Missing submodules in Nixos

[leenaars]

It is no longer possible to build nixcloud-webservices with current nixos-unstable:

building Nix...
building the system configuration...
error: attribute 'submodule' missing, at /home/username/repo/nixcloud-webservices/modules/web/core/webserver.nix:66:39
(use '--show-trace' to show detailed location information)

[leenaars]

There were some changes in modules related to nixcloud-webservices::

https://nixos.org/nixos/manual/release-notes.html#sec-release-19.09

[fgaz]

This prevents nixcloud-webservices to work on the newly released 20.03

[infinisil]

A couple days ago I had a discussion with @Melkor333 on IRC regarding this: https://logs.nix.samueldr.com/nixos/2020-07-12#1594566523-1594572059; where I also suggested a non-optimal solution

The change in nixpkgs that introduced this problem is my PR NixOS/nixpkgs#75031. I don't think this is a problem with the PR though, because the problematic code in nixcloud-webservices at

nixcloud-webservices/modules/web/core/webserver.nix

Lines 64 to 66 in 3a0767f

	type = let
	submodules = toplevel.options.users.users.type.getSubModules;
	in lib.types.submodule (map (m: m.submodule) submodules);

(among others) relies on module system internals, which I removed in that PR: https://github.com/NixOS/nixpkgs/pull/75031/files#diff-490491facef0aa6a6dbe8ffc5bd97097L174-L184

After messing with it for a bit, here is how the same functionality can be achieved without relying on internals:

{
  options.webserver.userOptions = lib.mkOption {
    type = lib.types.submodule options.users.users.type.functor.wrapped.getSubModules;
    default = {};
  };

  config.users.users.webserver = lib.modules.mkAliasAndWrapDefsWithPriority lib.id options.webserver.userOptions;

Also, make sure to not use // for merging in the module system like in

nixcloud-webservices/modules/web/core/webserver.nix

Lines 120 to 122 in 3a0767f

	users.${config.webserver.user} = {
	inherit (config.webserver) group;
	} // removeAttrs config.webserver.userOptions [ "name" "group" ];

, because it can lead to problems. Prefer mkMerge instead. And to prevent attributes from being changed, a mkForce is recommended. So in the end that part looks about like this:

{
  users.${config.webserver.user} = lib.mkMerge [
    (lib.mkForce { inherit (config.webserver) user group; })
    (lib.modules.mkAliasAndWrapDefsWithPriority lib.id options.webserver.userOptions)
  ];
}

To prevent name and group from being changed you could set group and name with a mkForce.

[Melkor333]

Oh wow thank you for taking another look at it!! 😯 I hope I’ll have time next weekend to run the tests with this code and create a PR...