listfilter: Bypass QListView.dropEvent

On Qt >= 5.15.2 QListView.dropEvent depends on private state tracking
that is setup in startDrag. Since startDrag is overridden here and does
not dispatch to the base implementation, this causes items loss when
performing internal move.

Author: ales-erjavec

Orange/widgets/utils/listfilter.py

@@ -1,4 +1,4 @@
-from AnyQt.QtWidgets import QListView, QLineEdit, QCompleter
+from AnyQt.QtWidgets import QListView, QLineEdit, QCompleter, QAbstractItemView
 from AnyQt.QtGui import QDrag
 from AnyQt.QtCore import (
     Qt, QObject, QEvent, QModelIndex,
@@ -85,6 +85,13 @@ def startDrag(self, supported_actions):
                     delslice(self.model(), s1, s2)
             self.dragDropActionDidComplete.emit(res)
 
+    def dropEvent(self, event):
+        # Bypass QListView.dropEvent on Qt >= 5.15.2.
+        # Because `startDrag` is overridden and does not dispatch to base
+        # implementation then `dropEvent` would need to be overridden also
+        # (private `d->dropEventMoved` state tracking due to QTBUG-87057 fix).
+        QAbstractItemView.dropEvent(self, event)
+
     def dragEnterEvent(self, event):
         """
         Reimplemented from QListView.dragEnterEvent