Prevent static functions of Q[Gui]Application from crashing if there is no instance.

Add tests.

Task-number: QTBUG-44499
Change-Id: I160b089ad3f23ab71a87519e50f8a2ef5d2a4a6f
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/gui/kernel/qguiapplication.cpp

@@ -105,6 +105,14 @@
 
 QT_BEGIN_NAMESPACE
 
+// Helper macro for static functions to check on the existence of the application class.
+#define CHECK_QAPP_INSTANCE(...) \
+    if (Q_LIKELY(QCoreApplication::instance())) { \
+    } else { \
+        qWarning("Must construct a QGuiApplication first."); \
+        return __VA_ARGS__; \
+    }
+
 Q_GUI_EXPORT bool qt_is_gui_used = true;
 
 Qt::MouseButtons QGuiApplicationPrivate::mouse_buttons = Qt::NoButton;
@@ -648,6 +656,7 @@ QString QGuiApplication::applicationDisplayName()
 */
 QWindow *QGuiApplication::modalWindow()
 {
+    CHECK_QAPP_INSTANCE(Q_NULLPTR)
     if (QGuiApplicationPrivate::self->modalWindowList.isEmpty())
         return 0;
     return QGuiApplicationPrivate::self->modalWindowList.first();
@@ -1430,6 +1439,7 @@ Qt::KeyboardModifiers QGuiApplication::keyboardModifiers()
 */
 Qt::KeyboardModifiers QGuiApplication::queryKeyboardModifiers()
 {
+    CHECK_QAPP_INSTANCE(Qt::KeyboardModifiers(0))
     QPlatformIntegration *pi = QGuiApplicationPrivate::platformIntegration();
     return pi->queryKeyboardModifiers();
 }
@@ -3167,6 +3177,7 @@ Qt::LayoutDirection QGuiApplication::layoutDirection()
 #ifndef QT_NO_CURSOR
 QCursor *QGuiApplication::overrideCursor()
 {
+    CHECK_QAPP_INSTANCE(Q_NULLPTR)
     return qGuiApp->d_func()->cursor_list.isEmpty() ? 0 : &qGuiApp->d_func()->cursor_list.first();
 }
 
@@ -3180,6 +3191,7 @@ QCursor *QGuiApplication::overrideCursor()
  */
 void QGuiApplication::changeOverrideCursor(const QCursor &cursor)
 {
+    CHECK_QAPP_INSTANCE()
     if (qGuiApp->d_func()->cursor_list.isEmpty())
         return;
     qGuiApp->d_func()->cursor_list.removeFirst();
@@ -3254,6 +3266,7 @@ static inline void applyWindowCursor(const QList<QWindow *> &l)
 */
 void QGuiApplication::setOverrideCursor(const QCursor &cursor)
 {
+    CHECK_QAPP_INSTANCE()
     qGuiApp->d_func()->cursor_list.prepend(cursor);
     applyCursor(QGuiApplicationPrivate::window_list, cursor);
 }
@@ -3271,6 +3284,7 @@ void QGuiApplication::setOverrideCursor(const QCursor &cursor)
 */
 void QGuiApplication::restoreOverrideCursor()
 {
+    CHECK_QAPP_INSTANCE()
     if (qGuiApp->d_func()->cursor_list.isEmpty())
         return;
     qGuiApp->d_func()->cursor_list.removeFirst();
@@ -3338,6 +3352,7 @@ bool QGuiApplication::desktopSettingsAware()
   */
 QInputMethod *QGuiApplication::inputMethod()
 {
+    CHECK_QAPP_INSTANCE(Q_NULLPTR)
     if (!qGuiApp->d_func()->inputMethod)
         qGuiApp->d_func()->inputMethod = new QInputMethod();
     return qGuiApp->d_func()->inputMethod;

src/widgets/kernel/qapplication.cpp

@@ -117,6 +117,14 @@ static void initResources()
 
 QT_BEGIN_NAMESPACE
 
+// Helper macro for static functions to check on the existence of the application class.
+#define CHECK_QAPP_INSTANCE(...) \
+    if (Q_LIKELY(QCoreApplication::instance())) { \
+    } else { \
+        qWarning("Must construct a QApplication first."); \
+        return __VA_ARGS__; \
+    }
+
 Q_CORE_EXPORT void qt_call_post_routines();
 
