Impure installations for NixOS (home-manager)

[endereyewxy]

I use the following to install Helix from master to NixOS:

# flake.nix
{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-24.11";

    home-manager.url = "github:nix-community/home-manager/release-24.11";
    home-manager.inputs.nixpkgs.follows = "nixpkgs";

    helix.url = "github:helix-editor/helix";
  };

  ...
}

# helix.nix
{ config, pkgs, helix, ... }:

{
  programs.helix = {
    enable = true;
    package = helix.packages.${pkgs.system}.default;
  };
}

But when running nixos-rebuild switch, it complains about impurity:

error: access to absolute path '/home' is forbidden in pure evaluation mode (use '--impure' to override)

Is there a way to do all this stuff purely? Or does the --impure have to be there?

[TornaxO7]

Are you sure that the issue is from helix?
I'm using home-manager as well but I'm not getting this error message.