stylix: support multiple testbeds per module (#858)

Support multiple testbeds per module with
/modules/<MODULE>/testbeds/<TESTBED>.nix, while validating various
invariants.

README.md

@@ -54,8 +54,8 @@ Photos by [Clay Banks](https://unsplash.com/photos/three-bicycles-parked-in-fron
 and [Derrick Cooper](https://unsplash.com/photos/brown-road-in-forest-during-daytime-L505cPnmIds).
 
 Try a live demo of this theme by running
-`nix run github:danth/stylix#testbed-gnome-light` or
-`nix run github:danth/stylix#testbed-gnome-dark`.
+`nix run github:danth/stylix#testbed-gnome-default-light` or
+`nix run github:danth/stylix#testbed-gnome-default-dark`.
 
 ### KDE Plasma 5
 

docs/src/testbeds.md

@@ -17,11 +17,10 @@ otherwise.
 
 ## Creation
 
-New testbeds are defined by creating a file called `testbed.nix` within the
-folder for the corresponding target. This file will automatically be loaded
-as a NixOS module, with options such as `stylix.image` already defined.
-The module should include any options necessary to install the target and
-any supporting software - for example, a window manager.
+Testbeds are defined at `/modules/«module»/testbeds/«testbed».nix` and are are
+automatically loaded as a NixOS module with options such as `stylix.image`
+already defined. The testbed should include any options necessary to install the
+target and any supporting software - for example, a window manager.
 
 If the target can only be used through Home Manager, you can write a
 Home Manager module within the NixOS module using the following format:
@@ -53,19 +52,19 @@ github:danth/stylix
     └───x86_64-linux
         ├───docs: package 'stylix-book'
         ├───palette-generator: package 'palette-generator'
-        ├───testbed-gnome-dark: package 'testbed-gnome-dark'
-        ├───testbed-gnome-light: package 'testbed-gnome-light'
-        ├───testbed-kde-dark: package 'testbed-kde-dark'
-        └───testbed-kde-light: package 'testbed-kde-light'
+        ├───testbed-gnome-default-dark: package 'testbed-gnome-default-dark'
+        ├───testbed-gnome-default-light: package 'testbed-gnome-default-light'
+        ├───testbed-kde-default-dark: package 'testbed-kde-default-dark'
+        └───testbed-kde-default-light: package 'testbed-kde-default-light'
 ```
 
 (This has been edited down to only the relevant parts.)
 
 To start a testbed, each of which is named in the format
-`testbed-«target»-«polarity»`, run the following command:
+`testbed-«module»-«testbed»-«polarity»`, run the following command:
 
 ```console
-user@host:~$ nix run .#testbed-«target»-«polarity»
+user@host:~$ nix run .#testbed-«module»-«testbed»-«polarity»
 ```
 
 Any package with a name not fitting the given format is not a testbed,
@@ -75,7 +74,7 @@ Once the virtual machine starts, a window should open, similar to the screenshot
 below. The contents of the virtual machine will vary depending on the target you
 selected earlier.
 
-![GDM login screen with a dark background color and showing a guest user](testbed-gnome-dark.png)
+![GDM login screen with a dark background color and showing a guest user](testbed-gnome-default-dark.png)
 
 If the testbed includes a login screen, the guest user should log in
 automatically when selected. Depending on the software used, you may still be

stylix/testbed.nix

@@ -90,23 +90,48 @@ let
       };
     };
 
-  autoload = builtins.concatLists (
-    lib.mapAttrsToList (
-      name: _:
-      let
-        testbed = {
-          inherit name;
-          module = "${inputs.self}/modules/${name}/testbed.nix";
-        };
-      in
-      lib.optional (builtins.pathExists testbed.module) testbed
-    ) (builtins.readDir "${inputs.self}/modules")
-  );
+  autoload =
+    let
+      directory = "testbeds";
+      modules = "${inputs.self}/modules";
+    in
+    lib.flatten (
+      lib.mapAttrsToList (
+        module: _:
+        let
+          testbeds = "${modules}/${module}/${directory}";
+        in
+        lib.mapAttrsToList (
+          testbed: type:
+          if type != "regular" then
+            builtins.throw "${testbed} must be regular: ${type}"
+
+          else if !lib.hasSuffix ".nix" testbed then
+            builtins.throw "testbed must be a Nix file: ${testbeds}/${testbed}"
+
+          else if testbed == ".nix" then
+            builtins.throw "testbed must have a name: ${testbed}"
+
+          # To prevent ambiguity with the final derivation's hyphen field
+          # separator, testbed names should not contain hyphens.
+          else if lib.hasInfix "-" testbed then
+            builtins.throw "testbed name must not contain hyphens (-): ${testbed}"
+
+          else
+            {
+              inherit module;
+
+              name = lib.removeSuffix ".nix" testbed;
+              path = "${testbeds}/${testbed}";
+            }
+        ) (lib.optionalAttrs (builtins.pathExists testbeds) (builtins.readDir testbeds))
+      ) (builtins.readDir modules)
+    );
 
   makeTestbed =
     testbed: stylix:
     let
-      name = "testbed-${testbed.name}-${stylix.polarity}";
+      name = "testbed-${testbed.module}-${testbed.name}-${stylix.polarity}";
 
       system = lib.nixosSystem {
         inherit (pkgs) system;
@@ -116,7 +141,7 @@ let
           applicationModule
           inputs.self.nixosModules.stylix
           inputs.home-manager.nixosModules.home-manager
-          testbed.module
+          testbed.path
 
           {
             inherit stylix;