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>

7 files changed, 7 insertions, 9 deletions

diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index 45af766db9..3498351639 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -102,8 +102,7 @@ public:
     QDebug(const QDebug &o) : stream(o.stream) { ++stream->ref; }
     QDebug(QDebug &&other) noexcept : stream{qExchange(other.stream, nullptr)} {}
     inline QDebug &operator=(const QDebug &other);
-    QDebug &operator=(QDebug &&other) noexcept
-    { QDebug{std::move(other)}.swap(*this); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QDebug)
     ~QDebug();
     inline void swap(QDebug &other) noexcept { qSwap(stream, other.stream); }
 
diff --git a/src/corelib/io/qdir.h b/src/corelib/io/qdir.h
index 8b8aa05223..92b3faee7e 100644
--- a/src/corelib/io/qdir.h
+++ b/src/corelib/io/qdir.h
@@ -121,7 +121,7 @@ public:
     ~QDir();
 
     QDir &operator=(const QDir &);
-    QDir &operator=(QDir &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QDir)
 
     void swap(QDir &other) noexcept
     { qSwap(d_ptr, other.d_ptr); }
diff --git a/src/corelib/io/qfileinfo.h b/src/corelib/io/qfileinfo.h
index e578848be0..344c16abf8 100644
--- a/src/corelib/io/qfileinfo.h
+++ b/src/corelib/io/qfileinfo.h
@@ -79,7 +79,7 @@ public:
     ~QFileInfo();
 
     QFileInfo &operator=(const QFileInfo &fileinfo);
-    QFileInfo &operator=(QFileInfo &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFileInfo)
 
     void swap(QFileInfo &other) noexcept
     { qSwap(d_ptr, other.d_ptr); }
diff --git a/src/corelib/io/qprocess.h b/src/corelib/io/qprocess.h
index 4ed01197b3..cfa86c8508 100644
--- a/src/corelib/io/qprocess.h
+++ b/src/corelib/io/qprocess.h
@@ -68,7 +68,7 @@ public:
     QProcessEnvironment();
     QProcessEnvironment(const QProcessEnvironment &other);
     ~QProcessEnvironment();
-    QProcessEnvironment &operator=(QProcessEnvironment && other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QProcessEnvironment)
     QProcessEnvironment &operator=(const QProcessEnvironment &other);
 
     void swap(QProcessEnvironment &other) noexcept { qSwap(d, other.d); }
diff --git a/src/corelib/io/qstorageinfo.h b/src/corelib/io/qstorageinfo.h
index 237e68d2a1..ec95ea3b23 100644
--- a/src/corelib/io/qstorageinfo.h
+++ b/src/corelib/io/qstorageinfo.h
@@ -62,7 +62,7 @@ public:
     ~QStorageInfo();
 
     QStorageInfo &operator=(const QStorageInfo &other);
-    QStorageInfo &operator=(QStorageInfo &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QStorageInfo)
 
     inline void swap(QStorageInfo &other) noexcept
     { qSwap(d, other.d); }
diff --git a/src/corelib/io/qurl.h b/src/corelib/io/qurl.h
index c4903ebce4..c13b21ef44 100644
--- a/src/corelib/io/qurl.h
+++ b/src/corelib/io/qurl.h
@@ -184,8 +184,7 @@ public:
 #endif
     QUrl(QUrl &&other) noexcept : d(other.d)
     { other.d = nullptr; }
-    inline QUrl &operator=(QUrl &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QUrl)
     ~QUrl();
 
     inline void swap(QUrl &other) noexcept { qSwap(d, other.d); }
diff --git a/src/corelib/io/qurlquery.h b/src/corelib/io/qurlquery.h
index c1917a4bf5..de474924ce 100644
--- a/src/corelib/io/qurlquery.h
+++ b/src/corelib/io/qurlquery.h
@@ -67,7 +67,7 @@ public:
 
     QUrlQuery(const QUrlQuery &other);
     QUrlQuery &operator=(const QUrlQuery &other);
-    QUrlQuery &operator=(QUrlQuery &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QUrlQuery)
     ~QUrlQuery();
 
     bool operator==(const QUrlQuery &other) const;