From d8bbae877a6049867625ac86134422f8765b2157 Mon Sep 17 00:00:00 2001
From: Nicolas Pierron <nicolas.b.pierron@gmail.com>
Date: Thu, 5 Nov 2009 15:39:45 +0000
Subject: [PATCH] * 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
---
 pkgs/lib/types.nix | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pkgs/lib/types.nix b/pkgs/lib/types.nix
index 8b0f61549b5d..01a5d98fca62 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;