QV4Engine: Do not construct invalid QVariant

If the provided typeHint is -1, it does not make sense to construct a
QVariant of this type and to check whether it is appendable.

Fixes: QTBUG-81945
Change-Id: I32cbb9e70e210a7eca8d55801c1783338d1173b7
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

2 files changed, 27 insertions, 20 deletions

diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 81f55673cd..d885c28166 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -1515,27 +1515,29 @@ static QVariant toVariant(QV4::ExecutionEngine *e, const QV4::Value &value, int
         if (succeeded)
             return retn;
 #endif
-        retn = QVariant(typeHint, QMetaType::create(typeHint));
-        auto retnAsIterable = retn.value<QtMetaTypePrivate::QSequentialIterableImpl>();
-        if (retnAsIterable._iteratorCapabilities & QtMetaTypePrivate::ContainerIsAppendable) {
-            auto const length = a->getLength();
-            QV4::ScopedValue arrayValue(scope);
-            for (qint64 i = 0; i < length; ++i) {
-                arrayValue = a->get(i);
-                QVariant asVariant = toVariant(e, arrayValue, retnAsIterable._metaType_id, false, visitedObjects);
-                auto originalType = asVariant.userType();
-                bool couldConvert = asVariant.convert(retnAsIterable._metaType_id);
-                if (!couldConvert) {
-                    qWarning() << QLatin1String("Could not convert array value at position %1 from %2 to %3")
-                                                .arg(QString::number(i),
-                                                     QMetaType::typeName(originalType),
-                                                     QMetaType::typeName(retnAsIterable._metaType_id));
-                    // create default constructed value
-                    asVariant = QVariant(retnAsIterable._metaType_id, nullptr);
+        if (typeHint != -1) {
+            retn = QVariant(typeHint, QMetaType::create(typeHint));
+            auto retnAsIterable = retn.value<QtMetaTypePrivate::QSequentialIterableImpl>();
+            if (retnAsIterable._iteratorCapabilities & QtMetaTypePrivate::ContainerIsAppendable) {
+                auto const length = a->getLength();
+                QV4::ScopedValue arrayValue(scope);
+                for (qint64 i = 0; i < length; ++i) {
+                    arrayValue = a->get(i);
+                    QVariant asVariant = toVariant(e, arrayValue, retnAsIterable._metaType_id, false, visitedObjects);
+                    auto originalType = asVariant.userType();
+                    bool couldConvert = asVariant.convert(retnAsIterable._metaType_id);
+                    if (!couldConvert) {
+                        qWarning() << QLatin1String("Could not convert array value at position %1 from %2 to %3")
+                                                    .arg(QString::number(i),
+                                                         QMetaType::typeName(originalType),
+                                                         QMetaType::typeName(retnAsIterable._metaType_id));
+                        // create default constructed value
+                        asVariant = QVariant(retnAsIterable._metaType_id, nullptr);
+                    }
+                    retnAsIterable.append(asVariant.constData());
                 }
-                retnAsIterable.append(asVariant.constData());
+                return retn;
             }
-            return retn;
         }
     }
 
diff --git a/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp b/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
index 95f554776f..cab4686c37 100644
--- a/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
+++ b/tests/auto/qml/qjsvalue/tst_qjsvalue.cpp
@@ -1128,6 +1128,10 @@ void tst_QJSValue::toVariant()
 
     // array
     {
+        auto handler = qInstallMessageHandler([](QtMsgType type, const QMessageLogContext &, const QString &) {
+            if (type == QtMsgType::QtWarningMsg)
+                QFAIL("Converting QJSValue to QVariant should not cause error messages");
+        });
         QVariantList listIn;
         listIn << 123 << "hello";
         QJSValue array = eng.toScriptValue(listIn);
@@ -1145,8 +1149,9 @@ void tst_QJSValue::toVariant()
         QCOMPARE(array2.property("length").toInt(), array.property("length").toInt());
         for (int i = 0; i < array.property("length").toInt(); ++i)
             QVERIFY(array2.property(i).strictlyEquals(array.property(i)));
-    }
 
+        qInstallMessageHandler(handler);
+    }
 }
 
 void tst_QJSValue::toQObject_nonQObject_data()