xresources: add option extraConfig

modules/xresources.nix

@@ -28,17 +28,40 @@ in
         "Emacs*toolBar" = 0;
       };
       description = ''
-        X server resources that should be set. If <code>null</code>,
-        then this feature is disabled and no
+        X server resources that should be set.
+        If this and all other xresources options are
+        <code>null</code>, then this feature is disabled and no
+        <filename>~/.Xresources</filename> link is produced.
+      '';
+    };
+
+    xresources.extraConfig = mkOption {
+      type = types.lines;
+      default = "";
+      example = literalExample ''
+        builtins.readFile (
+            pkgs.fetchFromGitHub {
+                owner = "solarized";
+                repo = "xresources";
+                rev = "025ceddbddf55f2eb4ab40b05889148aab9699fc";
+                sha256 = "0lxv37gmh38y9d3l8nbnsm1mskcv10g3i83j0kac0a2qmypv1k9f";
+            } + "/Xresources.dark"
+        )
+      '';
+      description = ''
+        Additional X server resources contents.
+        If this and all other xresources options are
+        <code>null</code>, then this feature is disabled and no
         <filename>~/.Xresources</filename> link is produced.
       '';
     };
   };
 
-  config = mkIf (cfg.properties != null) {
+  config = mkIf (cfg.properties != null || cfg.extraConfig != "") {
     home.file.".Xresources".text =
-      concatStringsSep "\n" (
-        mapAttrsToList formatLine cfg.properties
+      concatStringsSep "\n" ([]
+        ++ (optional (cfg.extraConfig != "") cfg.extraConfig)
+        ++ (optionals (cfg.properties != null) (mapAttrsToList formatLine cfg.properties))
       ) + "\n";
   };
 }