evalService: more versatile customConfig support.

lib/default.nix

@@ -15,14 +15,26 @@ lib: with lib; rec {
   ) (attrNames p));
 
   evalService = { pkgs, serviceName, modules, customConfig }:
-    let customConfig' = if (isAttrs customConfig) && !(customConfig ? service) then {
-      services.${serviceName} = customConfig;
-    } else customConfig;
+    let mkConfig = c: if (isAttrs c)
+    then (
+      if c ? nixosModules.${serviceName}
+      then c.nixosModules.${serviceName}
+      else if c ? nixosModule
+      then mkConfig c.nixosModule
+      else if c ? services then {
+        services.${serviceName} = c.services.${serviceName} or {};
+      } else {options, ...}: {
+        services.${serviceName} =
+          let validOptions = attrNames options.services.${serviceName};
+          in filterAttrs (n: _: elem n validOptions) c;
+      })
+    else c;
+
     in (lib.modules.evalModules {
       prefix = [];
       modules = modules ++ [
         { services.${serviceName}.enable = true; }
-        customConfig'
+        (mkConfig customConfig)
         systemdCompatModule
       ];
       args = { inherit pkgs; };