Stop using mixed enum arithmetic

It's deprecated. Port some unnamed enumerations (used only to
declare constants) to constexpr integers instead. Apply qToUnderlying
as needed.

Task-number: QTBUG-94059
Change-Id: Ifaa64ece966ce08df40dc71ffcfa7ac038110e0b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qvariant.cpp

@@ -1155,17 +1155,17 @@ static const ushort mapIdFromQt3ToCurrent[MapFromThreeCount] =
 #endif
 };
 
-// enum values needed to map Qt5 based type id's to Qt6 based ones
-enum Qt5Types {
-    Qt5UserType = 1024,
-    Qt5LastCoreType = QMetaType::QCborMap,
-    Qt5FirstGuiType = 64,
-    Qt5LastGuiType = 87,
-    Qt5SizePolicy = 121,
-    Qt5RegExp = 27,
-    Qt5KeySequence = 75,
-    Qt5QQuaternion = 85
-};
+// values needed to map Qt5 based type id's to Qt6 based ones
+constexpr int Qt5UserType = 1024;
+constexpr int Qt5LastCoreType = QMetaType::QCborMap;
+constexpr int Qt5FirstGuiType = 64;
+constexpr int Qt5LastGuiType = 87;
+constexpr int Qt5SizePolicy = 121;
+constexpr int Qt5RegExp = 27;
+constexpr int Qt5KeySequence = 75;
+constexpr int Qt5QQuaternion = 85;
+
+constexpr int Qt6ToQt5GuiTypeDelta = qToUnderlying(QMetaType::FirstGuiType) - Qt5FirstGuiType;
 
 /*!
     Internal function for loading a variant from stream \a s. Use the
@@ -1205,7 +1205,7 @@ void QVariant::load(QDataStream &s)
         if (typeId == Qt5UserType) {
             typeId = QMetaType::User;
         } else if (typeId >= Qt5FirstGuiType && typeId <= Qt5LastGuiType) {
-            typeId += QMetaType::FirstGuiType - Qt5FirstGuiType;
+            typeId += Qt6ToQt5GuiTypeDelta;
         } else if (typeId == Qt5SizePolicy) {
             typeId = QMetaType::QSizePolicy;
         } else if (typeId == Qt5RegExp) {
@@ -1273,7 +1273,7 @@ void QVariant::save(QDataStream &s) const
             typeId = Qt5UserType;
             saveAsUserType = true;
         } else if (typeId >= QMetaType::FirstGuiType && typeId <= QMetaType::LastGuiType) {
-            typeId -= QMetaType::FirstGuiType - Qt5FirstGuiType;
+            typeId -= Qt6ToQt5GuiTypeDelta;
             if (typeId > Qt5LastGuiType) {
                 typeId = Qt5UserType;
                 saveAsUserType = true;

src/corelib/time/qdatetime.cpp

@@ -76,17 +76,15 @@ QT_BEGIN_NAMESPACE
   Date/Time Constants
  *****************************************************************************/
 
-enum : qint64 {
-    SECS_PER_DAY = 86400,
-    MSECS_PER_DAY = 86400000,
-    SECS_PER_HOUR = 3600,
-    MSECS_PER_HOUR = 3600000,
-    SECS_PER_MIN = 60,
-    MSECS_PER_MIN = 60000,
-    MSECS_PER_SEC = 1000,
-    TIME_T_MAX = std::numeric_limits<time_t>::max(),
-    JULIAN_DAY_FOR_EPOCH = 2440588 // result of julianDayFromDate(1970, 1, 1)
-};
+constexpr qint64 SECS_PER_DAY = 86400;
+constexpr qint64 MSECS_PER_DAY = 86400000;
+constexpr qint64 SECS_PER_HOUR = 3600;
+constexpr qint64 MSECS_PER_HOUR = 3600000;
+constexpr qint64 SECS_PER_MIN = 60;
+constexpr qint64 MSECS_PER_MIN = 60000;
+constexpr qint64 MSECS_PER_SEC = 1000;
+constexpr qint64 TIME_T_MAX = std::numeric_limits<time_t>::max();
+constexpr qint64 JULIAN_DAY_FOR_EPOCH = 2440588; // result of julianDayFromDate(1970, 1, 1)
 
 /*****************************************************************************
   QDate static helper functions

src/gui/kernel/qpalette.cpp

@@ -52,7 +52,7 @@ static int qt_palette_count = 1;
 
 static constexpr QPalette::ResolveMask colorRoleOffset(QPalette::ColorGroup colorGroup)
 {
-    return QPalette::NColorRoles * colorGroup;
+    return qToUnderlying(QPalette::NColorRoles) * qToUnderlying(colorGroup);
 }
 
 static constexpr QPalette::ResolveMask bitPosition(QPalette::ColorGroup colorGroup,

src/gui/painting/qdrawhelper.cpp

@@ -71,10 +71,8 @@ Q_LOGGING_CATEGORY(lcQtGuiDrawHelper, "qt.gui.drawhelper")
   constants and structures
 */
 
-enum {
-    fixed_scale = 1 << 16,
-    half_point = 1 << 15
-};
+constexpr int fixed_scale = 1 << 16;
+constexpr int half_point = 1 << 15;
 
 template <QPixelLayout::BPP bpp> static
 inline uint QT_FASTCALL fetch1Pixel(const uchar *, int)