19 files changed, 248 insertions, 168 deletions

diff --git a/src/corelib/serialization/qcborvalue.cpp b/src/corelib/serialization/qcborvalue.cpp
index 288446878c..ba616c0a7d 100644
--- a/src/corelib/serialization/qcborvalue.cpp
+++ b/src/corelib/serialization/qcborvalue.cpp
@@ -766,8 +766,8 @@ static void writeDoubleToCbor(QCborStreamWriter &writer, double d, QCborValue::E
     if (qt_is_nan(d)) {
         if (opt & QCborValue::UseFloat16) {
             if ((opt & QCborValue::UseFloat16) == QCborValue::UseFloat16)
-                return writer.append(qfloat16(qt_qnan()));
-            return writer.append(float(qt_qnan()));
+                return writer.append(std::numeric_limits<qfloat16>::quiet_NaN());
+            return writer.append(std::numeric_limits<float>::quiet_NaN());
         }
         return writer.append(qt_qnan());
     }
@@ -849,7 +849,7 @@ QCborContainerPrivate *QCborContainerPrivate::clone(QCborContainerPrivate *d, qs
 
 QCborContainerPrivate *QCborContainerPrivate::detach(QCborContainerPrivate *d, qsizetype reserved)
 {
-    if (!d || d->ref.load() != 1)
+    if (!d || d->ref.loadRelaxed() != 1)
         return clone(d, reserved);
     return d;
 }
@@ -884,12 +884,12 @@ void QCborContainerPrivate::replaceAt_complex(Element &e, const QCborValue &valu
 
         // detect self-assignment
         if (Q_UNLIKELY(this == value.container)) {
-            Q_ASSERT(ref.load() >= 2);
+            Q_ASSERT(ref.loadRelaxed() >= 2);
             if (disp == MoveContainer)
                 ref.deref();    // not deref() because it can't drop to 0
             QCborContainerPrivate *d = QCborContainerPrivate::clone(this);
             d->elements.detach();
-            d->ref.store(1);
+            d->ref.storeRelaxed(1);
             e.container = d;
         } else {
             e.container = value.container;
@@ -1368,7 +1368,7 @@ static Element decodeBasicValueFromCbor(QCborStreamReader &reader)
 static inline QCborContainerPrivate *createContainerFromCbor(QCborStreamReader &reader)
 {
     auto d = new QCborContainerPrivate;
-    d->ref.store(1);
+    d->ref.storeRelaxed(1);
     d->decodeFromCbor(reader);
     return d;
 }
@@ -1643,7 +1643,7 @@ QCborValue::QCborValue(const QByteArray &ba)
     : n(0), container(new QCborContainerPrivate), t(ByteArray)
 {
     container->appendByteData(ba.constData(), ba.size(), t);
-    container->ref.store(1);
+    container->ref.storeRelaxed(1);
 }
 
 /*!
@@ -1656,7 +1656,7 @@ QCborValue::QCborValue(const QString &s)
     : n(0), container(new QCborContainerPrivate), t(String)
 {
     container->append(s);
-    container->ref.store(1);
+    container->ref.storeRelaxed(1);
 }
 
 /*!
@@ -1671,7 +1671,7 @@ QCborValue::QCborValue(QLatin1String s)
     : n(0), container(new QCborContainerPrivate), t(String)
 {
     container->append(s);
-    container->ref.store(1);
+    container->ref.storeRelaxed(1);
 }
 
 /*!
@@ -1719,7 +1719,7 @@ QCborValue::QCborValue(const QCborMap &m)
 QCborValue::QCborValue(QCborTag t, const QCborValue &tv)
     : n(-1), container(new QCborContainerPrivate), t(Tag)
 {
-    container->ref.store(1);
+    container->ref.storeRelaxed(1);
     container->append(t);
     container->append(tv);
 }
@@ -2941,7 +2941,7 @@ static QDebug debugContents(QDebug &dbg, const QCborValue &v)
     }
     if (v.isSimpleType())
         return dbg << v.toSimpleType();
-    return dbg << "<unknown type " << hex << int(v.type()) << dec << '>';
+    return dbg << "<unknown type " << Qt::hex << int(v.type()) << Qt::dec << '>';
 }
 QDebug operator<<(QDebug dbg, const QCborValue &v)
 {
diff --git a/src/corelib/serialization/qdatastream.cpp b/src/corelib/serialization/qdatastream.cpp
index 02c1d1c573..b3330d6cea 100644
--- a/src/corelib/serialization/qdatastream.cpp
+++ b/src/corelib/serialization/qdatastream.cpp
@@ -98,6 +98,10 @@ QT_BEGIN_NAMESPACE
     ensures that you get integers of the size you want and insulates
     you from compiler and platform differences.
 
+    Enumerations can be serialized through QDataStream without the
+    need of manually defining streaming operators. Enum classes are
+    serialized using the declared size.
+
     To take one example, a \c{char *} string is written as a 32-bit
     integer equal to the length of the string including the '\\0' byte,
     followed by all the characters of the string including the
@@ -273,7 +277,7 @@ QT_BEGIN_NAMESPACE
 
 QDataStream::QDataStream()
 {
-    dev = 0;
+    dev = nullptr;
     owndev = false;
     byteorder = BigEndian;
     ver = Qt_DefaultCompiledVersion;
@@ -429,7 +433,7 @@ bool QDataStream::atEnd() const
 */
 QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
 {
-    return d == 0 ? QDataStream::DoublePrecision : d->floatingPointPrecision;
+    return d ? d->floatingPointPrecision : QDataStream::DoublePrecision;
 }
 
 /*!
@@ -454,7 +458,7 @@ QDataStream::FloatingPointPrecision QDataStream::floatingPointPrecision() const
 */
 void QDataStream::setFloatingPointPrecision(QDataStream::FloatingPointPrecision precision)
 {
-    if (d == 0)
+    if (!d)
         d.reset(new QDataStreamPrivate());
     d->floatingPointPrecision = precision;
 }
@@ -561,6 +565,7 @@ void QDataStream::setByteOrder(ByteOrder bo)
     \value Qt_5_11 Same as Qt_5_6
     \value Qt_5_12 Version 18 (Qt 5.12)
     \value Qt_5_13 Version 19 (Qt 5.13)
+    \value Qt_5_14 Same as Qt_5_13
     \omitvalue Qt_DefaultCompiledVersion
 
     \sa setVersion(), version()
@@ -634,7 +639,7 @@ void QDataStream::startTransaction()
 {
     CHECK_STREAM_PRECOND(Q_VOID)
 
-    if (d == 0)
+    if (!d)
         d.reset(new QDataStreamPrivate());
 
     if (++d->transactionDepth == 1) {
@@ -1038,7 +1043,7 @@ QDataStream &QDataStream::operator>>(char *&s)
 
 QDataStream &QDataStream::readBytes(char *&s, uint &l)
 {
-    s = 0;
+    s = nullptr;
     l = 0;
     CHECK_STREAM_PRECOND(*this)
 
