QML: Fix call frame conversion for QVariant return types

The function may return a QVariant in place of the actual type because
it cannot express the actual type as-is. This case needs special care
because QMetaType::convert() doesn't know what to do with it.

Pick-to: 6.5
Fixes: QTBUG-112837
Change-Id: Ibf93a28aa6a60d49c5ab63fa7eed5f5a8e58e163
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

6 files changed, 169 insertions, 0 deletions

diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index 5e4e93fbd9..38a7652ef0 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -514,6 +514,17 @@ void VME::exec(MetaTypesStackFrame *frame, ExecutionEngine *engine)
                     = (resultObj && resultObj->metaObject()->inherits(frameReturn.metaObject()))
                             ? resultObj
                             : nullptr;
+        } else if (returnType == QMetaType::fromType<QVariant>()) {
+            const QVariant *resultVariant = static_cast<QVariant *>(transformedResult);
+            if (resultVariant->metaType() == frameReturn) {
+                frameReturn.construct(frame->returnValue(), resultVariant->data());
+            } else {
+                // Convert needs a pre-constructed target.
+                frameReturn.construct(frame->returnValue());
+                QMetaType::convert(resultVariant->metaType(), resultVariant->data(),
+                               frameReturn, frame->returnValue());
+            }
+            resultVariant->~QVariant();
         } else {
             // Convert needs a pre-constructed target.
             frameReturn.construct(frame->returnValue());
diff --git a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
index 7e3ffc06c6..74f56f0bb3 100644
--- a/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
+++ b/tests/auto/qml/qmlcppcodegen/data/CMakeLists.txt
@@ -20,6 +20,8 @@ set(cpp_sources
     theme.cpp theme.h
     timelinetheme.cpp timelinetheme.h
     variantMapLookup.h
+    variantreturn.h
+    weathermoduleurl.h
     wrapwithvariant.h
     withlength.h
 )
@@ -221,6 +223,7 @@ set(qml_files
     valueTypeProperty.qml
     valueTypeReference.qml
     variantMapLookup.qml
+    variantReturn.qml
     variantlist.qml
     versionmismatch.qml
     voidfunction.qml
diff --git a/tests/auto/qml/qmlcppcodegen/data/variantReturn.qml b/tests/auto/qml/qmlcppcodegen/data/variantReturn.qml
new file mode 100644
index 0000000000..cca26265c9
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/variantReturn.qml
@@ -0,0 +1,15 @@
+pragma Strict
+import QtQml
+import TestTypes
+
+QtObject {
+    property DirectBindable a: DirectBindable {
+        id: aId
+        x: WeatherModelUrlUtils.url(1)
+    }
+
+    property IndirectBindable b: IndirectBindable {
+        id: bId
+        y: aId.x
+    }
+}
diff --git a/tests/auto/qml/qmlcppcodegen/data/variantreturn.h b/tests/auto/qml/qmlcppcodegen/data/variantreturn.h
new file mode 100644
index 0000000000..bb8ba75839
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/variantreturn.h
@@ -0,0 +1,63 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#ifndef VARIANTERETURN_H
+#define VARIANTERETURN_H
+
+#include <QtCore/qobject.h>
+#include <QtCore/qproperty.h>
+#include <QtQml/qqmlregistration.h>
+
+#include "weathermoduleurl.h"
+
+class DirectBindable : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    Q_PROPERTY(WeatherModelUrl x READ x WRITE setX NOTIFY xChanged BINDABLE bindableX)
+
+public:
+    explicit DirectBindable(QObject *parent = nullptr) : QObject(parent) {}
+
+    WeatherModelUrl x() const { return m_x.value(); }
+    void setX(const WeatherModelUrl& newX) { m_x.setValue(newX);}
+    QBindable<WeatherModelUrl> bindableX() { return QBindable<WeatherModelUrl>(&m_x); }
+
+Q_SIGNALS:
+    void xChanged();
+
+private:
+    Q_OBJECT_BINDABLE_PROPERTY(DirectBindable, WeatherModelUrl, m_x, &DirectBindable::xChanged)
+};
+
+class IndirectBindable : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    Q_PROPERTY(WeatherModelUrl y READ y WRITE setY NOTIFY yChanged BINDABLE bindableY)
+    Q_PROPERTY(int z READ z NOTIFY zChanged)
+
+public:
+    explicit IndirectBindable(QObject *parent = nullptr) : QObject(parent) {
+        m_z.setBinding([this]()->int {
+            return m_y.value().timeIndex() * 2;
+        });
+    }
+
+    WeatherModelUrl y() const { return m_y.value(); }
+    void setY(const WeatherModelUrl& newY) { m_y.setValue(newY); }
+    QBindable<WeatherModelUrl> bindableY() { return QBindable<WeatherModelUrl>(&m_y); }
+
+    int z() const { return m_z.value(); }
+    QBindable<int> bindableZ() const { return QBindable<int>(&m_z); }
+
+Q_SIGNALS:
+    void yChanged();
+    void zChanged();
+
+private:
+    Q_OBJECT_BINDABLE_PROPERTY(IndirectBindable, WeatherModelUrl, m_y, &IndirectBindable::yChanged)
+    Q_OBJECT_BINDABLE_PROPERTY(IndirectBindable, int, m_z, &IndirectBindable::zChanged)
+};
+
+#endif // VARIANTRETURN_H
diff --git a/tests/auto/qml/qmlcppcodegen/data/weathermoduleurl.h b/tests/auto/qml/qmlcppcodegen/data/weathermoduleurl.h
new file mode 100644
index 0000000000..51d464fb2c
--- /dev/null
+++ b/tests/auto/qml/qmlcppcodegen/data/weathermoduleurl.h
@@ -0,0 +1,51 @@
+// Copyright (C) 2023 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#ifndef WEATHERMODELURL_H
+#define WEATHERMODELURL_H
+
+#include <QtQml/qqmlregistration.h>
+#include <QtCore/qobject.h>
+
+class WeatherModelUrl
+{
+    Q_GADGET
+    QML_VALUE_TYPE(weatherModelUrl)
+    Q_PROPERTY(qsizetype timeIndex READ timeIndex CONSTANT)
+
+public:
+    WeatherModelUrl() : m_timeIndex(-1) {}
+    WeatherModelUrl(qsizetype timeIdx) : m_timeIndex(timeIdx) {}
+
+    qsizetype timeIndex() const { return m_timeIndex; }
+
+private:
+    friend bool operator==(const WeatherModelUrl &a, const WeatherModelUrl &b)
+    {
+        return a.m_timeIndex == b.m_timeIndex;
+    }
+
+    friend bool operator!=(const WeatherModelUrl &a, const WeatherModelUrl &b)
+    {
+        return !(a == b);
+    }
+
+    qsizetype m_timeIndex;
+};
+
+class WeatherModelUrlUtils : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    QML_SINGLETON
+
+public:
+    WeatherModelUrlUtils(QObject *parent = nullptr) : QObject(parent) {}
+
+    Q_INVOKABLE static WeatherModelUrl url(int timeIdx)
+    {
+        return WeatherModelUrl(timeIdx);
+    }
+};
+
+#endif // WEATHERMODELURL_H
diff --git a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
index 0cad3eb68e..a856d57cfe 100644
--- a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
+++ b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
@@ -187,6 +187,7 @@ private slots:
     void shadowedMethod();
     void topLevelComponent();
     void intToEnum();
+    void variantReturn();
 };
 
