Easy development environment with nix and direnv

Why

Easy to maintain project dependencies and configuration with nix, without having a full nix install.

Steps

Install nix

Described here: https://nixos.org/guides/nix-pills/install-on-your-running-system.html

Simple solution:

curl -L https://nixos.org/nix/install | sh

Install direnv

Described here: https://direnv.net/docs/installation.html

Configure nix shell

Add a directory named nix.

Configure the package source

Add the following source file with the name source.nix in the nix directory.

{
  nixpkgs = builtins.fetchGit {
    url = "https://github.com/NixOS/nixpkgs.git";
    rev = "6ccc4a59c3f1b56d039d93da52696633e641bc71";
  };
}

The rev value represents the commit you want to reference from the nix-pkg repo. You can find here the latest version: https://github.com/NixOS/nixpkgs/tree/nixpkgs-unstable

Configure the nix shell

Add the configuration for the nix shell, in a file named shell.nix in the nix directory.

let
  sources = import ./sources.nix;
  pkgs = import sources.nixpkgs {};
in
pkgs.mkShell {
  buildInputs = [
    pkgs.hello
  ];
}

Configure direnv to load the nix shell

In the folder of the project, where the nix directory is found add the direnv file, named .envrc with the following content:

#!/usr/bin/env bash

if ! has nix_direnv_version || ! nix_direnv_version 2.2.1; then
  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.2.1/direnvrc" "sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs="
fi

use nix nix/shell.nix
nix_direnv_watch_file nix/sources.nix

This loads the https://github.com/nix-community/nix-direnv support for nix in direnv.

Done

Once everything isconfigured, and direnv is enabled using direnv allow you can test your setup by running hello.