@@ -1049,8 +1054,8 @@ QDataStream &QDataStream::readBytes(char *&s, uint &l)
 
     const quint32 Step = 1024 * 1024;
     quint32 allocated = 0;
-    char *prevBuf = 0;
-    char *curBuf = 0;
+    char *prevBuf = nullptr;
+    char *curBuf = nullptr;
 
     do {
         int blockSize = qMin(Step, len - allocated);
diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index 81134f74b0..cfcd89333b 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -55,7 +55,6 @@ class QByteArray;
 class QIODevice;
 
 template <typename T> class QList;
-template <typename T> class QLinkedList;
 template <typename T> class QVector;
 template <typename T> class QSet;
 template <class Key, class T> class QHash;
@@ -100,10 +99,19 @@ public:
         Qt_5_11 = Qt_5_10,
         Qt_5_12 = 18,
         Qt_5_13 = 19,
-#if QT_VERSION >= 0x050e00
+        Qt_5_14 = Qt_5_13,
+#if QT_VERSION >= 0x050f00
+        Qt_5_15 = Qt_5_14,
+        Qt_DefaultCompiledVersion = Qt_5_15
+#elif QT_VERSION >= 0x060000
+        Qt_6_0 = Qt_5_15,
+        Qt_DefaultCompiledVersion = Qt_6_0
+#else
+        Qt_DefaultCompiledVersion = Qt_5_14
+#endif
+#if QT_VERSION >= 0x060100
 #error Add the datastream version for this Qt version and update Qt_DefaultCompiledVersion
 #endif
-        Qt_DefaultCompiledVersion = Qt_5_13
     };
 
     enum ByteOrder {
@@ -377,25 +385,23 @@ inline QDataStream &operator>>(QDataStream &s, QFlags<Enum> &e)
 { return s >> e.i; }
 
 template <typename T>
-inline QDataStream &operator>>(QDataStream &s, QList<T> &l)
-{
-    return QtPrivate::readArrayBasedContainer(s, l);
-}
+typename std::enable_if<std::is_enum<T>::value, QDataStream &>::type&
+operator<<(QDataStream &s, const T &t)
+{ return s << static_cast<typename std::underlying_type<T>::type>(t); }
 
 template <typename T>
-inline QDataStream &operator<<(QDataStream &s, const QList<T> &l)
-{
-    return QtPrivate::writeSequentialContainer(s, l);
-}
+typename std::enable_if<std::is_enum<T>::value, QDataStream &>::type&
+operator>>(QDataStream &s, T &t)
+{ return s >> reinterpret_cast<typename std::underlying_type<T>::type &>(t); }
 
 template <typename T>
-inline QDataStream &operator>>(QDataStream &s, QLinkedList<T> &l)
+inline QDataStream &operator>>(QDataStream &s, QList<T> &l)
 {
-    return QtPrivate::readListBasedContainer(s, l);
+    return QtPrivate::readArrayBasedContainer(s, l);
 }
 
 template <typename T>
-inline QDataStream &operator<<(QDataStream &s, const QLinkedList<T> &l)
+inline QDataStream &operator<<(QDataStream &s, const QList<T> &l)
 {
     return QtPrivate::writeSequentialContainer(s, l);
 }
diff --git a/src/corelib/serialization/qjson_p.h b/src/corelib/serialization/qjson_p.h
index 40b2414e4a..9de53d5b74 100644
--- a/src/corelib/serialization/qjson_p.h
+++ b/src/corelib/serialization/qjson_p.h
@@ -304,7 +304,7 @@ public:
         return *this;
     }
 
-    QLatin1String toQLatin1String() const Q_DECL_NOTHROW {
+    QLatin1String toQLatin1String() const noexcept {
         return QLatin1String(d->latin1, d->length);
     }
 
@@ -339,23 +339,23 @@ public:
 };
 
 #define DEF_OP(op) \
-    inline bool operator op(Latin1String lhs, Latin1String rhs) Q_DECL_NOTHROW \
+    inline bool operator op(Latin1String lhs, Latin1String rhs) noexcept \
     { \
         return lhs.toQLatin1String() op rhs.toQLatin1String(); \
     } \
-    inline bool operator op(QLatin1String lhs, Latin1String rhs) Q_DECL_NOTHROW \
+    inline bool operator op(QLatin1String lhs, Latin1String rhs) noexcept \
     { \
         return lhs op rhs.toQLatin1String(); \
     } \
-    inline bool operator op(Latin1String lhs, QLatin1String rhs) Q_DECL_NOTHROW \
+    inline bool operator op(Latin1String lhs, QLatin1String rhs) noexcept \
     { \
         return lhs.toQLatin1String() op rhs; \
     } \
-    inline bool operator op(const QString &lhs, Latin1String rhs) Q_DECL_NOTHROW \
+    inline bool operator op(const QString &lhs, Latin1String rhs) noexcept \
     { \
         return lhs op rhs.toQLatin1String(); \
     } \
-    inline bool operator op(Latin1String lhs, const QString &rhs) Q_DECL_NOTHROW \
+    inline bool operator op(Latin1String lhs, const QString &rhs) noexcept \
     { \
         return lhs.toQLatin1String() op rhs; \
     } \
@@ -686,7 +686,7 @@ public:
     {
     }
     inline Data(int reserved, QJsonValue::Type valueType)
-        : rawData(0), compactionCounter(0), ownsData(true)
+        : rawData(nullptr), compactionCounter(0), ownsData(true)
     {
         Q_ASSERT(valueType == QJsonValue::Array || valueType == QJsonValue::Object);
 
@@ -719,7 +719,7 @@ public:
     Data *clone(Base *b, int reserve = 0)
     {
         int size = sizeof(Header) + b->size;
-        if (b == header->root() && ref.load() == 1 && alloc >= size + reserve)
+        if (b == header->root() && ref.loadRelaxed() == 1 && alloc >= size + reserve)
             return this;
 
         if (reserve) {
@@ -728,7 +728,7 @@ public:
             size = qMax(size + reserve, qMin(size *2, (int)Value::MaxSize));
             if (size > Value::MaxSize) {
                 qWarning("QJson: Document too large to store in data structure");
-                return 0;
+                return nullptr;
             }
         }
         char *raw = (char *)malloc(size);
diff --git a/src/corelib/serialization/qjsonarray.cpp b/src/corelib/serialization/qjsonarray.cpp
index f5f02b886a..9636ac5856 100644
--- a/src/corelib/serialization/qjsonarray.cpp
+++ b/src/corelib/serialization/qjsonarray.cpp
@@ -132,7 +132,7 @@ QT_BEGIN_NAMESPACE
     Creates an empty array.
  */
 QJsonArray::QJsonArray()
-    : d(0), a(0)
+    : d(nullptr), a(nullptr)
 {
 }
 
@@ -168,8 +168,8 @@ QJsonArray::QJsonArray(QJsonPrivate::Data *data, QJsonPrivate::Array *array)
  */
 void QJsonArray::initialize()
 {
-    d = 0;
-    a = 0;
+    d = nullptr;
+    a = nullptr;
 }
 
 /*!
@@ -1226,7 +1226,7 @@ bool QJsonArray::detach2(uint reserve)
         d->ref.ref();
         return true;
     }
-    if (reserve == 0 && d->ref.load() == 1)
+    if (reserve == 0 && d->ref.loadRelaxed() == 1)
         return true;
 
     QJsonPrivate::Data *x = d->clone(a, reserve);
diff --git a/src/corelib/serialization/qjsonarray.h b/src/corelib/serialization/qjsonarray.h
index ba346fb848..983a6753b5 100644
--- a/src/corelib/serialization/qjsonarray.h
+++ b/src/corelib/serialization/qjsonarray.h
@@ -42,9 +42,7 @@
 
 #include <QtCore/qjsonvalue.h>
 #include <QtCore/qiterator.h>
-#if defined(Q_COMPILER_INITIALIZER_LISTS)
 #include <initializer_list>
-#endif
 
 QT_BEGIN_NAMESPACE
 
@@ -58,21 +56,19 @@ class Q_CORE_EXPORT QJsonArray
 public:
     QJsonArray();
 
-#if defined(Q_COMPILER_INITIALIZER_LISTS) || defined(Q_QDOC)
     QJsonArray(std::initializer_list<QJsonValue> args)
     {
         initialize();
         for (std::initializer_list<QJsonValue>::const_iterator i = args.begin(); i != args.end(); ++i)
             append(*i);
     }
-#endif
 
     ~QJsonArray();
 
     QJsonArray(const QJsonArray &other);
     QJsonArray &operator =(const QJsonArray &other);
 
-    QJsonArray(QJsonArray &&other) Q_DECL_NOTHROW
+    QJsonArray(QJsonArray &&other) noexcept
         : d(other.d),
           a(other.a)
     {
@@ -80,7 +76,7 @@ public:
         other.a = nullptr;
     }
 
