Add QUntypedBindable::metaType function

This enables checking the metaType of a QUntypedBindable in the public
interface.
In addition, work around an oversight that can only be fully addressed
in Qt 7: The metatype function pointer does not take a
QUntypedPropertyData * parameter. However, we need this functionality
for an efficient QBindable proxy implementation in declarative (which is
needed to implement interceptors there). To work-aronud this in Qt 6,
reuse the value getter and turn it into a metatype getter if the value
pointer is flagged.

Change-Id: Ia3cce08ea761fce57bce59e02212525b996f2fee
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

2 files changed, 31 insertions, 4 deletions

diff --git a/src/corelib/kernel/qproperty.cpp b/src/corelib/kernel/qproperty.cpp
index 607048d94b..a1b2f83c5b 100644
--- a/src/corelib/kernel/qproperty.cpp
+++ b/src/corelib/kernel/qproperty.cpp
@@ -1006,6 +1006,16 @@ QString QPropertyBindingError::description() const
 */
 
 /*!
+  \fn QMetaType QUntypedBindable::metaType() const
+  \since 6.2
+
+  Returns the metatype of the property from which the QUntypedBindable was created.
+  If the bindable is invalid, an invalid metatype will be returned.
+
+  \sa isValid(), QUntypedPropertyBinding::valueMetaType()
+*/
+
+/*!
   \class QBindable
   \inmodule QtCore
   \brief QBindable is a wrapper class around binding-enabled properties. It allows type-safe
diff --git a/src/corelib/kernel/qproperty.h b/src/corelib/kernel/qproperty.h
index 9be10c0a31..7924049698 100644
--- a/src/corelib/kernel/qproperty.h
+++ b/src/corelib/kernel/qproperty.h
@@ -484,6 +484,8 @@ struct QBindableInterface
     MakeBinding makeBinding;
     SetObserver setObserver;
     GetMetaType metaType;
+
+    static constexpr quintptr MetaTypeAccessorFlag = 0x1;
 };
 
 template<typename Property, typename = void>
@@ -650,9 +652,9 @@ public:
 #endif
             return false;
         }
-        if (!binding.isNull() && binding.valueMetaType() != iface->metaType()) {
+        if (!binding.isNull() && binding.valueMetaType() != metaType()) {
 #ifndef QT_NO_DEBUG
-            QtPrivate::BindableWarnings::printMetaTypeMismatch(iface->metaType(), binding.valueMetaType());
+            QtPrivate::BindableWarnings::printMetaTypeMismatch(metaType(), binding.valueMetaType());
 #endif
             return false;
         }
@@ -664,6 +666,21 @@ public:
         return !binding().isNull();
     }
 
+    QMetaType metaType() const
+    {
+        if (!(iface && data))
+            return QMetaType();
+        if (iface->metaType)
+            return iface->metaType();
+        // ### Qt 7: Change the metatype function to take data as its argument
+        // special casing for QML's proxy bindable: allow multiplexing in the getter
+        // function to retrieve the metatype from data
+        Q_ASSERT(iface->getter);
+        QMetaType result;
+        iface->getter(data, reinterpret_cast<void *>(quintptr(&result) | QtPrivate::QBindableInterface::MetaTypeAccessorFlag));
+        return result;
+    }
+
 };
 
 template<typename T>
@@ -678,7 +695,7 @@ public:
     using QUntypedBindable::QUntypedBindable;
     explicit QBindable(const QUntypedBindable &b) : QUntypedBindable(b)
     {
-        if (iface && iface->metaType() != QMetaType::fromType<T>()) {
+        if (iface && metaType() != QMetaType::fromType<T>()) {
             data = nullptr;
             iface = nullptr;
         }
@@ -701,7 +718,7 @@ public:
     using QUntypedBindable::setBinding;
     QPropertyBinding<T> setBinding(const QPropertyBinding<T> &binding)
     {
-        Q_ASSERT(!iface || binding.isNull() || binding.valueMetaType() == iface->metaType());
+        Q_ASSERT(!iface || binding.isNull() || binding.valueMetaType() == metaType());
 
         if (iface && iface->setBinding)
             return static_cast<QPropertyBinding<T> &&>(iface->setBinding(data, binding));