[Qt-interest] QSortFilterProxyModel bug

[Pascal Patry]

Qt 4.5.0 introduced a bug inside QSortFilterProxyModel.

1. Create a QTreeView
2. Associate a model (class that inherit from QStandardItemModel)
3. Associate a proxy (QSortFilterProxyModel)
4. Set the sorting enabled on column 0
5. Insert a few items
 => At this point, everything is sorted correctly. All good.

6. Reimplement 'canFetchMore()' and 'fetchMore()' on the concrete model
 canFetchMore() { return true; }
 fetchMore() { // Create the children here }
7. Hit the "+" on the view where 'fetchMore' will create some items
 => At this point, the sort is totally broken.

The QTreeView has only one column. When we create the items, we use the 
function "QStandardItem::appendRows()". This function will 
cause "QSortFilterProxyModelPrivate::_q_sourceColumnsInserted(...)" to be called. Once 
this happens, we hit the bug on the line at "qsortfilterproxymodel.cpp:1189".

The line is:
	"source_sort_column += end - start + 1;"

Obviously, 'end' and 'start' are both 0 because we have only one column. So this will 
set "source_sort_column" to be 1. Since 1 is not a valid column, the sorting predicate 
(QSortFilterProxyModelLessThan) will use "sort_column" as being this value, hence 
retrieving 2 invalid QModelIndex. That will lead to a totally broken sort coming from the 
model.

Is this problem already known? If so, is there a patch somewhere to fix this?

Thank you,