Getting Started With Nix Flakes

Nix flakes provide a standard way to write Nix expressions (and therefore packages) whose dependencies are version-pinned in a lock file, improving reproducibility of Nix installations.

• A flake refers to a file-system tree whose root directory contains the Nix file specification called flake.nix.

https://nixos.wiki/wiki/Flakes

Generate a flake.nix file 🔗

To begin with, you need to generate a flake.nix file.

# Generate a very basic flake.nix.
nix flake init

# Generate a flake.nix from a template.
nix flake init --template "https://flakehub.com/f/the-nix-way/dev-templates/*#shell"

Allow Unfree 🔗

In order to allow the inclusion of unfree packages, you can set a config setting config.allowUnfree = true;.

To set it simply for a flake, you can add it to a nixpkgs input.

{
  ...

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs { inherit system; config.allowUnfree = true; };
      in
        ...
}

Git-related gotchas 🔗

For flakes in git repos, only files in the working tree will be copied to the store.

If you have a repo with dependencies for example that might have been added to a .gitignore file, these files will not be added to the store and will not be available during any nix build runs.

If you need to circumvent this limitation and reproducibility is not your primary goal, you can invoke nix build with a path to include everything, even files not tracked by git.

nix build path://$(pwd)