QtWidgets: prevent detach attempts from first()/etc. use [dialogs, kernel, util, widgets]

The algorithm used was:
- If possible, just declare the container const
- Otherwise, for first()/last(), use constFirst()/constLast()
  and for front()/back(), to not destroy the use of the STL
  API subset, use qAsConst()

Did some caching of function returns here and there, and
converted one 0 to nullptr as a drive-by.

Also saves almost 4KiB in text size on optimized GCC 4.9
Linux AMD64 builds.

Change-Id: I04b7bfd68dc85c22de247cb65a310e1cbbca1e8c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

14 files changed, 51 insertions, 42 deletions

diff --git a/src/widgets/dialogs/qfiledialog.cpp b/src/widgets/dialogs/qfiledialog.cpp
index 50667e2a91..c4ed72edc3 100644
--- a/src/widgets/dialogs/qfiledialog.cpp
+++ b/src/widgets/dialogs/qfiledialog.cpp
@@ -2689,7 +2689,7 @@ void QFileDialogPrivate::saveSettings()
     settings.beginGroup(QLatin1String("FileDialog"));
 
     if (usingWidgets()) {
-        settings.setValue(QLatin1String("sidebarWidth"), qFileDialogUi->splitter->sizes().first());
+        settings.setValue(QLatin1String("sidebarWidth"), qFileDialogUi->splitter->sizes().constFirst());
         settings.setValue(QLatin1String("shortcuts"), QUrl::toStringList(qFileDialogUi->sidebar->urls()));
         settings.setValue(QLatin1String("treeViewHeader"), qFileDialogUi->treeView->header()->saveState());
     }
@@ -3001,9 +3001,9 @@ void QFileDialogPrivate::createWidgets()
     q->selectNameFilter(options->initiallySelectedNameFilter());
     q->setDefaultSuffix(options->defaultSuffix());
     q->setHistory(options->history());
-    if (options->initiallySelectedFiles().count() == 1)
-        q->selectFile(options->initiallySelectedFiles().first().fileName());
     const auto initiallySelectedFiles = options->initiallySelectedFiles();
+    if (initiallySelectedFiles.size() == 1)
+        q->selectFile(initiallySelectedFiles.first().fileName());
     for (const QUrl &url : initiallySelectedFiles)
         q->selectUrl(url);
     lineEdit()->selectAll();
@@ -4095,7 +4095,7 @@ QStringList QFSCompleter::splitPath(const QString &path) const
                 parts.removeFirst();
                 currentLocationList.removeLast();
             }
-            if (!currentLocationList.isEmpty() && currentLocationList.last().isEmpty())
+            if (!currentLocationList.isEmpty() && currentLocationList.constLast().isEmpty())
                 currentLocationList.removeLast();
             return currentLocationList + parts;
         }
diff --git a/src/widgets/dialogs/qfileinfogatherer.cpp b/src/widgets/dialogs/qfileinfogatherer.cpp
index 48ae5f1fc4..b20db8fc7c 100644
--- a/src/widgets/dialogs/qfileinfogatherer.cpp
+++ b/src/widgets/dialogs/qfileinfogatherer.cpp
@@ -217,9 +217,9 @@ void QFileInfoGatherer::run()
             condition.wait(&mutex);
         if (abort.load())
             return;
-        const QString thisPath = path.front();
+        const QString thisPath = qAsConst(path).front();
         path.pop_front();
-        const QStringList thisList = files.front();
+        const QStringList thisList = qAsConst(files).front();
         files.pop_front();
         locker.unlock();
 
diff --git a/src/widgets/dialogs/qfilesystemmodel.cpp b/src/widgets/dialogs/qfilesystemmodel.cpp
index bfa40317eb..c72761f2ae 100644
--- a/src/widgets/dialogs/qfilesystemmodel.cpp
+++ b/src/widgets/dialogs/qfilesystemmodel.cpp
@@ -374,7 +374,7 @@ QFileSystemModelPrivate::QFileSystemNode *QFileSystemModelPrivate::node(const QS
     QModelIndex index = QModelIndex(); // start with "My Computer"
 #if defined(Q_OS_WIN) && !defined(Q_OS_WINCE)
     if (absolutePath.startsWith(QLatin1String("//"))) { // UNC path
-        QString host = QLatin1String("\\\\") + pathElements.first();
+        QString host = QLatin1String("\\\\") + pathElements.constFirst();
         if (absolutePath == QDir::fromNativeSeparators(host))
             absolutePath.append(QLatin1Char('/'));
         if (longPath.endsWith(QLatin1Char('/')) && !absolutePath.endsWith(QLatin1Char('/')))
diff --git a/src/widgets/dialogs/qsidebar.cpp b/src/widgets/dialogs/qsidebar.cpp
index 2e884e238d..1b1eb6472e 100644
--- a/src/widgets/dialogs/qsidebar.cpp
+++ b/src/widgets/dialogs/qsidebar.cpp
@@ -127,7 +127,7 @@ QMimeData *QUrlModel::mimeData(const QModelIndexList &indexes) const
 */
 bool QUrlModel::canDrop(QDragEnterEvent *event)
 {
-    if (!event->mimeData()->formats().contains(mimeTypes().first()))
+    if (!event->mimeData()->formats().contains(mimeTypes().constFirst()))
         return false;
 
