QMainWindowLayout: rewrite validateToolBarArea() to return by value

Coverity complains that QToolBarAreaLayout's
addToolBarBreak(QInternal::DockPosition) could access
QToolBarAreaLayout::docks out of bounds if passed
QInternal::DockCount.

That is correct, but a valid pos seems to be a precondition for this
function, judging from its sister functions, e.g.
addToolBar(DockPosition, .) or insertItem(DockPosition, .), which also
don't validate `pos`. All in-module callers of addToolBarBreak() only
pass valid positions, and use validateToolBarArea() to ensure that. So
it seems that Coverity doesn't grok the pass-by-in/out -parameter used
by that function. That, or it doesn't track back far enough.

Before attempting more drastic measures, first try rewriting the
function to return-by-value instead, and see what Coverity has to say
afterwards.

As a drive-by, make validateToolBarArea() constexpr.

Pick-to: 6.7 6.6 6.5 6.2 5.15
Coverity-Id: 444141
Coverity-Id: 444135
Change-Id: I5fcc664c3cea608429036cad75c37f5c38059733
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index 9008f023fa..db17e50d5c 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1431,17 +1431,18 @@ bool QMainWindowLayoutState::restoreState(QDataStream &_stream,
 
 #if QT_CONFIG(toolbar)
 
-static inline void validateToolBarArea(Qt::ToolBarArea &area)
+static constexpr Qt::ToolBarArea validateToolBarArea(Qt::ToolBarArea area)
 {
     switch (area) {
     case Qt::LeftToolBarArea:
     case Qt::RightToolBarArea:
     case Qt::TopToolBarArea:
     case Qt::BottomToolBarArea:
-        break;
+        return area;
     default:
-        area = Qt::TopToolBarArea;
+        break;
     }
+    return Qt::TopToolBarArea;
 }
 
 static QInternal::DockPosition toDockPos(Qt::ToolBarArea area)
@@ -1477,7 +1478,7 @@ static inline Qt::ToolBarArea toToolBarArea(int pos)
 
 void QMainWindowLayout::addToolBarBreak(Qt::ToolBarArea area)
 {
-    validateToolBarArea(area);
+    area = validateToolBarArea(area);
 
     layoutState.toolBarAreaLayout.addToolBarBreak(toDockPos(area));
     if (savedState.isValid())
@@ -1531,7 +1532,7 @@ void QMainWindowLayout::addToolBar(Qt::ToolBarArea area,
                                    QToolBar *toolbar,
                                    bool)
 {
-    validateToolBarArea(area);
+    area = validateToolBarArea(area);
     // let's add the toolbar to the layout
     addChildWidget(toolbar);
     QLayoutItem *item = layoutState.toolBarAreaLayout.addToolBar(toDockPos(area), toolbar);