More work on better parser logging.

extern/format.hpp

@@ -41,9 +41,12 @@ namespace util {
 
         char* endptr = nullptr;
         index = strtol(&item[0], &endptr, 10);
-        if (index < 0 || index >= (int)args.size()) {
+        if (index >= (int)args.size()) {
             return;
         }
+        if (index < 0) {
+            index = args.size() + index;
+        }
 
         if (*endptr == ',') {
             alignment = strtol(endptr + 1, &endptr, 10);
@@ -57,8 +60,21 @@ namespace util {
         if (*endptr == ':') {
             fmt = endptr + 1;
         }
+        if (*endptr == '.' && *(endptr + 1) == '.') {
+            auto endIndex = strtol(endptr + 2, &endptr, 10);
+            if (endIndex < 0) {
+                endIndex = args.size() + endIndex + 1;
+            }
 
-        args[index]->Format(ss, fmt);
+            for (; index < endIndex; index++) {
+                args[index]->Format(ss, fmt);
+                if (index != endIndex - 1) {
+                    ss << ", ";
+                }
+            }
+        } else {
+            args[index]->Format(ss, fmt);
+        }
 
         return;
     }