     const QList<QUrl> list = event->mimeData()->urls();
@@ -145,7 +145,7 @@ bool QUrlModel::canDrop(QDragEnterEvent *event)
 bool QUrlModel::dropMimeData(const QMimeData *data, Qt::DropAction action,
                                  int row, int column, const QModelIndex &parent)
 {
-    if (!data->formats().contains(mimeTypes().first()))
+    if (!data->formats().contains(mimeTypes().constFirst()))
         return false;
     Q_UNUSED(action);
     Q_UNUSED(column);
diff --git a/src/widgets/dialogs/qwizard.cpp b/src/widgets/dialogs/qwizard.cpp
index aa10f65389..53f947354c 100644
--- a/src/widgets/dialogs/qwizard.cpp
+++ b/src/widgets/dialogs/qwizard.cpp
@@ -850,9 +850,9 @@ void QWizardPrivate::switchToPage(int newId, Direction direction)
                 q->cleanupPage(oldId);
                 initialized.remove(oldId);
             }
-            Q_ASSERT(history.last() == oldId);
+            Q_ASSERT(history.constLast() == oldId);
             history.removeLast();
-            Q_ASSERT(history.last() == newId);
+            Q_ASSERT(history.constLast() == newId);
         }
     }
 
diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index ebdbdbd3e6..eee91fea47 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -786,7 +786,7 @@ void QApplicationPrivate::initializeWidgetFontHash()
 QWidget *QApplication::activePopupWidget()
 {
     return QApplicationPrivate::popupWidgets && !QApplicationPrivate::popupWidgets->isEmpty() ?
-        QApplicationPrivate::popupWidgets->last() : 0;
+        QApplicationPrivate::popupWidgets->constLast() : nullptr;
 }
 
 
@@ -2391,7 +2391,7 @@ void QApplicationPrivate::dispatchEnterLeave(QWidget* enter, QWidget* leave, con
         const QPoint globalPos = qIsInf(globalPosF.x())
             ? QPoint(QWIDGETSIZE_MAX, QWIDGETSIZE_MAX)
             : globalPosF.toPoint();
-        const QPoint windowPos = enterList.back()->window()->mapFromGlobal(globalPos);
+        const QPoint windowPos = qAsConst(enterList).back()->window()->mapFromGlobal(globalPos);
         for (auto it = enterList.crbegin(), end = enterList.crend(); it != end; ++it) {
             auto *w = *it;
             if (!QApplication::activeModalWidget() || QApplicationPrivate::tryModalHelper(w, 0)) {
@@ -3795,7 +3795,7 @@ void QApplicationPrivate::closePopup(QWidget *popup)
 
     } else {
         // A popup was closed, so the previous popup gets the focus.
-        QWidget* aw = QApplicationPrivate::popupWidgets->last();
+        QWidget* aw = QApplicationPrivate::popupWidgets->constLast();
         if (QWidget *fw = aw->focusWidget())
             fw->setFocus(Qt::PopupFocusReason);
 
diff --git a/src/widgets/util/qcompleter.cpp b/src/widgets/util/qcompleter.cpp
index 9c61a3a263..9f167f5924 100644
--- a/src/widgets/util/qcompleter.cpp
+++ b/src/widgets/util/qcompleter.cpp
@@ -755,9 +755,9 @@ void QUnsortedModelEngine::filterOnDemand(int n)
     const QAbstractItemModel *model = c->proxy->sourceModel();
     int lastRow = model->rowCount(curParent) - 1;
     QIndexMapper im(curMatch.indices.last() + 1, lastRow);
-    int lastIndex = buildIndices(curParts.last(), curParent, n, im, &curMatch);
+    int lastIndex = buildIndices(curParts.constLast(), curParent, n, im, &curMatch);
     curMatch.partial = (lastRow != lastIndex);
-    saveInCache(curParts.last(), curParent, curMatch);
+    saveInCache(curParts.constLast(), curParent, curMatch);
 }
 
