cargo update removes uninstalled deps from target/, when detected they have been removed from Cargo.toml

[ThatNerdyPikachu]

Describe the problem you are trying to solve

I get quite annoyed of having to clear my target folder and rebuild everytime this happens, and I don't feel like digging through target/ in search for my package.

Describe the solution you'd like

An extension to cargo update (maybe even a seperate command) that removes unused packages from target/.

[dwijnand]

This sounds a bit like --prune in git fetch.

[Eh2406]

This is a great example of #6229. The current discussion there is that we want to explore the possibilities in out of tree cargo commands and incorporate them into cargo as we see adoption. I and @holmgr are both planning on making progress on this before the end of the year. But the form that progress will take is still in flux. Probably the best discussion is happening at holmgr/cargo-sweep#2.

[epage]

A garbage collector is being worked on. The tracking issue is #12633. It is first starting with global resources and then we'll be looking at the target directory.