Infinite recursion when trying to use `pkgs` defined in `perSystem`

[sarunint]

Hello,

I've been trying to migrate my flake to using flake-parts, and I'd like to use pkgs that is defined in perSystem as outlined here, but when I try to build the system, I encountered the following error:

error:
       … while calling the 'seq' builtin
         at /nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/lib/modules.nix:403:18:
          402|         options = checked options;
          403|         config = checked (removeAttrs config [ "_module" ]);
             |                  ^
          404|         _module = checked (config._module);

       … while evaluating a branch condition
         at /nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/lib/modules.nix:306:9:
          305|       checkUnmatched =
          306|         if config._module.check && config._module.freeformType == null && merged.unmatchedDefns != [ ] then
             |         ^
          307|           let

       … while evaluating the module argument `pkgs' in "/nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/nixos/modules/services/hardware/bluetooth.nix":

       … noting that argument `pkgs` is not externally provided, so querying `_module.args` instead, requiring `config`

       … while evaluating definitions from `/nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/nixos/modules/misc/nixpkgs/read-only.nix':

       … while evaluating the option `nixpkgs.config':

       … while evaluating definitions from `/nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/nixos/modules/misc/nixpkgs/read-only.nix':

       … while evaluating the option `nixpkgs.pkgs':

       … while evaluating definitions from `/nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/flake.nix':

       … while evaluating the option `nixpkgs.hostPlatform':

       … while evaluating definitions from `/nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/nixos/modules/misc/nixpkgs/read-only.nix':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: infinite recursion encountered
       at /nix/store/ih9vmk2a3mrk6vhmibqzji6kjc6parzp-source/lib/modules.nix:1160:7:
         1159|     // {
         1160|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
             |       ^
         1161|       inherit (res.defsFinal') highestPrio;
Command 'nix --extra-experimental-features 'nix-command flakes' build --print-out-paths '.#nixosConfigurations."sarunint-workstation-nixos".config.system.build.toplevel'' returned non-zero exit status 1.

My flake is located here (Please use dev branch, since the commit that cause the error is there.)

From what I understand, config.nixpkgs.hostPlatform.system causes the error somehow? I'm not sure about this.

[sarunint]

Further searching reveals that I am not the only one who encountered this issue

https://github.com/abstrnoah/dotfiles/blob/b07cd56778e348dfa0e6882b4cec1b61a7f39af1/modules/brumal/nixpkgs.nix#L36-L43

[roberth]

Does it work if you change { config, ... }: to { ... }: at https://github.com/sarunint/nixos-config/blob/c45656d12866c06f00aad407abc3b99ef6fe87c3/flake.nix#L223C18-L223C25 ?
I think you meant to refer to top.

[sarunint]

Does it work if you change { config, ... }: to { ... }: at https://github.com/sarunint/nixos-config/blob/c45656d12866c06f00aad407abc3b99ef6fe87c3/flake.nix#L223C18-L223C25 ? I think you meant to refer to top.

I don't understand. If I remove config argument, where does config in config.nixpkgs.hostPlatform.system comes from?

[roberth]

Ah, I'm sorry. I was looking at the other code you linked.
Add a config parameter here at perSystem https://github.com/sarunint/nixos-config/blob/c45656d12866c06f00aad407abc3b99ef6fe87c3/flake.nix#L25

[sarunint]

Ah, I'm sorry. I was looking at the other code you linked. Add a config parameter here at perSystem https://github.com/sarunint/nixos-config/blob/c45656d12866c06f00aad407abc3b99ef6fe87c3/flake.nix#L25

Then the config argument is scoped to perSystem block? nixosConfigurations is in flake block.

[leon-erd]

I also stumbled across this when trying to implement the example from the official documentation :D
So I am interested in a solution as well :)

[drxxmy]

I also encountered an infinite recursion problem when trying to implement an example from the flake-parts documentation. After some time, I managed to fix it.

1. Define a module for nixpkgs like that:

# nixpkgs.nix
{ inputs, ... }:
{
  perSystem =
    { system, ... }:
    {
      _module.args.pkgs = import inputs.nixpkgs {
        inherit system;
        config.allowUnfree = true;
      };
    };
}

2. Create the host configuration:

# hostname.nix
{ withSystem, inputs, ... }:
{
  flake.nixosConfigurations.hostname = withSystem "x86_64-linux" (
    { pkgs, system, ... }:
    inputs.nixpkgs.lib.nixosSystem {
      inherit system;
      modules = [
        { nixpkgs.pkgs = pkgs; }
        # other modules...
      ];
    }
  );
}

Hope this helps! ❤️