I like the idea of granular permissions for libraries. When you include a dependency you whitelist permissions it gets. Package managers could automate this if the language supports it. But making it about permissions instead of metrics .akes it not arbitrary. This library gets no filesystem access, that one gets no network access. This one runs build time system commands... Austral is the only language I know of that supports such a thing. While it might be possible to bolt it on to rust, I think it would take so much rework to make it infeasible.