Mark all remaining RAII/smart pointer class ctors [[nodiscard]]

... like QUIP-0019 suggests.

The main problem here is finding these classes. We don't have markup
for RAII classes, so I had to find them by name. This patch is based
on the output of

    git grep -we Q[A-Z0-9a-z_]+er

extracting the matches and piping them through sort -u, then removing
a lot of suffixes like Manager and Handler, then visually inspecting
the remaining list.

Task-number: QTBUG-104164
Change-Id: I59b18d8d0a0237fcc11047857adc39b984ad7fcb
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 31d834a1c0d83d22fcf74624577013a558ad1974)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/ipc/qsharedmemory_p.h

@@ -43,7 +43,7 @@ class QSharedMemoryLocker
 {
 
 public:
-    inline QSharedMemoryLocker(QSharedMemory *sharedMemory) : q_sm(sharedMemory)
+    Q_NODISCARD_CTOR QSharedMemoryLocker(QSharedMemory *sharedMemory) : q_sm(sharedMemory)
     {
         Q_ASSERT(q_sm);
     }

src/corelib/kernel/qeventloop.h

@@ -54,8 +54,11 @@ class QEventLoopLockerPrivate;
 class Q_CORE_EXPORT QEventLoopLocker
 {
 public:
+    Q_NODISCARD_CTOR
     QEventLoopLocker();
+    Q_NODISCARD_CTOR
     explicit QEventLoopLocker(QEventLoop *loop);
+    Q_NODISCARD_CTOR
     explicit QEventLoopLocker(QThread *thread);
     ~QEventLoopLocker();
 

src/corelib/kernel/qiterable.h

@@ -19,16 +19,16 @@ namespace QtPrivate {
         QTaggedPointer<Storage, Tag> m_pointer;
 
     public:
-        QConstPreservingPointer(std::nullptr_t) : m_pointer(nullptr, Const) {}
+        Q_NODISCARD_CTOR QConstPreservingPointer(std::nullptr_t) : m_pointer(nullptr, Const) {}
 
-        QConstPreservingPointer(const void *pointer, qsizetype alignment)
+        Q_NODISCARD_CTOR QConstPreservingPointer(const void *pointer, qsizetype alignment)
             : m_pointer(reinterpret_cast<Storage *>(const_cast<void *>(pointer)), Const)
         {
             Q_UNUSED(alignment);
             Q_ASSERT(alignment > qsizetype(alignof(Storage)));
         }
 
-        QConstPreservingPointer(void *pointer, qsizetype alignment)
+        Q_NODISCARD_CTOR QConstPreservingPointer(void *pointer, qsizetype alignment)
             : m_pointer(reinterpret_cast<Storage *>(pointer), Mutable)
         {
             Q_UNUSED(alignment);
@@ -36,20 +36,20 @@ namespace QtPrivate {
         }
 
         template<typename InputType>
-        QConstPreservingPointer(const InputType *pointer)
+        Q_NODISCARD_CTOR QConstPreservingPointer(const InputType *pointer)
             : m_pointer(reinterpret_cast<Storage *>(const_cast<InputType *>(pointer)), Const)
         {
             static_assert(alignof(InputType) >= alignof(Storage));
         }
 
         template<typename InputType>
-        QConstPreservingPointer(InputType *pointer)
+        Q_NODISCARD_CTOR QConstPreservingPointer(InputType *pointer)
             : m_pointer(reinterpret_cast<Storage *>(pointer), Mutable)
         {
             static_assert(alignof(InputType) >= alignof(Storage));
         }
 
-        QConstPreservingPointer() = default;
+        Q_NODISCARD_CTOR QConstPreservingPointer() = default;
 
         const Type *constPointer() const
         {

src/corelib/tools/qarraydatapointer.h

@@ -27,27 +27,32 @@ public:
 
     typedef typename std::conditional<pass_parameter_by_value, T, const T &>::type parameter_type;
 
+    Q_NODISCARD_CTOR
     constexpr QArrayDataPointer() noexcept
         : d(nullptr), ptr(nullptr), size(0)
     {
     }
 
+    Q_NODISCARD_CTOR
     QArrayDataPointer(const QArrayDataPointer &other) noexcept
         : d(other.d), ptr(other.ptr), size(other.size)
     {
         ref();
     }
 
+    Q_NODISCARD_CTOR
     constexpr QArrayDataPointer(Data *header, T *adata, qsizetype n = 0) noexcept
         : d(header), ptr(adata), size(n)
     {
     }
 
