QCompleter: fix crash when setting the same model twice

Found when retesting the testcase completer.zip from QTBUG-54642 Pick-to: 6.3 6.2 5.15 Change-Id: Id84eefeb3a33dc6d790cfa23755352381cc097a9 Reviewed-by: Volker Hilsheimer <[email protected]>
fwcd · Mar 13, 2022 · 7382e57 · 7382e57
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diff --git a/src/widgets/util/qcompleter.cpp b/src/widgets/util/qcompleter.cpp
@@ -1100,6 +1100,8 @@ void QCompleter::setModel(QAbstractItemModel *model)
 {
     Q_D(QCompleter);
     QAbstractItemModel *oldModel = d->proxy->sourceModel();
+    if (oldModel == model)
+        return;
 #if QT_CONFIG(filesystemmodel)
     if (qobject_cast<const QFileSystemModel *>(oldModel))
         setCompletionRole(Qt::EditRole); // QTBUG-54642, clear FileNameRole set by QFileSystemModel

diff --git a/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp b/tests/auto/widgets/widgets/qcombobox/tst_qcombobox.cpp
@@ -1652,6 +1652,16 @@ void tst_QComboBox::setModel()
     QCOMPARE(box.rootModelIndex(), rootModelIndex);
     box.setModel(box.model());
     QCOMPARE(box.rootModelIndex(), rootModelIndex);
+
+    // check that setting the same model as the completer's doesn't crash
+    QCompleter *completer = new QCompleter(&box);
+    box.setEditable(true);
+    box.setCompleter(completer);
+    auto *listModel = new QStringListModel({ "one", "two" }, completer);
+    completer->setModel(listModel);
+    QCOMPARE(listModel->rowCount(), 2); // make sure it wasn't deleted
+    box.setModel(listModel);
+    QCOMPARE(listModel->rowCount(), 2); // make sure it wasn't deleted
 }
 
 void tst_QComboBox::setCustomModelAndView()