 QApplicationPrivate *QApplicationPrivate::self = 0;
@@ -2855,6 +2863,7 @@ void QApplicationPrivate::sendSyntheticEnterLeave(QWidget *widget)
 */
 QDesktopWidget *QApplication::desktop()
 {
+    CHECK_QAPP_INSTANCE(Q_NULLPTR)
     if (!qt_desktopWidget || // not created yet
          !(qt_desktopWidget->windowType() == Qt::Desktop)) { // reparented away
         qt_desktopWidget = new QDesktopWidget();
@@ -4110,6 +4119,7 @@ void QApplication::setEffectEnabled(Qt::UIEffect effect, bool enable)
 */
 bool QApplication::isEffectEnabled(Qt::UIEffect effect)
 {
+    CHECK_QAPP_INSTANCE(false)
     return QColormap::instance().depth() >= 16
            && (QApplicationPrivate::enabledAnimations & QPlatformTheme::GeneralUiEffect)
            && (QApplicationPrivate::enabledAnimations & uiEffectToFlag(effect));

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

@@ -77,6 +77,8 @@ private slots:
     void layoutDirection();
     void globalShareContext();
 
+    void staticFunctions();
+
     void settableStyleHints_data();
     void settableStyleHints(); // Needs to run last as it changes style hints.
 };
@@ -966,6 +968,42 @@ void tst_QGuiApplication::globalShareContext()
 #endif
 }
 
+// Test that static functions do not crash if there is no application instance.
+void tst_QGuiApplication::staticFunctions()
+{
+    QGuiApplication::setApplicationDisplayName(QString());
+    QGuiApplication::applicationDisplayName();
+    QGuiApplication::allWindows();
+    QGuiApplication::topLevelWindows();
+    QGuiApplication::topLevelAt(QPoint(0, 0));
+    QGuiApplication::setWindowIcon(QIcon());
+    QGuiApplication::windowIcon();
+    QGuiApplication::platformName();
+    QGuiApplication::modalWindow();
+    QGuiApplication::focusWindow();
+    QGuiApplication::focusObject();
+    QGuiApplication::primaryScreen();
+    QGuiApplication::screens();
+    QGuiApplication::overrideCursor();
+    QGuiApplication::setOverrideCursor(QCursor());
+    QGuiApplication::changeOverrideCursor(QCursor());
+    QGuiApplication::restoreOverrideCursor();
+    QGuiApplication::keyboardModifiers();
+    QGuiApplication::queryKeyboardModifiers();
+    QGuiApplication::mouseButtons();
+    QGuiApplication::setLayoutDirection(Qt::LeftToRight);
+    QGuiApplication::layoutDirection();
+    QGuiApplication::styleHints();
+    QGuiApplication::setDesktopSettingsAware(true);
+    QGuiApplication::desktopSettingsAware();
+    QGuiApplication::inputMethod();
+    QGuiApplication::platformNativeInterface();
+    QGuiApplication::platformFunction(QByteArrayLiteral("bla"));
+    QGuiApplication::setQuitOnLastWindowClosed(true);
+    QGuiApplication::quitOnLastWindowClosed();
+    QGuiApplication::applicationState();
+}
+
 void tst_QGuiApplication::settableStyleHints_data()
 {
     QTest::addColumn<bool>("appInstance");

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

@@ -172,6 +172,8 @@ private slots:
 
     void abortQuitOnShow();
 
+    void staticFunctions();
+
     void settableStyleHints_data();
     void settableStyleHints();  // Needs to run last as it changes style hints.
 };
@@ -2299,6 +2301,28 @@ void tst_QApplication::abortQuitOnShow()
     QCOMPARE(app.exec(), 1);
 }
 
+// Test that static functions do not crash if there is no application instance.
+void tst_QApplication::staticFunctions()
+{
+    QApplication::setStyle(QStringLiteral("blub"));
+    QApplication::colorSpec();
+    QApplication::setColorSpec(42);
+    QApplication::allWidgets();
+    QApplication::topLevelWidgets();
+    QApplication::desktop();
+    QApplication::activePopupWidget();
+    QApplication::activeModalWidget();
+    QApplication::focusWidget();
+    QApplication::activeWindow();
+    QApplication::setActiveWindow(Q_NULLPTR);
+    QApplication::widgetAt(QPoint(0, 0));
+    QApplication::topLevelAt(QPoint(0, 0));
+    QApplication::setGlobalStrut(QSize(0, 0));
+    QApplication::globalStrut();
+    QApplication::isEffectEnabled(Qt::UI_General);
+    QApplication::setEffectEnabled(Qt::UI_General, false);
+}
+
 void tst_QApplication::settableStyleHints_data()
 {
     QTest::addColumn<bool>("appInstance");