-    QJsonArray &operator =(QJsonArray &&other) Q_DECL_NOTHROW
+    QJsonArray &operator =(QJsonArray &&other) noexcept
     {
         swap(other);
         return *this;
@@ -115,7 +111,7 @@ public:
     bool operator==(const QJsonArray &other) const;
     bool operator!=(const QJsonArray &other) const;
 
-    void swap(QJsonArray &other) Q_DECL_NOTHROW
+    void swap(QJsonArray &other) noexcept
     {
         qSwap(d, other.d);
         qSwap(a, other.a);
diff --git a/src/corelib/serialization/qjsondocument.cpp b/src/corelib/serialization/qjsondocument.cpp
index 179a87c699..f8027efb58 100644
--- a/src/corelib/serialization/qjsondocument.cpp
+++ b/src/corelib/serialization/qjsondocument.cpp
@@ -84,7 +84,7 @@ QT_BEGIN_NAMESPACE
  * Constructs an empty and invalid document.
  */
 QJsonDocument::QJsonDocument()
-    : d(0)
+    : d(nullptr)
 {
 }
 
@@ -92,7 +92,7 @@ QJsonDocument::QJsonDocument()
  * Creates a QJsonDocument from \a object.
  */
 QJsonDocument::QJsonDocument(const QJsonObject &object)
-    : d(0)
+    : d(nullptr)
 {
     setObject(object);
 }
@@ -101,7 +101,7 @@ QJsonDocument::QJsonDocument(const QJsonObject &object)
  * Constructs a QJsonDocument from \a array.
  */
 QJsonDocument::QJsonDocument(const QJsonArray &array)
-    : d(0)
+    : d(nullptr)
 {
     setArray(array);
 }
@@ -236,7 +236,7 @@ const char *QJsonDocument::rawData(int *size) const
 {
     if (!d) {
         *size = 0;
-        return 0;
+        return nullptr;
     }
     *size = d->alloc;
     return d->rawData;
@@ -635,7 +635,7 @@ bool QJsonDocument::operator==(const QJsonDocument &other) const
  */
 bool QJsonDocument::isNull() const
 {
-    return (d == 0);
+    return (d == nullptr);
 }
 
 #if !defined(QT_NO_DEBUG_STREAM) && !defined(QT_JSON_READONLY)
diff --git a/src/corelib/serialization/qjsondocument.h b/src/corelib/serialization/qjsondocument.h
index a749439b7d..a8006a6cc5 100644
--- a/src/corelib/serialization/qjsondocument.h
+++ b/src/corelib/serialization/qjsondocument.h
@@ -93,19 +93,19 @@ public:
     QJsonDocument(const QJsonDocument &other);
     QJsonDocument &operator =(const QJsonDocument &other);
 
-    QJsonDocument(QJsonDocument &&other) Q_DECL_NOTHROW
+    QJsonDocument(QJsonDocument &&other) noexcept
         : d(other.d)
     {
         other.d = nullptr;
     }
 
-    QJsonDocument &operator =(QJsonDocument &&other) Q_DECL_NOTHROW
+    QJsonDocument &operator =(QJsonDocument &&other) noexcept
     {
         swap(other);
         return *this;
     }
 
-    void swap(QJsonDocument &other) Q_DECL_NOTHROW
+    void swap(QJsonDocument &other) noexcept
     {
         qSwap(d, other.d);
     }
diff --git a/src/corelib/serialization/qjsonobject.cpp b/src/corelib/serialization/qjsonobject.cpp
index a9f25a119c..c1a6328b2f 100644
--- a/src/corelib/serialization/qjsonobject.cpp
+++ b/src/corelib/serialization/qjsonobject.cpp
@@ -110,7 +110,7 @@ QT_BEGIN_NAMESPACE
     \sa isEmpty()
  */
 QJsonObject::QJsonObject()
-    : d(0), o(0)
+    : d(nullptr), o(nullptr)
 {
 }
 
@@ -149,8 +149,8 @@ QJsonObject::QJsonObject(QJsonPrivate::Data *data, QJsonPrivate::Object *object)
 
 void QJsonObject::initialize()
 {
-    d = 0;
-    o = 0;
+    d = nullptr;
+    o = nullptr;
 }
 
 /*!
@@ -646,7 +646,7 @@ bool QJsonObject::operator!=(const QJsonObject &other) const
  */
 QJsonObject::iterator QJsonObject::erase(QJsonObject::iterator it)
 {
-    Q_ASSERT(d && d->ref.load() == 1);
+    Q_ASSERT(d && d->ref.loadRelaxed() == 1);
     if (it.o != this || it.i < 0 || it.i >= (int)o->length)
         return iterator(this, o->length);
 
@@ -1231,7 +1231,7 @@ bool QJsonObject::detach2(uint reserve)
         d->ref.ref();
         return true;
     }
-    if (reserve == 0 && d->ref.load() == 1)
+    if (reserve == 0 && d->ref.loadRelaxed() == 1)
         return true;
 
     QJsonPrivate::Data *x = d->clone(o, reserve);
diff --git a/src/corelib/serialization/qjsonobject.h b/src/corelib/serialization/qjsonobject.h
index 80fe6b2f3f..d8e2ab9ca7 100644
--- a/src/corelib/serialization/qjsonobject.h
+++ b/src/corelib/serialization/qjsonobject.h
@@ -42,10 +42,8 @@
 
 #include <QtCore/qjsonvalue.h>
 #include <QtCore/qiterator.h>
-#ifdef Q_COMPILER_INITIALIZER_LISTS
 #include <QtCore/qpair.h>
 #include <initializer_list>
-#endif
 
 QT_BEGIN_NAMESPACE
 
@@ -60,34 +58,32 @@ class Q_CORE_EXPORT QJsonObject
 public:
     QJsonObject();
 
-#if defined(Q_COMPILER_INITIALIZER_LISTS) || defined(Q_QDOC)
     QJsonObject(std::initializer_list<QPair<QString, QJsonValue> > args)
     {
         initialize();
         for (std::initializer_list<QPair<QString, QJsonValue> >::const_iterator i = args.begin(); i != args.end(); ++i)
             insert(i->first, i->second);
     }
-#endif
 
     ~QJsonObject();
 
     QJsonObject(const QJsonObject &other);
     QJsonObject &operator =(const QJsonObject &other);
 
-    QJsonObject(QJsonObject &&other) Q_DECL_NOTHROW
+    QJsonObject(QJsonObject &&other) noexcept
         : d(other.d), o(other.o)
     {
         other.d = nullptr;
         other.o = nullptr;
     }
 
-    QJsonObject &operator =(QJsonObject &&other) Q_DECL_NOTHROW
+    QJsonObject &operator =(QJsonObject &&other) noexcept
     {
         swap(other);
         return *this;
     }
 
-    void swap(QJsonObject &other) Q_DECL_NOTHROW
+    void swap(QJsonObject &other) noexcept
     {
         qSwap(d, other.d);
         qSwap(o, other.o);
diff --git a/src/corelib/serialization/qjsonparser.cpp b/src/corelib/serialization/qjsonparser.cpp
index bfba95520e..cd36bd5a5b 100644
--- a/src/corelib/serialization/qjsonparser.cpp
+++ b/src/corelib/serialization/qjsonparser.cpp
@@ -198,7 +198,9 @@ QString QJsonParseError::errorString() const
 using namespace QJsonPrivate;
 
 Parser::Parser(const char *json, int length)
-    : head(json), json(json), data(0), dataLength(0), current(0), nestingLevel(0), lastError(QJsonParseError::NoError)
+    : head(json), json(json), data(nullptr)
+    , dataLength(0), current(0), nestingLevel(0)
+    , lastError(QJsonParseError::NoError)
 {
     end = json + length;
 }
@@ -316,7 +318,7 @@ QJsonDocument Parser::parse(QJsonParseError *error)
     eatBOM();
     char token = nextToken();
 
