flake: add basic-nix-module-flake template

configs/flake-parts/templates.nix

@@ -6,6 +6,10 @@
       path = ../../templates/basic-devshell;
       description = "Basic development shell template";
     };
+    basic-nix-module-flake = {
+      path = ../../templates/basic-nix-module-flake;
+      description = "Basic Nix module flake template";
+    };
     basic-overlay-flake = {
       path = ../../templates/basic-overlay-flake;
       description = "Basic overlay as a flake";

templates/basic-nix-module-flake/flake.nix

@@ -0,0 +1,20 @@
+{
+  description = "Basic Nix module flake description";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+  };
+
+  outputs = inputs@{ self, nixpkgs, ... }:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+      ];
+
+      imports = [
+        ./nix/flake
+      ];
+    };
+}

templates/basic-nix-module-flake/nix/flake/default.nix

@@ -0,0 +1,32 @@
+{ lib, inputs, ... }: {
+  flake = {
+    nixosModules.default = ../modules;
+  };
+
+  perSystem = { lib, pkgs, system, ... }: {
+    formatter = pkgs.treefmt;
+
+    devShells.default = import ../../shell.nix { inherit pkgs; };
+
+    # Just make sure it actually compiles with a very minimal NixOS
+    # configuration.
+    checks.nixos-module-test =
+      let
+        nixosSystem = args:
+          import "${inputs.nixpkgs}/nixos/lib/eval-config.nix" args;
+      in
+      nixosSystem {
+        modules = [
+          ({ modulesPath, ... }: {
+            imports = [
+              "${modulesPath}/profiles/minimal.nix"
+            ];
+
+            nixpkgs.hostPlatform = system;
+            boot.loader.grub.enable = false;
+            fileSystems."/".device = "nodev";
+          })
+        ];
+      };
+  };
+}

templates/basic-nix-module-flake/nix/modules/default.nix

@@ -0,0 +1,21 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.programs.foo;
+
+  settingsFormat = pkgs.format.json { };
+in
+{
+  options.programs.foo = {
+    enable = lib.mkEnableOption "foo, a sample program";
+    package = lib.mkPackageOption pkgs "foo" { };
+    settings = lib.mkOption {
+      type = settingsFormat.type;
+      default = { };
+      # TODO: Don't forget to set an example here.
+      description = ''
+        The settings of the program.
+      '';
+    };
+  };
+}

templates/basic-nix-module-flake/shell.nix

@@ -0,0 +1,10 @@
+{ pkgs ? import <nixpkgs> { } }:
+
+with pkgs;
+
+mkShell {
+  packages = [
+    nixpkgs-fmt
+    treefmt
+  ];
+}

templates/basic-nix-module-flake/treefmt.toml

@@ -0,0 +1,3 @@
+[formatter.nix]
+command = "nixpkgs-fmt"
+includes = [ "*.nix" ]