That would work if not type of default should match type of option. So
to make it work, I'd need to invent magic values for every type I use,
and then filter them all out, which doesn't seem to be very elegant
solution. The problem is that access to any attribute in
config.services.xyz triggers evaluation of the value and if default is
missing the error is thrown.
So in normal case it enforces values to be set, unless mkOption is
used with default attribute. My minimal goal here is at least to keep
enforcing as it is, and mark "optional" values so that they don't
appear (or can be removed) from config.services.xyz
On Mon, Jun 30, 2014 at 8:48 AM, Mateusz Kowalczyk
<fuuze...@fuuzetsu.co.uk> wrote:
> On 06/30/2014 09:42 AM, Max Ivanov wrote:
>> Hi Nixers,
>>
>> I am building a nix os module and stumbled upon a problem which I
>> might need your advice on how to approach it.
>>
>> What I can't figure out, is how to filter out unset values even if
>> they don't have a default value set in mkOption. The idea is that
>> application itself handles missing values using defaults and I don't
>> want to duplicate them in a config.
>>
>> On the other hand, there are some values which are mandatory, so that
>> if they are missing from configuration.nix config build should fail.
>> Worth mentioning is that number of mandatory attrs is << number of
>> handled by default attrs, so I'd prefer to whitelist mandatories if it
>> is possible. Also the solution whatever it is should process cfg
>> recursively as cfg is actually nested set of types.submodules.
>>
>> Here is a minimal example, which demonstrates the problem I am trying
>> to solve. It doesn't make sense overall, so don't judge me for missing
>> mkIf or silly system services ;) it just shows what I am trying to
>> achieve.
>>
>> { config, lib, pkgs, ... }:
>> with lib;
>> let
>> # question is how to write this function
>> filter_cfg = cfg: cfg;
>>
>> cfg = filter_cfg config.services.xyz;
>> confFile = pkgs.writeText "xyz.json" (builtins.toJSON cfg);
>> in
>> {
>> options.services.xyz = {
>> opt1 = mkOption { type = types.str; default="default_opt1"; };
>>
>> # should be excluded from cfg if missing in configuration
>> opt_devs_defaults = mkOption { type = types.str; };
>>
>> # error should be raised if missing in conf
>> opt_mandatory = mkOption { type = types.str; };
>> };
>>
>> config = {
>> systemd.services.xyz = {
>> serviceConfig = {
>> ExecStart = "${pkgs.bash} -c 'touch ${confFile}'";
>> };
>> };
>> };
>> }
>> _______________________________________________
>> nix-dev mailing list
>> nix-dev@lists.science.uu.nl
>> http://lists.science.uu.nl/mailman/listinfo/nix-dev
>>
>
> For optional values, you could set default to null and then checking for
> null later. If it's null, don't include it in the command and if it
> isn't then do include it. Effectively ‘not set’ becomes default.
>
> I'm unsure how you can enforce a presence of an option. Things like
> ‘assert’ &c could be used to catch such things but I don't know whether
> this is recommended course of action.
>
> --
> Mateusz K.
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> nix-dev@lists.science.uu.nl
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