Rust, Cargo, et al do not have a "every crate or package on your hard drive" concept, nor a "the crates and packages you have used in the last year" ...you get the idea.

The tools are super awesome which is why I feel confident that someone could create the following functionality in a very slick cargo-y manner:

When you do a rustup update, or when you add some profiling thing that requires recompilation, or when you do anything that will require your next build to be mostly a "rebuild", you end up with the problem of having all or much of your ./target data totally becoming obsolete and useless.

Tools like sccache can mitigate this some, but only some, and what's left is potentially hours of compilation that you'll end up needing to do over the next few weeks or months. You will forget all about this and try to re-boot some project you put aside a while ago and whamo you've got to recompile all that crap.

It would be nice if some reasonably intelligent effort was made to identify this stuff ahead of time and give you a chance to do it, say overnight. Or over several nights.

Not only would this help you but it would remove some barriers to just, say, doing a rustup update every night in a crontab. The more people who ride the bleeding edge, the faster progress will (might??) go.