Which mainline compilers or runtimes use a generated parser? I know that CRuby does, though they've recently standardized on Prism as their public AST, and it's possible that they'll switch to Prism for parsing eventually. I know that Go used to, as well as ancient versions of GCC.

It seems that, from the outside looking in, ~all significant PL projects end up using a hand-written recursive descent parser, eventually.

The problem remains how to verify that the hand-written parser matches the purported grammar, and that the grammar isn’t ambiguous in the first place.