qdbusxml2cpp: initialize the return value for adapters

If the interface has a method with a specified return value, the
generated adapter will contain a code like:

  bool out;
  QMetaObject::invokeMethod(parent(), "Func", Q_RETURN_ARG(bool, out));
  return out;

In this case Q_RETURN_ARG macro makes sure that the variable `out` is
properly initialized before being returned from a function, but only
if invokeMethod() call is executed successfully.

Update the generator to zero-initialize (or value-initialize) the
return variable, so that it returns some reasonable value even if
invokeMethod() fails.

Extend the unit-tests to make sure that the generated adapters always
initialize the return variables.

Coverity-Id: 479703
Pick-to: 6.9 6.8 6.5
Change-Id: I4d15ccc6844b5ca454ab9f0cf72fd8e3f0c1b704
Reviewed-by: Matthias Rauter <[email protected]>

2 files changed, 9 insertions, 4 deletions

diff --git a/src/tools/qdbusxml2cpp/qdbusxml2cpp.cpp b/src/tools/qdbusxml2cpp/qdbusxml2cpp.cpp
index 0b089178835..f727e7094d6 100644
--- a/src/tools/qdbusxml2cpp/qdbusxml2cpp.cpp
+++ b/src/tools/qdbusxml2cpp/qdbusxml2cpp.cpp
@@ -1089,9 +1089,10 @@ void QDBusXmlToCpp::writeAdaptor(const QString &filename,
 
             if (usingInvokeMethod) {
                 // we are using QMetaObject::invokeMethod
-                if (!returnType.isEmpty())
+                if (!returnType.isEmpty()) {
                     cs << "    " << returnType << " " << argNames.at(method.inputArgs.size())
-                       << ";\n";
+                       << "{};\n";
+                }
 
                 static const char invoke[] = "    QMetaObject::invokeMethod(parent(), \"";
                 cs << invoke << name << "\"";
diff --git a/tests/auto/tools/qdbusxml2cpp/tst_qdbusxml2cpp.cpp b/tests/auto/tools/qdbusxml2cpp/tst_qdbusxml2cpp.cpp
index 5474c4f7470..146f591bad0 100644
--- a/tests/auto/tools/qdbusxml2cpp/tst_qdbusxml2cpp.cpp
+++ b/tests/auto/tools/qdbusxml2cpp/tst_qdbusxml2cpp.cpp
@@ -203,7 +203,9 @@ void tst_qdbusxml2cpp::process_data()
                    .arg(basicTypeList[i].dbusType)
                 << QRegularExpression(QString("Q_SLOTS:.*\\bQDBusPendingReply<%1> Method\\((const )?%1 ")
                                       .arg(basicTypeList[i].cppType), QRegularExpression::DotMatchesEverythingOption)
-                << QRegularExpression(QString("Q_SLOTS:.*\\b%1 Method\\((const )?%1 ")
+                << QRegularExpression(QString("Q_SLOTS:.*\\b%1 Method\\((const )?%1 &?in0\\);"
+                                              ".*%1 .*::Method\\((const )?%1 &?in0\\)\n{\n"
+                                              ".*%1 out0{};")
                                       .arg(basicTypeList[i].cppType), QRegularExpression::DotMatchesEverythingOption);
     }
 
@@ -226,7 +228,9 @@ void tst_qdbusxml2cpp::process_data()
                "</method>"
             << QRegularExpression("Q_SLOTS:.*\\bQDBusPendingReply<Point> Method\\(PointF ",
                                   QRegularExpression::DotMatchesEverythingOption)
-            << QRegularExpression("Q_SLOTS:.*\\bPoint Method\\(PointF ",
+            << QRegularExpression("Q_SLOTS:.*\\bPoint Method\\(PointF in0\\);"
+                                  ".*Point .*::Method\\(PointF in0\\)\n{\n"
+                                  ".*Point out0{};",
                                   QRegularExpression::DotMatchesEverythingOption);
 
     QTest::newRow("method-ss")