QCompleter::setPopup() - refactor and cleanup

QCompleter::setPopup() sets window flags, focus policy, parent, focus
proxy, item delate and installs an event filter, before the popup
argument is assigned to d->popup.

In the QCompleter::eventFilter override, QObject::eventFilter is called
(under more) if d->popup is nullptr.

If a custom class is inherited from QCompleter and it overrides
QObject::eventFilter(), this causes an infinite loop.

This patch re-factors the method.
- early return is added if the new popup != d->popup
- remembering the existing widget's focus policy is constified and
  moved ahead of the delete secion.
- assignment of d->popup to popup argument is moved after the delete
  section.
- after assignment, the argument variable is no longer used.

The refactoring eliminates two issues:
- potential risk of double-installing event filter due to missing
  early return.
- inifite loop if inherited class installs another event filter.

The patch adds a test function to tst_QCompleter, which implements an
inherited class, installs an event filter on a popup and checks if a
ChildAdded event hass been recorded.

Fixes: QTBUG-111869
Pick-to: 6.5 6.2
Change-Id: I3f7a2434a11476077a5260e7686a912da9f6c60d
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 38 insertions, 0 deletions

diff --git a/tests/auto/widgets/util/qcompleter/tst_qcompleter.cpp b/tests/auto/widgets/util/qcompleter/tst_qcompleter.cpp
index e8ebaf1491..030bb1cf5b 100644
--- a/tests/auto/widgets/util/qcompleter/tst_qcompleter.cpp
+++ b/tests/auto/widgets/util/qcompleter/tst_qcompleter.cpp
@@ -123,6 +123,7 @@ private slots:
     void QTBUG_52028_tabAutoCompletes();
     void QTBUG_51889_activatedSentTwice();
     void showPopupInGraphicsView();
+    void inheritedEventFilter();
 
 private:
     void filter(bool assync = false);
@@ -1863,5 +1864,42 @@ void tst_QCompleter::showPopupInGraphicsView()
     QVERIFY(lineEdit.completer()->popup()->geometry().bottom() < lineEdit.mapToGlobal(QPoint(0, 0)).y());
 }
 
+void tst_QCompleter::inheritedEventFilter()
+{
+    class Completer : public QCompleter
+    {
+    public:
+        explicit Completer(QWidget *parent) : QCompleter(parent)
+        {
+            Q_ASSERT(parent);
+            setPopup(new QListView());
+            popup()->installEventFilter(this);
+        }
+
+        bool m_popupChildAdded = false;
+
+    protected:
+        bool eventFilter(QObject *watched, QEvent *event) override
+        {
+            if (watched == popup() && event->type() == QEvent::ChildAdded)
+                m_popupChildAdded = true;
+
+            return QCompleter::eventFilter(watched, event);
+        }
+    };
+
+    QComboBox comboBox;
+    comboBox.setEditable(true);
+    Completer *completer = new Completer(&comboBox);
+    comboBox.setCompleter(completer);
+
+    // comboBox.show() must not crash with an infinite loop in the event filter
+    comboBox.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&comboBox));
+
+    // Since event orders are platform dependent, only the the ChildAdded event is checked.
+    QVERIFY(QTest::qWaitFor([completer](){return completer->m_popupChildAdded; }));
+}
+
 QTEST_MAIN(tst_QCompleter)
 #include "tst_qcompleter.moc"