ldbus: Allow specifying variant types for args

On the ldbus backend the function dbus.new_variant has been added.
This allows overriding the variant type autodetection for types not
expressable as arguments on the LUA type system, e.g. 'o', which gets
translated to string.

Note that this function gets available as dbus.raw.new_variant

Example usage:

local variant = dbus.raw.new_variant

myvariant = {
	'v',
	variant('aa{sv}', {
		{ k1 = 'v1' }, --val is string variant (autodetected)
		{ k2 = variant ('o', '/some/dbus/path')}
	})
}

Author: Rafael Gago

awesome/dbus.lua

@@ -180,6 +180,13 @@ for _, v in pairs (ldbus.basic_types) do
     dbus.set_of_basic_types[v] = true
 end
 
+dbus.variant_mt = {}
+function dbus.new_variant(vtype, value)
+    assert(value)
+    vtype = vtype or dbus.type(value)
+    return setmetatable ({ t = vtype, v = value }, dbus.variant_mt)
+end
+
 function dbus.consume_type(dtype)
     if not dtype then
         return nil
@@ -230,7 +237,15 @@ function dbus.append_arg(iter, value, dbus_type)
         end
         iter:close_container(arr_iter)
     elseif dt == ldbus.types.variant then
-        local val, var_dt = value, dbus.type(value)
+        local val, var_dt
+        if type(value) == "table" and
+                getmetatable(value) == dbus.variant_mt then
+            val    = value.v
+            var_dt = value.t
+        else
+            val    = value
+            var_dt = dbus.type(value)
+        end
         local var_iter = iter:open_container(dt, var_dt)
         dbus.append_arg(var_iter, val, var_dt)
         iter:close_container(var_iter)