QStyleSheetStyle: don't hold ButtonInfo in QList

ButtonInfo is larger than a void*, so holding them in a QList 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 holding it in QVector. Also reserve() the vector, even though we
can't tell the size exectly. It's a short-lived vector.

When appending, add an optimistic qMove().

I would have liked to use std::vector instead, but QRenderRule, thus
ButtonInfo, isn't nothrow-move-constructible, because of missing
move constructors on QBrush and QFont, among others.

Change-Id: I89164f4ed5745498093102f022a7ef32186e8045
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index bf06ebdc1c..662e1f9b96 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -746,8 +746,10 @@ QHash<QStyle::SubControl, QRect> QStyleSheetStyle::titleBarLayout(const QWidget
 
     int offsets[3] = { 0, 0, 0 };
     enum Where { Left, Right, Center, NoWhere } where = Left;
-    QList<ButtonInfo> infos;
-    for (int i = 0; i < layout.count(); i++) {
+    QVector<ButtonInfo> infos;
+    const int numLayouts = layout.size();
+    infos.reserve(numLayouts);
+    for (int i = 0; i < numLayouts; i++) {
         const int element = layout[i].toInt();
         if (element == '(') {
             where = Center;
@@ -801,14 +803,14 @@ QHash<QStyle::SubControl, QRect> QStyleSheetStyle::titleBarLayout(const QWidget
             info.rule = subRule;
             info.offset = offsets[where];
             info.where = where;
-            infos.append(info);
+            infos.append(qMove(info));
 
             offsets[where] += info.width;
         }
     }
 
-    for (int i = 0; i < infos.count(); i++) {
-        ButtonInfo info = infos[i];
+    for (int i = 0; i < infos.size(); i++) {
+        const ButtonInfo &info = infos[i];
         QRect lr = cr;
         switch (info.where) {
         case Center: {