-    DEBUG << hex << (uint)token;
+    DEBUG << Qt::hex << (uint)token;
     if (token == BeginArray) {
         if (!parseArray())
             goto error;
diff --git a/src/corelib/serialization/qjsonvalue.cpp b/src/corelib/serialization/qjsonvalue.cpp
index 1fc610d7c7..0bd28581f3 100644
--- a/src/corelib/serialization/qjsonvalue.cpp
+++ b/src/corelib/serialization/qjsonvalue.cpp
@@ -112,7 +112,7 @@ QT_BEGIN_NAMESPACE
     The default is to create a Null value.
  */
 QJsonValue::QJsonValue(Type type)
-    : ui(0), d(0), t(type)
+    : ui(0), d(nullptr), t(type)
 {
 }
 
@@ -120,7 +120,7 @@ QJsonValue::QJsonValue(Type type)
     \internal
  */
 QJsonValue::QJsonValue(QJsonPrivate::Data *data, QJsonPrivate::Base *base, const QJsonPrivate::Value &v)
-    : d(0)
+    : d(nullptr)
 {
     t = (Type)(uint)v.type;
     switch (t) {
@@ -154,7 +154,7 @@ QJsonValue::QJsonValue(QJsonPrivate::Data *data, QJsonPrivate::Base *base, const
     Creates a value of type Bool, with value \a b.
  */
 QJsonValue::QJsonValue(bool b)
-    : d(0), t(Bool)
+    : d(nullptr), t(Bool)
 {
     this->b = b;
 }
@@ -163,7 +163,7 @@ QJsonValue::QJsonValue(bool b)
     Creates a value of type Double, with value \a n.
  */
 QJsonValue::QJsonValue(double n)
-    : d(0), t(Double)
+    : d(nullptr), t(Double)
 {
     this->dbl = n;
 }
@@ -173,7 +173,7 @@ QJsonValue::QJsonValue(double n)
     Creates a value of type Double, with value \a n.
  */
 QJsonValue::QJsonValue(int n)
-    : d(0), t(Double)
+    : d(nullptr), t(Double)
 {
     this->dbl = n;
 }
@@ -185,7 +185,7 @@ QJsonValue::QJsonValue(int n)
     If you pass in values outside this range expect a loss of precision to occur.
  */
 QJsonValue::QJsonValue(qint64 n)
-    : d(0), t(Double)
+    : d(nullptr), t(Double)
 {
     this->dbl = double(n);
 }
@@ -194,7 +194,7 @@ QJsonValue::QJsonValue(qint64 n)
     Creates a value of type String, with value \a s.
  */
 QJsonValue::QJsonValue(const QString &s)
-    : d(0), t(String)
+    : d(nullptr), t(String)
 {
     stringDataFromQStringHelper(s);
 }
@@ -221,7 +221,7 @@ void QJsonValue::stringDataFromQStringHelper(const QString &string)
     Creates a value of type String, with value \a s.
  */
 QJsonValue::QJsonValue(QLatin1String s)
-    : d(0), t(String)
+    : d(nullptr), t(String)
 {
     // ### FIXME: Avoid creating the temp QString below
     QString str(s);
diff --git a/src/corelib/serialization/qjsonvalue.h b/src/corelib/serialization/qjsonvalue.h
index 0339eb59f7..37d84f9e60 100644
--- a/src/corelib/serialization/qjsonvalue.h
+++ b/src/corelib/serialization/qjsonvalue.h
@@ -92,7 +92,7 @@ public:
     QJsonValue(const QJsonValue &other);
     QJsonValue &operator =(const QJsonValue &other);
 
-    QJsonValue(QJsonValue &&other) Q_DECL_NOTHROW
+    QJsonValue(QJsonValue &&other) noexcept
         : ui(other.ui),
           d(other.d),
           t(other.t)
@@ -102,13 +102,13 @@ public:
         other.t = Null;
     }
 
-    QJsonValue &operator =(QJsonValue &&other) Q_DECL_NOTHROW
+    QJsonValue &operator =(QJsonValue &&other) noexcept
     {
         swap(other);
         return *this;
     }
 
-    void swap(QJsonValue &other) Q_DECL_NOTHROW
+    void swap(QJsonValue &other) noexcept
     {
         qSwap(ui, other.ui);
         qSwap(d, other.d);
diff --git a/src/corelib/serialization/qtextstream.cpp b/src/corelib/serialization/qtextstream.cpp
index c9ba183a50..a675c3cede 100644
--- a/src/corelib/serialization/qtextstream.cpp
+++ b/src/corelib/serialization/qtextstream.cpp
@@ -135,30 +135,30 @@ static const int QTEXTSTREAM_BUFFERSIZE = 16384;
 
     \table
     \header \li Manipulator        \li Description
-    \row    \li \c bin             \li Same as setIntegerBase(2).
-    \row    \li \c oct             \li Same as setIntegerBase(8).
-    \row    \li \c dec             \li Same as setIntegerBase(10).
-    \row    \li \c hex             \li Same as setIntegerBase(16).
-    \row    \li \c showbase        \li Same as setNumberFlags(numberFlags() | ShowBase).
-    \row    \li \c forcesign       \li Same as setNumberFlags(numberFlags() | ForceSign).
-    \row    \li \c forcepoint      \li Same as setNumberFlags(numberFlags() | ForcePoint).
-    \row    \li \c noshowbase      \li Same as setNumberFlags(numberFlags() & ~ShowBase).
-    \row    \li \c noforcesign     \li Same as setNumberFlags(numberFlags() & ~ForceSign).
-    \row    \li \c noforcepoint    \li Same as setNumberFlags(numberFlags() & ~ForcePoint).
-    \row    \li \c uppercasebase   \li Same as setNumberFlags(numberFlags() | UppercaseBase).
-    \row    \li \c uppercasedigits \li Same as setNumberFlags(numberFlags() | UppercaseDigits).
-    \row    \li \c lowercasebase   \li Same as setNumberFlags(numberFlags() & ~UppercaseBase).
-    \row    \li \c lowercasedigits \li Same as setNumberFlags(numberFlags() & ~UppercaseDigits).
-    \row    \li \c fixed           \li Same as setRealNumberNotation(FixedNotation).
-    \row    \li \c scientific      \li Same as setRealNumberNotation(ScientificNotation).
-    \row    \li \c left            \li Same as setFieldAlignment(AlignLeft).
-    \row    \li \c right           \li Same as setFieldAlignment(AlignRight).
-    \row    \li \c center          \li Same as setFieldAlignment(AlignCenter).
-    \row    \li \c endl            \li Same as operator<<('\\n') and flush().
-    \row    \li \c flush           \li Same as flush().
-    \row    \li \c reset           \li Same as reset().
-    \row    \li \c ws              \li Same as skipWhiteSpace().
-    \row    \li \c bom             \li Same as setGenerateByteOrderMark(true).
+    \row    \li \c Qt::bin             \li Same as setIntegerBase(2).
+    \row    \li \c Qt::oct             \li Same as setIntegerBase(8).
+    \row    \li \c Qt::dec             \li Same as setIntegerBase(10).
+    \row    \li \c Qt::hex             \li Same as setIntegerBase(16).
+    \row    \li \c Qt::showbase        \li Same as setNumberFlags(numberFlags() | ShowBase).
+    \row    \li \c Qt::forcesign       \li Same as setNumberFlags(numberFlags() | ForceSign).
+    \row    \li \c Qt::forcepoint      \li Same as setNumberFlags(numberFlags() | ForcePoint).
+    \row    \li \c Qt::noshowbase      \li Same as setNumberFlags(numberFlags() & ~ShowBase).
+    \row    \li \c Qt::noforcesign     \li Same as setNumberFlags(numberFlags() & ~ForceSign).
+    \row    \li \c Qt::noforcepoint    \li Same as setNumberFlags(numberFlags() & ~ForcePoint).
+    \row    \li \c Qt::uppercasebase   \li Same as setNumberFlags(numberFlags() | UppercaseBase).
+    \row    \li \c Qt::uppercasedigits \li Same as setNumberFlags(numberFlags() | UppercaseDigits).
+    \row    \li \c Qt::lowercasebase   \li Same as setNumberFlags(numberFlags() & ~UppercaseBase).
+    \row    \li \c Qt::lowercasedigits \li Same as setNumberFlags(numberFlags() & ~UppercaseDigits).
+    \row    \li \c Qt::fixed           \li Same as setRealNumberNotation(FixedNotation).
+    \row    \li \c Qt::scientific      \li Same as setRealNumberNotation(ScientificNotation).
+    \row    \li \c Qt::left            \li Same as setFieldAlignment(AlignLeft).
+    \row    \li \c Qt::right           \li Same as setFieldAlignment(AlignRight).
+    \row    \li \c Qt::center          \li Same as setFieldAlignment(AlignCenter).
+    \row    \li \c Qt::endl            \li Same as operator<<('\\n') and flush().
+    \row    \li \c Qt::flush           \li Same as flush().
+    \row    \li \c Qt::reset           \li Same as reset().
+    \row    \li \c Qt::ws              \li Same as skipWhiteSpace().
+    \row    \li \c Qt::bom             \li Same as setGenerateByteOrderMark(true).
     \endtable
 