 QMatchData QUnsortedModelEngine::filter(const QString& part, const QModelIndex& parent, int n)
diff --git a/src/widgets/util/qscroller.cpp b/src/widgets/util/qscroller.cpp
index 2d6bcf72c6..02e3c2b82a 100644
--- a/src/widgets/util/qscroller.cpp
+++ b/src/widgets/util/qscroller.cpp
@@ -575,8 +575,11 @@ QPointF QScroller::pixelPerMeter() const
     if (QGraphicsObject *go = qobject_cast<QGraphicsObject *>(d->target)) {
         QTransform viewtr;
         //TODO: the first view isn't really correct - maybe use an additional field in the prepare event?
-        if (go->scene() && !go->scene()->views().isEmpty())
-            viewtr = go->scene()->views().first()->viewportTransform();
+        if (const auto *scene = go->scene()) {
+            const auto views = scene->views();
+            if (!views.isEmpty())
+                viewtr = views.first()->viewportTransform();
+        }
         QTransform tr = go->deviceTransform(viewtr);
         if (tr.isScaling()) {
             QPointF p0 = tr.map(QPointF(0, 0));
@@ -1121,12 +1124,15 @@ void QScrollerPrivate::pushSegment(ScrollType type, qreal deltaTime, qreal stopP
         return;
 
     ScrollSegment s;
-    if (orientation == Qt::Horizontal && !xSegments.isEmpty())
-        s.startTime = xSegments.last().startTime + xSegments.last().deltaTime * xSegments.last().stopProgress;
-    else if (orientation == Qt::Vertical && !ySegments.isEmpty())
-        s.startTime = ySegments.last().startTime + ySegments.last().deltaTime * ySegments.last().stopProgress;
-    else
+    if (orientation == Qt::Horizontal && !xSegments.isEmpty()) {
+        const auto &lastX = xSegments.constLast();
+        s.startTime = lastX.startTime + lastX.deltaTime * lastX.stopProgress;
+    } else if (orientation == Qt::Vertical && !ySegments.isEmpty()) {
+        const auto &lastY = ySegments.constLast();
+        s.startTime = lastY.startTime + lastY.deltaTime * lastY.stopProgress;
+    } else {
         s.startTime = monotonicTimer.elapsed();
+    }
 
     s.startPos = startPos;
     s.deltaPos = deltaPos;
@@ -1463,8 +1469,11 @@ bool QScrollerPrivate::prepareScrolling(const QPointF &position)
 #ifndef QT_NO_GRAPHICSVIEW
         if (QGraphicsObject *go = qobject_cast<QGraphicsObject *>(target)) {
             //TODO: the first view isn't really correct - maybe use an additional field in the prepare event?
-            if (go->scene() && !go->scene()->views().isEmpty())
-                setDpiFromWidget(go->scene()->views().first());
+            if (const auto *scene = go->scene()) {
+                const auto views = scene->views();
+                if (!views.isEmpty())
+                    setDpiFromWidget(views.first());
+            }
         }
 #endif
 
diff --git a/src/widgets/util/qundostack.cpp b/src/widgets/util/qundostack.cpp
index 6643b4429c..6f733f99d5 100644
--- a/src/widgets/util/qundostack.cpp
+++ b/src/widgets/util/qundostack.cpp
@@ -588,9 +588,9 @@ void QUndoStack::push(QUndoCommand *cmd)
 
     QUndoCommand *cur = 0;
     if (macro) {
-        QUndoCommand *macro_cmd = d->macro_stack.last();
+        QUndoCommand *macro_cmd = d->macro_stack.constLast();
         if (!macro_cmd->d->child_list.isEmpty())
-            cur = macro_cmd->d->child_list.last();
+            cur = macro_cmd->d->child_list.constLast();
     } else {
         if (d->index > 0)
             cur = d->command_list.at(d->index - 1);
@@ -616,7 +616,7 @@ void QUndoStack::push(QUndoCommand *cmd)
         }
     } else {
         if (macro) {
-            d->macro_stack.last()->d->child_list.append(cmd);
+            d->macro_stack.constLast()->d->child_list.append(cmd);
         } else {
             d->command_list.append(cmd);
             d->checkUndoLimit();
@@ -963,7 +963,7 @@ void QUndoStack::beginMacro(const QString &text)
             d->clean_index = -1; // we've deleted the clean state
         d->command_list.append(cmd);
     } else {
-        d->macro_stack.last()->d->child_list.append(cmd);
+        d->macro_stack.constLast()->d->child_list.append(cmd);
     }
     d->macro_stack.append(cmd);
 
