Rustup backend does not detect missing components

[InnocentZero]

Basically the title. I came across this on a fresh arch install when I noticed the rust-analyzer was missing. Now, the way we handle missing packages is just by checking the keys, which does not suffice for Rustup (since the components are stored in InstallOptions and that is discarded).

One way to deal with this would be to convert them into an enum of components and toolchains, but I'm not sure how much of a 'hack' it'll be.

[ripytide]

I don't really want to make it a hacky method again like it was in pacdef, perhaps we could instead fix this by delegating the "is this package missing, and if so which bits do we need to install?" question to be have a per backend implementation. Something like:

trait Backend {
    fn missing(managed: Self::InstallOptions, installed: Option<Self::QueryInfo>) -> Option<Self::InstallOptions>;
}

[ripytide]

Also I don't like the managed variable name as it's a bit vague, perhaps we could rename it to required throughout the codebase?

[InnocentZero]

I don't really want to make it a hacky method again like it was in pacdef, perhaps we could instead fix this by delegating the "is this package missing, and if so which bits do we need to install?" question to be have a per backend implementation. Something like:

trait Backend {
    fn missing(managed: Self::InstallOptions, installed: Option<Self::QueryInfo>) -> Option<Self::InstallOptions>;
}

Yeah, this sounds good, and I was also thinking of "let the backend decide how to install things"