bpo-40334: Support CO_FUTURE_BARRY_AS_BDFL in the new parser by pablogsal · Pull Request #19721 · python/cpython

(I guess some later check will eventually detect the exception.)

In the exception path, we can return anything IIRC because upstream code will catch that and propagate it. The return value is only used to signal if the subrule for the token should return NULL or the token (indicating that it parses).

Maybe is best to always return an error (0) even after the raise.