From a40ca88b63933f176d408e7820e3c423fd44669c Mon Sep 17 00:00:00 2001
From: Ahmad Samir <a.samirh78@gmail.com>
Date: Sun, 15 Oct 2023 13:51:48 +0300
Subject: [PATCH] QObject: assert connection type isn't UniqueConnection for
 lambdas
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An assert is harder to miss than a warning, which makes it more likely
to get fixed. Thanks to Mårten Nordheim for the idea.

Add the assert in inline code so that users compiling their code in
debug mode (or with -DQT_FORCE_ASSERTS) can hit the assert even when
built agaist a release build of Qt (not everyone compile their code with
a debug build of Qt). Thanks to Giuseppe D'Angelo for the idea.

Pick-to: 6.5
Task-number: QTBUG-115125
Change-Id: I2935d32ea5a2c288d7a836abbae66ac53cb5ab2f
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit afddb327bd866ac693e475901d4d10acc6c83757)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit fd664000625bca62db20f0954240e0dcbd32cad5)
---
 src/corelib/kernel/qobject.h                  |  7 +++-
 .../corelib/kernel/qobject/tst_qobject.cpp    | 37 ++++++++++++++++++-
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index f6a3ebc5c36..0b196b901b8 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -227,8 +227,13 @@ public:
             types = QtPrivate::ConnectionTypes<typename SignalType::Arguments>::types();
 
         void **pSlot = nullptr;
-        if constexpr (std::is_member_function_pointer_v<std::decay_t<Func2>>)
+        if constexpr (std::is_member_function_pointer_v<std::decay_t<Func2>>) {
             pSlot = const_cast<void **>(reinterpret_cast<void *const *>(&slot));
+        } else {
+            Q_ASSERT_X((type & Qt::UniqueConnection) == 0, "",
+                       "QObject::connect: Unique connection requires the slot to be a pointer to "
+                       "a member function of a QObject subclass.");
+        }
 
         return connectImpl(sender, reinterpret_cast<void **>(&signal), context, pSlot,
                            QtPrivate::makeCallableObject<Func1>(std::forward<Func2>(slot)),
diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 31345cc3333..e69a19c8c66 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -6303,11 +6303,46 @@ void tst_QObject::connectFunctorWithContextUnique()
     QVERIFY(QObject::connect(&sender, &SenderObject::signal1, &receiver, &ReceiverObject::slot1));
     receiver.count_slot1 = 0;
 
-    QTest::ignoreMessage(QtWarningMsg, "QObject::connect(SenderObject, ReceiverObject): unique connections require a pointer to member function of a QObject subclass");
+    QVERIFY(QObject::connect(&sender, &SenderObject::signal2, &receiver, &ReceiverObject::slot2));
+    receiver.count_slot2 = 0;
+
+    const auto oredType = Qt::ConnectionType(Qt::DirectConnection | Qt::UniqueConnection);
+
+    // Will assert in debug builds, so only test in release builds
+#if defined(QT_NO_DEBUG) && !defined(QT_FORCE_ASSERTS)
+    auto ignoreMsg = [] {
+        QTest::ignoreMessage(QtWarningMsg,
+                             "QObject::connect(SenderObject, ReceiverObject): unique connections "
+                             "require a pointer to member function of a QObject subclass");
+    };
+
+    ignoreMsg();
     QVERIFY(!QObject::connect(&sender, &SenderObject::signal1, &receiver, [&](){ receiver.slot1(); }, Qt::UniqueConnection));
 
+    ignoreMsg();
+    QVERIFY(!QObject::connect(
+        &sender, &SenderObject::signal2, &receiver, [&]() { receiver.slot2(); }, oredType));
+#endif
+
     sender.emitSignal1();
     QCOMPARE(receiver.count_slot1, 1);
+
+    sender.emitSignal2();
+    QCOMPARE(receiver.count_slot2, 1);
+
+    // Check connecting to PMF doesn't hit the assert
+
+    QVERIFY(QObject::connect(&sender, &SenderObject::signal3, &receiver, &ReceiverObject::slot3,
+                             Qt::UniqueConnection));
+    receiver.count_slot3 = 0;
+    sender.emitSignal3();
+    QCOMPARE(receiver.count_slot3, 1);
+
+    QVERIFY(QObject::connect(&sender, &SenderObject::signal4, &receiver, &ReceiverObject::slot4,
+                             oredType));
+    receiver.count_slot4 = 0;
+    sender.emitSignal4();
+    QCOMPARE(receiver.count_slot4, 1);
 }
 
 class MyFunctor