Introduce QMetaObject::metaType

This function returns the metatype corresponding to the metaobject, or
an invalid metatype for namespaces.

This works as follows: First we increment the metaobject revision for
new metaobjects. Metaobjects with older revisions are handled by doing a
lookup by name. That fallback is also used for dynamic metaobjects (from
QtDBUS and those created by QMetaObjectBuilder).
For new metaobjects, we store the metatype in its metatype array, behind
the property metatypes. This avoids any changes to the property and
method metatype extraction logic: For properties, the metatype access
does not change, as the new metatype is after their metatypes. For
method metatypes, we already have an indirection layer (using offsets),
so by adjusting those offsets by one, the same logic keeps working.

To distinguish between namespaces and dynamic metaobjects, namespaces
store the metatypeinterface pointer for void in the metatype array,
whereas dynamic metaobjects store a nullptr.

One nice additional benefit is that this simplifies the generator logic
in moc, as the metatype array is now never empty.

Task-number: QTBUG-92077
Change-Id: Id3f920f28553f12032a71a1a87dad29e5374dbe7
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

4 files changed, 37 insertions, 3 deletions

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index 650ea60617..a574bec179 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -384,6 +384,33 @@ QString QMetaObject::tr(const char *s, const char *c, int n) const
 {
     return QCoreApplication::translate(objectClassName(this), s, c, n);
 }
+
+/*!
+    \since 6.2
+    Returns the metatype corresponding to this metaobject.
+    If the metaobject originates from a namespace, an invalid metatype is returned.
+ */
+QMetaType QMetaObject::metaType() const
+{
+
+    const QMetaObjectPrivate *d = priv(this->d.data);
+    if (d->revision < 10) {
+        // before revision 10, we did not store the metatype in the metatype array
+        return QMetaType::fromName(className());
+    } else {
+        /* in the metatype array, we store
+         idx: 0                      propertyCount - 1           propertyCount
+         data:QMetaType(prop0), ..., QMetaType(propPropCount-1), QMetaType(class),...
+         */
+        auto iface = this->d.metaTypes[d->propertyCount];
+        if (iface == QtPrivate::qMetaTypeInterfaceForType<void>())
+            return QMetaType(); // return invalid meta-type for namespaces
+        if (iface)
+            return QMetaType(iface);
+        else // in case of a dynamic metaobject, we might have no metatype stored
+            return QMetaType::fromName(className()); // try lookup by name in that case
+    }
+}
 #endif // QT_NO_TRANSLATION
 
 /*!
diff --git a/src/corelib/kernel/qmetaobject_p.h b/src/corelib/kernel/qmetaobject_p.h
index dbd82ba27b..c25735cb86 100644
--- a/src/corelib/kernel/qmetaobject_p.h
+++ b/src/corelib/kernel/qmetaobject_p.h
@@ -172,7 +172,7 @@ struct QMetaObjectPrivate
     // revision 7 is Qt 5.0 everything lower is not supported
     // revision 8 is Qt 5.12: It adds the enum name to QMetaEnum
     // revision 9 is Qt 6.0: It adds the metatype of properties and methods
-    enum { OutputRevision = 9 }; // Used by moc, qmetaobjectbuilder and qdbus
+    enum { OutputRevision = 10 }; // Used by moc, qmetaobjectbuilder and qdbus
     enum { IntsPerMethod = QMetaMethod::Data::Size };
     enum { IntsPerEnum = QMetaEnum::Data::Size };
     enum { IntsPerProperty = QMetaProperty::Data::Size };
diff --git a/src/corelib/kernel/qmetaobjectbuilder.cpp b/src/corelib/kernel/qmetaobjectbuilder.cpp
index 3ee7d17545..8c55bdb3ae 100644
--- a/src/corelib/kernel/qmetaobjectbuilder.cpp
+++ b/src/corelib/kernel/qmetaobjectbuilder.cpp
@@ -1203,7 +1203,7 @@ static int buildMetaObject(QMetaObjectBuilderPrivate *d, char *buf,
             - int(d->methods.size())       // return "parameters" don't have names
             - int(d->constructors.size()); // "this" parameters don't have names
     if constexpr (mode == Construct) {
-        static_assert(QMetaObjectPrivate::OutputRevision == 9, "QMetaObjectBuilder should generate the same version as moc");
+        static_assert(QMetaObjectPrivate::OutputRevision == 10, "QMetaObjectBuilder should generate the same version as moc");
         pmeta->revision = QMetaObjectPrivate::OutputRevision;
         pmeta->flags = d->flags;
         pmeta->className = 0;   // Class name is always the first string.
@@ -1281,7 +1281,8 @@ static int buildMetaObject(QMetaObjectBuilderPrivate *d, char *buf,
 
     // Output the methods in the class.
     Q_ASSERT(!buf || dataIndex == pmeta->methodData);
-    int parameterMetaTypesIndex = int(d->properties.size());
+    // + 1 for metatype of this metaobject
+    int parameterMetaTypesIndex = int(d->properties.size()) + 1;
     for (const auto &method : d->methods) {
         [[maybe_unused]] int name = strings.enter(method.name());
         int argc = method.parameterCount();
@@ -1448,6 +1449,10 @@ static int buildMetaObject(QMetaObjectBuilderPrivate *d, char *buf,
                 *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
                 types++;
             }
+            // add metatype interface for this metaobject - must be null
+            // as we can't know our metatype
+            *types = nullptr;
+            types++;
             for (const auto &method: d->methods) {
                 QMetaType mt(QMetaType::fromName(method.returnType).id());
                 *types = reinterpret_cast<QtPrivate::QMetaTypeInterface *&>(mt);
diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index 5ade222ac5..00a6b62eab 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -173,6 +173,8 @@ struct Q_CORE_EXPORT QMetaObject
     QString tr(const char *s, const char *c, int n = -1) const;
 #endif // QT_NO_TRANSLATION
 
+    QMetaType metaType() const;
+
     int methodOffset() const;
     int enumeratorOffset() const;
     int propertyOffset() const;