QtQml: Avoid double-wrapping when converting to QVariantList

Amends commit 1b89c1edca

Fixes: QTBUG-139764
Pick-to: 6.10 6.9 6.8
Change-Id: I1488527a235d74fc0352c72b9bfb69589c2f3d93
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

src/qml/jsruntime/qv4engine.cpp

@@ -2516,15 +2516,29 @@ bool convertToIterable(QMetaType metaType, void *data, Source *sequence)
     if (!QMetaType::view(metaType, data, QMetaType::fromType<QSequentialIterable>(), &iterable))
         return false;
 
-    const QMetaType elementMetaType = iterable.valueMetaType();
+    // Clear the sequence before appending. There may be stale data in there.
+    metaType.destruct(data);
+    metaType.construct(data);
+
     QV4::Scope scope(sequence->engine());
     QV4::ScopedValue v(scope);
+
+    const QMetaType elementMetaType = iterable.valueMetaType();
+    QVariant element;
+    void *elementData = nullptr;
+    if (elementMetaType == QMetaType::fromType<QVariant>()) {
+        elementData = &element;
+    } else {
+        element = QVariant(elementMetaType);
+        elementData = element.data();
+    }
+
     for (qsizetype i = 0, end = sequence->getLength(); i < end; ++i) {
-        QVariant element(elementMetaType);
         v = sequence->get(i);
-        ExecutionEngine::metaTypeFromJS(v, elementMetaType, element.data());
+        ExecutionEngine::metaTypeFromJS(v, elementMetaType, elementData);
         iterable.addValue(element, QSequentialIterable::AtEnd);
     }
+
     return true;
 }
 

tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt

@@ -285,6 +285,7 @@ set(qml_files
     script.js
     script.mjs
     sequenceToIterable.qml
+    sequenceToIterable2.qml
     setLookupConversion.qml
     setLookupOriginalScope.qml
     shadowedAsCasts.qml

tests/auto/qml/qmlcppcodegen/data/sequenceToIterable.h

@@ -48,6 +48,13 @@ public:
         }
     }
     Q_INVOKABLE QList<Entry *> getEntries() const { return m_entries; }
+    Q_INVOKABLE QList<Entry *> convertEntries(const QVariantList &entries) const
+    {
+        QList<Entry *> converted;
+        for (const QVariant &entry : entries)
+            converted.push_back(entry.value<Entry *>());
+        return converted;
+    }
 
 private:
     QList<Entry*> m_entries;

tests/auto/qml/qmlcppcodegen/data/sequenceToIterable2.qml

@@ -0,0 +1,6 @@
+import QtQml
+import TestTypes
+
+QtObject {
+    property list<Entry> converted: EntrySource.convertEntries(EntrySource.getEntries());
+}

tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp

@@ -12,6 +12,7 @@
 #include <data/objectwithmethod.h>
 #include <data/qmlusing.h>
 #include <data/resettable.h>
+#include <data/sequenceToIterable.h>
 #include <data/takenumber.h>
 #include <data/weathermoduleurl.h>
 #include <data/withlength.h>
@@ -5086,6 +5087,19 @@ void tst_QmlCppCodegen::sequenceToIterable()
         QVERIFY(match.hasMatch());
         QCOMPARE(match.captured(1), QString::number(i));
     }
+
+    QQmlComponent component2(&engine, QUrl(u"qrc:/qt/qml/TestTypes/sequenceToIterable2.qml"_s));
+    QVERIFY2(!component2.isError(), component.errorString().toUtf8());
+    QScopedPointer<QObject> object2(component2.create());
+    QVERIFY(!object2.isNull());
+
+    QQmlListReference converted(object2.data(), "converted");
+    QCOMPARE(converted.count(), 10);
+    for (int i = 0; i < 10; ++i) {
+        Entry *e = qobject_cast<Entry *>(converted.at(i));
+        QVERIFY(e);
+        QCOMPARE(e->objectName(), QStringLiteral("Item %1").arg(i));
+    }
 }
 
 void tst_QmlCppCodegen::setLookupConversion()