Failed flags support

Author: obenjiro

.eslintrc.json

@@ -230,7 +230,7 @@
         "prefer-numeric-literals": "error",
         "prefer-reflect": "off",
         "prefer-rest-params": "off",
-        "prefer-spread": "error",
+        "prefer-spread": "off",
         "prefer-template": "off",
         "quote-props": "off",
         "quotes": "off",

src/speg_visitor.js

@@ -61,19 +61,24 @@ SPEG_actions.prototype.parsing_ordered_choice = function(node) {
 };
 
 SPEG_actions.prototype.parsing_sub_expression = function(node) {
-    return function() {
-        var result = node.children[1].children[0].apply(this, arguments);
+    return function(state) {
+        var result = node.children[1].children[0].call(this, state);
+        var tags = node.children[0].children.map(function(tag_node){
+            return tag_node.children[0].match;
+        });
         if (result) {
-            var tags = node.children[0].children.map(function(tag_node){
-                return tag_node.children[0].match;
-            });
             if (tags.length > 0) {
                 if (result.tags) {
                     result.tags = tags.concat(result.tags);
                 } else {
                     result.tags = tags;
                 }
             }
+        } else {
+            if (!state.failedTags) {
+                state.failedTags = [];
+            }
+            state.failedTags.push.apply(state.failedTags, tags);
         }
         return result;
     }