     In addition, Qt provides three global manipulators that take a
@@ -327,7 +327,7 @@ QT_BEGIN_NAMESPACE
 QTextStreamPrivate::QTextStreamPrivate(QTextStream *q_ptr)
     :
 #if QT_CONFIG(textcodec)
-    readConverterSavedState(0),
+    readConverterSavedState(nullptr),
 #endif
     readConverterSavedStateOffset(0),
     locale(QLocale::c())
@@ -381,7 +381,7 @@ void QTextStreamPrivate::Params::reset()
     padChar = QLatin1Char(' ');
     fieldAlignment = QTextStream::AlignRight;
     realNumberNotation = QTextStream::SmartNotation;
-    numberFlags = 0;
+    numberFlags = { };
 }
 
 /*!
@@ -391,9 +391,9 @@ void QTextStreamPrivate::reset()
 {
     params.reset();
 
-    device = 0;
+    device = nullptr;
     deleteDevice = false;
-    string = 0;
+    string = nullptr;
     stringOffset = 0;
     stringOpenMode = QIODevice::NotOpen;
 
@@ -406,7 +406,7 @@ void QTextStreamPrivate::reset()
     resetCodecConverterStateHelper(&readConverterState);
     resetCodecConverterStateHelper(&writeConverterState);
     delete readConverterSavedState;
-    readConverterSavedState = 0;
+    readConverterSavedState = nullptr;
     writeConverterState.flags |= QTextCodec::IgnoreHeader;
     autoDetectUnicode = true;
 #endif
@@ -888,7 +888,7 @@ inline bool QTextStreamPrivate::getChar(QChar *ch)
     if ((string && stringOffset == string->size())
         || (device && readBuffer.isEmpty() && !fillReadBuffer())) {
         if (ch)
-            *ch = 0;
+            *ch = QChar();
         return false;
     }
     if (ch)
@@ -1207,7 +1207,7 @@ bool QTextStream::seek(qint64 pos)
         resetCodecConverterStateHelper(&d->readConverterState);
         resetCodecConverterStateHelper(&d->writeConverterState);
         delete d->readConverterSavedState;
-        d->readConverterSavedState = 0;
+        d->readConverterSavedState = nullptr;
         d->writeConverterState.flags |= QTextCodec::IgnoreHeader;
 #endif
         return true;
@@ -1295,7 +1295,7 @@ void QTextStream::skipWhiteSpace()
 {
     Q_D(QTextStream);
     CHECK_VALID_STREAM(Q_VOID);
-    d->scan(0, 0, 0, QTextStreamPrivate::NotSpace);
+    d->scan(nullptr, nullptr, 0, QTextStreamPrivate::NotSpace);
     d->consumeLastToken();
 }
 
@@ -1751,7 +1751,7 @@ QString QTextStream::read(qint64 maxlen)
 */
 QTextStreamPrivate::NumberParsingStatus QTextStreamPrivate::getNumber(qulonglong *ret)
 {
-    scan(0, 0, 0, NotSpace);
+    scan(nullptr, nullptr, 0, NotSpace);
     consumeLastToken();
 
     // detect int encoding
@@ -1980,7 +1980,7 @@ bool QTextStreamPrivate::getReal(double *f)
     ParserState state = Init;
     InputToken input = None;
 
-    scan(0, 0, 0, NotSpace);
+    scan(nullptr, nullptr, 0, NotSpace);
     consumeLastToken();
 
     const int BufferSize = 128;
@@ -2084,7 +2084,7 @@ QTextStream &QTextStream::operator>>(QChar &c)
 {
     Q_D(QTextStream);
     CHECK_VALID_STREAM(*this);
-    d->scan(0, 0, 0, QTextStreamPrivate::NotSpace);
+    d->scan(nullptr, nullptr, 0, QTextStreamPrivate::NotSpace);
     if (!d->getChar(&c))
         setStatus(ReadPastEnd);
     return *this;
@@ -2245,7 +2245,7 @@ QTextStream &QTextStream::operator>>(QString &str)
     CHECK_VALID_STREAM(*this);
 
     str.clear();
-    d->scan(0, 0, 0, QTextStreamPrivate::NotSpace);
+    d->scan(nullptr, nullptr, 0, QTextStreamPrivate::NotSpace);
     d->consumeLastToken();
 
     const QChar *ptr;
@@ -2273,7 +2273,7 @@ QTextStream &QTextStream::operator>>(QByteArray &array)
     CHECK_VALID_STREAM(*this);
 
     array.clear();
-    d->scan(0, 0, 0, QTextStreamPrivate::NotSpace);
+    d->scan(nullptr, nullptr, 0, QTextStreamPrivate::NotSpace);
     d->consumeLastToken();
 
     const QChar *ptr;
@@ -2308,7 +2308,7 @@ QTextStream &QTextStream::operator>>(char *c)
     Q_D(QTextStream);
     *c = 0;
     CHECK_VALID_STREAM(*this);
-    d->scan(0, 0, 0, QTextStreamPrivate::NotSpace);
+    d->scan(nullptr, nullptr, 0, QTextStreamPrivate::NotSpace);
     d->consumeLastToken();
 
     const QChar *ptr;
@@ -2356,7 +2356,7 @@ void QTextStreamPrivate::putNumber(qulonglong number, bool negative)
     } else if (negative) {
         // Workaround for backward compatibility for writing negative
         // numbers in octal and hex:
-        // QTextStream(result) << showbase << hex << -1 << oct << -1
+        // QTextStream(result) << Qt::showbase << Qt::hex << -1 << oct << -1
         // should output: -0x1 -0b1
         result = dd->unsLongLongToString(number, -1, base, -1, flags);
         result.prepend(locale.negativeSign());
@@ -2689,6 +2689,11 @@ QTextStream &QTextStream::operator<<(const void *ptr)
     d->params.numberFlags = oldFlags;
     return *this;
 }
+#if defined(Q_QDOC) || QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+namespace Qt {
+#else
+namespace QTextStreamFunctions {
+#endif
 
 /*!
     \relates QTextStream
@@ -2973,7 +2978,7 @@ QTextStream &center(QTextStream &stream)
 */
 QTextStream &endl(QTextStream &stream)
 {
-    return stream << QLatin1Char('\n') << flush;
+    return stream << QLatin1Char('\n') << Qt::flush;
 }
 
