Refactor to symlinkJoin with passthru

flake.nix

@@ -10,33 +10,30 @@
       nixpkgs,
       flake-utils,
     }:
-    let
-      motdFiles = {
-        "40k" = ./40k-thought-for-the-day.txt;
-        rebirth = ./boi-rebirth-fortunes.txt;
-        bofh = ./bofh-excuses.txt;
-        discordium = ./discordium.txt;
-      };
-    in
     flake-utils.lib.eachDefaultSystem (
       system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
-        motd = pkgs.stdenv.mkDerivation {
-          pname = "motd";
-          version = "1.0";
-          builder = builtins.toFile "motd-builder.sh" ''
-            source $stdenv/setup
-            mkdir -p $out
-            ${builtins.foldl' (a: b: "${a}\n${b}") "" (
-              map (attr: "cp ${motdFiles.${attr}} $out/${attr}.txt") (builtins.attrNames motdFiles)
-            )}
-          '';
-        };
+        inherit (pkgs) symlinkJoin;
       in
       {
-        defaultPackage = motd;
         formatter = pkgs.nixfmt-rfc-style;
+
+        packages.default = self.packages.${system}.motd;
+        packages.motd = symlinkJoin {
+          name = "motd";
+          paths = [ ./motd ];
+          passthru =
+            let
+              motd = "${self.packages.${system}.motd}";
+            in
+            {
+              "40k" = "${motd}/40k-thought-for-the-day.txt";
+              rebirth = "${motd}/boi-rebirth-fortunes.txt";
+              bofh = "${motd}/bofh-excuses.txt";
+              discordium = "${motd}/discordium.txt";
+            };
+        };
       }
     );
 }