lib: add generator functions for toJSON & toYAML

They both reference the toJSON builtin, so we get semantic identifiers
that express the intent of the generation.
Both should be able to map each nix value (minus functions) to the
destination config files.

Includes two invocation unit tests.

lib/generators.nix

@@ -10,7 +10,7 @@ let
   flipMapAttrs = flip libAttr.mapAttrs;
 in
 
-{
+rec {
 
   /* Generates an INI-style config file from an
    * attrset of sections to an attrset of key-value pairs.
@@ -50,4 +50,18 @@ in
     in
       # map input to ini sections
       mapAttrsToStringsSep "\n" mkSection attrsOfAttrs;
+
+
+  /* Generates JSON from an arbitrary (non-function) value.
+    * For more information see the documentation of the builtin.
+    */
+  toJSON = {}: builtins.toJSON;
+
+
+  /* YAML has been a strict superset of JSON since 1.2, so we
+    * use toJSON. Before it only had a few differences referring
+    * to implicit typing rules, so it should work with older
+    * parsers as well.
+    */
+  toYAML = {}@args: toJSON args;
 }

lib/tests.nix

@@ -181,4 +181,27 @@ runTests {
     '';
   };
 
+  /* right now only invocation check */
+  testToJSONSimple =
+    let val = {
+      foobar = [ "baz" 1 2 3 ];
+    };
+    in {
+      expr = generators.toJSON {} val;
+      # trival implementation
+      expected = builtins.toJSON val;
+  };
+
+  /* right now only invocation check */
+  testToYAMLSimple =
+    let val = {
+      list = [ { one = 1; } { two = 2; } ];
+      all = 42;
+    };
+    in {
+      expr = generators.toYAML {} val;
+      # trival implementation
+      expected = builtins.toJSON val;
+  };
+
 }