unsupported argument 'fetchSubmodules' to 'fetchGit'

I’m specifying a fetchGit repository and including fetchSubmodules

let
  mach-nix = import (builtins.fetchGit {
    url = "https://github.com/DavHau/mach-nix/";
    ref = "3.3.0";
  }) {};
  raylib-python-cffi = mach-nix.buildPythonPackage {
    src = builtins.fetchGit {
      url = "https://github.com/electronstudio/raylib-python-cffi/";
      ref = "master";
      rev = "a15d6e2d2ec8ce39e90c101164d460b9797e0c11";
      fetchSubmodules = true;
    };
  };
... <snip>

I get the following error:

unsupported argument 'fetchSubmodules' to 'fetchGit', at /home/adam/Workspace/koine-py/shell.nix:28:7

I’m not sure what’s causing this, because I believe this is using the Nixpkgs builtin and not Mach-nix, and it should support “fetchSubmodules”. I’m running Nix 20.09, from what I can tell that should support fetchSubmodules without any trouble.

Any help understanding what’s going on would be appreciated.

[adamlwgriffiths]

Ok thanks for clarifying.

[bjornfor]

So what do I do to utilise nixUnstable builtin’s in a nix shell?

You have to install nixUnstable. (The builtins are tied to the Nix distribution – they’re built-in 😃 )