Centralize the implementation of move assignment operators

At the moment we have two main strategies for dealing with move
assignment in Qt:

1) move-and-swap, used by "containers" (in the broad sense): containers,
but also smart pointers and similar classes that can hold user-defined
types;

2) pure swap, used by containers that hold only memory (e.g. QString,
QByteArray, ...) as well as most implicitly shared datatypes.

Given the fact that a move assignment operator's code is just
boilerplate (whether it's move-and-swap or pure swap), provide two
_strictly internal_ macros to help write them, and apply the macros
across corelib and gui, porting away from the hand-rolled
implementations.

The rule of thumb when porting to the new macros is:

* Try to stick to the existing code behavior, unless broken

* if changing, then follow this checklist:

  * if the class does not have a move constructor => pure swap
    (but consider ADDING a move constructor, if possible!)

  * if the class does have a move constructor, try to follow the
     criteria above, namely:

    * if the class holds only memory, pure swap;

    * if the class may hold anything else but memory (file handles,
      etc.), then move and swap.

Noteworthy details:

* some operators planned to be removed in Qt 6 were not ported;

* as drive-by, some move constructors were simplified to be using
qExchange(); others were outright broken and got fixed;

* some contained some more interesting code and were not touched.

Change-Id: Idaab3489247dcbabb6df3fa1e5286b69e1d372e9
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

8 files changed, 10 insertions, 23 deletions

diff --git a/src/gui/painting/qbrush.h b/src/gui/painting/qbrush.h
index 3b7b949bde..fea5afad57 100644
--- a/src/gui/painting/qbrush.h
+++ b/src/gui/painting/qbrush.h
@@ -78,8 +78,7 @@ public:
 
     ~QBrush();
     QBrush &operator=(const QBrush &brush);
-    inline QBrush &operator=(QBrush &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QBrush)
     inline void swap(QBrush &other) noexcept
     { qSwap(d, other.d); }
 
diff --git a/src/gui/painting/qcolorspace.h b/src/gui/painting/qcolorspace.h
index 08c9944301..7505c6eca7 100644
--- a/src/gui/painting/qcolorspace.h
+++ b/src/gui/painting/qcolorspace.h
@@ -95,12 +95,7 @@ public:
     QColorSpace(QColorSpace &&colorSpace) noexcept
             : d_ptr(qExchange(colorSpace.d_ptr, nullptr))
     { }
-    QColorSpace &operator=(QColorSpace &&colorSpace) noexcept
-    {
-        // Make the deallocation of this->d_ptr happen in ~QColorSpace()
-        QColorSpace(std::move(colorSpace)).swap(*this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QColorSpace)
 
     void swap(QColorSpace &colorSpace) noexcept
     { qSwap(d_ptr, colorSpace.d_ptr); }
diff --git a/src/gui/painting/qcolortransform.h b/src/gui/painting/qcolortransform.h
index 94b6b3a385..fa52f2e152 100644
--- a/src/gui/painting/qcolortransform.h
+++ b/src/gui/painting/qcolortransform.h
@@ -64,11 +64,7 @@ public:
         QColorTransform{other}.swap(*this);
         return *this;
     }
-    QColorTransform &operator=(QColorTransform &&other) noexcept
-    {
-        QColorTransform{std::move(other)}.swap(*this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QColorTransform)
 
     void swap(QColorTransform &other) noexcept { qSwap(d, other.d); }
 
diff --git a/src/gui/painting/qpagelayout.h b/src/gui/painting/qpagelayout.h
index 6965606252..a7858edfaf 100644
--- a/src/gui/painting/qpagelayout.h
+++ b/src/gui/painting/qpagelayout.h
@@ -81,7 +81,7 @@ public:
                 const QMarginsF &margins, Unit units = Point,
                 const QMarginsF &minMargins = QMarginsF(0, 0, 0, 0));
     QPageLayout(const QPageLayout &other);
-    QPageLayout &operator=(QPageLayout &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPageLayout)
     QPageLayout &operator=(const QPageLayout &other);
     ~QPageLayout();
 
diff --git a/src/gui/painting/qpagesize.h b/src/gui/painting/qpagesize.h
index 1fa6c86081..fbaec0da3f 100644
--- a/src/gui/painting/qpagesize.h
+++ b/src/gui/painting/qpagesize.h
@@ -232,7 +232,7 @@ public:
                        const QString &name = QString(),
                        SizeMatchPolicy matchPolicy = FuzzyMatch);
     QPageSize(const QPageSize &other);
-    QPageSize &operator=(QPageSize &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPageSize)
     QPageSize &operator=(const QPageSize &other);
     ~QPageSize();
 
diff --git a/src/gui/painting/qpainterpath.h b/src/gui/painting/qpainterpath.h
index a839a73b4b..0099a7408a 100644
--- a/src/gui/painting/qpainterpath.h
+++ b/src/gui/painting/qpainterpath.h
@@ -92,8 +92,7 @@ public:
     explicit QPainterPath(const QPointF &startPoint);
     QPainterPath(const QPainterPath &other);
     QPainterPath &operator=(const QPainterPath &other);
-    inline QPainterPath &operator=(QPainterPath &&other) noexcept
-    { qSwap(d_ptr, other.d_ptr); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPainterPath)
     ~QPainterPath();
 
     inline void swap(QPainterPath &other) noexcept { d_ptr.swap(other.d_ptr); }
diff --git a/src/gui/painting/qpen.h b/src/gui/painting/qpen.h
index 38282bda39..db280c765b 100644
--- a/src/gui/painting/qpen.h
+++ b/src/gui/painting/qpen.h
@@ -71,9 +71,8 @@ public:
 
     QPen &operator=(const QPen &pen) noexcept;
     QPen(QPen &&other) noexcept
-        : d(other.d) { other.d = nullptr; }
-    QPen &operator=(QPen &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+        : d(qExchange(other.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPen)
     void swap(QPen &other) noexcept { qSwap(d, other.d); }
 
     Qt::PenStyle style() const;
diff --git a/src/gui/painting/qregion.h b/src/gui/painting/qregion.h
index 8b991f2fb2..8f52185ed9 100644
--- a/src/gui/painting/qregion.h
+++ b/src/gui/painting/qregion.h
@@ -70,12 +70,11 @@ public:
     QRegion(const QPolygon &pa, Qt::FillRule fillRule = Qt::OddEvenFill);
     QRegion(const QRegion &region);
     QRegion(QRegion &&other) noexcept
-        : d(other.d) { other.d = const_cast<QRegionData*>(&shared_empty); }
+        : d(qExchange(other.d, const_cast<QRegionData*>(&shared_empty))) {}
     QRegion(const QBitmap &bitmap);
     ~QRegion();
     QRegion &operator=(const QRegion &);
-    inline QRegion &operator=(QRegion &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QRegion);
     inline void swap(QRegion &other) noexcept { qSwap(d, other.d); }
     bool isEmpty() const;
     bool isNull() const;