when `rustdoc` finishes building a documentation bundle, it prints its path, which is often nested deep in the build directory. however, `rustbook` does not do the same, which is confusing, since they both use the `./x doc` command as a frontend. reproduction: `./x doc src/doc/rustdoc/` it's also worth noting that this information *does* get printed when you do use `--open`, so it is easily accessible.