stylix: add testbeds for desktop environments (#320)

Co-authored-by: NAHO <[email protected]>

flake.nix

@@ -76,15 +76,22 @@
         "x86_64-linux"
       ] (
         system:
-        let pkgs = nixpkgs.legacyPackages.${system};
-        in {
-          docs = import ./docs {
-            inherit pkgs inputs;
-            inherit (nixpkgs) lib;
+        let
+          inherit (nixpkgs) lib;
+          pkgs = nixpkgs.legacyPackages.${system};
+
+          universalPackages = {
+            docs = import ./docs { inherit pkgs inputs lib; };
+            palette-generator = pkgs.callPackage ./palette-generator { };
           };
 
-          palette-generator = pkgs.callPackage ./palette-generator { };
-        }
+          # Testbeds are virtual machines based on NixOS, therefore they are
+          # only available for Linux systems.
+          testbedPackages = lib.optionalAttrs
+            (lib.hasSuffix "-linux" system)
+            (import ./stylix/testbed.nix { inherit pkgs inputs lib; });
+        in
+          universalPackages // testbedPackages
       );
 
       nixosModules.stylix = { pkgs, ... }@args: {

modules/gnome/testbed.nix

@@ -0,0 +1,7 @@
+{
+  services.xserver = {
+    enable = true;
+    desktopManager.gnome.enable = true;
+    displayManager.gdm.enable = true;
+  };
+}

modules/kde/testbed.nix

@@ -0,0 +1,7 @@
+{
+  services.xserver = {
+    enable = true;
+    desktopManager.plasma5.enable = true;
+    displayManager.sddm.enable = true;
+  };
+}

stylix/testbed.nix

@@ -0,0 +1,94 @@
+{ pkgs, inputs, lib, ... }:
+
+let
+  username = "guest";
+
+  commonModule = { config, ... }: {
+    users.users.${username} = {
+      description = "Guest";
+      hashedPassword = "";
+      isNormalUser = true;
+    };
+
+    # The state version can safely track the latest release because the disk
+    # image is ephermal.
+    system.stateVersion = config.system.nixos.release;
+    home-manager.users.${username}.home.stateVersion = config.system.nixos.release;
+
+    virtualisation.vmVariant.virtualisation = {
+      # This is a maximum limit; the VM should still work if the host has fewer cores.
+      cores = 4;
+      memorySize = lib.mkDefault 2048;
+    };
+  };
+
+  autoload = builtins.concatLists
+    (lib.mapAttrsToList
+      (name: _:
+        let testbed = {
+          inherit name;
+          module = "${../modules}/${name}/testbed.nix";
+        };
+        in
+          lib.optional (builtins.pathExists testbed.module) testbed
+      )
+      (builtins.readDir ../modules));
+
+  makeTestbed =
+    testbed: stylix:
+    let
+      name = "testbed-${testbed.name}-${stylix.polarity}";
+
+      system = lib.nixosSystem {
+        inherit (pkgs) system;
+
+        modules = [
+          commonModule
+          inputs.self.nixosModules.stylix
+          inputs.home-manager.nixosModules.home-manager
+          testbed.module
+
+          {
+            inherit stylix;
+            system.name = name;
+          }
+        ];
+      };
+
+      script = pkgs.writeShellApplication {
+        inherit name;
+        text = ''
+          cleanup() {
+            if rm --recursive "$directory"; then
+              printf '%s\n' 'Virtualisation disk image removed.'
+            fi
+          }
+
+          # We create a temporary directory rather than a temporary file, since
+          # temporary files are created empty and are not valid disk images.
+          directory="$(mktemp --directory)"
+          trap cleanup EXIT
+
+          NIX_DISK_IMAGE="$directory/nixos.qcow2" \
+            ${lib.getExe system.config.system.build.vm}
+        '';
+      };
+    in
+      lib.nameValuePair name script;
+
+  # This generates a copy of each testbed for each of the following themes.
+  makeTestbeds = testbed: map (makeTestbed testbed) [
+    {
+      image = "${pkgs.pantheon.elementary-wallpapers}/share/backgrounds/Photo of Valley.jpg";
+      base16Scheme = "${pkgs.base16-schemes}/share/themes/catppuccin-latte.yaml";
+      polarity = "light";
+    }
+    {
+      image = "${pkgs.pantheon.elementary-wallpapers}/share/backgrounds/Snow-Capped Mountain.jpg";
+      base16Scheme = "${pkgs.base16-schemes}/share/themes/catppuccin-macchiato.yaml";
+      polarity = "dark";
+    }
+  ];
+
+in
+  lib.listToAttrs (lib.flatten (map makeTestbeds autoload))