Merge some of the crates (probably only rustup and rustup-dist)

[dwijnand]

Split out from #1611

The current crates tree is:

rustup-win-installer
└── rustup
    └── rustup-dist
        └── rustup-utils
            └── download

[dev-dependencies]
└── rustup-mock

WDYT about squashing that down to:

rustup-win-installer
└── rustup

And the only reason to keep those separate is because I can't run rustup-win-installer with its build.rs. WDYT?

[nrc]

👍 I'm keen on this and have contemplated something similar myself in the past. I'd also be keen to turn Rustup into a workspace, rather than a bunch of separate crates. I think it might make sense to keep rustup-mock separate since it is only used for testing and is quite different from the rest. I think it might also make sense to keep download separate, if it can be a strongly encapsulated crate (ideally shared with Cargo).

[dwijnand]

Ok I'll make it a workspace and keep download separate. But rustup-mock I was just going to have as a module of the rustup tests (much like the "support" module in cargo's testsuite).

[dwijnand]

Root layout-wise @kinnison prefers

/Cargo.lock
/Cargo.toml
/src/ (the sources of the rustup crate)
/download/ (the separate download crate)

The code in rustup-mock would either become #[cfg(test)]-gated code in the rustup crate, or directly a module in the tests.