 void tst_QmlCppCodegen::initTestCase()
@@ -3807,6 +3808,31 @@ void tst_QmlCppCodegen::intToEnum()
     QCOMPARE(m->property("b").toInt(), 24);
 }
 
+void tst_QmlCppCodegen::variantReturn()
+{
+    QQmlEngine e;
+    QQmlComponent c(&e, QUrl(u"qrc:/qt/qml/TestTypes/variantReturn.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+
+    QObject *a = o->property("a").value<QObject *>();
+    QVERIFY(a);
+    const QVariant x = a->property("x");
+    const QMetaObject *meta = x.metaType().metaObject();
+    QVERIFY(meta);
+    const QMetaProperty property = meta->property(meta->indexOfProperty("timeIndex"));
+    QVERIFY(property.isValid());
+    const QVariant timeIndex = property.readOnGadget(x.data());
+    QCOMPARE(timeIndex.metaType(), QMetaType::fromType<qsizetype>());
+    QCOMPARE(timeIndex.value<qsizetype>(), qsizetype(1));
+
+    QObject *b = o->property("b").value<QObject *>();
+    QVERIFY(b);
+    QCOMPARE(b->property("z").toInt(), 2);
+}
+
 QTEST_MAIN(tst_QmlCppCodegen)
 
 #include "tst_qmlcppcodegen.moc"