Do not crash on non-QVariant return types

Patch e354bdc5 introduced a regression that triggers a crash
in Qt 5.9 when returning a type that is not implicitly convertible
to QVariant, such as a QJsonValue, from an invoked method/slot.

This patch fixes this situation and adds proper unit test coverage.

Change-Id: Ib8cb0c96e7496bc8dc9a628245d7a44e4234aff0
Task-number: QTBUG-62045
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>
Reviewed-by: Kai Dohmen <psykai1993@googlemail.com>

3 files changed, 41 insertions, 12 deletions

diff --git a/src/webchannel/qmetaobjectpublisher.cpp b/src/webchannel/qmetaobjectpublisher.cpp
index dcc589c..cfc6ad2 100644
--- a/src/webchannel/qmetaobjectpublisher.cpp
+++ b/src/webchannel/qmetaobjectpublisher.cpp
@@ -383,12 +383,12 @@ QVariant QMetaObjectPublisher::invokeMethod(QObject *const object, const int met
                   arguments[0], arguments[1], arguments[2], arguments[3], arguments[4],
                   arguments[5], arguments[6], arguments[7], arguments[8], arguments[9]);
     } else {
-        QGenericReturnArgument returnArgument(method.typeName(), returnValue.data());
-
         // Only init variant with return type if its not a variant itself, which would
         // lead to nested variants which is not what we want.
         if (method.returnType() != QMetaType::QVariant)
             returnValue = QVariant(method.returnType(), 0);
+
+        QGenericReturnArgument returnArgument(method.typeName(), returnValue.data());
         method.invoke(object, returnArgument,
                   arguments[0], arguments[1], arguments[2], arguments[3], arguments[4],
                   arguments[5], arguments[6], arguments[7], arguments[8], arguments[9]);
diff --git a/tests/auto/webchannel/tst_webchannel.cpp b/tests/auto/webchannel/tst_webchannel.cpp
index 2e80477..f214b7e 100644
--- a/tests/auto/webchannel/tst_webchannel.cpp
+++ b/tests/auto/webchannel/tst_webchannel.cpp
@@ -536,6 +536,10 @@ void TestWebChannel::testInvokeMethodConversion()
         QVERIFY(method != -1);
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastInt, args.at(0).toInt());
+        int getterMethod = metaObject()->indexOfMethod("readInt()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, args.at(0).toVariant());
     }
     {
         int method = metaObject()->indexOfMethod("setBool(bool)");
@@ -544,24 +548,40 @@ void TestWebChannel::testInvokeMethodConversion()
         args.append(QJsonValue(!m_lastBool));
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastBool, args.at(0).toBool());
+        int getterMethod = metaObject()->indexOfMethod("readBool()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, args.at(0).toVariant());
     }
     {
         int method = metaObject()->indexOfMethod("setDouble(double)");
         QVERIFY(method != -1);
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastDouble, args.at(0).toDouble());
+        int getterMethod = metaObject()->indexOfMethod("readDouble()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, args.at(0).toVariant());
     }
     {
         int method = metaObject()->indexOfMethod("setVariant(QVariant)");
         QVERIFY(method != -1);
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastVariant, args.at(0).toVariant());
+        int getterMethod = metaObject()->indexOfMethod("readVariant()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, args.at(0).toVariant());
     }
     {
         int method = metaObject()->indexOfMethod("setJsonValue(QJsonValue)");
         QVERIFY(method != -1);
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastJsonValue, args.at(0));
+        int getterMethod = metaObject()->indexOfMethod("readJsonValue()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, args.at(0).toVariant());
     }
     {
         int method = metaObject()->indexOfMethod("setJsonObject(QJsonObject)");
@@ -572,16 +592,24 @@ void TestWebChannel::testInvokeMethodConversion()
         args[0] = object;
         channel.d_func()->publisher->invokeMethod(this, method, args);
         QCOMPARE(m_lastJsonObject, object);
+        int getterMethod = metaObject()->indexOfMethod("readJsonObject()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, QVariant::fromValue(object));
     }
     {
-        int method = metaObject()->indexOfMethod("setJsonArray(QJsonArray)");
-        QVERIFY(method != -1);
+        int setterMethod = metaObject()->indexOfMethod("setJsonArray(QJsonArray)");
+        QVERIFY(setterMethod != -1);
         QJsonArray array;
         array << QJsonValue(123);
         array <<  QJsonValue(4.2);
         args[0] = array;
-        channel.d_func()->publisher->invokeMethod(this, method, args);
+        channel.d_func()->publisher->invokeMethod(this, setterMethod, args);
         QCOMPARE(m_lastJsonArray, array);
+        int getterMethod = metaObject()->indexOfMethod("readJsonArray()");
+        QVERIFY(getterMethod != -1);
+        auto retVal = channel.d_func()->publisher->invokeMethod(this, getterMethod, {});
+        QCOMPARE(retVal, QVariant::fromValue(array));
     }
 }
 
diff --git a/tests/auto/webchannel/tst_webchannel.h b/tests/auto/webchannel/tst_webchannel.h
index aaacb5a..d2597e5 100644
--- a/tests/auto/webchannel/tst_webchannel.h
+++ b/tests/auto/webchannel/tst_webchannel.h
@@ -258,20 +258,21 @@ public:
     explicit TestWebChannel(QObject *parent = 0);
     virtual ~TestWebChannel();
 
+public slots:
     int readInt() const;
-    Q_INVOKABLE void setInt(int i);
+    void setInt(int i);
     bool readBool() const;
-    Q_INVOKABLE void setBool(bool b);
+    void setBool(bool b);
     double readDouble() const;
-    Q_INVOKABLE void setDouble(double d);
+    void setDouble(double d);
     QVariant readVariant() const;
-    Q_INVOKABLE void setVariant(const QVariant &v);
+    void setVariant(const QVariant &v);
     QJsonValue readJsonValue() const;
-    Q_INVOKABLE void setJsonValue(const QJsonValue &v);
+    void setJsonValue(const QJsonValue &v);
     QJsonObject readJsonObject() const;
-    Q_INVOKABLE void setJsonObject(const QJsonObject &v);
+    void setJsonObject(const QJsonObject &v);
     QJsonArray readJsonArray() const;
-    Q_INVOKABLE void setJsonArray(const QJsonArray &v);
+    void setJsonArray(const QJsonArray &v);
 
 signals:
     void lastIntChanged();