diff --git a/src/widgets/widgets/qdockarealayout.cpp b/src/widgets/widgets/qdockarealayout.cpp
index 29089311c6..c14fd5a942 100644
--- a/src/widgets/widgets/qdockarealayout.cpp
+++ b/src/widgets/widgets/qdockarealayout.cpp
@@ -3096,7 +3096,7 @@ void QDockAreaLayout::addDockWidget(QInternal::DockPosition pos, QDockWidget *do
 
 void QDockAreaLayout::tabifyDockWidget(QDockWidget *first, QDockWidget *second)
 {
-    QList<int> path = indexOf(first);
+    const QList<int> path = indexOf(first);
     if (path.isEmpty())
         return;
 
@@ -3133,7 +3133,7 @@ void QDockAreaLayout::resizeDocks(const QList<QDockWidget *> &docks,
         while (path.size() > 1) {
             QDockAreaLayoutInfo *info = this->info(path);
             if (!info->tabbed && info->o == o) {
-                info->item_list[path.last()].size = size;
+                info->item_list[path.constLast()].size = size;
                 int totalSize = 0;
                 foreach (const QDockAreaLayoutItem &item, info->item_list) {
                     if (!item.skip()) {
@@ -3147,7 +3147,7 @@ void QDockAreaLayout::resizeDocks(const QList<QDockWidget *> &docks,
             path.removeLast();
         }
 
-        const int dockNum = path.first();
+        const int dockNum = path.constFirst();
         Q_ASSERT(dockNum < QInternal::DockCount);
         QRect &r = this->docks[dockNum].rect;
         QSize s = r.size();
diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index ae87ea526d..e46063917d 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1163,7 +1163,7 @@ void QMainWindowLayout::insertToolBar(QToolBar *before, QToolBar *toolbar)
             // copy the toolbar also in the saved state
             savedState.toolBarAreaLayout.insertItem(before, item);
         }
-        if (!currentGapPos.isEmpty() && currentGapPos.first() == 0) {
+        if (!currentGapPos.isEmpty() && currentGapPos.constFirst() == 0) {
             currentGapPos = layoutState.toolBarAreaLayout.currentGapIndex();
             if (!currentGapPos.isEmpty()) {
                 currentGapPos.prepend(0);
@@ -1501,7 +1501,7 @@ void QMainWindowLayout::splitDockWidget(QDockWidget *after,
 
 Qt::DockWidgetArea QMainWindowLayout::dockWidgetArea(QWidget *widget) const
 {
-    QList<int> pathToWidget = layoutState.dockAreaLayout.indexOf(widget);
+    const QList<int> pathToWidget = layoutState.dockAreaLayout.indexOf(widget);
     if (pathToWidget.isEmpty())
         return Qt::NoDockWidgetArea;
     return toDockWidgetArea(pathToWidget.first());
@@ -1783,7 +1783,7 @@ QLayoutItem *QMainWindowLayout::takeAt(int index)
         }
 
 #ifndef QT_NO_TOOLBAR
-        if (!currentGapPos.isEmpty() && currentGapPos.first() == 0) {
+        if (!currentGapPos.isEmpty() && currentGapPos.constFirst() == 0) {
             currentGapPos = layoutState.toolBarAreaLayout.currentGapIndex();
             if (!currentGapPos.isEmpty()) {
                 currentGapPos.prepend(0);
@@ -2057,7 +2057,7 @@ void QMainWindowLayout::animationFinished(QWidget *widget)
 
             if (parentInfo->tabbed) {
                 // merge the two tab widgets
-                int idx = path.last();
+                int idx = path.constLast();
                 Q_ASSERT(parentInfo->item_list[idx].widgetItem->widget() == dwgw);
                 delete parentInfo->item_list[idx].widgetItem;
                 parentInfo->item_list.removeAt(idx);
@@ -2283,7 +2283,7 @@ QLayoutItem *QMainWindowLayout::unplug(QWidget *widget, bool group)
 
