flake-parts/setups/nixos: add specialArgs through declarative setups

modules/flake-parts/setups/default.nix

@@ -39,5 +39,20 @@
         allowUnfree = true;
       };
     };
+
+    sharedSpecialArgs = lib.mkOption {
+      type = with lib.types; attrsOf anything;
+      description = ''
+        Shared set of arguments to be assigned as part of `_module.specialArgs`
+        of each of the declarative setups.
+      '';
+      default = { };
+      example = lib.literalExpression ''
+        {
+          location = "Inside of your walls";
+          utilsLib = import ./lib/utils.nix;
+        }
+      '';
+    };
   };
 }

modules/flake-parts/setups/nixos.nix

@@ -170,6 +170,7 @@ let
     };
 
     config.nixpkgs.config = cfg.sharedNixpkgsConfig;
+    config.specialArgs = cfg.sharedSpecialArgs;
 
     config.modules = [
       # Bring in the required modules.
@@ -209,6 +210,13 @@ in
       '';
     };
 
+    sharedSpecialArgs = options.setups.sharedSpecialArgs // {
+      description = ''
+        Shared set of module arguments as part of `_module.specialArgs` of the
+        configuration.
+      '';
+    };
+
     sharedModules = lib.mkOption {
       type = with lib.types; listOf deferredModule;
       default = [ ];
@@ -222,6 +230,7 @@ in
         (import ./shared/nix-conf.nix { inherit inputs; })
         (import ./shared/config-options.nix { inherit (config) systems; })
         ./shared/nixpkgs-options.nix
+        ./shared/special-args-options.nix
         configType
       ]);
       default = { };
@@ -318,6 +327,7 @@ in
                     in
                     lib.nameValuePair system (mkHost {
                       inherit pkgs system;
+                      inherit (metadata) specialArgs;
                       extraModules = cfg.sharedModules ++ metadata.modules;
                     })
                   )

modules/flake-parts/setups/shared/special-args-options.nix

@@ -0,0 +1,14 @@
+{ config, lib, ... }:
+
+{
+  options.specialArgs = lib.mkOption {
+    type = with lib.types; attrsOf anything;
+    default = { };
+    example = lib.literalExpression ''
+      {
+        location = "Your mom's home";
+        utilsLib = import ./lib/utils.nix;
+      }
+    '';
+  };
+}