dbus: Include some debug messages when failing to connect

When using dbus, there's a number of cases where resolution happens at
runtime. It's useful to see dbus complain when connects don't work,
because otherwise the system doesn't work but we don't know what is
happening.
Added this to debug such an issue, already helped me address other cases
that had gone unnoticed elsewhere, so this is something that benefits
from being in QtDBus.

Change-Id: I5eefb94fcf775182edf1ad0c24e8a6692f84b15f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

3 files changed, 37 insertions, 17 deletions

diff --git a/src/dbus/qdbusconnection_p.h b/src/dbus/qdbusconnection_p.h
index 99c1687661..3431992eac 100644
--- a/src/dbus/qdbusconnection_p.h
+++ b/src/dbus/qdbusconnection_p.h
@@ -316,7 +316,8 @@ public:
 
 public:
     // static methods
-    static int findSlot(QObject *obj, const QByteArray &normalizedName, QList<QMetaType> &params);
+    static int findSlot(QObject *obj, const QByteArray &normalizedName, QList<QMetaType> &params,
+                        QString &errorMsg);
     static bool prepareHook(QDBusConnectionPrivate::SignalHook &hook, QString &key,
                             const QString &service,
                             const QString &path, const QString &interface, const QString &name,
diff --git a/src/dbus/qdbusintegrator.cpp b/src/dbus/qdbusintegrator.cpp
index 8b190b8e5f..09f29f9556 100644
--- a/src/dbus/qdbusintegrator.cpp
+++ b/src/dbus/qdbusintegrator.cpp
@@ -6,7 +6,7 @@
 
 #include <qcoreapplication.h>
 #include <qelapsedtimer.h>
-#include <qdebug.h>
+#include <qloggingcategory.h>
 #include <qmetaobject.h>
 #include <qobject.h>
 #include <qsocketnotifier.h>
@@ -50,6 +50,8 @@ QT_IMPL_METATYPE_EXTERN(QDBusSlotCache)
 // used with dbus_server_allocate_data_slot
 static dbus_int32_t server_slot = -1;
 
+Q_LOGGING_CATEGORY(dbusIntegration, "qt.dbus.integration", QtWarningMsg)
+
 Q_CONSTINIT static QBasicAtomicInt isDebugging = Q_BASIC_ATOMIC_INITIALIZER(-1);
 #define qDBusDebug              if (::isDebugging.loadRelaxed() == 0); else qDebug
 
@@ -860,6 +862,9 @@ bool QDBusConnectionPrivate::activateCall(QObject* object, int flags, const QDBu
                 slotData.metaTypes.clear();
                 slotCache.hash.insert(cacheKey, slotData);
                 object->setProperty(cachePropertyName, QVariant::fromValue(slotCache));
+
+                qCWarning(dbusIntegration).nospace() << "Could not find slot " << mo->className()
+                                                     << "::" << memberName.constData();
                 return false;
             }
         }
@@ -1288,16 +1293,16 @@ void QDBusConnectionPrivate::serviceOwnerChangedNoLock(const QString &name,
 }
 
 int QDBusConnectionPrivate::findSlot(QObject *obj, const QByteArray &normalizedName,
-                                     QList<QMetaType> &params)
+                                     QList<QMetaType> &params, QString &errorMsg)
 {
+    errorMsg.clear();
     int midx = obj->metaObject()->indexOfMethod(normalizedName);
     if (midx == -1)
         return -1;
 
-    QString errorMsg;
     int inputCount = qDBusParametersForMethod(obj->metaObject()->method(midx), params, errorMsg);
-    if ( inputCount == -1 || inputCount + 1 != params.size() )
-        return -1;              // failed to parse or invalid arguments or output arguments
+    if (inputCount == -1 || inputCount + 1 != params.size())
+        return -1;
 
     return midx;
 }
@@ -1310,10 +1315,11 @@ bool QDBusConnectionPrivate::prepareHook(QDBusConnectionPrivate::SignalHook &hoo
                                          bool buildSignature)
 {
     QByteArray normalizedName = signal + 1;
-    hook.midx = findSlot(receiver, signal + 1, hook.params);
+    QString errorMsg;
+    hook.midx = findSlot(receiver, signal + 1, hook.params, errorMsg);
     if (hook.midx == -1) {
         normalizedName = QMetaObject::normalizedSignature(signal + 1);
-        hook.midx = findSlot(receiver, normalizedName, hook.params);
+        hook.midx = findSlot(receiver, normalizedName, hook.params, errorMsg);
     }
     if (hook.midx < minMIdx) {
         return false;
@@ -2210,8 +2216,11 @@ bool QDBusConnectionPrivate::connectSignal(const QString &service,
     QString key;
 
     hook.signature = signature;
-    if (!prepareHook(hook, key, service, path, interface, name, argumentMatch, receiver, slot, 0, false))
+    if (!prepareHook(hook, key, service, path, interface, name, argumentMatch, receiver, slot, 0,
+                     false)) {
+        qCWarning(dbusIntegration) << "Could not connect" << interface << "to" << slot + 1;
         return false;           // don't connect
+    }
 
