wallust: add module

closes #6566

modules/programs/wallust.nix

@@ -0,0 +1,46 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+
+let
+  inherit (lib)
+    mkEnableOption
+    mkPackageOption
+    mkOption
+    mkIf
+    literalExpression
+    ;
+  cfg = config.programs.wallust;
+  tomlFormat = pkgs.formats.toml { };
+in
+{
+  meta.maintainers = with lib.hm.maintainers; [ kiara ];
+
+  options.programs.wallust = {
+    enable = mkEnableOption "Wallust color scheme generator";
+    package = mkPackageOption pkgs "wallust" { };
+    settings = mkOption {
+      type = tomlFormat.type;
+      default = { };
+      example = literalExpression ''
+        {
+          palette = "softdark";
+        }
+      '';
+      description = ''
+        Configuration written to {file}`$XDG_CONFIG_HOME/wallust/wallust.toml`.
+        See <https://explosion-mental.codeberg.page/wallust/config/> for
+        documentation.
+      '';
+    };
+  };
+  config = mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+    xdg.configFile."wallust/wallust.toml" = mkIf (cfg.settings != { }) {
+      source = tomlFormat.generate "wallust.toml" cfg.settings;
+    };
+  };
+}