Fix crash when accessing QStyleHints before QGuiApplication is constructed.

Make styleHints a static member variable of QGuiApplicationPrivate and
fix accessor accordingly. Extend tst_QApplication::settableStyleHints()
to run without QApplication instance as well and add a similar test
to  QGuiApplication.

Task-number: QTBUG-44499
Change-Id: I42b92ef38f7dd512d08d70accfa7dd4f09a22f01
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/gui/kernel/qguiapplication.cpp

@@ -163,6 +163,7 @@ QWindow *QGuiApplicationPrivate::focus_window = 0;
 
 static QBasicMutex applicationFontMutex;
 QFont *QGuiApplicationPrivate::app_font = 0;
+QStyleHints *QGuiApplicationPrivate::styleHints = Q_NULLPTR;
 bool QGuiApplicationPrivate::obey_desktop_settings = true;
 
 QInputDeviceManager *QGuiApplicationPrivate::m_inputDeviceManager = 0;
@@ -595,7 +596,6 @@ QGuiApplication::~QGuiApplication()
 
 QGuiApplicationPrivate::QGuiApplicationPrivate(int &argc, char **argv, int flags)
     : QCoreApplicationPrivate(argc, argv, flags),
-      styleHints(0),
       inputMethod(0),
       lastTouchType(QEvent::TouchEnd),
       ownGlobalShareContext(false)
@@ -1349,7 +1349,8 @@ QGuiApplicationPrivate::~QGuiApplicationPrivate()
 
     cleanupThreadData();
 
-    delete styleHints;
+    delete QGuiApplicationPrivate::styleHints;
+    QGuiApplicationPrivate::styleHints = Q_NULLPTR;
     delete inputMethod;
 
     qt_cleanupFontDatabase();
@@ -1717,7 +1718,7 @@ void QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::Mo
         }
         mouse_buttons = buttons = e->buttons;
         if (button & e->buttons) {
-            ulong doubleClickInterval = static_cast<ulong>(qApp->styleHints()->mouseDoubleClickInterval());
+            ulong doubleClickInterval = static_cast<ulong>(QGuiApplication::styleHints()->mouseDoubleClickInterval());
             doubleClick = e->timestamp - mousePressTime < doubleClickInterval && button == mousePressButton;
             type = frameStrut ? QEvent::NonClientAreaMouseButtonPress : QEvent::MouseButtonPress;
             mousePressTime = e->timestamp;
@@ -3294,9 +3295,9 @@ void QGuiApplication::restoreOverrideCursor()
   */
 QStyleHints *QGuiApplication::styleHints()
 {
-    if (!qGuiApp->d_func()->styleHints)
-        qGuiApp->d_func()->styleHints = new QStyleHints();
-    return qGuiApp->d_func()->styleHints;
+    if (!QGuiApplicationPrivate::styleHints)
+        QGuiApplicationPrivate::styleHints = new QStyleHints();
+    return QGuiApplicationPrivate::styleHints;
 }
 
 /*!

src/gui/kernel/qguiapplication_p.h

@@ -218,7 +218,7 @@ public:
 
     static QFont *app_font;
 
-    QStyleHints *styleHints;
+    static QStyleHints *styleHints;
     static bool obey_desktop_settings;
     QInputMethod *inputMethod;
 

src/gui/kernel/qstylehints.cpp

@@ -35,6 +35,7 @@
 #include <qpa/qplatformintegration.h>
 #include <qpa/qplatformtheme.h>
 #include <private/qguiapplication_p.h>
+#include <qdebug.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -46,6 +47,10 @@ static inline QVariant hint(QPlatformIntegration::StyleHint h)
 static inline QVariant themeableHint(QPlatformTheme::ThemeHint th,
                                      QPlatformIntegration::StyleHint ih)
 {
+    if (!QCoreApplication::instance()) {
+        qWarning() << "Must construct a QGuiApplication before accessing a platform theme hint.";
+        return QVariant();
+    }
     if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme()) {
         const QVariant themeHint = theme->themeHint(th);
         if (themeHint.isValid())

src/widgets/kernel/qapplication.cpp

@@ -2892,7 +2892,7 @@ void QApplication::setStartDragTime(int ms)
 
 int QApplication::startDragTime()
 {
-    return qApp->styleHints()->startDragTime();
+    return QGuiApplication::styleHints()->startDragTime();
 }
 
 /*
@@ -2930,7 +2930,7 @@ void QApplication::setStartDragDistance(int l)
 
 int QApplication::startDragDistance()
 {
-    return qApp->styleHints()->startDragDistance();
+    return QGuiApplication::styleHints()->startDragDistance();
 }
 
 /*!
@@ -3973,7 +3973,7 @@ void QApplication::setCursorFlashTime(int msecs)
 
 int QApplication::cursorFlashTime()
 {
-    return qApp->styleHints()->cursorFlashTime();
+    return QGuiApplication::styleHints()->cursorFlashTime();
 }
 
 /*!
@@ -3991,7 +3991,7 @@ void QApplication::setDoubleClickInterval(int ms)
 
 int QApplication::doubleClickInterval()
 {
-    return qApp->styleHints()->mouseDoubleClickInterval();
+    return QGuiApplication::styleHints()->mouseDoubleClickInterval();
 }
 
