Introduce QWindow::setFlag and QWidget::setWindowFlag

Analogous to QWidget::setAttribute(), introduce an API to easily
enable/disable a single window flag without having to resort to
w.setFlags(w.flags() | Qt::NewFlag).

Change-Id: Ib0f7254a34c8d884cdec181c41b99e5ef035d954
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>

src/gui/kernel/qwindow.cpp

@@ -821,6 +821,8 @@ QSurfaceFormat QWindow::format() const
 
     The actual window flags might differ from the flags set with setFlags()
     if the requested flags could not be fulfilled.
+
+    \sa setFlag()
 */
 void QWindow::setFlags(Qt::WindowFlags flags)
 {
@@ -839,6 +841,23 @@ Qt::WindowFlags QWindow::flags() const
     return d->windowFlags;
 }
 
+/*!
+    \since 5.9
+
+    Sets the window flag \a flag on this window if \a on is true;
+    otherwise clears the flag.
+
+    \sa setFlags(), flags(), type()
+*/
+void QWindow::setFlag(Qt::WindowType flag, bool on)
+{
+    Q_D(QWindow);
+    if (on)
+        setFlags(d->windowFlags | flag);
+    else
+        setFlags(d->windowFlags & ~flag);
+}
+
 /*!
     Returns the type of the window.
 

src/gui/kernel/qwindow.h

@@ -163,6 +163,7 @@ public:
 
     void setFlags(Qt::WindowFlags flags);
     Qt::WindowFlags flags() const;
+    void setFlag(Qt::WindowType, bool on = true);
     Qt::WindowType type() const;
 
     QString title() const;

src/widgets/kernel/qwidget.cpp

@@ -10357,7 +10357,7 @@ void QWidget::updateGeometry()
     a window, causing the widget to be hidden. You must call show() to make
     the widget visible again..
 
-    \sa windowType(), {Window Flags Example}
+    \sa windowType(), setWindowFlag(), {Window Flags Example}
 */
 void QWidget::setWindowFlags(Qt::WindowFlags flags)
 {
@@ -10365,6 +10365,23 @@ void QWidget::setWindowFlags(Qt::WindowFlags flags)
     d->setWindowFlags(flags);
 }
 
+/*!
+    \since 5.9
+
+    Sets the window flag \a flag on this widget if \a on is true;
+    otherwise clears the flag.
+
+    \sa setWindowFlags(), windowFlags(), windowType()
+*/
+void QWidget::setWindowFlag(Qt::WindowType flag, bool on)
+{
+    Q_D(QWidget);
+    if (on)
+        d->setWindowFlags(data->window_flags | flag);
+    else
+        d->setWindowFlags(data->window_flags & ~flag);
+}
+
 /*! \internal
 
     Implemented in QWidgetPrivate so that QMdiSubWindowPrivate can reimplement it.

src/widgets/kernel/qwidget.h

@@ -562,6 +562,7 @@ public:
 
     void setWindowFlags(Qt::WindowFlags type);
     inline Qt::WindowFlags windowFlags() const;
+    void setWindowFlag(Qt::WindowType, bool on = true);
     void overrideWindowFlags(Qt::WindowFlags type);
 
     inline Qt::WindowType windowType() const;

tests/auto/gui/kernel/qwindow/tst_qwindow.cpp

@@ -102,6 +102,7 @@ private slots:
     void initTestCase();
     void stateChange_data();
     void stateChange();
+    void flags();
     void cleanup();
 
 private:
@@ -2194,6 +2195,18 @@ void tst_QWindow::requestUpdate()
     QTRY_COMPARE(window.received(QEvent::UpdateRequest), 2);
 }
 
+void tst_QWindow::flags()
+{
+    Window window;
+    const auto baseFlags = window.flags();
+    window.setFlags(window.flags() | Qt::FramelessWindowHint);
+    QCOMPARE(window.flags(), baseFlags | Qt::FramelessWindowHint);
+    window.setFlag(Qt::WindowStaysOnTopHint, true);
+    QCOMPARE(window.flags(), baseFlags | Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
+    window.setFlag(Qt::FramelessWindowHint, false);
+    QCOMPARE(window.flags(), baseFlags | Qt::WindowStaysOnTopHint);
+}
+
 #include <tst_qwindow.moc>
 QTEST_MAIN(tst_QWindow)
 

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -8957,8 +8957,13 @@ void tst_QWidget::taskQTBUG_4055_sendSyntheticEnterLeave()
 void tst_QWidget::windowFlags()
 {
     QWidget w;
+    const auto baseFlags = w.windowFlags();
     w.setWindowFlags(w.windowFlags() | Qt::FramelessWindowHint);
     QVERIFY(w.windowFlags() & Qt::FramelessWindowHint);
+    w.setWindowFlag(Qt::WindowStaysOnTopHint, true);
+    QCOMPARE(w.windowFlags(), baseFlags | Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
+    w.setWindowFlag(Qt::FramelessWindowHint, false);
+    QCOMPARE(w.windowFlags(), baseFlags | Qt::WindowStaysOnTopHint);
 }
 
 void tst_QWidget::initialPosForDontShowOnScreenWidgets()