 /*!
@@ -3015,6 +3020,8 @@ QTextStream &ws(QTextStream &stream)
     return stream;
 }
 
+} // namespace QTextStreamFunctions
+
 /*!
     \fn QTextStreamManipulator qSetFieldWidth(int width)
     \relates QTextStream
@@ -3037,6 +3044,12 @@ QTextStream &ws(QTextStream &stream)
 */
 
 #if QT_CONFIG(textcodec)
+
+#if defined(Q_QDOC) || QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+namespace Qt {
+#else
+namespace QTextStreamFunctions {
+#endif
 /*!
     \relates QTextStream
 
@@ -3051,6 +3064,8 @@ QTextStream &bom(QTextStream &stream)
     return stream;
 }
 
+} // namespace QTextStreamFunctions
+
 /*!
     Sets the codec for this stream to \a codec. The codec is used for
     decoding any data that is read from the assigned device, and for
@@ -3200,6 +3215,43 @@ QLocale QTextStream::locale() const
     return d->locale;
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0) && !defined(Q_QDOC)
+// Binary compatible definitions for Qt<5.14
+Q_CORE_EXPORT QTextStream &bin(QTextStream &s) { return Qt::bin(s); }
+Q_CORE_EXPORT QTextStream &oct(QTextStream &s) { return Qt::oct(s); }
+Q_CORE_EXPORT QTextStream &dec(QTextStream &s) { return Qt::dec(s); }
+Q_CORE_EXPORT QTextStream &hex(QTextStream &s) { return Qt::hex(s); }
+
+Q_CORE_EXPORT QTextStream &showbase(QTextStream &s) { return Qt::showbase(s); }
+Q_CORE_EXPORT QTextStream &forcesign(QTextStream &s) { return Qt::forcesign(s); }
+Q_CORE_EXPORT QTextStream &forcepoint(QTextStream &s) { return Qt::forcepoint(s); }
+Q_CORE_EXPORT QTextStream &noshowbase(QTextStream &s) { return Qt::noshowbase(s); }
+Q_CORE_EXPORT QTextStream &noforcesign(QTextStream &s) { return Qt::noforcesign(s); }
+Q_CORE_EXPORT QTextStream &noforcepoint(QTextStream &s) { return Qt::noforcepoint(s); }
+
+Q_CORE_EXPORT QTextStream &uppercasebase(QTextStream &s) { return Qt::uppercasebase(s); }
+Q_CORE_EXPORT QTextStream &uppercasedigits(QTextStream &s) { return Qt::uppercasedigits(s); }
+Q_CORE_EXPORT QTextStream &lowercasebase(QTextStream &s) { return Qt::lowercasebase(s); }
+Q_CORE_EXPORT QTextStream &lowercasedigits(QTextStream &s) { return Qt::lowercasedigits(s); }
+
+Q_CORE_EXPORT QTextStream &fixed(QTextStream &s) { return Qt::fixed(s); }
+Q_CORE_EXPORT QTextStream &scientific(QTextStream &s) { return Qt::scientific(s); }
+
+Q_CORE_EXPORT QTextStream &left(QTextStream &s) { return Qt::left(s); }
+Q_CORE_EXPORT QTextStream &right(QTextStream &s) { return Qt::right(s); }
+Q_CORE_EXPORT QTextStream &center(QTextStream &s) { return Qt::center(s); }
+
+Q_CORE_EXPORT QTextStream &endl(QTextStream &s) { return Qt::endl(s); }
+Q_CORE_EXPORT QTextStream &flush(QTextStream &s) { return Qt::flush(s); }
+Q_CORE_EXPORT QTextStream &reset(QTextStream &s) { return Qt::reset(s); }
+
+Q_CORE_EXPORT QTextStream &ws(QTextStream &s) { return Qt::ws(s); }
+
+#if QT_CONFIG(textcodec)
+Q_CORE_EXPORT QTextStream &bom(QTextStream &s) { return Qt::bom(s); }
+#endif
+#endif
+
 QT_END_NAMESPACE
 
 #ifndef QT_NO_QOBJECT
diff --git a/src/corelib/serialization/qtextstream.h b/src/corelib/serialization/qtextstream.h
index 1d86a18b9c..4efa84f1f1 100644
--- a/src/corelib/serialization/qtextstream.h
+++ b/src/corelib/serialization/qtextstream.h
@@ -213,8 +213,8 @@ typedef void (QTextStream::*QTSMFC)(QChar); // manipulator w/QChar argument
 class Q_CORE_EXPORT QTextStreamManipulator
 {
 public:
-    Q_DECL_CONSTEXPR QTextStreamManipulator(QTSMFI m, int a) Q_DECL_NOTHROW : mf(m), mc(nullptr), arg(a), ch() {}
-    Q_DECL_CONSTEXPR QTextStreamManipulator(QTSMFC m, QChar c) Q_DECL_NOTHROW : mf(nullptr), mc(m), arg(-1), ch(c) {}
+    Q_DECL_CONSTEXPR QTextStreamManipulator(QTSMFI m, int a) noexcept : mf(m), mc(nullptr), arg(a), ch() {}
+    Q_DECL_CONSTEXPR QTextStreamManipulator(QTSMFC m, QChar c) noexcept : mf(nullptr), mc(m), arg(-1), ch(c) {}
     void exec(QTextStream &s) { if (mf) { (s.*mf)(arg); } else { (s.*mc)(ch); } }
 
 private:
@@ -233,6 +233,13 @@ inline QTextStream &operator<<(QTextStream &s, QTextStreamFunction f)
 inline QTextStream &operator<<(QTextStream &s, QTextStreamManipulator m)
 { m.exec(s); return s; }
 
+#if defined(Q_QDOC) || QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+namespace Qt {
+#else
+// This namespace only exists for 'using namespace' declarations.
+namespace QTextStreamFunctions {
+#endif
+
 Q_CORE_EXPORT QTextStream &bin(QTextStream &s);
 Q_CORE_EXPORT QTextStream &oct(QTextStream &s);
 Q_CORE_EXPORT QTextStream &dec(QTextStream &s);
@@ -265,6 +272,18 @@ Q_CORE_EXPORT QTextStream &bom(QTextStream &s);
 
 Q_CORE_EXPORT QTextStream &ws(QTextStream &s);
 
+} // namespace QTextStreamFunctions
+
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0) && !defined(Q_QDOC)
+namespace Qt {
+using namespace QTextStreamFunctions;
+}
+
+// We use 'using namespace' as that doesn't cause
+// conflicting definitions compiler errors.
+using namespace QTextStreamFunctions;
+#endif // QT_VERSION < QT_VERSION_CHECK(6, 0, 0) && !defined(Q_QDOC)
+
 inline QTextStreamManipulator qSetFieldWidth(int width)
 {
     QTSMFI func = &QTextStream::setFieldWidth;
diff --git a/src/corelib/serialization/qxmlstream.cpp b/src/corelib/serialization/qxmlstream.cpp
index 0170be7602..27a5137fc9 100644
--- a/src/corelib/serialization/qxmlstream.cpp
+++ b/src/corelib/serialization/qxmlstream.cpp
@@ -58,9 +58,9 @@
 // case for most bootstrapped applications.
 #define Q_DECLARE_TR_FUNCTIONS(context) \
 public: \
-    static inline QString tr(const char *sourceText, const char *comment = 0) \
+    static inline QString tr(const char *sourceText, const char *comment = nullptr) \
         { Q_UNUSED(comment); return QString::fromLatin1(sourceText); } \
-    static inline QString trUtf8(const char *sourceText, const char *comment = 0) \
+    static inline QString trUtf8(const char *sourceText, const char *comment = nullptr) \
         { Q_UNUSED(comment); return QString::fromLatin1(sourceText); } \
     static inline QString tr(const char *sourceText, const char*, int) \
         { return QString::fromLatin1(sourceText); } \
@@ -548,7 +548,7 @@ void QXmlStreamReader::clear()
     if (d->device) {
         if (d->deleteDevice)
             delete d->device;
-        d->device = 0;
+        d->device = nullptr;
     }
 }
 
