rust-overlay VS nixpkgs-mozilla

I'm trying to understand overlays in order to make a proper rustup install (I've read that this overlay is the best way to go).

real-world example: https://github.com/oxalica/rust-overlay/blob/master/flake.nix

In this language context specifically, if one wanted to manage their workspace with Nix I would reach for Riff and/or oxalica/rust-overlay first, since they are deliberately more aware of Rust-specific nuance. In the latter's case it has compatibility paths with rustup-toolchain files as well, for allowing your peers who can't or won't adopt Nix to continue to feel like first-class participants in the project. Another alternative I don't have experience with would be nix-community/fenix.

p.s. I'm not sure if it's mentioned much of anywhere, but it'd be neat if there was a way to figure out the appropriate cargo from a rust-toolchain/rust-toolchain.toml if present, ala https://github.com/oxalica/rust-overlay. Funnily enough 95% of my development time is in Rust, but I don't actually have it installed globally, fun times being a NixOS user. I'd definitely make the argument that cargo is an external dependency!

Many of us have moved to https://github.com/oxalica/rust-overlay over Mozilla's overlay.

We added rust-overlay, so we can easily specify different rust versions without relying on nixpkgs to give us what ever rust version in there.

If it's Rust, you can use https://github.com/oxalica/rust-overlay to get any version you want very easily without pinning an instance of nixpkgs just for it.

asdf does not allow you to keep three different versions of the same language, so I'm not sure how that compares? It's not super-trivial to do in Nix, but at least you can do it.

asdf is also no different than Nix when it comes to minor/major versions. You're at the mercy of what the plugin does, other than that you have to create your own plugin from scratch or make a fork. Nix has the option to patch things up more easily at least.

How does this compare to https://github.com/oxalica/rust-overlay/ ? Can fenix ingest a rust-toolchain file and provide packages from it?

Can you say a bit about how this compares to oxalica’s rust overlay?

I frequently try to do something, say use (from the README of rust overlay):

Do I know how to do this? No, but this real-world and the wiki might be places to start. I'll eventually have to figure this out myself so if I get around to that I'll post what I learn too

Is there a way to still keep it pure? From the nixpkgs-mozilla repo:

Fenix provides the minimal, default, and complete profile of rust toolchains, latest profile of nightly toolchains, nightly version of rust analyzer and its vscode extension. It aims to be a replacement for rustup and the rust overlay provided by nixpkgs-mozilla.

Firefox-nightly is maintained in the official nixpkgs-mozilla repo, so you're incorrect on that point. It's unreasonable to ask me to pick out examples for you, just to prove that numbers have actual meaning. However, feel free to peruse recently added packages and see which ones do and don't make their way to the AUR.

4. I would suggest Mozilla's Rust overlay or fenix or similar instead of Rustup - that would be more of the "Nix-way" to acquire the toolchain and you can still manage multiple versions. Not sure what the Ruby equivalent is, I don't do Ruby.

and for building software, I'd suggest using flakes for both the software repo and the system configuration, because then you can just add the software flake as an input to the configuration flake and that's it, and you have the build code separated from your system. Using e.g. "ssh+git://git.example.com/secret-project" as the input should work, though I don't know which user's SSH keys it will try to use. I think mozilla-overlay is a good example, the flake outputs are a couple overlays you can add to your system's nixpkgs (here's how to add overlays in nixos), especially take a look at phlay-overlay in the mozilla repo, it's an overlay that adds one package so it's pretty simple. You can do something similar without using flakes though, fetching the sources needs to be done differently though, I know there's the builtins.fetchGit and builtins.fetchTarball functions, the former I assume would work similarly with SSH keys, no idea about the latter. The rest, making a derivation for building the software and adding it to your configuration's nixpkgs, should work the same.

I am on NixOS at the moment, Widevine (Nightly) on Arch was working well. I installed Nightly from https://github.com/mozilla/nixpkgs-mozilla.

Fenix provides the minimal, default, and complete profile of rust toolchains, latest profile of nightly toolchains, nightly version of rust analyzer and its vscode extension. It aims to be a replacement for rustup and the rust overlay provided by nixpkgs-mozilla.