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QObject::connect(): fail to connect to a functor if UniqueConnection is passed

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The connect() documentation makes it clear that UniqueConnection does
not work with free functions / function objects and the like; only with
actual PMFs. Rather than silently *ignoring* the flag, be vocal about its
presence by warning, and make the connection fail (as the user has
passed an illegal argument).

[ChangeLog][QtCore][QObject] QObject::connect() now will refuse to
connect a signal to a free function / function object if UniqueConnection
is passed. Note that UniqueConnection has never worked for such
connections -- the flag was simply ignored, and they were established
multiple times. Now, the flag is not ignored and results in a connection
failure (as well as a runtime warning by Qt).

Change-Id: I6509667018c74f9bd24910cde0a1b16c5f84f064
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Giuseppe D'Angelo 2021-08-26 17:18:40 +02:00
parent c9830c2fb9
commit 7d4d47de70
2 changed files with 29 additions and 9 deletions
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33
src/corelib/kernel/qobject.cpp
View File

@ -4974,6 +4974,19 @@ QMetaObject::Connection QObject::connectImpl(const QObject *sender, void **signa
return QObjectPrivate::connectImpl(sender, signal_index, receiver, slot, slotObj, type, types, senderMetaObject);
}
static void connectWarning(const QObject *sender,
const QMetaObject *senderMetaObject,
const QObject *receiver,
const char *message)
{
const char *senderString = sender ? sender->metaObject()->className()
: senderMetaObject ? senderMetaObject->className()
: "Unknown";
const char *receiverString = receiver ? receiver->metaObject()->className()
: "Unknown";
qCWarning(lcConnect, "QObject::connect(%s, %s): %s", senderString, receiverString, message);
}
/*!
\internal
@ -4986,18 +4999,24 @@ QMetaObject::Connection QObjectPrivate::connectImpl(const QObject *sender, int s
QtPrivate::QSlotObjectBase *slotObj, int type,
const int *types, const QMetaObject *senderMetaObject)
{
if (!sender || !receiver || !slotObj || !senderMetaObject) {
const char *senderString = sender ? sender->metaObject()->className()
: senderMetaObject ? senderMetaObject->className()
: "Unknown";
const char *receiverString = receiver ? receiver->metaObject()->className()
: "Unknown";
qCWarning(lcConnect, "QObject::connect(%s, %s): invalid nullptr parameter", senderString, receiverString);
auto connectFailureGuard = qScopeGuard([&]()
{
if (slotObj)
slotObj->destroyIfLastRef();
});
if (!sender || !receiver || !slotObj || !senderMetaObject) {
connectWarning(sender, senderMetaObject, receiver, "invalid nullptr parameter");
return QMetaObject::Connection();
}
if (type & Qt::UniqueConnection && !slot) {
connectWarning(sender, senderMetaObject, receiver, "unique connections require a pointer to member function of a QObject subclass");
return QMetaObject::Connection();
}
connectFailureGuard.dismiss();
QObject *s = const_cast<QObject *>(sender);
QObject *r = const_cast<QObject *>(receiver);

5
tests/auto/corelib/kernel/qobject/tst_qobject.cpp
View File

@ -6241,10 +6241,11 @@ void tst_QObject::connectFunctorWithContextUnique()
SenderObject sender;
ReceiverObject receiver;
QObject::connect(&sender, &SenderObject::signal1, &receiver, &ReceiverObject::slot1);
QVERIFY(QObject::connect(&sender, &SenderObject::signal1, &receiver, &ReceiverObject::slot1));
receiver.count_slot1 = 0;
QObject::connect(&sender, &SenderObject::signal1, &receiver, SlotFunctor(), Qt::UniqueConnection);
QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SenderObject, ReceiverObject): unique connections require a pointer to member function of a QObject subclass");
QVERIFY(!QObject::connect(&sender, &SenderObject::signal1, &receiver, [&](){ receiver.slot1(); }, Qt::UniqueConnection));
sender.emitSignal1();
QCOMPARE(receiver.count_slot1, 1);