Add function providing the canonical andRestArguments

The field catching the remaining fields will always be of the same
shape, so add a function for this to make usage simple.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

src/Ganeti/THH.hs

@@ -48,6 +48,7 @@ module Ganeti.THH ( declareSADT
                   , genLuxiOp
                   , Field (..)
                   , simpleField
+                  , andRestArguments
                   , specialNumericalField
                   , withDoc
                   , defaultField
@@ -127,6 +128,20 @@ simpleField fname ftype =
         , fieldDoc         = ""
         }
 
+-- | Generate an AndRestArguments catch-all field.
+andRestArguments :: String -> Field
+andRestArguments fname =
+  Field { fieldName        = fname
+        , fieldType        = [t| M.Map String JSON.JSValue |]
+        , fieldRead        = Nothing
+        , fieldShow        = Nothing
+        , fieldExtraKeys   = []
+        , fieldDefault     = Nothing
+        , fieldConstr      = Nothing
+        , fieldIsOptional  = AndRestArguments
+        , fieldDoc         = ""
+        }
+
 withDoc :: String -> Field -> Field
 withDoc doc field =
   field { fieldDoc = doc }