From fd664000625bca62db20f0954240e0dcbd32cad5 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: 6.6 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>
---
 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 9916626a3ce..713a62c2499 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -241,8 +241,13 @@ 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 a06238a494b..b626d0e3c4e 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -6429,11 +6429,46 @@ 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