Nix, Direnv, Just, the trio that makes life easier

Nothing is more frustrating when working on a project than having to:

Search for the necessary tools to work on this project (compilation, development, etc.).

Manage the versions of installed packages based on their installation date.

Manage the distributions on which these packages are installed (used package manager).

During the development phase of a project, maintaining a consistent development environment that evolves over time is quite challenging, due in part to the following:

Some packages are not available on all distributions of Windows, MacOS, Linux (Ubuntu, Archlinux, Fedora, Suse, etc.).
Package versions may become unavailable due to distribution changes.

Some modern programming languages have recognized this challenge and have dependency management systems with locking features to ensure the reproducibility of development environments, including:

Go
Python
Ruby
Rust
etc …

These systems allow for maintaining the same dependencies throughout the project’s lifecycle, but this only applies to the libraries used and not to all third-party tools.

That’s why I use the trio:

Nix: Enables obtaining a reproducible system.
Direnv: Allows executing a command upon entering a directory.
Just: Provides a command runner and help display.

Installation

Direnv

Install the direnv package

# install direnv
curl -sfL https://direnv.net/install.sh | bash

Configure the shell to take direnv into account during a new shell.

Bash

Add the following line to the end of the ~/.bashrc file:

eval "$(direnv hook bash)"

Add the following line to the end of the ~/.zshrc file:

ZSH

eval "$(direnv hook zsh)"

FISH

Add the following line to the end of the ~/.config/fish/config.fish file:

direnv hook fish | source

Fish supports 3 modes which you can set with environment variable global direnv_fish_mode:

set -g direnv_fish_mode eval_on_arrow    # Trigger direnv at the prompt, and on each directory change with arrow (default)
set -g direnv_fish_mode eval_after_arrow # Trigger direnv at prompt, and only after arrow changes directory before executing command
set -g direnv_fish_mode disable_arrow    # Trigger direnv at prompt only, this is similar functionality to the original behavior

Nix

Linux

sh <(curl -L https://nixos.org/nix/install) --daemon
grep 'experimental-features' /etc/nix/nix.conf || (echo 'experimental-features = nix-command flakes' | sudo tee -a /etc/nix/nix.conf)

Windows

sh <(curl -L https://nixos.org/nix/install) --daemon
grep 'experimental-features' /etc/nix/nix.conf || (echo 'experimental-features = nix-command flakes' | sudo tee -a /etc/nix/nix.conf)

MacOS

sh <(curl -L https://nixos.org/nix/install)
grep 'experimental-features' /etc/nix/nix.conf || (echo 'experimental-features = nix-command flakes' | sudo tee -a /etc/nix/nix.conf)

Once nix and direnv are installed, when you first access the directory of a project, you will have to authorize the automatic execution of direnv with the following command: direnv allow

You can also launch onboarding with the following command nix develop

just

The just tool will be installed automatically with nix and flake, see the next section.

Configuration of the onboarding project

To activate the onboarding of the project, simply copy the 3 files below in the root directory of your project.

projet
├─ .envrc
├─ flake.nix
└─ justfile

Configuring the .envrc file

use flake

Configuring the flake.nix file

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };
  outputs = { nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; };
      in
      {
        devShells.default = with pkgs;
          mkShell {
            name = "Default developpement shell";
            packages = [
              cocogitto
              nixpkgs-fmt
              nodePackages.markdownlint-cli
              pre-commit

              deno
              gum
              just
            ];
            shellHook = ''
              export PROJ="devops.jesuislibre.org"

              echo ""
              echo "⭐ Welcome to the $PROJ project ⭐"
              echo ""
            '';
          };
      });
}

Configuring the justfile file

#!/usr/bin/env just -f

# This help
# Help it showed if just is called without arguments
@help:
    just -lu | column -s '#' -t | sed 's/[ \t]*$//'

###############################################################################
# pre-commit
###############################################################################

# Setup pre-commit
precommit-install:
    #!/usr/bin/env bash
    test ! -f .git/hooks/pre-commit && pre-commit install || true

# Update pre-commit
@precommit-update:
    pre-commit autoupdate

# precommit check
@precommit-check:
    pre-commit run --all-files

###############################################################################
# Tools
###############################################################################

# Update documentation
@doc-update FAKEFILENAME:
    ./updatedoc.ts

# Lint the project
@lint:
    pre-commit run --all-files

# Repl the project
@repl:
    nix repl --extra-experimental-features repl-flake .#

# Show installed packages
@packages:
    echo $PATH | tr ":" "\n" | grep -E "/nix/store" | sed -e "s/\/nix\/store\/[a-z0-9]\+\-//g" | sed -e "s/\/.*//g"

Example of use

Here is an example of use for the documentation project of JSL Devops

At first, you will notice that the just and hugo tools are not available in the user’s distribution. However, without intervention on his part, you will find that they become available thanks to Nix and the flake.nix file.