QDBusConnection: output error message from findSlot

This helps debugging why an adaptor's method fails to be called.
Example output:
QDBusConnection: couldn't handle call to LaunchCommand: Type not registered with QtDBus in parameter list: QByteArrayList

tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall shows many warnings
after this commit, since it's testing many cases of "no such slot".

Pick-to: 6.0 6.1 5.15
Change-Id: Ic4ddcd91d005555a02d531fc8960aea2c809e20b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 16 insertions, 1 deletions

diff --git a/src/dbus/qdbusintegrator.cpp b/src/dbus/qdbusintegrator.cpp
index 119a354d82..89b9b2d17e 100644
--- a/src/dbus/qdbusintegrator.cpp
+++ b/src/dbus/qdbusintegrator.cpp
@@ -665,6 +665,7 @@ static int findSlot(const QMetaObject *mo, const QByteArray &name, int flags,
                     const QString &signature_, QList<QMetaType> &metaTypes)
 {
     QByteArray msgSignature = signature_.toLatin1();
+    QString parametersErrorMsg;
 
     for (int idx = mo->methodCount() - 1 ; idx >= QObject::staticMetaObject.methodCount(); --idx) {
         QMetaMethod mm = mo->method(idx);
@@ -691,8 +692,10 @@ static int findSlot(const QMetaObject *mo, const QByteArray &name, int flags,
 
         QString errorMsg;
         int inputCount = qDBusParametersForMethod(mm, metaTypes, errorMsg);
-        if (inputCount == -1)
+        if (inputCount == -1) {
+            parametersErrorMsg = errorMsg;
             continue;           // problem parsing
+        }
 
         metaTypes[0] = returnType;
         bool hasMessage = false;
@@ -754,6 +757,13 @@ static int findSlot(const QMetaObject *mo, const QByteArray &name, int flags,
     }
 
     // no slot matched
+    if (!parametersErrorMsg.isEmpty()) {
+        qCWarning(dbusIntegration, "QDBusConnection: couldn't handle call to %s: %ls",
+                  name.constData(), qUtf16Printable(parametersErrorMsg));
+    } else {
+        qCWarning(dbusIntegration, "QDBusConnection: couldn't handle call to %s, no slot matched",
+                  name.constData());
+    }
     return -1;
 }
 
diff --git a/tests/auto/dbus/qdbusmarshall/qpong/qpong.cpp b/tests/auto/dbus/qdbusmarshall/qpong/qpong.cpp
index c5952c3b36..52c1ee8fa1 100644
--- a/tests/auto/dbus/qdbusmarshall/qpong/qpong.cpp
+++ b/tests/auto/dbus/qdbusmarshall/qpong/qpong.cpp
@@ -4,6 +4,7 @@
 #include <QCoreApplication>
 #include <QDBusMessage>
 #include <QDBusConnection>
+#include <QLoggingCategory>
 
 static const char serviceName[] = "org.qtproject.autotests.qpong";
 static const char objectPath[] = "/org/qtproject/qpong";
@@ -32,6 +33,9 @@ int main(int argc, char *argv[])
 {
     QCoreApplication app(argc, argv);
 
+    // Silence many warnings from findSlot() about ping() not having the expected argument types
+    QLoggingCategory::setFilterRules("qt.dbus.integration=false");
+
     QDBusConnection con = QDBusConnection::sessionBus();
     if (!con.isConnected())
         exit(1);
diff --git a/tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall.cpp b/tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall.cpp
index 9df9f78248..8ab4121e8f 100644
--- a/tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall.cpp
+++ b/tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall.cpp
@@ -1146,6 +1146,7 @@ void tst_QDBusMarshall::receiveUnknownType()
         // now spin our event loop. We don't catch this call, so let's get the reply
         QEventLoop loop;
         QTimer::singleShot(200, &loop, SLOT(quit()));
+        QTest::ignoreMessage(QtWarningMsg, "QDBusConnection: couldn't handle call to theSlot, no slot matched");
         loop.exec();
 
         // now try to receive the reply