module.nix

{ config, lib, pkgs, ... }:

let

  fcio = config.fcio;

  optionalAttr = set: name: default:
    if builtins.hasAttr name set then set.${name} else default;

  enc_roles = optionalAttr fcio.enc "classes" [];

in

{

  options = {

    fcio.roles = lib.mkOption {
      default = enc_roles;
      type = lib.types.listOf lib.types.str;

      description = ''
        Which roles to activate. E.g:

          fcio.roles = [ "generic" "webgateway" "webproxy" ];

        Defaults to the roles provided by the ENC. ENC-provided roles
        will have been stripped the 'role::' prefix automatically.

      '';
    };

  };

  config =
    # Map list of roles to a list of attribute sets enabling each role.
    let
      # Optionally remove the old "role::" prefix from Puppet/ENC
      stripped_roles = map (lib.removePrefix "role::") fcio.roles;
      # Turn the list of role names (["a", "b"]) into an attribute set
      # ala { <role> = { enable = true;}; }
      role_set = lib.listToAttrs (
        map (role: { name = role; value = { enable = true; }; })
          stripped_roles);
    in
      {
        flyingcircus.roles = role_set;
      };

}

[root@default:~]# nixos-rebuild -I nixpkgs=/root/nixos switch --show-trace
building Nix...
error: while evaluating the attribute ‘config’ at /root/nixos/nixos/lib/eval-config.nix:53:5:
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:86:25:
while evaluating ‘yieldConfig’ at /root/nixos/lib/modules.nix:73:29, called from /root/nixos/lib/modules.nix:72:16:
while evaluating the attribute ‘_module.check.value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `_module.check':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:191:19:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:175:8:
while evaluating anonymous function at /root/nixos/lib/modules.nix:175:19, called from undefined position:
while evaluating ‘pushDownProperties’ at /root/nixos/lib/modules.nix:341:24, called from /root/nixos/lib/modules.nix:175:75:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:343:7:
while evaluating the attribute ‘contents’ at /root/nixos/lib/modules.nix:447:14:
while evaluating the module argument `config' in "/nix/store/gbml1hacdvbag5jn8y0siwbhkypq0rr5-modules/flyingcircus/role.nix":
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:58:71:
infinite recursion encountered, at /root/nixos/lib/modules.nix:58:71
error: while evaluating the attribute ‘pkgs’ at /root/nixos/nixos/lib/eval-config.nix:66:32:
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:86:25:
while evaluating ‘yieldConfig’ at /root/nixos/lib/modules.nix:73:29, called from /root/nixos/lib/modules.nix:72:16:
while evaluating the attribute ‘_module.check.value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `_module.check':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:191:19:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:175:8:
while evaluating anonymous function at /root/nixos/lib/modules.nix:175:19, called from undefined position:
while evaluating ‘pushDownProperties’ at /root/nixos/lib/modules.nix:341:24, called from /root/nixos/lib/modules.nix:175:75:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:343:7:
while evaluating the attribute ‘contents’ at /root/nixos/lib/modules.nix:447:14:
while evaluating the module argument `config' in "/nix/store/gbml1hacdvbag5jn8y0siwbhkypq0rr5-modules/flyingcircus/role.nix":
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:58:71:
infinite recursion encountered, at /root/nixos/lib/modules.nix:58:71
building the system configuration...
error: while evaluating the attribute ‘config.system.build.toplevel’ at /root/nixos/nixos/lib/eval-config.nix:53:5:
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:86:25:
while evaluating ‘yieldConfig’ at /root/nixos/lib/modules.nix:73:29, called from /root/nixos/lib/modules.nix:72:16:
while evaluating the attribute ‘_module.check.value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `_module.check':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:191:19:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:175:8:
while evaluating anonymous function at /root/nixos/lib/modules.nix:175:19, called from undefined position:
while evaluating ‘pushDownProperties’ at /root/nixos/lib/modules.nix:341:24, called from /root/nixos/lib/modules.nix:175:75:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:343:7:
while evaluating the attribute ‘contents’ at /root/nixos/lib/modules.nix:447:14:
while evaluating the module argument `config' in "/nix/store/gbml1hacdvbag5jn8y0siwbhkypq0rr5-modules/flyingcircus/role.nix":
while evaluating the attribute ‘config’ at /root/nixos/lib/modules.nix:58:71:
infinite recursion encountered, at /root/nixos/lib/modules.nix:58:71

Here's the repl for when I do not set any roles:

[root@default:~/nixos]# nix-repl -I nixpkgs=/root/nixos/ '<nixpkgs/nixos>'
Welcome to Nix version 1.10. Type :? for help.

Loading ‘<nixpkgs/nixos>’...
Added 6 variables.

nix-repl> config.flyingcircus.roles.nginx
{ enable = false; }

nix-repl> config.flyingcircus.roles.haproxy
{ enable = false; }

nix-repl> config.fcio.roles
[ ]

nix-repl> config.flyingcircus.roles
{ dovecot = { ... }; haproxy = { ... }; mysql = { ... }; nginx = { ... }; postgresql = { ... }; varnish = { ... }; }

And here is the error when I actually set a role

[root@default:~/nixos]# nix-repl -I nixpkgs=/root/nixos/ '<nixpkgs/nixos>'
Welcome to Nix version 1.10. Type :? for help.

