Installs rust even if rust is installed already

[kornelski]

I've installed rust via brew install rust. On top of that I wanted to install cargo only, but when
I run rustup.sh it tries to install (another copy of) rust again.

I'd prefer if the install script checked for existence of rust first, or if there was a cargo-only install script.

[alexcrichton]

Closing as working as intended, the rustup.sh script is used to install both rust and cargo. If you'd like to install only cargo you can download just the cargo tarball and run the install script contained within.

[kornelski]

I've found that script on crates.io, listed as the way to install cargo.

I think in that context it's reasonable to expect it to be able to just
install cargo, and the fact it uses a generic unconditional rust installer
is an unfortunate implementation detail.

[alexcrichton]

The wording around the installation procedure explicitly says:

This will get you the latest nightly build for your platform along with the latest Cargo.

If you're interested in just cargo itself, you'd likely come to this repository which has instructions in the README about how to install from just the cargo nightly.

It seems prudent to have some only-cargo instructions, however, and I would recommend opening an issue/PR at https://github.com/wycats/cargo-website for tweaks to the website.