With Nix's Flake being the future of nix and a better solution than the current combo of NIX_PATH/nix-channel. I refactored my NixOS configuration but often needed a way to pass flake's inputs to nixos configurations top modules.

After digging a bit in the nixos build system, I found that SpecialArgs can be used to pass arbitrary arguments to modules.

# flake.nix
{
  description = "NixOS configurations";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-21.05";
    nixos-hardware.url = "github:nixos/nixos-hardware";
  };

  outputs = { self, nixpkgs, nixos-hardware, ... }@args: {
    nixosConfigurations = {
      t250 = nixpkgs.lib.nixosSystem {
        specialArgs = {
          flakeInputs = args;
        };
        
        imports = [
          ./t250.nix
        ];
      };
    };
  };
}

# t250.nix;
{ flakeInputs, ... }:
{
  imports = [
    flakeInputs.nixos-hardware.nixosModules.lenovo-thinkpad-x250
  ];
}