factorio: let us change mod settings

nixos/modules/services/games/factorio.nix

@@ -39,7 +39,7 @@ let
   } // cfg.extraSettings;
   serverSettingsFile = pkgs.writeText "server-settings.json" (builtins.toJSON (filterAttrsRecursive (n: v: v != null) serverSettings));
   serverAdminsFile = pkgs.writeText "server-adminlist.json" (builtins.toJSON cfg.admins);
-  modDir = pkgs.factorio-utils.mkModDirDrv cfg.mods;
+  modDir = pkgs.factorio-utils.mkModDirDrv cfg.mods cfg.mods-dat;
 in
 {
   options = {
@@ -136,6 +136,13 @@ in
           derivations via nixos-channel. Until then, this is for experts only.
         '';
       };
+      mods-dat = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = lib.mdDoc ''
+        Mods settings can be changed by specifying a dat file.
+        '';
+      };
       game-name = mkOption {
         type = types.nullOr types.str;
         default = "Factorio Game";

pkgs/games/factorio/default.nix

@@ -3,6 +3,7 @@
 , libSM, libICE, libXext, factorio-utils
 , releaseType
 , mods ? []
+, mods-dat ? null
 , versionsJson ? ./versions.json
 , username ? "", token ? "" # get/reset token at https://factorio.com/profile
 , experimental ? false # true means to always use the latest branch
@@ -130,7 +131,7 @@ let
     fi
   '';
 
-  modDir = factorio-utils.mkModDirDrv mods;
+  modDir = factorio-utils.mkModDirDrv mods mods-dat;
 
   base = with actual; {
     pname = "factorio-${releaseType}";

pkgs/games/factorio/utils.nix

@@ -3,7 +3,7 @@
 { lib, stdenv }:
 with lib;
 {
-  mkModDirDrv = mods: # a list of mod derivations
+  mkModDirDrv = mods: modsDatFile: # a list of mod derivations
     let
       recursiveDeps = modDrv: [modDrv] ++ map recursiveDeps modDrv.deps;
       modDrvs = unique (flatten (map recursiveDeps mods));
@@ -18,7 +18,9 @@ with lib;
           # NB: there will only ever be a single zip file in each mod derivation's output dir
           ln -s $modDrv/*.zip $out
         done
-      '';
+      '' + (if modsDatFile != null then ''
+       cp ${modsDatFile} $out/mod-settings.dat
+      '' else "");
     };
 
     modDrv = { allRecommendedMods, allOptionalMods }: