How to install packages from unstable channel via overlays?

[Kazuto]

I'm trying to install a single package from the unstable channel but don't have the slightest clue about how because the docs aren't really helpful at all. They only show how to create overlays etc. but not how to use them.

This overlay will be made available on your flake’s overlays output with the same name as the directory that you created. is not really an explanation for users who never worked with overlays before. The docs need more examples and not just on how to create the file.

# overlays/sketchybar-app-font/default.nix

{
channels,
namespace,
inputs,
... }:

final: prev: {
    inherit (channels.unstable) sketchybar-app-font;
}

Where do I have to register the overlay?
How do I install the unstable package now in my modules/sketchybar/default.nix?

{ options, config, lib, pkgs, ... }:

with lib;
with lib.shiro;
let
  cfg = config.shiro.tools.sketchybar;
in
{
  options.shiro.tools.sketchybar = with types; {
    enable = mkBoolOpt false "Whether or not to install sketchybar";
  };

  config = mkIf cfg.enable {
    environment.systemPackages = with pkgs; [ sketchybar ];

    fonts.packages = with pkgs; [
        sketchybar-app-font
    ];

    services.sketchybar = {
      enable = true;
      package = pkgs.sketchybar;
    };
  };
}

[pinage404]

i like to be explicit from which source it come from when i install packages (ex pkgs.unstable.some-package)

i did it like this

overlays/unstable_packages_overlay/default.nix

{
  inputs,
  ...
}:

_final: pkgs: {
  unstable = import inputs.nixpkgs-unstable {
    inherit (pkgs) system;
  };
}

somewhere else in a .nix file

{
  pkgs,
  ...
}:

{
  // ...
  services.ollama.package = pkgs.unstable.ollama;
  // ...
}

But sometimes, it's easier to have implicit source (e.g. for steam which implicitly include several packages)

overlays/unfree_packages_overlay/default.nix

{
  inputs,
  ...
}:

_final: pkgs:
let
  unfreePkgs = import inputs.nixpkgs-current {
    inherit (pkgs) system;
    config = {
      allowUnfree = true;
    };
  };
in
{
  unfree = unfreePkgs;

  inherit (unfreePkgs)
    steam
    steamPackages
    steam-unwrapped
    ;
}

somewhere else in a .nix file

{
  programs.steam = {
    enable = true;
  };
}

it also could have been something like

{
  pkgs,
  ...
}:

{
  environment.systemPackages = [
    pkgs.steam
  ];
}

i hope this help

[jakehamilton]

@Kazuto I am not sure I understand, you have already overlaid the version of the package you want from unstable and are using it in your configuration. Am I missing something?

[jakehamilton]

@pinage404 if you want to provide the entirety of unstable I would recommend assigning the channel to the package set so that you can benefit from its overlays and configuration.

{ channels, ... }:
final: prev: {
  inherit (channels) unstable;
}

[Kazuto]

@Kazuto I am not sure I understand, you have already overlaid the version of the package you want from unstable and are using it in your configuration. Am I missing something?

I thought I was missing something because it did not install the most recent version (2.0.32) according to the unstable channel but 2.0.27, as icons were missing which would be available in the latest version.

[jakehamilton]

@Kazuto is your unstable input up to date?

[Kazuto]

@Kazuto is your unstable input up to date?

I think so. How can I check if it's up to date?