Nix mixing sources

configuration.nix

{ config, pkgs, ... }:

let
  # 20.03 channel
  pkgs-2003 = import (fetchTarball https://github.com/nixos/nixpkgs-channels/archive/nixos-20.03.tar.gz) {};

  # unstable channel
  pkgs-unstable = import (fetchTarball https://github.com/nixos/nixpkgs-channels/archive/nixos-unstable.tar.gz) {};

  # specific commit
  pkgs-22a81aa = import (fetchTarball https://github.com/nixos/nixpkgs/archive/22a81aa5fc15b2d41b12f7160a71cd4a9f3c3fa1.tar.gz) {};
in
{

  environment.systemPackages = [
    # from <nixpkgs>
    pkgs.tree

    # from 20.03
    pkgs-2003.hello

    # from unstable
    pkgs-unstable.neovim

    # from 58d44a3 commit
    pkgs-22a81aa.janet
  ];

}