Fix crash with stylesheet if widget change style in the changeEvent

The problem appeared with KLineEdit and its proxy style.

When setting a stylesheet, we create a QStyleSheetStyle in 9# and set it
to the widget, which receive a changeEvent, that will set again the style
so 3# will create a new QStyleSheetStyle with the new proxy. and set it.
in 2# we will dereference the 'old' QStyleSheetStyle (the one created in #9)
that will destroy it.
Then, later in #7, we will still access that style ('newStyle') and we crash

0# QStyleSheetStyle::~QStyleSheetStyle()
1# QStyleSheetStyle::deref()
2# QWidgetPrivate::setStyle_helper(QStyle*, bool, bool)
3# QWidget::setStyle(QStyle*) (qwidget.cpp:2523)
4# ChangeEventWidget::changeEvent(QEvent*)
[...]
6# QCoreApplication::sendEvent(QObject*, QEvent*)
7# QWidgetPrivate::setStyle_helper(QStyle*, bool, bool)
9# QWidget::setStyleSheet(QString const&) (qwidget.cpp:2470)

The solution is to change the order, and do not use 'newstyle' after
we sent the event.

The origStyle is now protected wy a QWeakPointer, but this is
just for safety reason and not related to the crash.

Reviewed-by: JBache

2 files changed, 40 insertions, 11 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 20d1d30..be0a8a0 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -2535,7 +2535,7 @@ void QWidgetPrivate::setStyle_helper(QStyle *newStyle, bool propagate, bool
     Q_Q(QWidget);
     QStyle *oldStyle  = q->style();
 #ifndef QT_NO_STYLE_STYLESHEET
-    QStyle *origStyle = 0;
+    QWeakPointer<QStyle> origStyle;
 #endif
 
 #ifdef Q_WS_MAC
@@ -2549,7 +2549,7 @@ void QWidgetPrivate::setStyle_helper(QStyle *newStyle, bool propagate, bool
         createExtra();
 
 #ifndef QT_NO_STYLE_STYLESHEET
-        origStyle = extra->style;
+        origStyle = extra->style.data();
 #endif
         extra->style = newStyle;
     }
@@ -2578,23 +2578,23 @@ void QWidgetPrivate::setStyle_helper(QStyle *newStyle, bool propagate, bool
         }
     }
 
-    QEvent e(QEvent::StyleChange);
-    QApplication::sendEvent(q, &e);
-#ifdef QT3_SUPPORT
-    q->styleChange(*oldStyle);
-#endif
-
 #ifndef QT_NO_STYLE_STYLESHEET
     if (!qobject_cast<QStyleSheetStyle*>(newStyle)) {
-        if (const QStyleSheetStyle* cssStyle = qobject_cast<QStyleSheetStyle*>(origStyle)) {
+        if (const QStyleSheetStyle* cssStyle = qobject_cast<QStyleSheetStyle*>(origStyle.data())) {
             cssStyle->clearWidgetFont(q);
         }
     }
 #endif
 
+    QEvent e(QEvent::StyleChange);
+    QApplication::sendEvent(q, &e);
+#ifdef QT3_SUPPORT
+    q->styleChange(*oldStyle);
+#endif
+
 #ifndef QT_NO_STYLE_STYLESHEET
     // dereference the old stylesheet style
-    if (QStyleSheetStyle *proxy = qobject_cast<QStyleSheetStyle *>(origStyle))
+    if (QStyleSheetStyle *proxy = qobject_cast<QStyleSheetStyle *>(origStyle.data()))
         proxy->deref();
 #endif
 }
diff --git a/tests/auto/qstylesheetstyle/tst_qstylesheetstyle.cpp b/tests/auto/qstylesheetstyle/tst_qstylesheetstyle.cpp
index e0512a9..e370309 100644
--- a/tests/auto/qstylesheetstyle/tst_qstylesheetstyle.cpp
+++ b/tests/auto/qstylesheetstyle/tst_qstylesheetstyle.cpp
@@ -98,6 +98,7 @@ private slots:
     void complexWidgetFocus();
     void task188195_baseBackground();
     void task232085_spinBoxLineEditBg();
+    void changeStyleInChangeEvent();
 
     //at the end because it mess with the style.
     void widgetStyle();
@@ -1256,7 +1257,7 @@ void tst_QStyleSheetStyle::proxyStyle()
     QStyleOptionViewItemV4 opt;
     opt.initFrom(w);
     opt.features |= QStyleOptionViewItemV2::HasCheckIndicator;
-    QVERIFY(pb5->style()->subElementRect(QStyle::SE_ItemViewItemCheckIndicator, 
+    QVERIFY(pb5->style()->subElementRect(QStyle::SE_ItemViewItemCheckIndicator,
             &opt, pb5).width() == 3);
     delete w;
     delete proxy;
@@ -1579,6 +1580,34 @@ void tst_QStyleSheetStyle::task232085_spinBoxLineEditBg()
             .toLocal8Bit().constData());
 }
 
+class ChangeEventWidget : public QWidget
+{ public:
+    void changeEvent(QEvent * event)
+    {
+        if(event->type() == QEvent::StyleChange) {
+            static bool recurse = false;
+            if (!recurse) {
+                recurse = true;
+                QStyle *style = new QMotifStyle;
+                style->setParent(this);
+                setStyle(style);
+                recurse = false;
+            }
+        }
+        QWidget::changeEvent(event);
+    }
+};
+
+void tst_QStyleSheetStyle::changeStyleInChangeEvent()
+{   //must not crash;
+    ChangeEventWidget wid;
+    wid.ensurePolished();
+    wid.setStyleSheet(" /* */ ");
+    wid.ensurePolished();
+    wid.setStyleSheet(" /* ** */ ");
+    wid.ensurePolished();
+}
+
 QTEST_MAIN(tst_QStyleSheetStyle)
 #include "tst_qstylesheetstyle.moc"