nix: minimum viable dev shell for `make build` and `make test`

[jhillyerd]

Background: The current cargo2nix based nix flake is broken, and cannot be used to provide a development environment to nix users, it errors out.

This PR introduces a minimal viable devShell that provides a rustup environment for building auraed and auraescript. It uses a shellHook to set a default rust toolchain, as the existing Makefile makes changes to the rustup environment. We may want to switch the project to use a rust-toolchain.toml file in the future, but I don't know enough about aurae to properly test that.

This is a first step towards removing cargo2nix as agreed in #398. I'll send a followup PR to remove the cargo2nix portions of the flake.

Update: Added libseccomp dependency, and confirmed all of make build and make test succeed.

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[jhillyerd]

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[ph]

I've been looking at this situation too, I am kinda new to nix. I wonder if we should really clean the file up as you mentioned and also use the rust-toolchain.yml directly using the overlay helpers fromRustupToolchainFile something like this in the flake.nix:

{
  description = "Aurae development";

  inputs = {
    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-unstable";
    rust-overlay.url = "github:oxalica/rust-overlay";
    flake-utils.url  = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, rust-overlay, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        overlays = [ (import rust-overlay) ];
        pkgs = import nixpkgs {
          inherit system overlays;
        };

        rustVersion = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
      in {
        devShell = pkgs.mkShell {
          buildInputs =
            [
              (rustVersion.override { extensions = [ "rust-src" ]; })
              pkgs.rust-analyzer
              pkgs.protobuf
              pkgs.buf
              pkgs.libseccomp
            ];
        };
      });
}

file: rust-toolchain.toml

[toolchain]
channel = "1.68.0"
components = [ "rustfmt", "clippy", "rust-analyzer"]
targets = [ "x86_64-unknown-linux-musl", "aarch64-unknown-linux-musl" ]

We would also need to patch the Makefile to short circuit the rustup calls. I used the following, Note I don't know what are the good practice in nix for theses situation. But it seems to make everything in local environment work.

.PHONY: musl
musl: ## Add target for musl
ifeq ($(origin IN_NIX_SHELL), undefined)
    rustup target list | grep -qc '$(uname_m)-unknown-linux-musl (installed)' || \
    rustup target add $(uname_m)-unknown-linux-musl
endif

[jhillyerd]

@ph yes, your example is very similar to what I was thinking. Instead of hacking the Makefile to check for nix shell, it may make sense for the entire project to switch over to rust-toolchain.toml, as that's part of rustup and not specific to nix. I suspect the Makefile is going about things the wrong way.

All that seems a bit much for my first PR to the project, I just want to make an incremental improvement (really a small break-fix) before I start deleting the broken aspects of the nix build.