QDBusMessage: add move-constructor

Since the class was not desigend to support a nullptr d_ptr, this
change requires modifications in the destructor and copy-ctor.
The change in destructor is straightforward - simply add a check
that d_ptr is not null.
The copy-constructor was using a qAtomicAssign() helper, which
was relying on the fact that the passed pointers are not null, so
we cannot use it anymore. Use copy-and-swap instead.

The other methods do not require any changes, because the
moved-from object can only be destroyed or assigned-to.

[ChangeLog][QtDBus][QDBusMessage] Added move constructor.

Change-Id: Ic8a0d913b9cf2f881369f7ad4f3a88c1f3fb345f
Reviewed-by: Marc Mutz <[email protected]>

3 files changed, 39 insertions, 2 deletions

diff --git a/src/dbus/qdbusmessage.cpp b/src/dbus/qdbusmessage.cpp
index 24a80528f65..b10266ac8b7 100644
--- a/src/dbus/qdbusmessage.cpp
+++ b/src/dbus/qdbusmessage.cpp
@@ -520,6 +520,15 @@ QDBusMessage::QDBusMessage()
 }
 
 /*!
+    \fn QDBusMessage::QDBusMessage(QDBusMessage &&other)
+    \since 6.11
+
+    Moves \a other into this object.
+
+    \include qdbusmessage.cpp partially-formed
+*/
+
+/*!
     Constructs a copy of the object given by \a other.
 
     Note: QDBusMessage objects are shared. Modifications made to the
@@ -537,7 +546,7 @@ QDBusMessage::QDBusMessage(const QDBusMessage &other)
 */
 QDBusMessage::~QDBusMessage()
 {
-    if (!d_ptr->ref.deref())
+    if (d_ptr && !d_ptr->ref.deref())
         delete d_ptr;
 }
 
@@ -562,7 +571,8 @@ QDBusMessage::~QDBusMessage()
 */
 QDBusMessage &QDBusMessage::operator=(const QDBusMessage &other)
 {
-    qAtomicAssign(d_ptr, other.d_ptr);
+    QDBusMessage copy(other);
+    swap(copy);
     return *this;
 }
 
diff --git a/src/dbus/qdbusmessage.h b/src/dbus/qdbusmessage.h
index f6db3bc21e6..608b9779d22 100644
--- a/src/dbus/qdbusmessage.h
+++ b/src/dbus/qdbusmessage.h
@@ -31,6 +31,7 @@ public:
 
     QDBusMessage();
     QDBusMessage(const QDBusMessage &other);
+    QDBusMessage(QDBusMessage &&other) noexcept : d_ptr(std::exchange(other.d_ptr, nullptr)) {}
     QDBusMessage &operator=(QDBusMessage &&other) noexcept { swap(other); return *this; }
     QDBusMessage &operator=(const QDBusMessage &other);
     ~QDBusMessage();
diff --git a/tests/auto/dbus/qdbusmessage/tst_qdbusmessage.cpp b/tests/auto/dbus/qdbusmessage/tst_qdbusmessage.cpp
index 475dbcec0bb..bc2e28e7d24 100644
--- a/tests/auto/dbus/qdbusmessage/tst_qdbusmessage.cpp
+++ b/tests/auto/dbus/qdbusmessage/tst_qdbusmessage.cpp
@@ -23,6 +23,7 @@ class tst_QDBusMessage : public QObject
     Q_OBJECT
 private Q_SLOTS:
     void moveAssign();
+    void moveConstruct();
 };
 
 void tst_QDBusMessage::moveAssign()
@@ -49,6 +50,31 @@ void tst_QDBusMessage::moveAssign()
     }
 }
 
+void tst_QDBusMessage::moveConstruct()
+{
+    QDBusMessage referenceMessage =
+            QDBusMessage::createMethodCall("org.kde.selftest"_L1, "/org/kde/selftest"_L1,
+                                           "org.kde.selftest"_L1, "Ping"_L1);
+    referenceMessage << "ping"_L1;
+
+    // moved-from object can be destroyed...
+    {
+        QDBusMessage copy = referenceMessage;
+        QDBusMessage other = std::move(copy);
+        COMPARE_MESSAGES(other, referenceMessage);
+    }
+    // ... or assigned-to
+    {
+        QDBusMessage copy = referenceMessage;
+        QDBusMessage other = std::move(copy);
+        COMPARE_MESSAGES(other, referenceMessage);
+        other << "other_arg"_L1; // also affects referenceMessage
+        copy = other;
+        COMPARE_MESSAGES(copy, other);
+        COMPARE_MESSAGES(copy, referenceMessage);
+    }
+}
+
 #undef COMPARE_MESSAGES
 
 QTEST_MAIN(tst_QDBusMessage)