flake-utils VS rust-overlay

The ‘flake-utils’ readme is a pretty good jumping off point: https://github.com/numtide/flake-utils

I have this or that nitpick with FL and FLP but overall it’s very solid stuff. FLP is a little more “magical”, and that’s not always the best starting out, but you really can’t go wrong with either.

We added two inputs, the first is nixpkgs which lets us specify which version of nixpkgs we should use. There are many thousands of packages in the nixpkg repository, and they are updated often so here will use the unstable branch. We also added flake-utils which helps us generalize the flake to support multiple systems, not just Linux.

The inputs is how you can import external sources of other flakes into the flake project you have. In other words, any project you may need or tools required to get started, this is where you will define their source. Example below is using the standard nixpkgs and a tool called flake-utils, which provides a set of functions to make flake nix packages simpler to set up without external dependencies.

I'm not sure what nix-shell --pure does, but is it equivalent to using a flakes.nix in your projects? Ie i use https://github.com/numtide/flake-utils and direnv to replicate the old shell.nix with a Flakes setup. Per project i have a flakes.nix and a flakes.lock, so it feels just like my old shell.nix setup, but using flakes instead.

A Nix Flake is just an object - check out those surrounding curly braces. This object has two keys, inputs and outputs. The inputs are where we define the flake's dependencies and where to find all the tools we use. This one has two, nixpkgs and flake-utils. Each of these just points to a GitHub URL, and if you follow those links, you'll see each repo provides its own flake.nix. The outputs of each remote flake get piped into the inputs of my flake, so we can use what they provide.

You can easily transition your shell.nix (and default.nix) to a flake-based one by using flake-utils and flake-compat. The former is actually unnecessary, but I would recommend it for typical project environments. Unless you have an impure dependency, this transition would be easy.

Flakes can provide different types of things: - some flakes provide applications that you can nix run, - some flakes provide functions that you can import (e.g. https://github.com/numtide/flake-utils), - some flakes provide overlays to use with nixpkgs (e.g. that emacs-overlay you posted).

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):