Improve usage of roles. It should be much easier to read and use now.

common/machine-info/roles.nix

@@ -1,19 +1,55 @@
 { config, lib, ... }:
 
-# Maps roles to their hosts
+# Maps roles to their hosts.
+# machines.withRole = {
+#   personal = [
+#     "machine1" "machine3"
+#   ];
+#   cache = [
+#     "machine2"
+#   ];
+# };
+#
+# A list of all possible roles
+# machines.allRoles = [
+#   "personal"
+#   "cache"
+# ];
+#
+# For each role has true or false if the current machine has that role
+# thisMachine.hasRole = {
+#   personal = true;
+#   cache = false;
+# };
 
 {
-  options.machines.roles = lib.mkOption {
+  options.machines.withRole = lib.mkOption {
     type = lib.types.attrsOf (lib.types.listOf lib.types.str);
   };
 
+  options.machines.allRoles = lib.mkOption {
+    type = lib.types.listOf lib.types.str;
+  };
+
+  options.thisMachine.hasRole = lib.mkOption {
+    type = lib.types.attrsOf lib.types.bool;
+  };
+
   config = {
-    machines.roles = lib.zipAttrs
+    machines.withRole = lib.zipAttrs
       (lib.mapAttrsToList
         (host: cfg:
           lib.foldl (lib.mergeAttrs) { }
             (builtins.map (role: { ${role} = host; })
               cfg.systemRoles))
         config.machines.hosts);
+
+    machines.allRoles = lib.attrNames config.machines.withRole;
+
+    thisMachine.hasRole = lib.mapAttrs
+      (role: cfg:
+        builtins.elem config.networking.hostName config.machines.withRole.${role}
+      )
+      config.machines.withRole;
   };
 }