Not very useful

This doesn't seem particularly useful, at least in Rust. This seems to only work with the AST, which doesn't allow for much analysis.
If this were to integrate with something like clippy it could have much deeper analysis by inspecting the HIR and MIR.

To me it looks like what we really want is something like clippy plugins. The reason they don't exist is of course because clippy uses permanently unstable rustc libraries so any clippy plugin would need high maintanance...