commit cbfb6bda1d1ce3e169db6a0deb9bd901076653e4
Author: Anna Wojciechowska <anna.wojciechowska@qt.io>
Date:   Fri Oct 20 08:51:16 2017 -0700

    Fix restoring geometry of dockwidget
    
    In the past if the window with dock widgets was closed in maximized
    mode, after reopening the dock widget size was different from the
    original one. It was caused due to consecutive resizes of dock widgets
    when the window was shown. During resizing dock widget geometry restored
    from property file was lost. The solution was to  keep restored size of
    dock widgets in QDockAreaLayoutInfo and use as hints for the dock layout
    engine.
    
    Task-number: QTBUG-16252
    Change-Id: I94f4e895922063fa51150b68464fea4ddcb1d2a2
    Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

diff --git a/src/widgets/widgets/qdockarealayout.cpp b/src/widgets/widgets/qdockarealayout.cpp
index 21d1d4cb85..bef7214c75 100644
--- a/src/widgets/widgets/qdockarealayout.cpp
+++ b/src/widgets/widgets/qdockarealayout.cpp
@@ -226,7 +226,7 @@ static quintptr tabId(const QDockAreaLayoutItem &item)
 static const int zero = 0;
 
 QDockAreaLayoutInfo::QDockAreaLayoutInfo()
-    : sep(&zero), dockPos(QInternal::LeftDock), o(Qt::Horizontal), mainWindow(0)
+    : restoredSizeHint(0,0), sep(&zero), dockPos(QInternal::LeftDock), o(Qt::Horizontal), mainWindow(0)
 #if QT_CONFIG(tabbar)
     , tabbed(false), tabBar(0), tabBarShape(QTabBar::RoundedSouth)
 #endif
@@ -236,7 +236,7 @@ QDockAreaLayoutInfo::QDockAreaLayoutInfo()
 QDockAreaLayoutInfo::QDockAreaLayoutInfo(const int *_sep, QInternal::DockPosition _dockPos,
                                             Qt::Orientation _o, int tbshape,
                                             QMainWindow *window)
-    : sep(_sep), dockPos(_dockPos), o(_o), mainWindow(window)
+    : restoredSizeHint(0,0), sep(_sep), dockPos(_dockPos), o(_o), mainWindow(window)
 #if QT_CONFIG(tabbar)
     , tabbed(false), tabBar(0), tabBarShape(static_cast<QTabBar::Shape>(tbshape))
 #endif
@@ -407,6 +407,9 @@ QSize QDockAreaLayoutInfo::sizeHint() const
     if (isEmpty())
         return QSize(0, 0);
 
+    if (!restoredSizeHint.isNull())
+        return restoredSizeHint;
+
     int a = 0, b = 0;
     int min_perp = 0;
     int max_perp = QWIDGETSIZE_MAX;
@@ -2373,6 +2376,7 @@ bool QDockAreaLayout::restoreState(QDataStream &stream, const QList<QDockWidget*
         stream >> size;
         if (!testing) {
             docks[pos].rect = QRect(QPoint(0, 0), size);
+            docks[pos].restoredSizeHint = size;
         }
         if (!docks[pos].restoreState(stream, dockwidgets, testing)) {
             stream.setStatus(QDataStream::ReadCorruptData);
@@ -2674,6 +2678,8 @@ void QDockAreaLayout::getGrid(QVector<QLayoutStruct> *_ver_struct_list,
         center_rect.setBottom(rect.bottom() - docks[QInternal::BottomDock].rect.height() - sep);
 
     QSize left_hint = docks[QInternal::LeftDock].size();
+    if (!docks[QInternal::LeftDock].restoredSizeHint.isNull())
+        left_hint = docks[QInternal::LeftDock].restoredSizeHint;
     if (left_hint.isNull() || fallbackToSizeHints)
         left_hint = docks[QInternal::LeftDock].sizeHint();
     QSize left_min = docks[QInternal::LeftDock].minimumSize();
@@ -2681,6 +2687,8 @@ void QDockAreaLayout::getGrid(QVector<QLayoutStruct> *_ver_struct_list,
     left_hint = left_hint.boundedTo(left_max).expandedTo(left_min);
 
     QSize right_hint = docks[QInternal::RightDock].size();
+    if (!docks[QInternal::RightDock].restoredSizeHint.isNull())
+        right_hint = docks[QInternal::RightDock].restoredSizeHint;
     if (right_hint.isNull() || fallbackToSizeHints)
         right_hint = docks[QInternal::RightDock].sizeHint();
     QSize right_min = docks[QInternal::RightDock].minimumSize();
@@ -2688,6 +2696,8 @@ void QDockAreaLayout::getGrid(QVector<QLayoutStruct> *_ver_struct_list,
     right_hint = right_hint.boundedTo(right_max).expandedTo(right_min);
 
     QSize top_hint = docks[QInternal::TopDock].size();
+    if (!docks[QInternal::TopDock].restoredSizeHint.isNull())
+        top_hint = docks[QInternal::TopDock].restoredSizeHint;
     if (top_hint.isNull() || fallbackToSizeHints)
         top_hint = docks[QInternal::TopDock].sizeHint();
     QSize top_min = docks[QInternal::TopDock].minimumSize();
@@ -2695,6 +2705,8 @@ void QDockAreaLayout::getGrid(QVector<QLayoutStruct> *_ver_struct_list,
     top_hint = top_hint.boundedTo(top_max).expandedTo(top_min);
 
     QSize bottom_hint = docks[QInternal::BottomDock].size();
+    if (!docks[QInternal::BottomDock].restoredSizeHint.isNull())
+        bottom_hint = docks[QInternal::BottomDock].restoredSizeHint;
     if (bottom_hint.isNull() || fallbackToSizeHints)
         bottom_hint = docks[QInternal::BottomDock].sizeHint();
     QSize bottom_min = docks[QInternal::BottomDock].minimumSize();
@@ -3276,6 +3288,10 @@ int QDockAreaLayout::separatorMove(const QList<int> &separator, const QPoint &or
     int delta = 0;
     int index = separator.last();
 
+    for (int i = 0; i < QInternal::DockCount; ++i)
+        if (!docks[i].restoredSizeHint.isNull())
+            docks[i].restoredSizeHint = QSize(0, 0);
+
     if (separator.count() > 1) {
         QDockAreaLayoutInfo *info = this->info(separator);
         delta = pick(info->o, dest - origin);
diff --git a/src/widgets/widgets/qdockarealayout_p.h b/src/widgets/widgets/qdockarealayout_p.h
index 82244c192e..ea397e00ac 100644
--- a/src/widgets/widgets/qdockarealayout_p.h
+++ b/src/widgets/widgets/qdockarealayout_p.h
@@ -189,6 +189,7 @@ public:
 
     QMainWindowLayout *mainWindowLayout() const;
 
+    QSize restoredSizeHint;
     const int *sep;
     mutable QVector<QWidget*> separatorWidgets;
     QInternal::DockPosition dockPos;