nixos/i18n: handle C locale better (#460010)

2 files changed, 46 insertions, 14 deletions

diff --git a/nixos/modules/config/i18n.nix b/nixos/modules/config/i18n.nix
index e9955859bffd..aa8f06d1c7f2 100644
--- a/nixos/modules/config/i18n.nix
+++ b/nixos/modules/config/i18n.nix
@@ -7,19 +7,22 @@
 let
   sanitizeUTF8Capitalization =
     lang: (lib.replaceStrings [ "utf8" "utf-8" "UTF8" ] [ "UTF-8" "UTF-8" "UTF-8" ] lang);
-  aggregatedLocales = [
-    "${config.i18n.defaultLocale}/${config.i18n.defaultCharset}"
-  ]
-  ++ lib.pipe config.i18n.extraLocaleSettings [
-    # See description of extraLocaleSettings for why is this ignored here.
-    (x: lib.removeAttrs x [ "LANGUAGE" ])
-    (lib.mapAttrs (n: v: (sanitizeUTF8Capitalization v)))
-    (lib.mapAttrsToList (LCRole: lang: lang + "/" + (config.i18n.localeCharsets.${LCRole} or "UTF-8")))
-  ]
-  ++ (map sanitizeUTF8Capitalization (
-    lib.optionals (builtins.isList config.i18n.extraLocales) config.i18n.extraLocales
-  ))
-  ++ (lib.optional (builtins.isString config.i18n.extraLocales) config.i18n.extraLocales);
+  aggregatedLocales =
+    lib.optionals (config.i18n.defaultLocale != "C") [
+      "${config.i18n.defaultLocale}/${config.i18n.defaultCharset}"
+    ]
+    ++ lib.pipe config.i18n.extraLocaleSettings [
+      # See description of extraLocaleSettings for why is this ignored here.
+      (x: lib.removeAttrs x [ "LANGUAGE" ])
+      (lib.mapAttrs (n: v: (sanitizeUTF8Capitalization v)))
+      # C locales are always installed
+      (lib.filterAttrs (n: v: v != "C"))
+      (lib.mapAttrsToList (LCRole: lang: lang + "/" + (config.i18n.localeCharsets.${LCRole} or "UTF-8")))
+    ]
+    ++ (map sanitizeUTF8Capitalization (
+      lib.optionals (builtins.isList config.i18n.extraLocales) config.i18n.extraLocales
+    ))
+    ++ (lib.optional (builtins.isString config.i18n.extraLocales) config.i18n.extraLocales);
 in
 {
   ###### interface
@@ -111,6 +114,9 @@ in
         description = ''
           Per each {option}`i18n.extraLocaleSettings`, choose the character set
           to use for it. Essentially defaults to UTF-8 for all of them.
+
+          Note that for a locale category that uses the `C` locale, setting a
+          character set to it via this setting is ignored.
         '';
       };
 
diff --git a/nixos/tests/i18n.nix b/nixos/tests/i18n.nix
index a0493b7c62f5..77f0cc579d5d 100644
--- a/nixos/tests/i18n.nix
+++ b/nixos/tests/i18n.nix
@@ -38,6 +38,32 @@
         };
       };
     };
+    Csimple = {
+      i18n = {
+        defaultLocale = "C";
+      };
+    };
+    CnonDefault = {
+      i18n = {
+        defaultLocale = "en_US.UTF-8";
+        extraLocaleSettings = {
+          LC_COLLATE = "C";
+          LC_MESSAGES = "C";
+          LC_TIME = "C";
+        };
+      };
+    };
   };
-  testScript = { nodes, ... }: "";
+  testScript =
+    { nodes, ... }:
+    lib.pipe nodes [
+      builtins.attrNames
+      (map (node: ''
+        ${node}.copy_from_vm(
+            ${node}.succeed("readlink -f /etc/locale.conf").strip(),
+            "${node}"
+        )
+      ''))
+      (lib.concatStringsSep "\n")
+    ];
 }