system/state-version: init

nixos/modules/system/state-version.nix

@@ -0,0 +1,48 @@
+# Portions of this file are sourced from
+# https://github.com/linyinfeng/dotfiles/blob/b618b0fd16fb9c79ab7199ed51c4c0f98a392cea/nixos/modules/system/state-version.nix
+{
+  config,
+  options,
+  lib,
+  ...
+}:
+with lib;
+let
+  cfg = config.system;
+in
+{
+  options = {
+    system.targetStateVersion = mkOption {
+      inherit (options.system.stateVersion) type;
+      default = config.system.stateVersion;
+      description = ''
+        System is going to be upgraded to the targetStateVersion.
+      '';
+    };
+    system.pendingStateVersionUpgrade = mkOption {
+      type = types.bool;
+      default = cfg.stateVersion != cfg.targetStateVersion;
+      readOnly = true;
+    };
+  };
+
+  config = {
+    specialisation = mkIf cfg.pendingStateVersionUpgrade {
+      target-state-version = {
+        configuration = {
+          system.stateVersion = mkForce targetStateVersion;
+        };
+      };
+    };
+
+    warnings = mkIf cfg.pendingStateVersionUpgrade [
+      ''
+
+        host: ${config.networking.hostName}
+        pending stateVersion upgrade from ${cfg.stateVersion} to ${cfg.targetStateVersion}
+        release notes: https://nixos.org/manual/nixos/stable/release-notes.html#sec-release-${cfg.targetStateVersion}
+
+      ''
+    ];
+  };
+}