QOpenGLBuffer: add move-SMFs and swap()s

- add move special member functions (docs copied from QHostInfo)

- add member swap

- use move-and-swap, not pure-swap, because these objects hold
  resources (handles) other than just memory

- Q_DECLARE_SHARED (it's not implicitly shared, but explicitly)
  - adds ADL swap and Q_DECLARE_TYPEINFO

[ChangeLog][QtOpenGL][QOpenGLBuffer] Added member-swap(), move
constructor, move assignment operator.

Change-Id: I22dc92108bdd393fff4361db23e94eaf3d7ea9cc
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/opengl/qopenglbuffer.cpp

@@ -166,7 +166,7 @@ QOpenGLBuffer::QOpenGLBuffer(const QOpenGLBuffer &other)
 */
 QOpenGLBuffer::~QOpenGLBuffer()
 {
-    if (!d_ptr->ref.deref()) {
+    if (d_ptr && !d_ptr->ref.deref()) {
         destroy();
         delete d_ptr;
     }
@@ -182,7 +182,7 @@ QOpenGLBuffer &QOpenGLBuffer::operator=(const QOpenGLBuffer &other)
 {
     if (d_ptr != other.d_ptr) {
         other.d_ptr->ref.ref();
-        if (!d_ptr->ref.deref()) {
+        if (d_ptr && !d_ptr->ref.deref()) {
             destroy();
             delete d_ptr;
         }
@@ -191,6 +191,36 @@ QOpenGLBuffer &QOpenGLBuffer::operator=(const QOpenGLBuffer &other)
     return *this;
 }
 
+/*!
+    \fn QOpenGLBuffer::QOpenGLBuffer(QOpenGLBuffer &&other)
+    \since 6.5
+
+    Move-constructs a new QOpenGLBuffer from \a other.
+
+    \note The moved-from object \a other is placed in a partially-formed state,
+    in which the only valid operations are destruction and assignment of a new
+    value.
+*/
+
+/*!
+    \fn QOpenGLBuffer &QOpenGLBuffer::operator=(QOpenGLBuffer &&other)
+    \since 6.5
+
+    Move-assigns \a other to this QOpenGLBuffer instance.
+
+    \note The moved-from object \a other is placed in a partially-formed state,
+    in which the only valid operations are destruction and assignment of a new
+    value.
+*/
+
+/*!
+    \fn QOpenGLBuffer::swap(QOpenGLBuffer &other)
+    \since 6.5
+
+    Swaps buffer \a other with this buffer. This operation is very fast and
+    never fails.
+*/
+
 /*!
     Returns the type of buffer represented by this object.
 */

src/opengl/qopenglbuffer.h

@@ -29,9 +29,15 @@ public:
     QOpenGLBuffer();
     explicit QOpenGLBuffer(QOpenGLBuffer::Type type);
     QOpenGLBuffer(const QOpenGLBuffer &other);
+    QOpenGLBuffer(QOpenGLBuffer &&other) noexcept
+        : d_ptr{std::exchange(other.d_ptr, nullptr)} {}
     ~QOpenGLBuffer();
 
     QOpenGLBuffer &operator=(const QOpenGLBuffer &other);
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QOpenGLBuffer)
+
+    void swap(QOpenGLBuffer &other) noexcept
+    { return qt_ptr_swap(d_ptr, other.d_ptr); }
 
     enum UsagePattern
     {
@@ -98,6 +104,7 @@ private:
 
     Q_DECLARE_PRIVATE(QOpenGLBuffer)
 };
+Q_DECLARE_SHARED(QOpenGLBuffer)
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QOpenGLBuffer::RangeAccessFlags)
 

tests/auto/gui/qopengl/tst_qopengl.cpp

@@ -1588,6 +1588,13 @@ void tst_QOpenGL::bufferCreate()
     buf.allocate(128);
     QCOMPARE(buf.size(), 128);
 
+    {
+        QOpenGLBuffer moved = std::move(buf);
+        QCOMPARE_EQ(moved.isCreated(), true);
+        QCOMPARE_EQ(moved.size(), 128);
+        buf = std::move(moved);
+    }
+
     buf.release();
 
     buf.destroy();