I've got some Vala:

          this.conn.request_handles (-1, HandleType.CONTACT, contacts,
            (c, ht, h, i, e, w) =>
              {
                try
                  {
                    this.change_favourites_by_request_handles ((Handle[]) h, i,
                        e, true);
                  }
                catch (GLib.Error e)
                  {
                    warning ("couldn't get list of favourite contacts: %s",
                        e.message);
                  }
              },
            this);

where this.conn.request_handles() is defined by the following VAPI:

	public async void request_handles (int timeout_ms, TelepathyGLib.HandleType handle_type, [CCode (array_length = false)] string[] ids, [CCode (delegate_target_pos = 4.33333)] owned TelepathyGLib.ConnectionRequestHandlesCb callback, GLib.Object weak_object);

	[CCode (cheader_filename = "telepathy-glib/telepathy-glib.h", instance_pos = 5.9)]
	public delegate void ConnectionRequestHandlesCb (TelepathyGLib.Connection connection, TelepathyGLib.HandleType handle_type, [CCode (array_length_pos = 2.5)] uint[] handles, [CCode (array_length_pos = 2.5)] string[] ids, GLib.Error error, GLib.Object weak_object);

When this is compiled, the following C code is generated:

Call:

tp_connection_request_handles (data->self->priv->conn, -1, TP_HANDLE_TYPE_CONTACT, data->contacts, __lambda7__tp_connection_request_handles_cb, g_object_ref (data->self), g_object_unref, (GObject*) data->self, NULL, NULL);

Callback:

static void _lambda7_ (TpConnection* c, TpHandleType ht, guint* h, int h_length1, char** i, int i_length1, GError* e, TpfPersonaStore* self, GObject* w);

static void __lambda7__tp_connection_request_handles_cb (TpConnection* connection, TpHandleType handle_type, int ids_length1, guint* handles, char** ids, GError* _error_, gpointer self, GObject* weak_object) {
	_lambda7_ (connection, handle_type, handles, handles_length1, ids, ids_length1, _error_, self, weak_object);
}

The length parameter for ids and handles in the callback should be the ids_length1 parameter in both cases (it's shared), but Vala's trying to use a non-existent handles_length1 variable for the length of handles.

The second problem is that Vala's adding two extraneous NULL parameters to the call to tp_connection_request_handles().

Overall, this is resulting in the following errors from gcc:

tpf-persona-store.c: In function ‘__lambda7__tp_connection_request_handles_cb’:
tpf-persona-store.c:774: error: ‘handles_length1’ undeclared (first use in this function)
tpf-persona-store.c:774: error: (Each undeclared identifier is reported only once
tpf-persona-store.c:774: error: for each function it appears in.)
tpf-persona-store.c: In function ‘tpf_persona_store_initialise_favourite_contacts_co’:
tpf-persona-store.c:825: error: too many arguments to function ‘tp_connection_request_handles’