QMetaType: add more static-less API

In prevision to Qt6 which is going to discourrage the use of the integer id,
add some missing API to the staticless QMetaType API:

 - Add a way to construct a QMetaType from a type without calling qMetaTypeId:
   QMetaType::fromType<T>()
 - Add equality operators
 - Add a QMetaType::name() function
 - Add a default constructor (by adding a default parameter to the existing ctor)

Change-Id: I95487c1c31bdf0d773717daa9d5452cbced30673
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 55 insertions, 2 deletions

diff --git a/src/corelib/kernel/qmetatype.cpp b/src/corelib/kernel/qmetatype.cpp
index 3f0b8900e4..af9a2e0dd2 100644
--- a/src/corelib/kernel/qmetatype.cpp
+++ b/src/corelib/kernel/qmetatype.cpp
@@ -506,6 +506,31 @@ struct DefinedTypesFilter {
     Destructs this object.
 */
 
+/*!
+    \fn template<typename T> QMetaType QMetaType::fromType()
+    \since 5.15
+
+    Returns the QMetaType corresponding to the type in the template parameter.
+*/
+
+/*! \fn bool operator==(const QMetaType &a, const QMetaType &b)
+    \since 5.15
+    \relates QMetaType
+    \overload
+
+    Returns \c true if the QMetaType \a a represents the same type
+    as the QMetaType \a b, otherwise returns \c false.
+*/
+
+/*! \fn bool operator!=(const QMetaType &a, const QMetaType &c)
+    \since 5.15
+    \relates QMetaType
+    \overload
+
+    Returns \c true if the QMetaType \a a represents a difference type
+    than the QMetaType \a b, otherwise returns \c false.
+*/
+
 #define QT_ADD_STATIC_METATYPE(MetaTypeName, MetaTypeId, RealName) \
     { #RealName, sizeof(#RealName) - 1, MetaTypeId },
 
@@ -930,7 +955,7 @@ constexpr MetaTypeOffsets<QtPrivate::Indexes<QMetaType::HighestInternalId + 1>::
     pointer if no matching type was found. The returned pointer must not be
     deleted.
 
-    \sa type(), isRegistered(), Type
+    \sa type(), isRegistered(), Type, name()
 */
 const char *QMetaType::typeName(int typeId)
 {
@@ -950,6 +975,20 @@ const char *QMetaType::typeName(int typeId)
 #undef QT_METATYPE_TYPEID_TYPENAME_CONVERTER
 }
 
+/*!
+    \since 5.15
+
+    Returns the type name associated with this QMetaType, or a null
+    pointer if no matching type was found. The returned pointer must not be
+    deleted.
+
+    \sa typeName()
+*/
+QByteArray QMetaType::name() const
+{
+    return QMetaType::typeName(m_typeId);
+}
+
 /*
     Similar to QMetaType::type(), but only looks in the static set of types.
 */
@@ -2214,6 +2253,8 @@ QMetaType QMetaType::typeInfo(const int type)
      \since 5.0
 
      Constructs a QMetaType object that contains all information about type \a typeId.
+
+     \note: The default parameter was added in Qt 5.15
 */
 QMetaType::QMetaType(const int typeId)
     : m_typeId(typeId)
diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 240828bc9a..825f767425 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -572,7 +572,7 @@ public:
     static bool load(QDataStream &stream, int type, void *data);
 #endif
 
-    explicit QMetaType(const int type); // ### Qt6: drop const
+    explicit QMetaType(const int type = QMetaType::UnknownType); // ### Qt6: drop const
     inline ~QMetaType();
 
     inline bool isValid() const;
@@ -581,12 +581,24 @@ public:
     inline int sizeOf() const;
     inline TypeFlags flags() const;
     inline const QMetaObject *metaObject() const;
+    QT_PREPEND_NAMESPACE(QByteArray) name() const;
 
     inline void *create(const void *copy = nullptr) const;
     inline void destroy(void *data) const;
     inline void *construct(void *where, const void *copy = nullptr) const;
     inline void destruct(void *data) const;
 
+    template<typename T>
+    static QMetaType fromType()
+    { return QMetaType(qMetaTypeId<T>()); }
+
+    friend bool operator==(const QMetaType &a, const QMetaType &b)
+    { return a.m_typeId == b.m_typeId; }
+
+    friend bool operator!=(const QMetaType &a, const QMetaType &b)
+    { return a.m_typeId != b.m_typeId; }
+
+
 public:
     template<typename T>
     static bool registerComparators()