Add a new way to handle option sets.

svn path=/nixpkgs/trunk/; revision=12505

pkgs/test/mkOption/declare.nix

@@ -0,0 +1,53 @@
+# sets of small configurations:
+# Each configuration
+rec {
+  # has 2 arguments pkgs and this.
+  configA = pkgs: this: {
+    # Can depends on other configuration
+    require = configB;
+
+    # Defines new options
+    optionA = pkgs.lib.mkOption {
+      # With default values
+      default = false;
+      # And merging functions.
+      merge = pkgs.lib.mergeEnableOption;
+    };
+
+    # Add a new definition to other options.
+    optionB = this.optionA;
+  };
+
+  # Can be used for option header.
+  configB = pkgs: this: {
+    # Can depends on more than one configuration.
+    require = [ configC configD ];
+
+    optionB = pkgs.lib.mkOption {
+      default = false;
+    };
+
+    # Is not obliged to define other options.
+  };
+
+  configC = pkgs: this: {
+    require = [ configA ];
+
+    optionC = pkgs.lib.mkOption {
+      default = false;
+    };
+
+    # Use the default value if it is not overwritten.
+    optionA = this.optionC;
+  };
+
+  # Can also be used as option configuration only.
+  # without any arguments (backward compatibility)
+  configD = {
+    # Is not forced to specify the require attribute.
+
+    # Is not force to make new options.
+    optionA = true;
+    optionD = false;
+  };
+}