nixpkgs/pkgs/applications/emulators/libretro/README.md

Libretro

libretro cores and related packages.

Adding new cores

The basic steps to add a new core are:

1. Add a new core using mkLibretroCore function (use one of the existing cores as an example)
2. Add your new core to default.nix file
3. Try to build your core with nix-build -A libretro.<core>

Using RetroArch with cores

To create a custom RetroArch derivation with the cores you want (instead of using retroarch-full that includes all cores), you can use .withCores like this:

{ pkgs, ... }:

let
  retroarchWithCores = (
    pkgs.retroarch.withCores (
      cores: with cores; [
        bsnes
        mgba
        quicknes
      ]
    )
  );
in
{
  environment.systemPackages = [ retroarchWithCores ];
}

For advanced customization, see wrapRetroArch wrapper.