     Q_ASSERT(thread() != QThread::currentThread());
     return emit signalNeedsConnecting(key, hook);
@@ -2300,8 +2309,11 @@ bool QDBusConnectionPrivate::disconnectSignal(const QString &service,
         name2.detach();
 
     hook.signature = signature;
-    if (!prepareHook(hook, key, service, path, interface, name, argumentMatch, receiver, slot, 0, false))
+    if (!prepareHook(hook, key, service, path, interface, name, argumentMatch, receiver, slot, 0,
+                     false)) {
+        qCWarning(dbusIntegration) << "Could not disconnect" << interface << "to" << slot + 1;
         return false;           // don't disconnect
+    }
 
     Q_ASSERT(thread() != QThread::currentThread());
     return emit signalNeedsDisconnecting(key, hook);
@@ -2428,8 +2440,10 @@ void QDBusConnectionPrivate::connectRelay(const QString &service,
     sig.append(QSIGNAL_CODE + '0');
     sig.append(signal.methodSignature());
     if (!prepareHook(hook, key, service, path, interface, QString(), ArgMatchRules(), receiver, sig,
-                     QDBusAbstractInterface::staticMetaObject.methodCount(), true))
+                     QDBusAbstractInterface::staticMetaObject.methodCount(), true)) {
+        qCWarning(dbusIntegration) << "Could not connect" << interface << "to" << signal.name();
         return;                 // don't connect
+    }
 
     Q_ASSERT(thread() != QThread::currentThread());
     emit signalNeedsConnecting(key, hook);
@@ -2449,8 +2463,11 @@ void QDBusConnectionPrivate::disconnectRelay(const QString &service,
     sig.append(QSIGNAL_CODE + '0');
     sig.append(signal.methodSignature());
     if (!prepareHook(hook, key, service, path, interface, QString(), ArgMatchRules(), receiver, sig,
-                     QDBusAbstractInterface::staticMetaObject.methodCount(), true))
+                     QDBusAbstractInterface::staticMetaObject.methodCount(), true)) {
+        qCWarning(dbusIntegration)
+                << "Could not disconnect" << interface << "to" << signal.methodSignature();
         return;                 // don't disconnect
+    }
 
     Q_ASSERT(thread() != QThread::currentThread());
     emit signalNeedsDisconnecting(key, hook);
diff --git a/src/dbus/qdbuspendingcall.cpp b/src/dbus/qdbuspendingcall.cpp
index 7674dd10f2..ff5dfc8967 100644
--- a/src/dbus/qdbuspendingcall.cpp
+++ b/src/dbus/qdbuspendingcall.cpp
@@ -123,16 +123,18 @@ bool QDBusPendingCallPrivate::setReplyCallback(QObject *target, const char *memb
         return false;
     }
 
-    methodIdx = QDBusConnectionPrivate::findSlot(target, member + 1, metaTypes);
+    QString errorMsg;
+    methodIdx = QDBusConnectionPrivate::findSlot(target, member + 1, metaTypes, errorMsg);
     if (methodIdx == -1) {
         QByteArray normalizedName = QMetaObject::normalizedSignature(member + 1);
-        methodIdx = QDBusConnectionPrivate::findSlot(target, normalizedName, metaTypes);
+        methodIdx = QDBusConnectionPrivate::findSlot(target, normalizedName, metaTypes, errorMsg);
     }
     if (methodIdx == -1) {
         // would not be able to deliver a reply
-        qWarning("QDBusPendingCall::setReplyCallback: error: cannot deliver a reply to %s::%s (%s)",
-                 target->metaObject()->className(),
-                 member + 1, qPrintable(target->objectName()));
+        qWarning("QDBusPendingCall::setReplyCallback: error: cannot deliver a reply to %s::%s (%s) "
+                 "because %s",
+                 target->metaObject()->className(), member + 1, qPrintable(target->objectName()),
+                 qPrintable(errorMsg));
         return false;
     }