beets: add enable option

(cherry picked from commit 797fbbf826)

modules/misc/news.nix

@@ -871,6 +871,23 @@ in
           A new module is available: 'services.nextcloud-client'.
         '';
       }
+
+      {
+        time = "2018-12-04T21:54:38+00:00";
+        condition = config.programs.beets.settings != {};
+        message = ''
+          A new option 'programs.beets.enable' has been added.
+          Starting with state version 19.03 this option defaults to
+          false. For earlier versions it defaults to true if
+          'programs.beets.settings' is non-empty.
+
+          It is recommended to explicitly add
+
+              programs.beets.enable = true;
+
+          to your configuration.
+        '';
+      }
     ];
   };
 }

modules/programs/beets.nix

@@ -13,6 +13,21 @@ in
 
   options = {
     programs.beets = {
+      enable = mkOption {
+        type = types.bool;
+        default =
+          if versionAtLeast config.home.stateVersion "19.03"
+          then false
+          else cfg.settings != {};
+        defaultText = "false";
+        description = ''
+          Whether to enable the beets music library manager. This
+          defaults to <literal>false</literal> for state
+          version ≥ 19.03. For earlier versions beets is enabled if
+          <option>programs.beets.settings</option> is non-empty.
+        '';
+      };
+
       settings = mkOption {
         type = types.attrs;
         default = {};
@@ -24,7 +39,7 @@ in
     };
   };
 
-  config = mkIf (cfg.settings != {}) {
+  config = mkIf cfg.enable {
     home.packages = [ pkgs.beets ];
 
     xdg.configFile."beets/config.yaml".text =