Qt6: fix possible build failure

* add CMake definitions 'QT_NO_KEYWORDS' to avoid the Qt definition of the 'slots' macro that causes a conflict when including Python headers
* drop QT3_SUPPORT define

cMake/FreeCAD_Helpers/SetupQt.cmake

@@ -38,6 +38,8 @@ set(CMAKE_AUTOMOC TRUE)
 set(CMAKE_AUTOUIC TRUE)
 set(QtCore_MOC_EXECUTABLE ${Qt${FREECAD_QT_MAJOR_VERSION}Core_MOC_EXECUTABLE})
 
+add_definitions(-DQT_NO_KEYWORDS)
+
 message(STATUS "Set up to compile with Qt ${Qt${FREECAD_QT_MAJOR_VERSION}Core_VERSION}")
 
 # In Qt 5.15 they added more generic names for these functions: "backport" those new names

src/FCConfig.h

@@ -230,9 +230,13 @@ typedef unsigned __int64    uint64_t;
 // Qt
 
 // Make sure to explicitly use the correct conversion
-#define QT_NO_CAST_FROM_ASCII
-#undef  QT3_SUPPORT
-#define QT_NO_KEYWORDS
+#ifndef QT_NO_CAST_FROM_ASCII
+# define QT_NO_CAST_FROM_ASCII
+#endif
+
+#ifndef QT_NO_KEYWORDS
+# define QT_NO_KEYWORDS
+#endif
 
 #if defined (FC_OS_WIN32) || defined(FC_OS_CYGWIN)
 # ifndef QT_DLL

src/Gui/QSint/actionpanel/actionbox.cpp

@@ -148,7 +148,7 @@ QList<ActionLabel*> ActionBox::createItems(QList<QAction*> actions)
 
     QLayout *l = createHBoxLayout();
 
-    foreach (QAction *action, actions) {
+    Q_FOREACH (QAction *action, actions) {
         ActionLabel *act = createItem(action, l);
         if (act)
             list.append(act);

src/Gui/QSint/actionpanel/actionpanel.cpp

@@ -39,7 +39,7 @@ void ActionPanel::setScheme(ActionPanelScheme *scheme)
 
     // set scheme for children
     QObjectList list(children());
-    foreach(QObject *obj, list) {
+    Q_FOREACH(QObject *obj, list) {
       if (dynamic_cast<ActionGroup*>(obj)) {
         ((ActionGroup*)obj)->setScheme(scheme);
         continue;

src/Gui/Quarter/ContextMenu.cpp

@@ -60,7 +60,7 @@ ContextMenu::ContextMenu(QuarterWidget * quarterwidget)
   QActionGroup * stereomodegroup = nullptr;
   QActionGroup * transparencytypegroup = nullptr;
 
-  foreach (QAction * action, quarterwidget->renderModeActions()) {
+  Q_FOREACH (QAction * action, quarterwidget->renderModeActions()) {
     if (!rendermodegroup) {
       rendermodegroup = action->actionGroup();
     } else {
@@ -73,7 +73,7 @@ ContextMenu::ContextMenu(QuarterWidget * quarterwidget)
     rendermenu->addAction(action);
   }
 
-  foreach (QAction * action, quarterwidget->stereoModeActions()) {
+  Q_FOREACH (QAction * action, quarterwidget->stereoModeActions()) {
     if (!stereomodegroup) {
       stereomodegroup = action->actionGroup();
     } else {
@@ -86,7 +86,7 @@ ContextMenu::ContextMenu(QuarterWidget * quarterwidget)
     stereomenu->addAction(action);
   }
 
-  foreach (QAction * action, quarterwidget->transparencyTypeActions()) {
+  Q_FOREACH (QAction * action, quarterwidget->transparencyTypeActions()) {
     if (!transparencytypegroup) {
       transparencytypegroup = action->actionGroup();
     } else {

src/Gui/Quarter/EventFilter.cpp

@@ -58,7 +58,7 @@ public:
     this->windowsize = SbVec2s(event->size().width(),
                                event->size().height());
 
-    foreach(InputDevice * device, this->devices) {
+    Q_FOREACH(InputDevice * device, this->devices) {
       device->setWindowSize(this->windowsize);
     }
   }
@@ -75,7 +75,7 @@ public:
     SbVec2s mousepos(event->pos().x(), this->windowsize[1] - event->pos().y() - 1);
     // the following corrects for high-dpi displays (e.g. mac retina)
     mousepos *= quarterwidget->devicePixelRatio();
-    foreach(InputDevice * device, this->devices) {
+    Q_FOREACH(InputDevice * device, this->devices) {
       device->setMousePosition(mousepos);
     }
   }
@@ -162,7 +162,7 @@ EventFilter::eventFilter(QObject * obj, QEvent * qevent)
 
   // translate QEvent into SoEvent and see if it is handled by scene
   // graph
-  foreach(InputDevice * device, PRIVATE(this)->devices) {
+  Q_FOREACH(InputDevice * device, PRIVATE(this)->devices) {
     const SoEvent * soevent = device->translateEvent(qevent);
     if (soevent && PRIVATE(this)->quarterwidget->processSoEvent(soevent)) {
       return true;

src/Gui/Quarter/QuarterWidget.cpp

@@ -828,7 +828,7 @@ QuarterWidget::updateDevicePixelRatio() {
     }
     if(PRIVATE(this)->device_pixel_ratio != dev_pix_ratio) {
         PRIVATE(this)->device_pixel_ratio = dev_pix_ratio;
-        emit devicePixelRatioChanged(dev_pix_ratio);
+        Q_EMIT devicePixelRatioChanged(dev_pix_ratio);
         return true;
     }
     return false;