code: function ReferencedIdentifier(node, parent, scope, state) {
      var ref = state.letReferences[node.name];
  
      // not a part of our scope
      if (!ref) return;
  
      // this scope has a variable with the same name so it couldn't belong
      // to our let scope
      var localBinding = scope.getBindingIdentifier(node.name);
      if (localBinding && localBinding !== ref) return;
  
      state.closurify = true;
    }
docs: [Please add a description.]