Flakes

Updated: September 28, 2024

Flakes help create standalone builds whether a single program or an entire OS.

Table of Contents

Basic Flake
Lock

It is the replacement of using channels. You are using either one or the other.
Channels work fine but flakes gives more granular control.

There are a few things to note about flakes:

Beware of perpetuation, may cause having many instances of nixpkgs.
dependencies should not have their own nixpkgs.
Avoid using overlays, use composition over inheritance instead.
Use nix follows will reduce nixpkgs instances. Less compute if less sources.

Basic flake

{
  description = "flake for cross platform";
  inputs = {
    nixpkgs.url = "githut:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { self, nixpkgs }:
    let
      supportedSystems = [ "x86_64-darwin" "x86_64-linux" "aarch64-darwin" "aarch64-linux" ]:
      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
  };
}

In regard to items above: when we dclare a default it is referring to self and pointing to an input.

{ }:              # set and semicolon means it is a function
self              # is a flake listed as a parameter, currently looking at
nixpkgs           # also a flake listed as a parameter, but comes from inputs

Lock

# update all flake inputs
nix flake update

# update inputs for commit changes
nix flake update --commit-lock-file

# update a specific input in the flake
nix flake lock --update-input <input>