Memory leak with callback return values

[arnetheduck]

miqt/qt/gen_qabstractitemview.cpp

Line 977 in 7ee9170

struct miqt_array /* of QModelIndex* */ callback_return_value = miqt_exec_callback_QAbstractItemView_SelectedIndexes(const_cast<MiqtVirtualQAbstractItemView*>(this), handle__SelectedIndexes);

In this callback handler, the miqt_array is allocated on the go side but never freed. Ditto for other, similar conversions.

[mappu]

The modelview example with QAbstractListModel_OnData is susceptible to this - it has to return a pointer to QVariant, because that is all that can traverse the ABI, but the Qt C++ method presumes a pass by value.

Probably, any callbacks that return a type by value (and the C ABI has to project as a pass by value) will need to destruct the value.

Currently, the destructors are embedded directly in the emitgo functions (e.g. emitParameterGo2CABIForwarding does a lot of defer C.free(...)). They'll need to be split out to separate functions and called more intelligently.

This is the dual of the problem in #86. A complete solution would fix both problems.

[arnetheduck]

This bug is more about miqt_array.data which miqt_exec_callback_QAbstractItemView_SelectedIndexes allocates - after the generated code has finished iterating over the items and adding them to the list, it could free data. Ditto other similar converters (miqt_string to QString etc).