctx.mem, List, *ARG("$args", List));
 
       Arguments* args = SASS_MEMORY_NEW(ctx.mem, Arguments, pstate);
+      std::string full_name(name + "[f]");
+      Definition* def = static_cast<Definition*>((d_env)[full_name]);
+      Parameters* params = def ? def->parameters() : 0;
+      size_t param_size = params ? params->length() : 0;
       for (size_t i = 0, L = arglist->length(); i < L; ++i) {
         Expression* expr = arglist->value_at_index(i);
+        Parameter* p = param_size > i ? (*params)[i] : 0;
+        if (List* list = dynamic_cast<List*>(expr)) {
+          if (p && !p->is_rest_parameter()) expr = (*list)[0];
+        }
         if (arglist->is_arglist()) {
-          Argument* arg = static_cast<Argument*>((*arglist)[i]);
+          Argument* arg = dynamic_cast<Argument*>((*arglist)[i]);
           *args << SASS_MEMORY_NEW(ctx.mem, Argument,
                                    pstate,
                                    expr,
                                    "",
-                                   arg->is_rest_argument(),
-                                   arg->is_keyword_argument());
+                                   arg ? arg->is_rest_argument() : false,
+                                   arg ? arg->is_keyword_argument() : false);
         } else {
           *args << SASS_MEMORY_NEW(ctx.mem, Argument, pstate, expr);
         }