Make dataChanged signal actually pass a QVector<int> filled with changed data roles as a parameter

QAbstractItemModel class introduces a crucial dataChanged signal which passes two QModelIndex objects representing the span and a QVector<int> of data roles which were changed.

Qt's QTableWidget is supposed to cover the majority of simple use cases and is provided so that users do not have to write view and model implementations on their own if the task at hand is not demanding enough. The problem is that its underlying QTableModel implementation does not use the roles parameter of dataChanged signal. Thus it is impossible to determine which data role was changed when a QTableWidgetItem changes. I reckon that being able to pinpoint the data role that led to emitting the itemChanged and dataChanged signals is very important.

Without knowing the role it is impossible to write slots that react only to eg. item's text change – quite a frequent case – or user's own data.

After reading the qtablewidget.cpp I see that the role which is supplied to QTableWidgetItem::setData method call is dropped and never reaches QTableModel::itemChanged which in turn emits the dataChanged signal with a default-initialized QVector<int> as the roles parameter.

Would you consider implementing roles parameter support in dataChanged methods of all the data view-model classes?