@@ -792,16 +792,16 @@ QXmlStreamPrivateTagStack::QXmlStreamPrivateTagStack()
 QXmlStreamReaderPrivate::QXmlStreamReaderPrivate(QXmlStreamReader *q)
     :q_ptr(q)
 {
-    device = 0;
+    device = nullptr;
     deleteDevice = false;
 #if QT_CONFIG(textcodec)
-    decoder = 0;
+    decoder = nullptr;
 #endif
     stack_size = 64;
-    sym_stack = 0;
-    state_stack = 0;
+    sym_stack = nullptr;
+    state_stack = nullptr;
     reallocateStack();
-    entityResolver = 0;
+    entityResolver = nullptr;
     init();
 #define ADD_PREDEFINED(n, v) \
     do { \
@@ -843,11 +843,11 @@ void QXmlStreamReaderPrivate::init()
 #if QT_CONFIG(textcodec)
     codec = QTextCodec::codecForMib(106); // utf8
     delete decoder;
-    decoder = 0;
+    decoder = nullptr;
 #endif
     attributeStack.clear();
     attributeStack.reserve(16);
-    entityParser = 0;
+    entityParser = nullptr;
     hasCheckedStartDocument = false;
     normalizeLiterals = false;
     hasSeenTag = false;
@@ -1423,7 +1423,7 @@ inline int QXmlStreamReaderPrivate::fastScanNMTOKEN()
     int n = 0;
     uint c;
     while ((c = getChar()) != StreamEOF) {
-        if (fastDetermineNameChar(c) == NotName) {
+        if (fastDetermineNameChar(QChar(c)) == NotName) {
             putChar(c);
             return n;
         } else {
@@ -2285,12 +2285,14 @@ QXmlStreamAttribute::QXmlStreamAttribute()
     m_isDefault = false;
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 /*!
   Destructs an attribute.
  */
 QXmlStreamAttribute::~QXmlStreamAttribute()
 {
 }
+#endif
 
 /*!  Constructs an attribute in the namespace described with \a
   namespaceUri with \a name and value \a value.
@@ -2366,6 +2368,7 @@ QXmlStreamAttribute::QXmlStreamAttribute(const QString &qualifiedName, const QSt
  */
 
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 /*!
   Creates a copy of \a other.
  */
@@ -2386,7 +2389,7 @@ QXmlStreamAttribute& QXmlStreamAttribute::operator=(const QXmlStreamAttribute &o
     m_isDefault = other.m_isDefault;
     return *this;
 }
-
+#endif
 
 /*!
     \class QXmlStreamAttributes
@@ -2442,6 +2445,8 @@ QXmlStreamAttribute& QXmlStreamAttribute::operator=(const QXmlStreamAttribute &o
 QXmlStreamNotationDeclaration::QXmlStreamNotationDeclaration()
 {
 }
+
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 /*!
   Creates a copy of \a other.
  */
@@ -2467,6 +2472,7 @@ Destructs this notation declaration.
 QXmlStreamNotationDeclaration::~QXmlStreamNotationDeclaration()
 {
 }
+#endif
 
 /*! \fn QStringRef QXmlStreamNotationDeclaration::name() const
 
@@ -2539,6 +2545,7 @@ QXmlStreamNamespaceDeclaration::QXmlStreamNamespaceDeclaration(const QString &pr
     m_namespaceUri = namespaceUri;
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 /*!
   Creates a copy of \a other.
  */
@@ -2562,6 +2569,7 @@ Destructs this namespace declaration.
 QXmlStreamNamespaceDeclaration::~QXmlStreamNamespaceDeclaration()
 {
 }
+#endif
 
 /*! \fn QStringRef QXmlStreamNamespaceDeclaration::prefix() const
 
@@ -2609,6 +2617,7 @@ QXmlStreamEntityDeclaration::QXmlStreamEntityDeclaration()
 {
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 /*!
   Creates a copy of \a other.
  */
@@ -2636,6 +2645,7 @@ QXmlStreamEntityDeclaration& QXmlStreamEntityDeclaration::operator=(const QXmlSt
 QXmlStreamEntityDeclaration::~QXmlStreamEntityDeclaration()
 {
 }
+#endif
 
 /*! \fn QXmlStreamStringRef::swap(QXmlStreamStringRef &other)
     \since 5.6
@@ -3014,8 +3024,8 @@ QXmlStreamWriterPrivate::QXmlStreamWriterPrivate(QXmlStreamWriter *q)
     :autoFormattingIndent(4, ' ')
 {
     q_ptr = q;
-    device = 0;
-    stringDevice = 0;
+    device = nullptr;
+    stringDevice = nullptr;
     deleteDevice = false;
 #if QT_CONFIG(textcodec)
     codec = QTextCodec::codecForMib(106); // utf8
@@ -3305,7 +3315,7 @@ void QXmlStreamWriter::setDevice(QIODevice *device)
     Q_D(QXmlStreamWriter);
     if (device == d->device)
         return;
-    d->stringDevice = 0;
+    d->stringDevice = nullptr;
     if (d->deleteDevice) {
         delete d->device;
         d->deleteDevice = false;
diff --git a/src/corelib/serialization/qxmlstream.g b/src/corelib/serialization/qxmlstream.g
index e6328a11ac..12ecc9bdb2 100644
--- a/src/corelib/serialization/qxmlstream.g
+++ b/src/corelib/serialization/qxmlstream.g
@@ -506,7 +506,7 @@ public:
     int fastScanLiteralContent();
     int fastScanSpace();
     int fastScanContentCharList();
-    int fastScanName(int *prefix = 0);
+    int fastScanName(int *prefix = nullptr);
     inline int fastScanNMTOKEN();
 
 
diff --git a/src/corelib/serialization/qxmlstream.h b/src/corelib/serialization/qxmlstream.h
index d30c6bc01f..7d0aa64570 100644
--- a/src/corelib/serialization/qxmlstream.h
+++ b/src/corelib/serialization/qxmlstream.h
@@ -59,19 +59,15 @@ public:
     inline QXmlStreamStringRef(const QStringRef &aString)
         :m_string(aString.string()?*aString.string():QString()), m_position(aString.position()), m_size(aString.size()){}
     QXmlStreamStringRef(const QString &aString) : m_string(aString), m_position(0), m_size(m_string.size()) {}
-#ifdef Q_COMPILER_RVALUE_REFS
-    QXmlStreamStringRef(QString &&aString) Q_DECL_NOTHROW : m_string(std::move(aString)), m_position(0), m_size(m_string.size()) {}
-#endif
+    QXmlStreamStringRef(QString &&aString) noexcept : m_string(std::move(aString)), m_position(0), m_size(m_string.size()) {}
 
 #if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     QXmlStreamStringRef(const QXmlStreamStringRef &other) // = default
         : m_string(other.m_string), m_position(other.m_position), m_size(other.m_size) {}
-#ifdef Q_COMPILER_RVALUE_REFS
-    QXmlStreamStringRef(QXmlStreamStringRef &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamStringRef(QXmlStreamStringRef &&other) noexcept // = default
         : m_string(std::move(other.m_string)), m_position(other.m_position), m_size(other.m_size) {}
-    QXmlStreamStringRef &operator=(QXmlStreamStringRef &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamStringRef &operator=(QXmlStreamStringRef &&other) noexcept // = default
     { swap(other); return *this; }
-#endif
     QXmlStreamStringRef &operator=(const QXmlStreamStringRef &other) // = default
     { m_string = other.m_string; m_position = other.m_position; m_size = other.m_size; return *this; }
     inline ~QXmlStreamStringRef() {} // ### this prevents (or deprecates) all the move/copy special member functions,
@@ -79,7 +75,7 @@ public:
                                      // ### Qt 5, since that would change the way its passed to functions. In Qt 6, remove all.
 #endif // Qt < 6.0
 
