Cannot list signals and slots in "connect" statements

In qt projects and every cpp file, when you want to have this statement:

QObject::connect(
a, SIGNAL(textChanged(const QString&)),
b, SLOT(setText(const QString&)) );

I expect after "SIGNAL(", code completion offer list of signals that can be emitted from object "a".
and also after "SLOT(", expect code completion offer list of slots which belong to object "b".
i test it with "ClangCodeModel plugin" and without it. in both caes this functionality does not work!