Loading ‘<nixpkgs/nixos>’...
Added 6 variables.

nix-repl> config.fcio.roles
[ "haproxy" ]

nix-repl> config.flyingcircus.roles.haproxy
error: The option `flyingcircus.roles.haproxy.enable' defined in `/nix/store/93sw5by95rf377s92kl06rs3harkak1f-modules/flyingcircus/role.nix' does not exist.

nix-repl> 

And here the traceback when making sure we don't stumble over names containing ".":

error: while evaluating the attribute ‘config.system.build.toplevel’ at /root/nixos/nixos/modules/system/activation/top-level.nix:241:5:
while evaluating ‘fold’ at /root/nixos/lib/lists.nix:20:19, called from /root/nixos/nixos/modules/system/activation/top-level.nix:125:12:
while evaluating ‘fold'’ at /root/nixos/lib/lists.nix:23:15, called from /root/nixos/lib/lists.nix:27:8:
while evaluating ‘showWarnings’ at /root/nixos/nixos/modules/system/activation/top-level.nix:93:18, called from /root/nixos/nixos/modules/system/activation/top-level.nix:100:16:
while evaluating ‘fold’ at /root/nixos/lib/lists.nix:20:19, called from /root/nixos/nixos/modules/system/activation/top-level.nix:93:23:
while evaluating ‘fold'’ at /root/nixos/lib/lists.nix:23:15, called from /root/nixos/lib/lists.nix:27:8:
while evaluating the attribute ‘warnings’ at /root/nixos/lib/attrsets.nix:145:44:
while evaluating anonymous function at /root/nixos/lib/modules.nix:74:45, called from /root/nixos/lib/attrsets.nix:145:52:
while evaluating the attribute ‘value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `warnings':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating anonymous function at /root/nixos/lib/modules.nix:298:28, called from undefined position:
while evaluating ‘dischargeProperties’ at /root/nixos/lib/modules.nix:361:25, called from /root/nixos/lib/modules.nix:299:62:
while evaluating the attribute ‘value’ at /root/nixos/lib/modules.nix:199:48:
while evaluating the attribute ‘config.warnings’ at /root/nixos/nixos/modules/system/boot/systemd.nix:600:5:
while evaluating ‘mapAttrsToList’ at /root/nixos/lib/attrsets.nix:169:23, called from /root/nixos/nixos/modules/system/boot/systemd.nix:600:29:
while evaluating the attribute ‘services’ at /root/nixos/lib/attrsets.nix:145:44:
while evaluating anonymous function at /root/nixos/lib/modules.nix:74:45, called from /root/nixos/lib/attrsets.nix:145:52:
while evaluating the attribute ‘value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `systemd.services':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating anonymous function at /root/nixos/lib/modules.nix:298:28, called from undefined position:
while evaluating ‘dischargeProperties’ at /root/nixos/lib/modules.nix:361:25, called from /root/nixos/lib/modules.nix:299:62:
while evaluating the attribute ‘value’ at /root/nixos/lib/modules.nix:199:48:
while evaluating the attribute ‘config.services’ at /root/nixos/nixos/modules/system/upstart/upstart.nix:284:5:
while evaluating ‘flip’ at /root/nixos/lib/trivial.nix:57:16, called from /root/nixos/nixos/modules/system/upstart/upstart.nix:285:7:
while evaluating ‘mapAttrs'’ at /root/nixos/lib/attrsets.nix:157:18, called from /root/nixos/lib/trivial.nix:57:19:
while evaluating the attribute ‘jobs’ at /root/nixos/lib/attrsets.nix:145:44:
while evaluating anonymous function at /root/nixos/lib/modules.nix:74:45, called from /root/nixos/lib/attrsets.nix:145:52:
while evaluating the attribute ‘value’ at /root/nixos/lib/modules.nix:287:9:
while evaluating the option `jobs':
while evaluating the attribute ‘isDefined’ at /root/nixos/lib/modules.nix:319:5:
while evaluating ‘filterOverrides’ at /root/nixos/lib/modules.nix:391:21, called from /root/nixos/lib/modules.nix:303:18:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:397:8:
while evaluating ‘concatMap’ at /root/nixos/lib/lists.nix:62:18, called from /root/nixos/lib/modules.nix:298:17:
while evaluating anonymous function at /root/nixos/lib/modules.nix:298:28, called from undefined position:
while evaluating ‘dischargeProperties’ at /root/nixos/lib/modules.nix:361:25, called from /root/nixos/lib/modules.nix:299:62:
while evaluating the attribute ‘condition’ at /root/nixos/lib/modules.nix:437:14:
while evaluating the attribute ‘condition’ at /root/nixos/lib/modules.nix:437:14:
while evaluating the attribute ‘flyingcircus.roles.haproxy.enable’ at /root/nixos/lib/attrsets.nix:145:44:
while evaluating anonymous function at /root/nixos/lib/modules.nix:74:45, called from /root/nixos/lib/attrsets.nix:145:52:
while evaluating ‘yieldConfig’ at /root/nixos/lib/modules.nix:73:29, called from /root/nixos/lib/modules.nix:76:16:
while evaluating anonymous function at /root/nixos/lib/modules.nix:79:24, called from /root/nixos/lib/modules.nix:79:11:
while evaluating the attribute ‘names’ at /root/nixos/lib/modules.nix:214:54:
value is a list while a set was expected, at /root/nixos/lib/modules.nix:214:62