Use the overlay, Luke!
When working with Rust on NixOS,
one always had the problem that the stable compiler was updated very sparsely.
One time I had to wait six weeks after the rustc release until I finally got
the compiler update for NixOS.
This is kind of annoying, especially because rustc is a fast-moving target
and each new compiler release brings more awesomeness included.
As an enthusiastic Rust programmer, I really want to be able to use the
latest stable compiler all the time. I don't want to wait several days or even
weeks until I can use it.
Use the overlay, Luke!
Finally, with NixOS 17.03 and unstable as of now, we have overlays for nixpkgs. This means that one can “inject” custom nix expressions into the nixpkgs set.
Meet the full awesomeness of nixpkgs!
Soon after overlays were introduced, the Mozilla nixpkgs overlay was announced on the nixos-dev mailinglist.
Now we can install rustc in stable, beta and nightly directly with pre-build
binaries from Mozilla.
So we do not need to compile rustc nightly from source on our local machines
if we want the latest great rust feature.
This is so awesome. Everybody should use the rust overlay now, in my opinion. It's really convenient to use and gives you more flexability with your rust installation on NixOS. So why not?