flake.nix

{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    naersk.url = "github:nix-community/naersk";
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    rust-overlay.url = "github:oxalica/rust-overlay";
  };
  outputs = { self, flake-utils, naersk, nixpkgs, rust-overlay, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        overlays = [ (import rust-overlay) ];
        pkgs = import nixpkgs { inherit system overlays; };
        toolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain;
        naersk' = pkgs.callPackage naersk {
          cargo = toolchain;
          rustc = toolchain;
        };
      in rec {

        # For `nix build` & `nix run`:
        defaultPackage = naersk'.buildPackage { src = ./.; };

        # For `nix develop`:
        devShell = pkgs.mkShell { nativeBuildInputs = [ toolchain ]; };
      });
}