 /*!
@@ -4019,7 +4019,7 @@ void QApplication::setKeyboardInputInterval(int ms)
 
 int QApplication::keyboardInputInterval()
 {
-    return qApp->styleHints()->keyboardInputInterval();
+    return QGuiApplication::styleHints()->keyboardInputInterval();
 }
 
 /*!

src/widgets/widgets/qabstractspinbox.cpp

@@ -1181,7 +1181,7 @@ void QAbstractSpinBox::timerEvent(QTimerEvent *event)
         killTimer(d->spinClickThresholdTimerId);
         d->spinClickThresholdTimerId = -1;
         d->effectiveSpinRepeatRate = d->buttonState & Keyboard
-                                     ? qApp->styleHints()->keyboardAutoRepeatRate()
+                                     ? QGuiApplication::styleHints()->keyboardAutoRepeatRate()
                                      : d->spinClickTimerInterval;
         d->spinClickTimerId = startTimer(d->effectiveSpinRepeatRate);
         doStep = true;

src/widgets/widgets/qlineedit.cpp

@@ -2153,7 +2153,7 @@ QMenu *QLineEdit::createStandardContextMenu()
     d->selectAllAction = action;
     connect(action, SIGNAL(triggered()), SLOT(selectAll()));
 
-    if (!d->control->isReadOnly() && qApp->styleHints()->useRtlExtensions()) {
+    if (!d->control->isReadOnly() && QGuiApplication::styleHints()->useRtlExtensions()) {
         popup->addSeparator();
         QUnicodeControlCharacterMenu *ctrlCharacterMenu = new QUnicodeControlCharacterMenu(this, popup);
         popup->addMenu(ctrlCharacterMenu);

src/widgets/widgets/qwidgettextcontrol.cpp

@@ -2281,7 +2281,7 @@ QMenu *QWidgetTextControl::createStandardContextMenu(const QPointF &pos, QWidget
         a->setObjectName(QStringLiteral("select-all"));
     }
 
-    if ((d->interactionFlags & Qt::TextEditable) && qApp->styleHints()->useRtlExtensions()) {
+    if ((d->interactionFlags & Qt::TextEditable) && QGuiApplication::styleHints()->useRtlExtensions()) {
         menu->addSeparator();
         QUnicodeControlCharacterMenu *ctrlCharacterMenu = new QUnicodeControlCharacterMenu(this, menu);
         menu->addMenu(ctrlCharacterMenu);

tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp

@@ -37,7 +37,9 @@
 #include <QtGui/QWindow>
 #include <QtGui/QScreen>
 #include <QtGui/QCursor>
+#include <QtGui/QFont>
 #include <QtGui/QPalette>
+#include <QtGui/QStyleHints>
 #include <qpa/qwindowsysteminterface.h>
 #include <qgenericplugin.h>
 
@@ -74,6 +76,9 @@ private slots:
     void genericPluginsAndWindowSystemEvents();
     void layoutDirection();
     void globalShareContext();
+
+    void settableStyleHints_data();
+    void settableStyleHints(); // Needs to run last as it changes style hints.
 };
 
 void tst_QGuiApplication::cleanup()
@@ -961,4 +966,24 @@ void tst_QGuiApplication::globalShareContext()
 #endif
 }
 
+void tst_QGuiApplication::settableStyleHints_data()
+{
+    QTest::addColumn<bool>("appInstance");
+    QTest::newRow("app") << true;
+    QTest::newRow("no-app") << false;
+}
+
+void tst_QGuiApplication::settableStyleHints()
+{
+    QFETCH(bool, appInstance);
+    int argc = 0;
+    QScopedPointer<QGuiApplication> app;
+    if (appInstance)
+        app.reset(new QGuiApplication(argc, 0));
+
+    const int keyboardInputInterval = 555;
+    QGuiApplication::styleHints()->setKeyboardInputInterval(keyboardInputInterval);
+    QCOMPARE(QGuiApplication::styleHints()->keyboardInputInterval(), keyboardInputInterval);
+}
+
 QTEST_APPLESS_MAIN(tst_QGuiApplication)

tests/auto/widgets/kernel/qapplication/tst_qapplication.cpp

@@ -172,6 +172,7 @@ private slots:
 
     void abortQuitOnShow();
 
+    void settableStyleHints_data();
     void settableStyleHints();  // Needs to run last as it changes style hints.
 };
 
@@ -2298,10 +2299,21 @@ void tst_QApplication::abortQuitOnShow()
     QCOMPARE(app.exec(), 1);
 }
 
+void tst_QApplication::settableStyleHints_data()
+{
+    QTest::addColumn<bool>("appInstance");
+    QTest::newRow("app") << true;
+    QTest::newRow("no-app") << false;
+}
+
 void tst_QApplication::settableStyleHints()
 {
+    QFETCH(bool, appInstance);
     int argc = 0;
-    QApplication app(argc, 0);
+    QScopedPointer<QApplication> app;
+    if (appInstance)
+        app.reset(new QApplication(argc, 0));
+
     QApplication::setCursorFlashTime(437);
     QCOMPARE(QApplication::cursorFlashTime(), 437);
     QApplication::setDoubleClickInterval(128);