From 461549c35ade73b3c048e2c5ecfbd412c438c026 Mon Sep 17 00:00:00 2001
From: Sergio Martins <sergio.martins@kdab.com>
Date: Wed, 7 Dec 2016 12:28:05 +0000
Subject: [PATCH] Don't show bogus empty window when calling
 QMainWindow::restoreState()

Qt doesn't create the actual QDockWidgets when restoring, the user must
ensure they are created before restoring state. So lets not create an empty
QDockWidgetGroupWindow which you can't close and with no tabs.

Change-Id: If0a6aa7cf6f3932ff4274e03f787e27aef8fa53d
Task-Id: QTBUG-57492
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
---
 src/widgets/widgets/qdockarealayout.cpp   | 10 ++++++++++
 src/widgets/widgets/qdockarealayout_p.h   |  1 +
 src/widgets/widgets/qmainwindowlayout.cpp | 11 +++++++++--
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/widgets/widgets/qdockarealayout.cpp b/src/widgets/widgets/qdockarealayout.cpp
index 63f8172bf61..ad19e5d5f96 100644
--- a/src/widgets/widgets/qdockarealayout.cpp
+++ b/src/widgets/widgets/qdockarealayout.cpp
@@ -266,6 +266,16 @@ bool QDockAreaLayoutInfo::isEmpty() const
     return next(-1) == -1;
 }
 
+bool QDockAreaLayoutInfo::onlyHasPlaceholders() const
+{
+    for (const QDockAreaLayoutItem &item : item_list) {
+        if (!item.placeHolderItem)
+            return false;
+    }
+
+    return true;
+}
+
 QSize QDockAreaLayoutInfo::minimumSize() const
 {
     if (isEmpty())
diff --git a/src/widgets/widgets/qdockarealayout_p.h b/src/widgets/widgets/qdockarealayout_p.h
index f22a3d2de2c..21787283f49 100644
--- a/src/widgets/widgets/qdockarealayout_p.h
+++ b/src/widgets/widgets/qdockarealayout_p.h
@@ -167,6 +167,7 @@ public:
 
     void clear();
     bool isEmpty() const;
+    bool onlyHasPlaceholders() const;
     bool hasFixedSize() const;
     QList<int> findSeparator(const QPoint &pos) const;
     int next(int idx) const;
diff --git a/src/widgets/widgets/qmainwindowlayout.cpp b/src/widgets/widgets/qmainwindowlayout.cpp
index aef8b9cbd51..14d7f3d835c 100644
--- a/src/widgets/widgets/qmainwindowlayout.cpp
+++ b/src/widgets/widgets/qmainwindowlayout.cpp
@@ -1030,12 +1030,19 @@ bool QMainWindowLayoutState::restoreState(QDataStream &_stream,
                                                                  Qt::Horizontal, QTabBar::RoundedSouth, mainWindow);
                 QRect geometry;
                 stream >> geometry;
-                if (!floatingTab->layoutInfo()->restoreState(stream, dockWidgets, false))
+                QDockAreaLayoutInfo *info = floatingTab->layoutInfo();
+                if (!info->restoreState(stream, dockWidgets, false))
                     return false;
                 geometry = QDockAreaLayout::constrainedRect(geometry, floatingTab);
                 floatingTab->move(geometry.topLeft());
                 floatingTab->resize(geometry.size());
-                floatingTab->show();
+
+                // Don't show an empty QDockWidgetGroupWindow if no dock widget is available yet.
+                // reparentWidgets() would be triggered by show(), so do it explicitly here.
+                if (info->onlyHasPlaceholders())
+                    info->reparentWidgets(floatingTab);
+                else
+                    floatingTab->show();
             }
             break;
 #endif // QT_NO_TABBAR