QVariant: Tolerate QObject* metatypes without QMetaObject

QMetaType does. QVariant should do the same.

Change-Id: I3419276b78b3b5ce8bd144dee92685195797d568
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Daniel Nicoletti <daniel.nicoletti@kdab.com>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit 6f8ef8c64d4e7af92f585d10a1d5815fcb67831b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 53 insertions, 3 deletions

diff --git a/src/corelib/kernel/qvariant.cpp b/src/corelib/kernel/qvariant.cpp
index dcba73731c..8a1197dc5f 100644
--- a/src/corelib/kernel/qvariant.cpp
+++ b/src/corelib/kernel/qvariant.cpp
@@ -2341,9 +2341,11 @@ static bool numericEquals(const QVariant::Private *d1, const QVariant::Private *
 #ifndef QT_BOOTSTRAPPED
 static bool canConvertMetaObject(QMetaType fromType, QMetaType toType)
 {
-    if ((fromType.flags() & QMetaType::PointerToQObject) && (toType.flags() & QMetaType::PointerToQObject)) {
-        return fromType.metaObject()->inherits(toType.metaObject()) ||
-                toType.metaObject()->inherits(fromType.metaObject());
+    if ((fromType.flags() & QMetaType::PointerToQObject)
+            && (toType.flags() & QMetaType::PointerToQObject)) {
+        const QMetaObject *f = fromType.metaObject();
+        const QMetaObject *t = toType.metaObject();
+        return f && t && (f->inherits(t) || t->inherits(f));
     }
     return false;
 }
diff --git a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
index 4e5eb430a2..c26f09441b 100644
--- a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
+++ b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
@@ -63,6 +63,7 @@
 #include "qnumeric.h"
 
 #include <private/qlocale_p.h>
+#include <private/qmetatype_p.h>
 #include "tst_qvariant_common.h"
 
 #include <unordered_map>
@@ -309,6 +310,7 @@ private slots:
     void mutableView();
 
     void moveOperations();
+    void equalsWithoutMetaObject();
 
 private:
     void dataStream_data(QDataStream::Version version);
@@ -5084,5 +5086,51 @@ void tst_QVariant::moveOperations()
     QVERIFY(v2.value<std::list<int>>() == list);
 }
 
+class NoMetaObject : public QObject {};
+void tst_QVariant::equalsWithoutMetaObject()
+{
+    using T = NoMetaObject*;
+    QtPrivate::QMetaTypeInterface d = {
+        /*.revision=*/ 0,
+        /*.alignment=*/ alignof(T),
+        /*.size=*/ sizeof(T),
+        /*.flags=*/ QtPrivate::QMetaTypeTypeFlags<T>::Flags,
+        /*.typeId=*/ 0,
+        /*.metaObject=*/ nullptr, // on purpose.
+        /*.name=*/ "NoMetaObject*",
+        /*.defaultCtr=*/ [](const QtPrivate::QMetaTypeInterface *, void *addr) {
+            new (addr) T();
+        },
+        /*.copyCtr=*/ [](const QtPrivate::QMetaTypeInterface *, void *addr, const void *other) {
+            new (addr) T(*reinterpret_cast<const T *>(other));
+        },
+        /*.moveCtr=*/ [](const QtPrivate::QMetaTypeInterface *, void *addr, void *other) {
+            new (addr) T(std::move(*reinterpret_cast<T *>(other)));
+        },
+        /*.dtor=*/ [](const QtPrivate::QMetaTypeInterface *, void *addr) {
+            reinterpret_cast<T *>(addr)->~T();
+        },
+        /*.equals*/ nullptr,
+        /*.lessThan*/ nullptr,
+        /*.debugStream=*/ nullptr,
+        /*.dataStreamOut=*/ nullptr,
+        /*.dataStreamIn=*/ nullptr,
+        /*.legacyRegisterOp=*/ nullptr
+    };
+
+    QMetaType noMetaObjectMetaType(&d);
+    QMetaType qobjectMetaType = QMetaType::fromType<tst_QVariant*>();
+
+    QVERIFY(noMetaObjectMetaType.flags() & QMetaType::PointerToQObject);
+    QVERIFY(qobjectMetaType.flags() & QMetaType::PointerToQObject);
+
+    QVariant noMetaObjectVariant(noMetaObjectMetaType, nullptr);
+    QVariant qobjectVariant(qobjectMetaType, nullptr);
+
+    // Shouldn't crash
+    QVERIFY(noMetaObjectVariant != qobjectVariant);
+    QVERIFY(qobjectVariant != noMetaObjectVariant);
+}
+
 QTEST_MAIN(tst_QVariant)
 #include "tst_qvariant.moc"