QDirModel: replace an inefficient QList with QVector

SavedPersistent is larger than a void*, so holding it in QLists
is needlessly inefficient. Worse, the code could come to depend
on the fragile property of (inefficient) QLists that references
to elements therein never are invalidated.

Fix by marking it movable and holding it in a QVector instead.

Take advantage of rvalue-enabled QVector::push_back(); optimize
element construction by using aggregate initialization.

Change-Id: I4fd88879aa13e6536d59d164b3c33fbc2fead77f
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/widgets/itemviews/qdirmodel.cpp

@@ -136,11 +136,12 @@ public:
         QPersistentModelIndexData *data;
         QPersistentModelIndex index;
     };
-    QList<SavedPersistent> savedPersistent;
+    QVector<SavedPersistent> savedPersistent;
     QPersistentModelIndex toBeRefreshed;
 
     bool shouldStat; // use the "carefull not to stat directories" mode
 };
+Q_DECLARE_TYPEINFO(QDirModelPrivate::SavedPersistent, Q_MOVABLE_TYPE);
 
 void qt_setDirModelShouldNotStat(QDirModelPrivate *modelPrivate)
 {
@@ -1237,14 +1238,16 @@ void QDirModelPrivate::savePersistentIndexes()
 {
     Q_Q(QDirModel);
     savedPersistent.clear();
+    savedPersistent.reserve(persistent.indexes.size());
     foreach (QPersistentModelIndexData *data, persistent.indexes) {
-        SavedPersistent saved;
         QModelIndex index = data->index;
-        saved.path = q->filePath(index);
-        saved.column = index.column();
-        saved.data = data;
-        saved.index = index;
-        savedPersistent.append(saved);
+        SavedPersistent saved = {
+            q->filePath(index),
+            index.column(),
+            data,
+            index,
+        };
+        savedPersistent.push_back(std::move(saved));
     }
 }
 
@@ -1253,11 +1256,9 @@ void QDirModelPrivate::restorePersistentIndexes()
     Q_Q(QDirModel);
     bool allow = allowAppendChild;
     allowAppendChild = false;
-    for (int i = 0; i < savedPersistent.count(); ++i) {
-        QPersistentModelIndexData *data = savedPersistent.at(i).data;
-        QString path = savedPersistent.at(i).path;
-        int column = savedPersistent.at(i).column;
-        QModelIndex idx = q->index(path, column);
+    for (const SavedPersistent &sp : qAsConst(savedPersistent)) {
+        QPersistentModelIndexData *data = sp.data;
+        QModelIndex idx = q->index(sp.path, sp.column);
         if (idx != data->index || data->model == 0) {
             //data->model may be equal to 0 if the model is getting destroyed
             persistent.indexes.remove(data->index);