Introduce QMetaType::PointerToGadget flag for pointers to gadgets

A Q_GADGET class can be used both as a value class and a pointer, but
right now QMetaType::IsGadget is only set for value types. This change
introduces PointerToGadget metatype flag which is set for pointers.

This allow for better handling of gadgets in code as well as
disambiguating between value types and pointers to value types.

Change-Id: Id3bd9e18a8eec7ca1cc6b1c25ed03cdc8c0a75a1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 46 insertions, 1 deletions

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 3674ebc1a1..5e2e746bbc 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -462,7 +462,8 @@ public:
         WeakPointerToQObject = 0x40,
         TrackingPointerToQObject = 0x80,
         WasDeclaredAsMetaType = 0x100,
-        IsGadget = 0x200
+        IsGadget = 0x200,
+        PointerToGadget = 0x400
     };
     Q_DECLARE_FLAGS(TypeFlags, TypeFlag)
 
@@ -1388,6 +1389,19 @@ namespace QtPrivate
         enum { Value =  sizeof(checkType(&T::qt_check_for_QGADGET_macro)) == sizeof(void *) };
     };
 
+    template<typename T, typename Enable = void>
+    struct IsPointerToGadgetHelper { enum { Value = false }; };
+
+    template<typename T>
+    struct IsPointerToGadgetHelper<T*, typename T::QtGadgetHelper>
+    {
+        using BaseType = T;
+        template <typename X>
+        static char checkType(void (X::*)());
+        static void *checkType(void (T::*)());
+        enum { Value =  sizeof(checkType(&T::qt_check_for_QGADGET_macro)) == sizeof(void *) };
+    };
+
 
     template<typename T> char qt_getEnumMetaObject(const T&);
 
@@ -1423,6 +1437,11 @@ namespace QtPrivate
         static inline const QMetaObject *value() { return &T::staticMetaObject; }
     };
     template<typename T>
+    struct MetaObjectForType<T, typename QEnableIf<IsPointerToGadgetHelper<T>::Value>::Type>
+    {
+        static inline const QMetaObject *value() { return &IsPointerToGadgetHelper<T>::BaseType::staticMetaObject; }
+    };
+    template<typename T>
     struct MetaObjectForType<T, typename std::enable_if<IsQEnumHelper<T>::Value>::type >
     {
         static inline const QMetaObject *value() { return qt_getEnumMetaObject(T()); }
@@ -1578,6 +1597,7 @@ namespace QtPrivate
 template <typename T, int =
     QtPrivate::IsPointerToTypeDerivedFromQObject<T>::Value ? QMetaType::PointerToQObject :
     QtPrivate::IsGadgetHelper<T>::Value                    ? QMetaType::IsGadget :
+    QtPrivate::IsPointerToGadgetHelper<T>::Value           ? QMetaType::PointerToGadget :
     QtPrivate::IsQEnumHelper<T>::Value                     ? QMetaType::IsEnumeration : 0>
 struct QMetaTypeIdQObject
 {
@@ -1631,6 +1651,7 @@ namespace QtPrivate {
                      | (IsTrackingPointerToTypeDerivedFromQObject<T>::Value ? QMetaType::TrackingPointerToQObject : 0)
                      | (std::is_enum<T>::value ? QMetaType::IsEnumeration : 0)
                      | (IsGadgetHelper<T>::Value ? QMetaType::IsGadget : 0)
+                     | (IsPointerToGadgetHelper<T>::Value ? QMetaType::PointerToGadget : 0)
              };
     };
 
@@ -1798,6 +1819,30 @@ struct QMetaTypeIdQObject<T, QMetaType::IsGadget>
 };
 
 template <typename T>
+struct QMetaTypeIdQObject<T*, QMetaType::PointerToGadget>
+{
+    enum {
+        Defined = 1
+    };
+
+    static int qt_metatype_id()
+    {
+        static QBasicAtomicInt metatype_id = Q_BASIC_ATOMIC_INITIALIZER(0);
+        if (const int id = metatype_id.loadAcquire())
+            return id;
+        const char * const cName = T::staticMetaObject.className();
+        QByteArray typeName;
+        typeName.reserve(int(strlen(cName)) + 1);
+        typeName.append(cName).append('*');
+        const int newId = qRegisterNormalizedMetaType<T*>(
+            typeName,
+            reinterpret_cast<T**>(quintptr(-1)));
+        metatype_id.storeRelease(newId);
+        return newId;
+    }
+};
+
+template <typename T>
 struct QMetaTypeIdQObject<T, QMetaType::IsEnumeration>
 {
     enum {