From f6f7d22c6cb6a6e3b4ab280fc1b2ed534bbbde09 Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Tue, 1 Jun 2021 11:43:29 +0200
Subject: [PATCH] QMetaType: Avoid instantiating QMetaType in
 Q_DECLARE_METATYPE

Having a call to QMetaType::fromType in struct QMetaTypeId causes issues
if Q_DECLARE_TYPEINFO is used later, as it will already cause an
instantiation of QTypeInfo. Instead, use QtPrivate::typenameHelper to
obtain the name. We cannot use QMetaTypeForType::getName, as that would
cause similarissues with QMetaTypeId2. However, QMetaTypeId2 is only
used for builtin metatypes, which do not use Q_DECLARE_METATYPE. And
even if a user would use Q_DECLARE_METATYPE with them, the worst that
happens is a superfluous type normalization.

Fixes: QTBUG-94124
Change-Id: Ie4a993411214fd009a604de44306131c647095eb
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
---
 src/corelib/kernel/qmetatype.h | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index 30f31f54f60..5e53a970d42 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -1349,12 +1349,6 @@ struct QMetaTypeIdQObject<T, QMetaType::IsEnumeration>
     } QT_END_NAMESPACE                                                  \
     /**/
 
-template <typename T>
-int qRegisterMetatypeIndirection()
-{
-    return qRegisterNormalizedMetaType<T>(QMetaType::fromType<T>().name());
-}
-
 #ifndef Q_MOC_RUN
 #define Q_DECLARE_METATYPE(TYPE) Q_DECLARE_METATYPE_IMPL(TYPE)
 #define Q_DECLARE_METATYPE_IMPL(TYPE)                                   \
@@ -1368,11 +1362,12 @@ int qRegisterMetatypeIndirection()
                 static QBasicAtomicInt metatype_id = Q_BASIC_ATOMIC_INITIALIZER(0); \
                 if (const int id = metatype_id.loadAcquire())           \
                     return id;                                          \
-                const auto mt = QMetaType::fromType<TYPE>();            \
-                if (QByteArrayView(mt.name()) == (#TYPE)) {             \
-                    qRegisterMetatypeIndirection<TYPE>();               \
-                    metatype_id.storeRelease(mt.id());                  \
-                    return mt.id();                                     \
+                constexpr auto arr = QtPrivate::typenameHelper<TYPE>(); \
+                auto name = arr.data();                                 \
+                if (QByteArrayView(name) == (#TYPE)) {                  \
+                    const int id = qRegisterNormalizedMetaType<TYPE>(name); \
+                    metatype_id.storeRelease(id);                       \
+                    return id;                                          \
                 }                                                       \
                 const int newId = qRegisterMetaType< TYPE >(#TYPE);     \
                 metatype_id.storeRelease(newId);                        \
@@ -1576,7 +1571,6 @@ QT_END_NAMESPACE
 
 QT_FOR_EACH_STATIC_TYPE(Q_DECLARE_BUILTIN_METATYPE)
 
-Q_DECLARE_METATYPE(QtMetaTypePrivate::QPairVariantInterfaceImpl)
 
 QT_BEGIN_NAMESPACE
 
@@ -2465,4 +2459,6 @@ constexpr const QtPrivate::QMetaTypeInterface *const qt_incomplete_metaTypeArray
 
 QT_END_NAMESPACE
 
+Q_DECLARE_METATYPE(QtMetaTypePrivate::QPairVariantInterfaceImpl)
+
 #endif // QMETATYPE_H