Are you following the right branch?

• My Nixpkgs and Home Manager versions are in sync

Is there an existing issue for this?

• I have searched the existing issues

Issue description

I'm not sure if this is more of a bug report or feature request, but ultimately it's unexpected behavior to me and I couldn't find any other issues about this option...

I have a simple config like

  nix.checkConfig = false;
  nix.settings = {
    unknown-setting = "";
  };

From the description of checkConfig, I assumed this would work: https://github.com/nix-community/home-manager/blob/master/modules/misc/nix.nix#L239C1-L246C7
Especially since nix.conf allows unknown keys according to its manpages.

However the checkPhase as written seems to specifically disallow unknown values regardless of nix.checkConfig: https://github.com/nix-community/home-manager/blob/master/modules/misc/nix.nix#L95-L97 and this results in a build failure:

nix-repl> :b homeConfigurations."ianchamberlain@MacBook-Pro".config.xdg.configFile."nix/nix.conf".source
error: builder for '/nix/store/7p3bzjm46nxh20kfyn76fbdf3qgy890g-nix.conf.drv' failed with exit code 1;
       last 2 log lines:
       > Validating generated nix.conf
       > error: unknown setting 'unknown-setting'
       For full logs, run 'nix log /nix/store/7p3bzjm46nxh20kfyn76fbdf3qgy890g-nix.conf.drv'.

I would propose one of two changes:

• For checkConfig = false, skip the checkPhase entirely; the user has opted out of nix.conf validation
• Add a new option allowUnknownSettings or something like that, which could be toggled separately from checkConfig and specifically allows unknown settings but not other errors.

The first choice seems much simpler to implement (happy to open a PR), but maybe the second choice would make sense as a way to enable syntax / type checking but still allow unknown settings? I guess it would allow for type checking of known features but not unknown features...

Maintainer CC

Nix module no longer has an active maintainer and git blame seems mostly like one-off changes... not sure who might be the right person to see this?

System information

- system: `"aarch64-darwin"`
 - host os: `Darwin 23.6.0, macOS 14.6.1`
 - multi-user?: `no`
 - sandbox: `yes`
 - version: `nix-env (Lix, like Nix) 2.90.0`
 - nixpkgs: `not found`