Simplify the submodule syntax, triggering the issue

examples/minimal/arion-compose.nix

@@ -2,16 +2,11 @@
 {
   config.docker-compose.services = {
 
-    webserver = {
-      service.useHostStore = true;
-      service.command = [ "sh" "-c" ''
-                  cd "$$WEB_ROOT"
-                  ${pkgs.python3}/bin/python -m http.server
-                '' ];
-      service.ports = [
-        "8000:8000" # host:container
-      ];
-      service.environment.WEB_ROOT = "${pkgs.nix.doc}/share/doc/nix/manual";
-    };
+    webserver.imports = [ ./service-webserver.nix ];
+
+    # webserver = {...}: {
+    #  imports = [ ./service-webserver.nix ];
+    #};
+
   };
 }

examples/minimal/service-webserver.nix

@@ -0,0 +1,12 @@
+{ pkgs, ... }: {
+  service.useHostStore = true;
+  service.command = [ "sh" "-c"
+                      ''
+                        cd "$$WEB_ROOT"
+                        ${pkgs.python3}/bin/python -m http.server
+                      '' ];
+  service.ports = [
+    "8000:8000" # host:container
+  ];
+  service.environment.WEB_ROOT = "${pkgs.nix.doc}/share/doc/nix/manual";
+}