syncthing: Support remote declarative sync

flake.nix

@@ -213,6 +213,10 @@
         system = "x86_64-linux";
         modules = [ ./abavorana/standin.nix ];
       };
+      nixosConfigurations.ludwig = lib.nixosSystem {
+        system = "x86_64-linux";
+        modules = [ ./ludwig/standin.nix ];
+      };
       nixosConfigurations.sprinkles = lib.nixosSystem {
         system = "aarch64-linux";
         modules = [ ./sprinkles/standin.nix ];

ludwig/standin.nix

@@ -0,0 +1,10 @@
+{ ... }:
+{
+  config = {
+    frogeye = {
+      name = "ludwig";
+      storageSize = "big";
+      syncthing.name = "Ludwig";
+    };
+  };
+}

os/syncthing/default.nix

@@ -24,7 +24,9 @@ let
   );
   allDevices = nixosDevices;
   syncingDevices = builtins.filter (device: device.syncthing.id != null) allDevices;
-  peerDevices = builtins.filter (device: device.name != config.frogeye.name) syncingDevices;
+  peerDevices = builtins.filter (
+    device: device.syncthing.id != config.frogeye.syncthing.id
+  ) syncingDevices;
 
   # Can't use the module's folders enable option, as it still requests things somehow
   allFolders = builtins.attrValues config.frogeye.folders;
@@ -34,12 +36,58 @@ let
     folder: device:
     (lib.hasAttrByPath [ folder.name ] device.folders)
     && device.folders.${folder.name}.syncthing.enable;
-  folderDeviceEntry = folder: device: { deviceID = device.syncthing.id; };
 
   enable = (builtins.length syncedFolders) > 0;
 in
 {
   config = {
+    # Allow to export configuration to other systems
+    system.build.syncthingConfig = {
+      folders = lib.trivial.pipe syncedFolders [
+        (builtins.map (folder: {
+          name = folder.name;
+          value = folder;
+        }))
+        builtins.listToAttrs
+        (lib.attrsets.mapAttrs (
+          folderName: folder:
+          (lib.attrsets.filterAttrs (
+            k: v:
+            builtins.elem k [
+              "label"
+              "path"
+              "syncthing"
+              "user"
+            ]
+          ))
+            folder
+        ))
+      ];
+      devices = lib.trivial.pipe syncingDevices [
+        (builtins.map (device: {
+          name = device.name;
+          value = device;
+        }))
+        builtins.listToAttrs
+        (lib.attrsets.mapAttrs (
+          deviceName: device:
+          {
+            folders = lib.trivial.pipe device.folders [
+              (lib.attrsets.filterAttrs (folderName: folder: folder.syncthing.enable))
+              (lib.attrsets.mapAttrs (folderName: folder: { syncthing.enable = true; }))
+            ];
+          }
+          //
+            (lib.attrsets.filterAttrs (
+              k: v:
+              builtins.elem k [
+                "syncthing"
+              ]
+            ))
+              device
+        ))
+      ];
+    };
     services.${service} = {
       inherit enable;
       openDefaultPorts = true;
@@ -63,8 +111,6 @@ in
             value = {
               label = "${capitalizeFirstLetter folder.user} ${folder.label}";
               path = "${config.users.users.${folder.user}.home}/${folder.path}";
-              # Despite further in the code indicating this is possible, it is, actually not
-              # devices = builtins.map (folderDeviceEntry folder) (builtins.filter (folderShouldSyncWith folder) peerDevices);
               devices = builtins.map (device: device.name) (
                 builtins.filter (folderShouldSyncWith folder) peerDevices
               );