* Add a type for read-only options. Options which are only declared

  are used when a module produces read-only data for other modules.

svn path=/nixpkgs/trunk/; revision=18148

1 files changed, 6 insertions, 0 deletions

diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index 8b0f61549b5..01a5d98fca6 100644
--- a/pkgs/lib/types.nix
+++ b/pkgs/lib/types.nix
@@ -110,6 +110,12 @@ rec {
           throw "Multiple definitions. Only one is allowed for this option.";
     };
 
+    none = elemType: mkOptionType {
+      inherit (elemType) name check iter fold docPath hasOptions;
+      merge = list:
+        throw "No definitions are allowed for this option.";
+    };
+
     nullOr = elemType: mkOptionType {
       inherit (elemType) name merge docPath hasOptions;
       check = x: builtins.isNull x || elemType.check x;