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>

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)

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()

tests/auto/corelib/kernel/qmetatype/tst_qmetatype.cpp

@@ -125,6 +125,7 @@ private slots:
     void compareCustomEqualOnlyType();
     void customDebugStream();
     void unknownType();
+    void fromType();
 };
 
 struct BaseGenericType
@@ -482,6 +483,7 @@ void tst_QMetaType::id()
 {
     QCOMPARE(QMetaType(QMetaType::QString).id(), QMetaType::QString);
     QCOMPARE(QMetaType(::qMetaTypeId<TestSpace::Foo>()).id(), ::qMetaTypeId<TestSpace::Foo>());
+    QCOMPARE(QMetaType::fromType<TestSpace::Foo>().id(), ::qMetaTypeId<TestSpace::Foo>());
 }
 
 void tst_QMetaType::qMetaTypeId()
@@ -600,6 +602,12 @@ void tst_QMetaType::typeName()
     QCOMPARE(name, aTypeName);
     QCOMPARE(name.toLatin1(), QMetaObject::normalizedType(name.toLatin1().constData()));
     QCOMPARE(rawname == nullptr, aTypeName.isNull());
+
+    QMetaType mt(aType);
+    if (mt.isValid()) { // Gui type are not valid
+        QCOMPARE(QString::fromLatin1(QMetaType(aType).name()), aTypeName);
+    }
+
 }
 
 void tst_QMetaType::type_data()
@@ -1728,6 +1736,7 @@ void tst_QMetaType::automaticTemplateRegistration()
             const int type = QMetaType::type(tn); \
             const int expectedType = ::qMetaTypeId<CONTAINER< __VA_ARGS__ > >(); \
             QCOMPARE(type, expectedType); \
+            QCOMPARE((QMetaType::fromType<CONTAINER< __VA_ARGS__ >>().id()), expectedType); \
         }
 
     #define FOR_EACH_1ARG_TEMPLATE_TYPE(F, TYPE) \
@@ -2572,6 +2581,26 @@ void tst_QMetaType::unknownType()
     invalid.construct(&buffer);
     QCOMPARE(buffer, 0xBAD);
 }
+
+void tst_QMetaType::fromType()
+{
+    #define FROMTYPE_CHECK(MetaTypeName, MetaTypeId, RealType) \
+        QCOMPARE(QMetaType::fromType<RealType>(), QMetaType(MetaTypeId)); \
+        QVERIFY(QMetaType::fromType<RealType>() == QMetaType(MetaTypeId)); \
+        QVERIFY(!(QMetaType::fromType<RealType>() != QMetaType(MetaTypeId))); \
+        QCOMPARE(QMetaType::fromType<RealType>().id(), MetaTypeId);
+
+    FOR_EACH_CORE_METATYPE(FROMTYPE_CHECK)
+
+    QVERIFY(QMetaType::fromType<QString>() != QMetaType());
+    QCOMPARE(QMetaType(), QMetaType());
+    QCOMPARE(QMetaType(QMetaType::UnknownType), QMetaType());
+
+    FROMTYPE_CHECK(_, ::qMetaTypeId<Whity<int>>(), Whity<int>)
+    #undef FROMTYPE_CHECK
+}
+
+
 // Compile-time test, it should be possible to register function pointer types
 class Undefined;