Please note that although the latest commits on [1] were 2 months ago, for a long while it hasn't been updated and/or usable to a decent degree.

It seemed to have been deprecated in favor of [2] when the original author of lex-pass left Facebook.

Sorry if any of this information is a little off/incomplete, I think it's been 2 years when I oversaw a BSc paper revolving around extending lex-pass.

[1]: https://github.com/facebook/lex-pass [2]: https://github.com/facebook/pfff