+    Q_NODISCARD_CTOR
     explicit QArrayDataPointer(QPair<QTypedArrayData<T> *, T *> adata, qsizetype n = 0) noexcept
         : d(adata.first), ptr(adata.second), size(n)
     {
     }
 
+    Q_NODISCARD_CTOR
     static QArrayDataPointer fromRawData(const T *rawData, qsizetype length) noexcept
     {
         Q_ASSERT(rawData || !length);
@@ -61,6 +66,7 @@ public:
         return *this;
     }
 
+    Q_NODISCARD_CTOR
     QArrayDataPointer(QArrayDataPointer &&other) noexcept
         : d(other.d), ptr(other.ptr), size(other.size)
     {

src/corelib/tools/qtaggedpointer.h

@@ -43,10 +43,10 @@ public:
     static constexpr quintptr tagMask() { return QtPrivate::TagInfo<T>::alignment - 1; }
     static constexpr quintptr pointerMask() { return ~tagMask(); }
 
-    constexpr QTaggedPointer() noexcept : d(0) {}
+    Q_NODISCARD_CTOR constexpr QTaggedPointer() noexcept : d(0) {}
-    constexpr QTaggedPointer(std::nullptr_t) noexcept : QTaggedPointer() {}
+    Q_NODISCARD_CTOR constexpr QTaggedPointer(std::nullptr_t) noexcept : QTaggedPointer() {}
 
-    explicit QTaggedPointer(T *pointer, Tag tag = Tag()) noexcept
+    Q_NODISCARD_CTOR explicit QTaggedPointer(T *pointer, Tag tag = Tag()) noexcept
         : d(quintptr(pointer) | quintptr(tag))
     {
         static_assert(sizeof(Type*) == sizeof(QTaggedPointer));

src/dbus/qdbusintegrator.cpp

@@ -1944,7 +1944,7 @@ bool QDBusConnectionPrivate::send(const QDBusMessage& message)
 class QDBusBlockingCallWatcher
 {
 public:
-    QDBusBlockingCallWatcher(const QDBusMessage &message)
+    Q_NODISCARD_CTOR QDBusBlockingCallWatcher(const QDBusMessage &message)
         : m_message(message), m_maxCallTimeoutMs(0)
     {
 #if defined(QT_NO_DEBUG)

src/dbus/qdbusthreaddebug_p.h

@@ -93,7 +93,7 @@ struct QDBusReadLocker: QDBusLockerBase
 {
     QDBusConnectionPrivate *self;
     ThreadAction action;
-    inline QDBusReadLocker(ThreadAction a, QDBusConnectionPrivate *s)
+    Q_NODISCARD_CTOR QDBusReadLocker(ThreadAction a, QDBusConnectionPrivate *s)
         : self(s), action(a)
     {
         reportThreadAction(action, BeforeLock, self);
@@ -113,7 +113,7 @@ struct QDBusWriteLocker: QDBusLockerBase
 {
     QDBusConnectionPrivate *self;
     ThreadAction action;
-    inline QDBusWriteLocker(ThreadAction a, QDBusConnectionPrivate *s)
+    Q_NODISCARD_CTOR QDBusWriteLocker(ThreadAction a, QDBusConnectionPrivate *s)
         : self(s), action(a)
     {
         reportThreadAction(action, BeforeLock, self);

src/plugins/platforms/directfb/qdirectfbconvenience.h

@@ -62,7 +62,7 @@ template <typename T>
 class QDirectFBPointer : public QScopedPointer<T, QDirectFBInterfaceCleanupHandler<T> >
 {
 public:
-    QDirectFBPointer(T *t = nullptr)
+    Q_NODISCARD_CTOR QDirectFBPointer(T *t = nullptr)
         : QScopedPointer<T, QDirectFBInterfaceCleanupHandler<T> >(t)
     {}
 

src/plugins/platforms/xcb/qxcbconnection.h

@@ -367,7 +367,7 @@ Q_DECLARE_TYPEINFO(QXcbConnection::TabletData, Q_RELOCATABLE_TYPE);
 class QXcbConnectionGrabber
 {
 public:
-    QXcbConnectionGrabber(QXcbConnection *connection);
+    Q_NODISCARD_CTOR QXcbConnectionGrabber(QXcbConnection *connection);
     ~QXcbConnectionGrabber();
     void release();
 private: