[Nix-dev] NixOS module assertions

[Marc Weber]

Excerpts from ludo's message of Mon Mar 28 17:33:34 +0200 2011:
> Why is that?  How should we work around it?

In order to reproduce your problem having a configuration.nix file would
be benefical. I get the assertion only when setting kernelPackages and
enabling ttyBackgrounds.

I'd vote for moving the code checking the assertions (assertions.nix)

  # This option is evaluated always. Thus the assertions are checked as well. hacky!
  environment.systemPackages =
    if [] == failed then []
    else throw "\nFailed assertions:\n${concatStringsSep "\n" (map (x: "- ${x}") failed)}";


to eval-config.nix to ensure its evaluated first eg by adding this untested
code which surrounds the old config = by a let .. in catching the case that
assertion messages are present:

  # Optionally check wether all config values have corresponding
  # option declarations.
  config =
    let cfg =
        let doCheck = optionDefinitions.environment.checkConfigurationOptions; in
        assert doCheck -> pkgs.lib.checkModule "" systemModule;
        systemModule.config;
        failed = map (x: x.message) (filter (x: !x.assertion) cfg.assertions);
    in if failed == [] then cfg 
       else throw "\nFailed assertions:\n${concatStringsSep "\n" (map (x: "- ${x}") failed)}"

Marc Weber