Emit destroyed() signal before children get deleted

Make sure we always emit the destroyed() signal before
we delete our children. This wasn't working correctly
for QWidget based classes, as the QWidget destructor
deletes all children itself.

Task-number: QTBUG-24672
Change-Id: Iecdff3489196271177edfeba1c4a2c5800e255af
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

3 files changed, 119 insertions, 1 deletions

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 0d97266f4f..9d0854f3a9 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -766,7 +766,7 @@ QObject::~QObject()
             delete sharedRefcount;
     }
 
-    if (d->isSignalConnected(0)) {
+    if (!d->isWidget && d->isSignalConnected(0)) {
         QT_TRY {
             emit destroyed(this);
         } QT_CATCH(...) {
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 83dc406e17..d05f53697a 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -1429,11 +1429,29 @@ QWidget::~QWidget()
     delete d->needsFlush;
     d->needsFlush = 0;
 
+    // The next 20 lines are duplicated from QObject, but required here
+    // since QWidget deletes is children itself
+    bool blocked = d->blockSig;
+    d->blockSig = 0; // unblock signals so we always emit destroyed()
+
+    if (d->isSignalConnected(0)) {
+        QT_TRY {
+            emit destroyed(this);
+        } QT_CATCH(...) {
+            // all the signal/slots connections are still in place - if we don't
+            // quit now, we will crash pretty soon.
+            qWarning("Detected an unexpected exception in ~QWidget while emitting destroyed().");
+            QT_RETHROW;
+        }
+    }
+
     if (d->declarativeData) {
         QAbstractDeclarativeData::destroyed(d->declarativeData, this);
         d->declarativeData = 0;                 // don't activate again in ~QObject
     }
 
+    d->blockSig = blocked;
+
 #ifdef Q_WS_MAC
     // QCocoaView holds a pointer back to this widget. Clear it now
     // to make sure it's not followed later on. The lifetime of the
diff --git a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
index f3f63b2067..2a5e59f825 100644
--- a/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
+++ b/tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp
@@ -396,6 +396,8 @@ private slots:
     void touchEventSynthesizedMouseEvent();
 
     void styleSheetPropagation();
+
+    void destroyedSignal();
 private:
     bool ensureScreenSize(int width, int height);
     QWidget *testWidget;
@@ -9592,6 +9594,104 @@ void tst_QWidget::styleSheetPropagation()
     }
 }
 
+class DestroyTester : public QObject
+{
+    Q_OBJECT
+public:
+    DestroyTester(QObject *parent) : QObject(parent) { parentDestroyed = 0; }
+    static int parentDestroyed;
+public slots:
+    void parentDestroyedSlot() {
+        ++parentDestroyed;
+    }
+};
+
+int DestroyTester::parentDestroyed = 0;
+
+void tst_QWidget::destroyedSignal()
+{
+    {
+        QWidget *w = new QWidget;
+        DestroyTester *t = new DestroyTester(w);
+        connect(w, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete w;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+    }
+
+    {
+        QWidget *w = new QWidget;
+        DestroyTester *t = new DestroyTester(w);
+        connect(w, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        w->blockSignals(true);
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete w;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+    }
+
+    {
+        QObject *o = new QWidget;
+        DestroyTester *t = new DestroyTester(o);
+        connect(o, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete o;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+    }
+
+    {
+        QObject *o = new QWidget;
+        DestroyTester *t = new DestroyTester(o);
+        connect(o, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        o->blockSignals(true);
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete o;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+    }
+
+    {
+        QWidget *w = new QWidget;
+        DestroyTester *t = new DestroyTester(0);
+        connect(w, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete w;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+        delete t;
+    }
+
+    {
+        QWidget *w = new QWidget;
+        DestroyTester *t = new DestroyTester(0);
+        connect(w, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        w->blockSignals(true);
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete w;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+        delete t;
+    }
+
+    {
+        QObject *o = new QWidget;
+        DestroyTester *t = new DestroyTester(0);
+        connect(o, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete o;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+        delete t;
+    }
+
+    {
+        QObject *o = new QWidget;
+        DestroyTester *t = new DestroyTester(0);
+        connect(o, SIGNAL(destroyed()), t, SLOT(parentDestroyedSlot()));
+        o->blockSignals(true);
+        QCOMPARE(DestroyTester::parentDestroyed, 0);
+        delete o;
+        QCOMPARE(DestroyTester::parentDestroyed, 1);
+        delete t;
+    }
+
+}
+
 #ifndef QTEST_NO_CURSOR
 void tst_QWidget::underMouse()
 {