From e57d7dbfa6d036f5f5b3014936900b93a60d2cfc Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Tue, 19 Jul 2022 12:58:36 -0700
Subject: [PATCH] QVariant: add missing const to QMetaTypeInterface pointers

They're ALWAYS const objects, though they also chock full of relocations
so they are never in read-only sections of memory (except maybe in final
executables that are position-dependent).

These are methods in a private sub-class of QVariant. No one outside of
QtCore (at least qtbase) should be using them directly. QVariant doesn't
have many friends (a bit anti-social); the one that matters is
qvariant_cast and that one does access QVariant::Private. This is not a
BC problem because QVariant::Private::type()'s signature is not
changing. In any case, QVariant's Q_CORE_EXPORT does not apply to
QVariant::Private anyway (see [1]).

[1] https://msvc.godbolt.org/z/r9cer8eWh

Change-Id: I3859764fed084846bcb0fffd17035355f823dc8f
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit eb9ace1cee4bb48005797b0b2d2d3d576a4cb4ce)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/kernel/qvariant.cpp | 11 ++++-------
 src/corelib/kernel/qvariant.h   | 10 +++++-----
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/src/corelib/kernel/qvariant.cpp b/src/corelib/kernel/qvariant.cpp
index ca724dbfac0..a2711a48f85 100644
--- a/src/corelib/kernel/qvariant.cpp
+++ b/src/corelib/kernel/qvariant.cpp
@@ -215,7 +215,7 @@ static qreal qConvertToRealNumber(const QVariant::Private *d, bool *ok)
 // the type of d has already been set, but other field are not set
 static void customConstruct(QVariant::Private *d, const void *copy)
 {
-    QtPrivate::QMetaTypeInterface *iface = d->typeInterface();
+    const QtPrivate::QMetaTypeInterface *iface = d->typeInterface();
     if (!(iface && iface->size)) {
         *d = QVariant::Private();
         return;
@@ -498,11 +498,8 @@ QVariant::QVariant(const QVariant &p)
 {
     if (d.is_shared) {
         d.data.shared->ref.ref();
-        return;
-    }
-    QtPrivate::QMetaTypeInterface *iface = d.typeInterface();
-    auto other = p.constData();
-    if (iface) {
+    } else if (const QtPrivate::QMetaTypeInterface *iface = d.typeInterface()) {
+        auto other = p.constData();
         if (other)
             iface->copyCtr(iface, &d.data, other);
         else
@@ -993,7 +990,7 @@ QVariant &QVariant::operator=(const QVariant &variant)
         d = variant.d;
     } else {
         d = variant.d;
-        QtPrivate::QMetaTypeInterface *iface = d.typeInterface();
+        const QtPrivate::QMetaTypeInterface *iface = d.typeInterface();
         const void *other = variant.constData();
         if (iface) {
             if (other)
diff --git a/src/corelib/kernel/qvariant.h b/src/corelib/kernel/qvariant.h
index 2a9b92f0c8c..dc73f46af51 100644
--- a/src/corelib/kernel/qvariant.h
+++ b/src/corelib/kernel/qvariant.h
@@ -428,7 +428,7 @@ public:
         static constexpr size_t MaxInternalSize = 3*sizeof(void *);
         template<typename T>
         static constexpr bool CanUseInternalSpace = (QTypeInfo<T>::isRelocatable && sizeof(T) <= MaxInternalSize && alignof(T) <= alignof(double));
-        static constexpr bool canUseInternalSpace(QtPrivate::QMetaTypeInterface *type)
+        static constexpr bool canUseInternalSpace(const QtPrivate::QMetaTypeInterface *type)
         {
             Q_ASSERT(type);
             return QMetaType::TypeFlags(type->flags) & QMetaType::RelocatableType &&
@@ -468,14 +468,14 @@ public:
         void set(const T &t)
         { *static_cast<T *>(CanUseInternalSpace<T> ? &data.data : data.shared->data()) = t; }
 
-        inline QMetaType type() const
+        inline const QtPrivate::QMetaTypeInterface* typeInterface() const
         {
-            return QMetaType(reinterpret_cast<QtPrivate::QMetaTypeInterface *>(packedType << 2));
+            return reinterpret_cast<const QtPrivate::QMetaTypeInterface *>(packedType << 2);
         }
 
-        inline QtPrivate::QMetaTypeInterface * typeInterface() const
+        inline QMetaType type() const
         {
-            return reinterpret_cast<QtPrivate::QMetaTypeInterface *>(packedType << 2);
+            return QMetaType(typeInterface());
         }
 
         inline int typeId() const