-    void swap(QXmlStreamStringRef &other) Q_DECL_NOTHROW
+    void swap(QXmlStreamStringRef &other) noexcept
     {
         qSwap(m_string, other.m_string);
         qSwap(m_position, other.m_position);
@@ -108,11 +104,10 @@ class Q_CORE_EXPORT QXmlStreamAttribute {
 public:
     QXmlStreamAttribute();
     QXmlStreamAttribute(const QString &qualifiedName, const QString &value);
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QXmlStreamAttribute(const QString &namespaceUri, const QString &name, const QString &value);
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QXmlStreamAttribute(const QXmlStreamAttribute &);
-#ifdef Q_COMPILER_RVALUE_REFS
-    QXmlStreamAttribute(QXmlStreamAttribute &&other) Q_DECL_NOTHROW // = default;
+    QXmlStreamAttribute(QXmlStreamAttribute &&other) noexcept // = default;
         : m_name(std::move(other.m_name)),
           m_namespaceUri(std::move(other.m_namespaceUri)),
           m_qualifiedName(std::move(other.m_qualifiedName)),
@@ -122,7 +117,7 @@ public:
     {
         other.reserved = nullptr;
     }
-    QXmlStreamAttribute &operator=(QXmlStreamAttribute &&other) Q_DECL_NOTHROW // = default;
+    QXmlStreamAttribute &operator=(QXmlStreamAttribute &&other) noexcept // = default;
     {
         m_name = std::move(other.m_name);
         m_namespaceUri = std::move(other.m_namespaceUri);
@@ -132,7 +127,6 @@ public:
         m_isDefault = other.m_isDefault;
         return *this;
     }
-#endif
     QXmlStreamAttribute& operator=(const QXmlStreamAttribute &);
     ~QXmlStreamAttribute();
 #endif // < Qt 6
@@ -197,23 +191,23 @@ class Q_CORE_EXPORT QXmlStreamNamespaceDeclaration {
     friend class QXmlStreamReaderPrivate;
 public:
     QXmlStreamNamespaceDeclaration();
+    QXmlStreamNamespaceDeclaration(const QString &prefix, const QString &namespaceUri);
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QXmlStreamNamespaceDeclaration(const QXmlStreamNamespaceDeclaration &);
-    QXmlStreamNamespaceDeclaration(QXmlStreamNamespaceDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamNamespaceDeclaration(QXmlStreamNamespaceDeclaration &&other) noexcept // = default
         : m_prefix(std::move(other.m_prefix)),
           m_namespaceUri(std::move(other.m_namespaceUri)),
           reserved(other.reserved)
     {
         other.reserved = nullptr;
     }
-    QXmlStreamNamespaceDeclaration &operator=(QXmlStreamNamespaceDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamNamespaceDeclaration &operator=(QXmlStreamNamespaceDeclaration &&other) noexcept // = default
     {
         m_prefix = std::move(other.m_prefix);
         m_namespaceUri = std::move(other.m_namespaceUri);
         qSwap(reserved, other.reserved);
         return *this;
     }
-    QXmlStreamNamespaceDeclaration(const QString &prefix, const QString &namespaceUri);
     ~QXmlStreamNamespaceDeclaration();
     QXmlStreamNamespaceDeclaration& operator=(const QXmlStreamNamespaceDeclaration &);
 #endif // < Qt 6
@@ -242,7 +236,7 @@ public:
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     ~QXmlStreamNotationDeclaration();
     QXmlStreamNotationDeclaration(const QXmlStreamNotationDeclaration &);
-    QXmlStreamNotationDeclaration(QXmlStreamNotationDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamNotationDeclaration(QXmlStreamNotationDeclaration &&other) noexcept // = default
         : m_name(std::move(other.m_name)),
           m_systemId(std::move(other.m_systemId)),
           m_publicId(std::move(other.m_publicId)),
@@ -251,7 +245,7 @@ public:
         other.reserved = nullptr;
     }
     QXmlStreamNotationDeclaration& operator=(const QXmlStreamNotationDeclaration &);
-    QXmlStreamNotationDeclaration &operator=(QXmlStreamNotationDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamNotationDeclaration &operator=(QXmlStreamNotationDeclaration &&other) noexcept // = default
     {
         m_name = std::move(other.m_name);
         m_systemId = std::move(other.m_systemId);
@@ -287,7 +281,7 @@ public:
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     ~QXmlStreamEntityDeclaration();
     QXmlStreamEntityDeclaration(const QXmlStreamEntityDeclaration &);
-    QXmlStreamEntityDeclaration(QXmlStreamEntityDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamEntityDeclaration(QXmlStreamEntityDeclaration &&other) noexcept // = default
         : m_name(std::move(other.m_name)),
           m_notationName(std::move(other.m_notationName)),
           m_systemId(std::move(other.m_systemId)),
@@ -298,7 +292,7 @@ public:
         other.reserved = nullptr;
     }
     QXmlStreamEntityDeclaration& operator=(const QXmlStreamEntityDeclaration &);
-    QXmlStreamEntityDeclaration &operator=(QXmlStreamEntityDeclaration &&other) Q_DECL_NOTHROW // = default
+    QXmlStreamEntityDeclaration &operator=(QXmlStreamEntityDeclaration &&other) noexcept // = default
     {
         m_name = std::move(other.m_name);
         m_notationName = std::move(other.m_notationName);
diff --git a/src/corelib/serialization/qxmlstream_p.h b/src/corelib/serialization/qxmlstream_p.h
index 61f501f81b..cde66a48a3 100644
--- a/src/corelib/serialization/qxmlstream_p.h
+++ b/src/corelib/serialization/qxmlstream_p.h
@@ -162,12 +162,12 @@ public:
 
 
 const char *const QXmlStreamReader_Table::spell [] = {
-  "end of file", 0, " ", "<", ">", "&", "#", "\'", "\"", "[", 
+  "end of file", nullptr, " ", "<", ">", "&", "#", "\'", "\"", "[",
   "]", "(", ")", "|", "=", "%", "/", ":", ";", ",", 
   "-", "+", "*", ".", "?", "!", "[a-zA-Z]", "[0-9]", "[CDATA[", "DOCTYPE", 
   "ELEMENT", "ATTLIST", "ENTITY", "NOTATION", "SYSTEM", "PUBLIC", "NDATA", "REQUIRED", "IMPLIED", "FIXED", 
-  "EMPTY", "ANY", "PCDATA", 0, 0, 0, 0, "CDATA", "ID", "IDREF", 
-  "IDREFS", "ENTITIES", "NMTOKEN", "NMTOKENS", "<?xml", "version", 0};
+  "EMPTY", "ANY", "PCDATA", nullptr, nullptr, nullptr, nullptr, "CDATA", "ID", "IDREF",
+  "IDREFS", "ENTITIES", "NMTOKEN", "NMTOKENS", "<?xml", "version", nullptr};
 
 const short QXmlStreamReader_Table::lhs [] = {
   57, 57, 59, 59, 59, 59, 59, 59, 59, 59, 
@@ -645,7 +645,7 @@ template <typename T> class QXmlStreamSimpleStack {
     T *data;
     int tos, cap;
 public:
-    inline QXmlStreamSimpleStack():data(0), tos(-1), cap(0){}
+    inline QXmlStreamSimpleStack():data(nullptr), tos(-1), cap(0){}
     inline ~QXmlStreamSimpleStack(){ if (data) free(data); }
 
     inline void reserve(int extraCapacity) {
@@ -995,7 +995,7 @@ public:
     int fastScanLiteralContent();
     int fastScanSpace();
     int fastScanContentCharList();
-    int fastScanName(int *prefix = 0);
+    int fastScanName(int *prefix = nullptr);
     inline int fastScanNMTOKEN();