 #ifndef QT_NO_DOCKWIDGET
     if (QDockWidget *dw = qobject_cast<QDockWidget*>(widget)) {
-        Q_ASSERT(path.first() == 1);
+        Q_ASSERT(path.constFirst() == 1);
         bool actualGroup = false;
 #ifndef QT_NO_TABBAR
         if (group && (dockOptions & QMainWindow::GroupedDragging) && path.size() > 3) {
diff --git a/src/widgets/widgets/qmenu.cpp b/src/widgets/widgets/qmenu.cpp
index 514cb1a8c9..c07d48a513 100644
--- a/src/widgets/widgets/qmenu.cpp
+++ b/src/widgets/widgets/qmenu.cpp
@@ -117,7 +117,7 @@ public:
     {
         Q_D(QTornOffMenu);
         // make the torn-off menu a sibling of p (instead of a child)
-        QWidget *parentWidget = d->causedStack.isEmpty() ? p : d->causedStack.last();
+        QWidget *parentWidget = d->causedStack.isEmpty() ? p : d->causedStack.constLast();
         if (parentWidget->parentWidget())
             parentWidget = parentWidget->parentWidget();
         setParent(parentWidget, Qt::Window | Qt::Tool);
diff --git a/src/widgets/widgets/qtabbar.cpp b/src/widgets/widgets/qtabbar.cpp
index cf485974f6..ba3fc2fcd7 100644
--- a/src/widgets/widgets/qtabbar.cpp
+++ b/src/widgets/widgets/qtabbar.cpp
@@ -590,7 +590,7 @@ QRect QTabBarPrivate::normalizedScrollRect(int index)
         }
 
         bool tearTopVisible = index != 0 && topEdge != -scrollOffset;
-        bool tearBottomVisible = index != tabList.size() - 1 && bottomEdge != tabList.last().rect.bottom() + 1 - scrollOffset;
+        bool tearBottomVisible = index != tabList.size() - 1 && bottomEdge != tabList.constLast().rect.bottom() + 1 - scrollOffset;
         if (tearTopVisible && !tearLeftRect.isNull())
             topEdge = tearLeftRect.bottom() + 1;
         if (tearBottomVisible && !tearRightRect.isNull())
@@ -621,7 +621,7 @@ QRect QTabBarPrivate::normalizedScrollRect(int index)
         }
 
         bool tearLeftVisible = index != 0 && leftEdge != -scrollOffset;
-        bool tearRightVisible = index != tabList.size() - 1 && rightEdge != tabList.last().rect.right() + 1 - scrollOffset;
+        bool tearRightVisible = index != tabList.size() - 1 && rightEdge != tabList.constLast().rect.right() + 1 - scrollOffset;
         if (tearLeftVisible && !tearLeftRect.isNull())
             leftEdge = tearLeftRect.right() + 1;
         if (tearRightVisible && !tearRightRect.isNull())
@@ -642,7 +642,7 @@ void QTabBarPrivate::makeVisible(int index)
     const bool horiz = !verticalTabs(shape);
     const int tabStart = horiz ? tabRect.left() : tabRect.top();
     const int tabEnd = horiz ? tabRect.right() : tabRect.bottom();
-    const int lastTabEnd = horiz ? tabList.last().rect.right() : tabList.last().rect.bottom();
+    const int lastTabEnd = horiz ? tabList.constLast().rect.right() : tabList.constLast().rect.bottom();
     const QRect scrollRect = normalizedScrollRect(index);
     const int scrolledTabBarStart = qMax(1, scrollRect.left() + scrollOffset);
     const int scrolledTabBarEnd = qMin(lastTabEnd - 1, scrollRect.right() + scrollOffset);
diff --git a/src/widgets/widgets/qtoolbararealayout.cpp b/src/widgets/widgets/qtoolbararealayout.cpp
index 2e79b502ea..05564bb6b1 100644
--- a/src/widgets/widgets/qtoolbararealayout.cpp
+++ b/src/widgets/widgets/qtoolbararealayout.cpp
@@ -347,7 +347,7 @@ void QToolBarAreaLayoutInfo::removeToolBar(QToolBar *toolBar)
 void QToolBarAreaLayoutInfo::insertToolBarBreak(QToolBar *before)
 {
     if (before == 0) {
-        if (!lines.isEmpty() && lines.last().toolBarItems.isEmpty())
+        if (!lines.isEmpty() && lines.constLast().toolBarItems.isEmpty())
             return;
         lines.append(QToolBarAreaLayoutLine(o));
         return;