Allow QObjects to opt in to receiving ParentAboutToChange/ParentChange

QWidget already handles this, but it might be useful for non-Widget
object hierarchies as well, such as in Qt Quick.

The flag is opt in, and as QWidget already handles these events by
itself (without checking any flags), we assert that we don't end up
in this code path, instead of enabling it for QWidget. The latter
would mean refactoring the QWidget code, with possible regressions.

Docs and header comments have been updated to reflect that this
event is not widget specific. (This is an issue with other events
as well, that are documented to say "widget", since they came
from a time when there was only QWidget, but nowadays apply to
e.g. QWindow as well. That's something for another fix though).

Change-Id: Ib71962131d6011c17dcce8c01bd8adcdaa58d798
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

1 files changed, 73 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index a4f761d6b9..5692615f29 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -80,6 +80,7 @@ private slots:
     void signalBlocking();
     void blockingQueuedConnection();
     void childEvents();
+    void parentEvents();
     void installEventFilter();
     void deleteSelfInSlot();
     void disconnectSelfInSlotAndDeleteAfterEmit();
@@ -3200,6 +3201,78 @@ void tst_QObject::childEvents()
     }
 }
 
+void tst_QObject::parentEvents()
+{
+#ifdef QT_BUILD_INTERNAL
+    EventSpy::EventList expected;
+
+    {
+        // Parent events not enabled
+        QObject parent;
+        QObject child;
+
+        EventSpy spy;
+        child.installEventFilter(&spy);
+
+        QCoreApplication::postEvent(&child, new QEvent(QEvent::Type(QEvent::User + 1)));
+
+        child.setParent(&parent);
+
+        QCoreApplication::postEvent(&child, new QEvent(QEvent::Type(QEvent::User + 2)));
+
+        expected =
+            EventSpy::EventList();
+        QCOMPARE(spy.eventList(), expected);
+        spy.clear();
+
+        QCoreApplication::processEvents();
+
+        expected =
+            EventSpy::EventList()
+            << qMakePair(&child, QEvent::Type(QEvent::User + 1))
+            << qMakePair(&child, QEvent::Type(QEvent::User + 2));
+        QCOMPARE(spy.eventList(), expected);
+    }
+
+    {
+        // Parent events enabled
+        QObject parent;
+        QObject child;
+        auto *childPrivate = QObjectPrivate::get(&child);
+        childPrivate->receiveParentEvents = true;
+
+        EventSpy spy;
+        child.installEventFilter(&spy);
+
+        QCoreApplication::postEvent(&child, new QEvent(QEvent::Type(QEvent::User + 1)));
+
+        child.setParent(&parent);
+        child.setParent(nullptr);
+
+        QCoreApplication::postEvent(&child, new QEvent(QEvent::Type(QEvent::User + 2)));
+
+        expected =
+            EventSpy::EventList()
+            << qMakePair(&child, QEvent::ParentAboutToChange)
+            << qMakePair(&child, QEvent::ParentChange)
+            << qMakePair(&child, QEvent::ParentAboutToChange)
+            << qMakePair(&child, QEvent::ParentChange);
+        QCOMPARE(spy.eventList(), expected);
+        spy.clear();
+
+        QCoreApplication::processEvents();
+
+        expected =
+            EventSpy::EventList()
+            << qMakePair(&child, QEvent::Type(QEvent::User + 1))
+            << qMakePair(&child, QEvent::Type(QEvent::User + 2));
+        QCOMPARE(spy.eventList(), expected);
+    }
+#else
+    QSKIP("Needs QT_BUILD_INTERNAL");
+#endif
+}
+
 void tst_QObject::installEventFilter()
 {
     QEvent event(QEvent::User);