code: public function process(Tokens $tokens, Token $token, $index)
      {
          if (
              $token->equals('&')
              && $tokens[$tokens->getPrevMeaningfulToken($index)]->isGivenKind(T_FUNCTION)
          ) {
              $tokens[$index] = new Token([CT::T_RETURN_REF, '&']);
          }
      }
docs: {@inheritdoc}