Ok, found it: https://matrix.to/#/!RRerllqmbATpmbJgCn:nixos.org/$0WVAvACN5DN8NLuPU7hmS2ZaGKNcCYMxB1jkhb99Lqk?via=nixos.org&via=matrix.org&via=tchncs.de Artur Manuel

Looks like you are trying to convert a list of config-spec-attrsets into an attrset of nixos configurations. Currently you're passing a list of attrs to genAttrs, which won't work because genAttrs expects a list of string; the strings are also used as the attr names.

I'd recommend having an attrset of config-sepcs instead of a list, and then using mapAttrs to convert them to actual nixos-configurations.

e.g.

let
  mkHosts = builtins.mapAttrs (name: configSpec: inputs.nixpkgs.lib.nixosSystem {
    # TODO
  });
in
nixosConfigurations = mkHosts {
  "freguson" = {
    hostname = "freguson";
    username = "amadal";
    system = "x86_64-linux";
    # etc
  };
};

You could also have something like this if you don't want to define the hostname twice:

  mkHosts = builtins.mapAttrs (hostname: configSpec: mkHost ({ inherit hostname; } // configSpec));

However, if you don't want to do that, you'll need to use listToAttrs, after maping the list such that the elements have the form { name = "attr_name"; value = "attr_value"; } (as expected by listToAttrs).

e.g.

  builtins.listToAttrs (
    builtins.map
    (configSpec: {
      name = configSpec.hostname;
      value = inputs.nixpkgs.lib.nixosSystem {
        # TODO
      };
    })
    configSpecList
  )

I have a function that internally calls lib.evalModules and returns the result's config.test.derivation (a types.package option that depends on several other option values).

I'm trying to write a regression test that checks whether this (correctly) fails to evaluate when some of those option dependencies are invalid. I figued I'd use builtins.tryEval and then pass the resulting .success into a test-derivation:

let
  module = { foo = null; };
  test = fnThatReturnsTest { inherit module; };
  result = builtins.tryEval test;
in
pkgs.runCommand "fail-to-eval-test" { inherit (result) success; } ''
  if [ $success ]; then
    echo "Failed to fail!"
    exit 1
  fi
  touch $out
''

However, success is always true. If I pass result.value into the derivation, however, my expression fails to evaluate (as expected).

I've also tried doing result = builtins.tryEval (builtins.deepSeq test) but this made no difference.

I could use nix-build to evaluate the result within my test-derivation's buildscript (and then check it fails and check its output), but I'd like to understand why tryEval isn't doing what I expected in this scenario.

@sem:one.ems.host toString should work?

(or just toString 10)