This is an internal (not published on crates.io) crate which is used to generate the files in the gen/ directory of syn. It is used to ensure that the implementations for Fold, Visit, and VisitMut remain in sync with the actual AST.
To run this program, run cargo run in this directory, and the gen/ folder will be re-generated.
This program is slow, and is therefore not run when building syn as part of the build script to save on compile time.