Unverified Commit 11376df6 authored by Maximilian Bosch's avatar Maximilian Bosch
Browse files

nixos/rust-motd: allow ordering sections by `priority` 

Closes #234802

The problem here is that with e.g.

    {
      uptime.prefix = "Up";
      banner.command = "hostname | figlet -f slant";
    }

`banner` still appears before `uptime` in the final motd text because
Nix sorts attribute names alphabetically internally.

To work around this without breaking compatibility or losing the
property to override individual sections in other modules - e.g.

    {
      banner.color = mkForce "blue";
    }

I decided to introduce an option `priority` here, similar to the
priority field for `nginx`[1] and with the same semantics (i.e. higher
value means lower priority).

Internally a bunch of env vars are generated, i.e. `env0` to `envN` for
`N` sections with each of them containing a declaration for the TOML,
i.e. `env0` contains `{ uptime.prefix = "Up"; }` and `env1` contains
`{ banner.command = "hostname | figlet -f slant"; }` if `uptime.priority`
is set to a value below 1000.

In this order, the declarations are concatenated together by `jq(1)`
which doesn't sort keys alphabetically which results in a JSON
representation with `uptime` before `banner`. This is finally piped to
`json2toml` which converts this into TOML for rust-motd.

[1] https://nixos.org/manual/nixos/unstable/options#opt-services.nginx.virtualHosts._name_.locations._name_.priority
parent 0a71cf07

nixos/modules/programs/rust-motd.nix

+56 −3
Original line number Diff line number Diff line
@@ -5,6 +5,33 @@ with lib; 
let

  cfg = config.programs.rust-motd;

  format = pkgs.formats.toml { };



  orderedSections = listToAttrs

    (imap0

      (i: items@{ sectionHeader, ... }: nameValuePair "env${toString i}" {

        ${sectionHeader} = removeAttrs items [ "priority" "sectionHeader" ];

      })

      (sortProperties (mapAttrsToList (k: v: v // { sectionHeader = k; }) cfg.settings)));



  # Order the sections in the TOML according to the `priority` field.

  # This is done by

  # * creating an attribute set with keys `env0`/`env1`/.../`envN`

  #   where `env0` contains the first section and `envN` the last

  #   (in the form of `{ sectionName = { /* ... */ }}`)

  # * the declarations of `env0` to `envN` in ascending order are

  #   concatenated with `jq`. Now we have a JSON representation of

  #   the config in the correct order.

  # * this is piped to `json2toml` to get the correct format for rust-motd.

  motdConf = pkgs.runCommand "motd.conf"

    (orderedSections // {

      __structuredAttrs = true;

      nativeBuildInputs = [ pkgs.remarshal pkgs.jq ];

    })

    ''

      cat "$NIX_BUILD_TOP"/.attrs.json \

        | jq '${concatMapStringsSep " + " (key: ''."${key}"'') (attrNames orderedSections)}' \

        | json2toml /dev/stdin "$out"

    '';

in {

  options.programs.rust-motd = {

    enable = mkEnableOption (lib.mdDoc "rust-motd");
@@ -28,9 +55,35 @@ in { 
      '';

    };

    settings = mkOption {

      type = types.submodule {

      type = types.attrsOf (types.submodule {

        freeformType = format.type;

        options.priority = mkOption {

          type = types.int;

          default = modules.defaultOrderPriority;

          description = mdDoc ''

            In `rust-motd`, the order of the sections in TOML correlates to the order

            of the items displayed in the resulting `motd`. Attributes in Nix are

            ordered alphabetically, e.g. `banner` would always be before `uptime`.



            To change that, this option can be used. The lower this number is, the higher

            is the priority and the more a section is at the top of the message.



            For instance



            ```nix

            {

              banner.command = "hostname | figlet -f slant";

              uptime = {

                prefix = "Up";

                priority = 0;

              };

            }

            ```



            would make the `uptime` appear before the banner.

          '';

        };

      });

      description = mdDoc ''

        Settings on what to generate. Please read the

        [upstream documentation](https://github.com/rust-motd/rust-motd/blob/main/README.md#configuration)
@@ -53,7 +106,7 @@ in { 
      wantedBy = [ "multi-user.target" ];

      serviceConfig = {

        ExecStart = "${pkgs.writeShellScript "update-motd" ''

          ${pkgs.rust-motd}/bin/rust-motd ${format.generate "motd.conf" cfg.settings} > motd

          ${pkgs.rust-motd}/bin/rust-motd ${motdConf} > motd

        ''}";

        CapabilityBoundingSet = [ "" ];

        LockPersonality = true;