ibus: fix installation of dconf database

Fixes this warning at ibus-daemon startup:

(ibus-dconf:15691): dconf-WARNING **: 21:49:24.018: unable to open file '/etc/dconf/db/ibus': Failed to open file ?/etc/dconf/db/ibus?: open() failed: No such file or directory; expect degraded performance

nixos/modules/i18n/input-method/ibus.nix

@@ -64,7 +64,7 @@ in
     # Without dconf enabled it is impossible to use IBus
     programs.dconf.enable = true;
 
-    programs.dconf.profiles.ibus = "${ibusPackage}/etc/dconf/profile/ibus";
+    programs.dconf.packages = [ ibusPackage ];
 
     services.dbus.packages = [
       ibusAutostart

nixos/modules/programs/dconf.nix

@@ -4,13 +4,24 @@ with lib;
 
 let
   cfg = config.programs.dconf;
-
+  cfgDir = pkgs.symlinkJoin {
-  mkDconfProfile = name: path:
+    name = "dconf-system-config";
-    {
+    paths = map (x: "${x}/etc/dconf") cfg.packages;
-      name = "dconf/profile/${name}";
+    postBuild = ''
-      value.source = path; 
+      mkdir -p $out/profile
+      mkdir -p $out/db
+    '' + (
+      concatStringsSep "\n" (
+        mapAttrsToList (
+          name: path: ''
+            ln -s ${path} $out/profile/${name}
+          ''
+        ) cfg.profiles
+      )
+    ) + ''
+      ${pkgs.dconf}/bin/dconf update $out/db
+    '';
   };
-
 in
 {
   ###### interface
@@ -22,18 +33,22 @@ in
       profiles = mkOption {
         type = types.attrsOf types.path;
         default = {};
-        description = "Set of dconf profile files.";
+        description = "Set of dconf profile files, installed at <filename>/etc/dconf/profiles/<replaceable>name</replaceable></filename>.";
         internal = true;
       };
 
+      packages = mkOption {
+        type = types.listOf types.package;
+        default = [];
+        description = "A list of packages which provide dconf profiles and databases in <filename>/etc/dconf</filename>.";
+      };
     };
   };
 
   ###### implementation
 
   config = mkIf (cfg.profiles != {} || cfg.enable) {
-    environment.etc = optionalAttrs (cfg.profiles != {})
+    environment.etc.dconf.source = mkIf (cfg.profiles != {} || cfg.packages != []) cfgDir;
-      (mapAttrs' mkDconfProfile cfg.profiles);
 
     services.dbus.packages = [ pkgs.dconf ];