QVariant: deprecate qVariantFromValue/qVariantSetValue()

qVariantFromValue/qVariantSetValue() was marked as obsolete since Qt4.
Therefore mark them as deprecated with Qt5.14.
Since QVariant::setValue/fromValue() were using the now deprecated
functions move the implementation to them and let
qVariantFromValue/qVariantSetValue() call
QVariant::setValue/fromValue().

Fixes: QTBUG-74043
Change-Id: I46617cc4d5c1e8c162d0f1f7ae32e4cfe9ce915c
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

examples/corelib/tools/doc/src/customtype.qdoc

@@ -117,18 +117,15 @@
 
     \snippet tools/customtype/main.cpp storing a custom value
 
-    Alternatively, the QVariant::fromValue() and qVariantSetValue() functions
-    can be used if you are using a compiler without support for member template
+    Alternatively, the QVariant::fromValue() function can be used if
+    you are using a compiler without support for member template
     functions.
 
     The value can be retrieved using the QVariant::value() member template
     function:
 
     \snippet tools/customtype/main.cpp retrieving a custom value
 
-    Alternatively, the qVariantValue() template function can be used if
-    you are using a compiler without support for member template functions.
-
     \section1 Further Reading
 
     The custom \c Message type can also be used with direct signal-slot

src/corelib/kernel/qvariant.cpp

@@ -4282,6 +4282,7 @@ QDebug operator<<(QDebug dbg, const QVariant::Type p)
     \sa fromValue()
 */
 
+#if QT_DEPRECATED_SINCE(5, 14)
 /*!
     \fn template<typename T> QVariant qVariantFromValue(const T &value)
     \relates QVariant
@@ -4319,6 +4320,7 @@ QDebug operator<<(QDebug dbg, const QVariant::Type p)
 
     \sa QVariant::setValue()
 */
+#endif
 
 /*!
     \fn template<typename T> T qvariant_cast(const QVariant &value)

src/corelib/kernel/qvariant.h

@@ -92,9 +92,6 @@ class QUrl;
 class QVariant;
 class QVariantComparisonHelper;
 
-template <typename T>
-inline QVariant qVariantFromValue(const T &);
-
 template<typename T>
 inline T qvariant_cast(const QVariant &);
 
@@ -365,7 +362,7 @@ class Q_CORE_EXPORT QVariant
 
     template<typename T>
     static inline QVariant fromValue(const T &value)
-    { return qVariantFromValue(value); }
+    { return QVariant(qMetaTypeId<T>(), &value, QTypeInfo<T>::isPointer); }
 
 #if QT_HAS_INCLUDE(<variant>) && __cplusplus >= 201703L
     template<typename... Types>
@@ -516,50 +513,61 @@ class Q_CORE_EXPORT QVariant
     inline const DataPtr &data_ptr() const { return d; }
 };
 
+#if QT_DEPRECATED_SINCE(5, 14)
 template <typename T>
+QT_DEPRECATED_X("Use QVariant::fromValue() instead.")
 inline QVariant qVariantFromValue(const T &t)
 {
-    return QVariant(qMetaTypeId<T>(), &t, QTypeInfo<T>::isPointer);
+    return QVariant::fromValue(t);
+}
+
+template <typename T>
+QT_DEPRECATED_X("Use QVariant::setValue() instead.")
+inline void qVariantSetValue(QVariant &v, const T &t)
+{
+    v.setValue(t);
 }
+#endif
 
-template <>
-inline QVariant qVariantFromValue(const QVariant &t) { return t; }
+template<>
+inline QVariant QVariant::fromValue(const QVariant &value)
+{
+    return value;
+}
 
 #if QT_HAS_INCLUDE(<variant>) && __cplusplus >= 201703L
-template <>
-inline QVariant qVariantFromValue(const std::monostate &) { return QVariant(); }
+template<>
+inline QVariant QVariant::fromValue(const std::monostate &)
+{
+    return QVariant();
+}
 #endif
 
-template <typename T>
-inline void qVariantSetValue(QVariant &v, const T &t)
+inline bool QVariant::isValid() const { return d.type != Invalid; }
+
+template<typename T>
+inline void QVariant::setValue(const T &avalue)
 {
-    //if possible we reuse the current QVariant private
+    // If possible we reuse the current QVariant private.
     const uint type = qMetaTypeId<T>();
-    QVariant::Private &d = v.data_ptr();
-    if (v.isDetached() && (type == d.type || (type <= uint(QVariant::Char) && d.type <= uint(QVariant::Char)))) {
+    if (isDetached() && (type == d.type || (type <= uint(QVariant::Char) && d.type <= uint(QVariant::Char)))) {
         d.type = type;
         d.is_null = false;
         T *old = reinterpret_cast<T*>(d.is_shared ? d.data.shared->ptr : &d.data.ptr);
         if (QTypeInfo<T>::isComplex)
             old->~T();
-        new (old) T(t); //call the copy constructor
+        new (old) T(avalue); // call the copy constructor
     } else {
-        v = QVariant(type, &t, QTypeInfo<T>::isPointer);
+        *this = QVariant(type, &avalue, QTypeInfo<T>::isPointer);
     }
 }
 
-template <>
-inline void qVariantSetValue<QVariant>(QVariant &v, const QVariant &t)
+template<>
+inline void QVariant::setValue(const QVariant &avalue)
 {
-    v = t;
+    *this = avalue;
 }
 
-inline bool QVariant::isValid() const { return d.type != Invalid; }
-
-template<typename T>
-inline void QVariant::setValue(const T &avalue)
-{ qVariantSetValue(*this, avalue); }
-
 #ifndef QT_NO_DATASTREAM
 Q_CORE_EXPORT QDataStream& operator>> (QDataStream& s, QVariant& p);
 Q_CORE_EXPORT QDataStream& operator<< (QDataStream& s, const QVariant& p);