From c08197ccab36c10287df2e509d0c7e0c87e29fa5 Mon Sep 17 00:00:00 2001
From: Lars Schmertmann <Lars.Schmertmann@governikus.de>
Date: Thu, 12 Apr 2018 15:20:26 +0200
Subject: [PATCH] QObject: Extend debug output of connect
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Sometimes it is hard to find the line, when the warning
"QObject::connect: invalid null parameter" appears in the log.
This change adds the class names of the sender and receiver
to give a hint where to search for the wrong call to connect.

Change-Id: I00cead7d943f96d60f198cb3f0bed34ba10285c5
Reviewed-by: André Hartmann <aha_1980@gmx.de>
---
 src/corelib/kernel/qobject.cpp                |  7 ++++++-
 .../corelib/kernel/qobject/tst_qobject.cpp    | 21 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index dcc1bb5814..25d17ecd6b 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -4802,7 +4802,12 @@ QMetaObject::Connection QObjectPrivate::connectImpl(const QObject *sender, int s
                                              const int *types, const QMetaObject *senderMetaObject)
 {
     if (!sender || !receiver || !slotObj || !senderMetaObject) {
-        qWarning("QObject::connect: invalid null parameter");
+        const char *senderString = sender ? sender->metaObject()->className()
+                                          : senderMetaObject ? senderMetaObject->className()
+                                          : "Unknown";
+        const char *receiverString = receiver ? receiver->metaObject()->className()
+                                              : "Unknown";
+        qWarning("QObject::connect(%s, %s): invalid null parameter", senderString, receiverString);
         if (slotObj)
             slotObj->destroyIfLastRef();
         return QMetaObject::Connection();
diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index c734cfe4dd..43dcb241e4 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -145,6 +145,7 @@ private slots:
     void disconnectDoesNotLeakFunctor();
     void contextDoesNotLeakFunctor();
     void connectBase();
+    void connectWarnings();
     void qmlConnect();
     void exceptions();
     void noDeclarativeParentChangedOnDestruction();
@@ -6685,6 +6686,26 @@ void tst_QObject::connectBase()
     QCOMPARE( r1.count_slot3, 1 );
 }
 
+void tst_QObject::connectWarnings()
+{
+    SubSender sub;
+    SenderObject obj;
+    ReceiverObject r1;
+    r1.reset();
+
+    QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SenderObject, ReceiverObject): invalid null parameter");
+    connect(nullptr, &SubSender::signal1, &r1, &ReceiverObject::slot1);
+
+    QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SubSender, Unknown): invalid null parameter");
+    connect(&sub, &SubSender::signal1, nullptr, &ReceiverObject::slot1);
+
+    QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SenderObject, ReceiverObject): invalid null parameter");
+    connect(nullptr, &SenderObject::signal1, &r1, &ReceiverObject::slot1);
+
+    QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SenderObject, Unknown): invalid null parameter");
+    connect(&obj, &SenderObject::signal1, nullptr, &ReceiverObject::slot1);
+}
+
 struct QmlReceiver : public QtPrivate::QSlotObjectBase
 {
     int callCount;