In reply to @thubrecht:matrix.org

You just have to find the right entrypoint, in that case, the following works:

    git-hooks = import (source."git-hooks.nix" + "/nix") {
      nixpkgs = source.nixos-unstable;
      gitignore-nix-src = null;

      system = builtins.currentSystem;
      isFlakes = false;
    };