Make QMetaObject::Connection check its state deeply

Since Connection can be copied, one copy could be used for
disconnecting, but the other's d_ptr wouldn't get updated and would
continue to report as still connected.

This patch fixes that by making it check the internal state. That is
only done after d_ptr is already known to be non-null. Unfortunately,
that is the common path:

  if (connect(sender, &Sender::signal, [] {}))

will call an out-of-line function. I don't see a way out.

Task-number: QTBUG-46213
Change-Id: I66a35ce5f88941f29aa6ffff13dfb45dca68a350
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/kernel/qobject.cpp

@@ -4913,6 +4913,16 @@ QMetaObject::Connection::~Connection()
         static_cast<QObjectPrivate::Connection *>(d_ptr)->deref();
 }
 
+/*! \internal Returns true if the object is still connected */
+bool QMetaObject::Connection::isConnected_helper() const
+{
+    Q_ASSERT(d_ptr);    // we're only called from operator RestrictedBool() const
+    QObjectPrivate::Connection *c = static_cast<QObjectPrivate::Connection *>(d_ptr);
+
+    return c->receiver;
+}
+
+
 /*!
     \fn QMetaObject::Connection::operator bool() const
 

src/corelib/kernel/qobjectdefs.h

@@ -472,6 +472,7 @@ class Q_CORE_EXPORT QMetaObject::Connection {
     friend class QObject;
     friend class QObjectPrivate;
     friend struct QMetaObject;
+    bool isConnected_helper() const;
 public:
     ~Connection();
     Connection();
@@ -481,7 +482,7 @@ public:
     operator bool() const;
 #else
     typedef void *Connection::*RestrictedBool;
-    operator RestrictedBool() const { return d_ptr ? &Connection::d_ptr : 0; }
+    operator RestrictedBool() const { return d_ptr && isConnected_helper() ? &Connection::d_ptr : 0; }
 #endif
 
 #ifdef Q_COMPILER_RVALUE_REFS

tests/auto/corelib/kernel/qobject/tst_qobject.cpp

@@ -918,6 +918,8 @@ void tst_QObject::connectDisconnectNotifyPMF()
     QMetaObject::Connection conn = connect((SenderObject*)s, &SenderObject::signal1,
                                            (ReceiverObject*)r, &ReceiverObject::slot1);
 
+    QVERIFY(conn);
+
     // Test disconnectNotify when disconnecting by QMetaObject::Connection
     QVERIFY(QObject::disconnect(conn));
     // disconnectNotify() is not called, but it probably should be.
@@ -5751,7 +5753,6 @@ void tst_QObject::connectFunctorWithContext()
 {
     int status = 1;
     SenderObject obj;
-    QMetaObject::Connection handle;
     ContextObject *context = new ContextObject;
     QEventLoop e;
 
@@ -6058,8 +6059,12 @@ void tst_QObject::disconnectDoesNotLeakFunctor()
             QVERIFY(c2);
             QCOMPARE(countedStructObjectsCount, 2);
             QVERIFY(QObject::disconnect(c1));
+            QVERIFY(!c1);
+            QVERIFY(!c2);
             // functor object has been destroyed
             QCOMPARE(countedStructObjectsCount, 1);
+            QVERIFY(!QObject::disconnect(c2));
+            QCOMPARE(countedStructObjectsCount, 1);
         }
         QCOMPARE(countedStructObjectsCount, 0);
     }