From f9bfbe713d1779d7f53db906e3b6a3b016996f32 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Tue, 26 May 2020 03:15:42 +0200
Subject: [PATCH] Add a QgsFocusKeeper class to avoid crashes related to focus
 loss

Will be use to solve crash of #30210

Credits to @nyalldawson for pointing out the fix of #31905 as a
reference.
---
 src/gui/CMakeLists.txt     |  1 +
 src/gui/qgsfocuskeeper.cpp | 40 +++++++++++++++++++++++++++++++
 src/gui/qgsfocuskeeper.h   | 48 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+)
 create mode 100644 src/gui/qgsfocuskeeper.cpp
 create mode 100644 src/gui/qgsfocuskeeper.h

diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index b8bc7282ee27..952151ef91d3 100644
--- a/src/gui/CMakeLists.txt
+++ b/src/gui/CMakeLists.txt
@@ -416,6 +416,7 @@ SET(QGIS_GUI_SRCS
   qgsfilterlineedit.cpp
   qgsfindfilesbypatternwidget.cpp
   qgsfloatingwidget.cpp
+  qgsfocuskeeper.cpp
   qgsfocuswatcher.cpp
   qgsfontbutton.cpp
   qgsformannotation.cpp
diff --git a/src/gui/qgsfocuskeeper.cpp b/src/gui/qgsfocuskeeper.cpp
new file mode 100644
index 000000000000..386f8808f9fa
--- /dev/null
+++ b/src/gui/qgsfocuskeeper.cpp
@@ -0,0 +1,40 @@
+/***************************************************************************
+    qgsfocuskeeper.cpp
+     -----------------
+    Date                 : May 2020
+    Copyright            : (C) 2020 Even Rouault
+    Email                : even dot rouault at spatialys dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsfocuskeeper.h"
+
+#include <QApplication>
+#include <QEvent>
+#include <QWidget>
+
+QgsFocusKeeper::QgsFocusKeeper(): mWidgetToKeepFocused( QApplication::focusWidget() )
+{
+  mWidgetToKeepFocused->installEventFilter( this );
+}
+
+QgsFocusKeeper::~QgsFocusKeeper()
+{
+  mWidgetToKeepFocused->removeEventFilter( this );
+}
+
+bool QgsFocusKeeper::eventFilter( QObject *obj, QEvent *event )
+{
+  if ( obj == mWidgetToKeepFocused && event &&
+       ( event->type() == QEvent::FocusOut ||  event->type() == QEvent::FocusAboutToChange ) )
+  {
+    return true;
+  }
+  return QObject::eventFilter( obj, event );
+}
diff --git a/src/gui/qgsfocuskeeper.h b/src/gui/qgsfocuskeeper.h
new file mode 100644
index 000000000000..1d86054aa88c
--- /dev/null
+++ b/src/gui/qgsfocuskeeper.h
@@ -0,0 +1,48 @@
+/***************************************************************************
+    qgsfocuskeeper.h
+     ---------------
+    Date                 : May 2020
+    Copyright            : (C) 2020 Even Rouault
+    Email                : even dot rouault at spatialys dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSFOCUSKEEPER_H
+#define QGSFOCUSKEEPER_H
+
+#include "qgis_gui.h"
+
+#define SIP_NO_FILE
+
+#include <QObject>
+
+class QWidget;
+
+/**
+ * \ingroup gui
+ * \class QgsFocusKeeper
+ * Trick to keep a widget focused and avoid QT crashes
+ * \note not available in Python bindings
+ * \since QGIS 3.14
+ */
+class GUI_EXPORT QgsFocusKeeper : public QObject
+{
+    Q_OBJECT
+
+    QWidget *mWidgetToKeepFocused = nullptr;
+
+  public:
+    QgsFocusKeeper();
+    ~QgsFocusKeeper() override;
+
+  protected:
+    bool eventFilter( QObject *obj, QEvent *event ) override;
+};
+
+#endif // QGSFOCUSKEEPER_H