nixos/i18n: add extraLocales option (#356477)

doc/release-notes/rl-2505.section.md

@@ -360,6 +360,11 @@
 
 ## Other Notable Changes {#sec-nixpkgs-release-25.05-notable-changes}
 
+- `i18n` module improvements:
+  - `i18n.extraLocales` should now be the preferred way to install additional locales.
+  - `i18n.supportedLocales` is now considered an implementation detail and will be hidden from the documentation. But the option will still continue to work.
+  - `i18n.supportedLocales` will now trigger a warning when it omits any locale set in `i18n.defaultLocale`, `i18n.extraLocales` or `i18n.extraLocaleSettings`.
+
 - `titaniumenv`, `titanium`, and `titanium-alloy` have been removed due to lack of maintenance in Nixpkgs []{#sec-nixpkgs-release-25.05-incompatibilities-titanium-removed}.
 
 - androidenv has been improved:

nixos/doc/manual/configuration/profiles/minimal.section.md

@@ -1,6 +1,6 @@
 # Minimal {#sec-profile-minimal}
 
 This profile defines a small NixOS configuration. It does not contain any
-graphical stuff. It's a very short file that sets [](#opt-i18n.supportedLocales)
+graphical stuff. It's a very short file that sets the supported locales
 to only support the user-selected locale, and
 [disables packages' documentation](#opt-documentation.enable).

nixos/modules/config/i18n.nix

@@ -4,6 +4,16 @@
   pkgs,
   ...
 }:
+let
+  aggregatedLocales =
+    builtins.map
+      (l: (lib.replaceStrings [ "utf8" "utf-8" "UTF8" ] [ "UTF-8" "UTF-8" "UTF-8" ] l) + "/UTF-8")
+      (
+        [ config.i18n.defaultLocale ]
+        ++ config.i18n.extraLocales
+        ++ (lib.attrValues (lib.filterAttrs (n: v: n != "LANGUAGE") config.i18n.extraLocaleSettings))
+      );
+in
 {
   ###### interface
 
@@ -42,6 +52,17 @@
         '';
       };
 
+      extraLocales = lib.mkOption {
+        type = lib.types.listOf lib.types.str;
+        default = [ ];
+        example = [ "nl_NL.UTF-8" ];
+        description = ''
+          Additional locales that the system should support, besides the ones
+          configured with {option}`i18n.defaultLocale` and
+          {option}`i18n.extraLocaleSettings`.
+        '';
+      };
+
       extraLocaleSettings = lib.mkOption {
         type = lib.types.attrsOf lib.types.str;
         default = { };
@@ -58,28 +79,14 @@
 
       supportedLocales = lib.mkOption {
         type = lib.types.listOf lib.types.str;
+        visible = false;
         default = lib.unique (
-          builtins.map
-            (l: (lib.replaceStrings [ "utf8" "utf-8" "UTF8" ] [ "UTF-8" "UTF-8" "UTF-8" ] l) + "/UTF-8")
-            (
           [
-                "C.UTF-8"
+            "C.UTF-8/UTF-8"
-                "en_US.UTF-8"
+            "en_US.UTF-8/UTF-8"
-                config.i18n.defaultLocale
           ]
-              ++ (lib.attrValues (lib.filterAttrs (n: v: n != "LANGUAGE") config.i18n.extraLocaleSettings))
+          ++ aggregatedLocales
-            )
         );
-        defaultText = lib.literalExpression ''
-          lib.unique
-            (builtins.map (l: (lib.replaceStrings [ "utf8" "utf-8" "UTF8" ] [ "UTF-8" "UTF-8" "UTF-8" ] l) + "/UTF-8") (
-              [
-                "C.UTF-8"
-                "en_US.UTF-8"
-                config.i18n.defaultLocale
-              ] ++ (lib.attrValues (lib.filterAttrs (n: v: n != "LANGUAGE") config.i18n.extraLocaleSettings))
-            ))
-        '';
         example = [
           "en_US.UTF-8/UTF-8"
           "nl_NL.UTF-8/UTF-8"
@@ -100,6 +107,18 @@
   ###### implementation
 
   config = {
+    warnings =
+      lib.optional ((lib.subtractLists config.i18n.supportedLocales aggregatedLocales) != [ ])
+        ''
+          `i18n.supportedLocales` is deprecated in favor of `i18n.extraLocales`,
+          and it seems you are using `i18n.supportedLocales` and forgot to
+          include some locales specified in `i18n.defaultLocale`,
+          `i18n.extraLocales` or `i18n.extraLocaleSettings`.
+
+          If you're trying to install additional locales not specified in
+          `i18n.defaultLocale` or `i18n.extraLocaleSettings`, consider adding
+          only those locales to `i18n.extraLocales`.
+        '';
 
     environment.systemPackages =
       # We increase the priority a little, so that plain glibc in systemPackages can't win.