Gtk.TreeDragSource.prototype.drag_data_get

function drag_data_get(path:Gtk.TreePath, selection_data:Gtk.SelectionData):Boolean {
    // Gjs wrapper for gtk_tree_drag_source_drag_data_get()
}

Asks the Gtk.TreeDragSource to fill in selection_data with a representation of the row at path. selection_data->target gives the required type of the data. Should robustly handle a path no longer found in the model!