Initial commit

modules/flake/configurations.nix

@@ -0,0 +1,102 @@
+{
+  nixpkgs,
+  darwin,
+  home-manager,
+}: {
+  config,
+  lib,
+  flake-parts-lib,
+  ...
+}: let
+  inherit (lib) mkOption mapAttrs;
+  inherit (flake-parts-lib) mkSubmoduleOptions;
+  possibleConfigurations = {
+    nixos = {};
+    darwin = {};
+    home = {};
+  };
+in {
+  _file = ./configurations.nix;
+
+  options = {
+    # Those functions take the final arguments and emit a valid configuration.
+    # Probably should hardly ever be overriden
+    builders = {
+      nixos = mkOption {
+        type = lib.types.functionTo lib.types.unspecified;
+        default = nixpkgs.lib.nixosSystem;
+      };
+      darwin = mkOption {
+        type = lib.types.functionTo lib.types.unspecified;
+        default = darwin.lib.darwinSystem;
+      };
+      home = mkOption {
+        type = lib.types.functionTo lib.types.unspecified;
+        default = home-manager.lib.homeManagerConfiguration;
+      };
+    };
+
+    # Those functions map the value of the configuration attribute
+    # and emit a list of arguments to be passed to respected evalModules
+    mappers =
+      mapAttrs
+      (_: _:
+        mkOption {
+          type = lib.types.functionTo lib.types.attrs;
+          default = lib.id;
+        })
+      possibleConfigurations;
+
+    configurations = {
+      nixos = mkOption {
+        type = lib.types.unspecified;
+        default = {};
+      };
+      darwin = mkOption {
+        type = lib.types.unspecified;
+        default = {};
+      };
+      home = mkOption {
+        type = lib.types.unspecified;
+        default = {};
+      };
+    };
+
+    # This is exposed so that it's possible to modify the arguments that get passed to a builder
+    # after they have been mapped. Probably shouldn't do it. Probably should remove it or make it read-only
+    configurationOptions =
+      mapAttrs
+      (_: _:
+        mkOption {
+          type = lib.types.attrsOf lib.types.attrs;
+        })
+      possibleConfigurations;
+  };
+
+  config = {
+    configurationOptions =
+      mapAttrs
+      (
+        name: _:
+          mapAttrs
+          (configurationName: val: let
+            mapped = config.mappers.${name} val;
+            # TODO: specialArgs is actually extraSpecialArgs in home-manager.
+            #       At which level should that be handled?
+            defaultArgs = {
+              specialArgs = {inherit configurationName;};
+            };
+          in
+            lib.recursiveUpdate defaultArgs mapped)
+          config.configurations.${name}
+      )
+      possibleConfigurations;
+
+    flake = {
+      nixosConfigurations =
+        mapAttrs
+        (_: args: config.builders.nixos args)
+        config.configurationOptions.nixos;
+    };
+  };
+}