The infinite recursion comes from the fact that osConfigs might contain home-manager user configurations.

I suggest to explicitly the top-level attributes that can be set to exclude users;

  osConfigs' = flatten …;
  # Generate an error if `users` is set.
  osConfigs = ({programs? {}, services? {}}: {
    inherit programs services;
  }) osConfigs';

The infinite recursion comes from the fact that osConfigs might contain home-manager user configurations.

I suggest to explicit the top-level attributes that can be set to exclude users;

  osConfigs' = flatten …;
  # Generate an error if `users` is set.
  osConfigs = ({programs? {}, services? {}}: {
    inherit programs services;
  }) osConfigs';

In reply to @mr-qubo:matrix.org

I'm trying to write nixos config where I can set nixos options from home-manager modules. But I can't get around infinite recursion errors.
I wrote this nixos module, I though this should work, but I'm still getting infinite recursion error, which I don't know how to debug.

{ lib, options, ... }:
with builtins; with lib;

let
  hmModuleBase = with options.home-manager.users.type.nestedTypes.elemType.functor.payload; evalModules {
    inherit class specialArgs;
    modules = modules ++ [{
      options.MrQubo = {
        osConfigs = {
          type = options.raw;
        };
      };
    }];
  };

  evalHmModule = module:
    hmModuleBase.extendModules { modules = [ module ]; };

  isImportableNV = { name, value }:
    (value == "regular" && match ".*\\.nix" name != null) || (value == "directory" && (readDir "${localOverlays}/${name}") ? "default.nix");

  parseNV = { name, value }: rec {
    username = removeSuffix ".nix" name;
    module = evalHmModule ../users/${name};
  };

  userModules = map parseNV (filter isImportableNV (attrsToList (readDir ../users)));

  osConfigs = flatten (map (attrs: attrs.module.MrQubo.osConfigs) userModules);

  hmUsersConfig = {
    home-manager.users = listToAttrs (map (attrs: { name = attrs.username; value = attrs.module; }) userModules);
  };

in mkMerge (osConfigs ++ [ hmUsersConfig ])

My second attempt:

{ lib, ... }:
with builtins; with lib;

let

  isImportable = { name, value }:
    (value == "regular" && match ".*\\.nix" name != null) || (value == "directory" && (readDir "${localOverlays}/${name}") ? "default.nix");

  parseUser = { name, value }: rec {
    username = removeSuffix ".nix" name;
    module = ../users/${name};
  };

  users = map parseUser (filter isImportable (attrsToList (readDir ../users)));

  evalHmModule = { username, module, config, pkgs, ... }:
    (import <home-manager/modules> {
      configuration = {
        options.MrQubo = {
          osConfig.services = mkOption {
            type = types.raw;
          };
        };
        config = {
          submoduleSupport.enable = true;
          submoduleSupport.externalPackageInstall = false;

          home.username = config.users.users.${username}.name;
          home.homeDirectory = config.users.users.${username}.home;

          # Make activation script use same version of Nix as system as a whole.
          # This avoids problems with Nix not being in PATH.
          nix.package = config.nix.package;
        };
      };
      inherit pkgs;
    }).extendModules {
      modules = [
        {
          MrQubo.osConfig.services = config.services;
        }
        module
      ];
    };

  osConfigModules = flip map users (user: { pkgs, config, ... }:
    { config.services = (evalHmModule ({ inherit pkgs config; } // user)).config.MrQubo.osConfig.services; }
  );

in {
  imports = osConfigModules;
}

It still doesn't work, even with just "services" option.
I get

       … while evaluating the option `services.sftpgo.user':

       error: infinite recursion encountered

In reply to @nbp:mozilla.org
mr-qubo: I do not have enough information with what you copied to give you any answer, apart that I do not see any reasons for an infinite recursion in this file.

I run it with nixos-rebuild -I nixos-config=$(pwd)/users-impl.nix dry-build --show-trace. ./user-impl.nix is the name of the file contents which I pasted. You also need to put some file in ../users/ dir. I have nix.nix file with those contents:

{
  home.stateVersion = "23.11";
}

home.stateVersion is needed, otherwise there's a different error from home-manager.

In reply to @nbp:mozilla.org
mr-qubo: I do not have enough information with what you copied to give you any answer, apart that I do not see any reasons for an infinite recursion in this file.

I run it with nixos-rebuild -I nixos-config=$(pwd)/users-impl.nix dry-build --show-trace. ./user-impl.nix is the name of the file contents which I pasted. You also need to put some file in ../users/ dir. I have nix.nix file with those contents:

{
  home.stateVersion = "23.11";
}

home.stateVersion is needed, otherwise there's a different error from home-manager.
And you also need <home-manager> channel.