nixos/redis: add migration path to redict or sspl-redis

nixos/modules/services/databases/redis.nix

@@ -54,7 +54,7 @@ in {
   options = {
 
     services.redis = {
-      package = mkPackageOption pkgs "redis" { };
+      package = mkPackageOption pkgs "redict" { };
 
       vmOverCommit = mkEnableOption (lib.mdDoc ''
         setting of vm.overcommit_memory to 1
@@ -304,6 +304,14 @@ in {
 
   config = mkIf (enabledServers != {}) {
 
+    warnings = mkIf (cfg.enable && cfg.package.pname == "redict") [
+      ''
+        The license of the Redis package has changed to SSPL. You have two options:
+        - Replace `services.redis` with `services.redict` to switch to https://redict.io, which will continue development under a LGPL-3-only license
+        - confirm you want to use the unfree redis going forward with `services.redis.package = pkgs.redis;`
+      ''
+    ];
+
     assertions = attrValues (mapAttrs (name: conf: {
       assertion = conf.requirePass != null -> conf.requirePassFile == null;
       message = ''