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>

5 files changed, 11 insertions, 11 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);
         }
     }