Fix a crash with focus handling when destructing QQAppWindow

Because QQuickApplicationWindow connected
  SIGNAL(activeFocusItemChanged())
to
  SLOT(_q_updateActiveFocus()));

it would enter _q_updateActiveFocus() from the dtor of QQuickWindow
(because dtor of QQuickWindow would emit activeFocusItemChanged()).
At that point the QQuickApplicationWindow object for the member function
_q_updateActiveFocus() was already destroyed, so we would crash.

Instead, make sure we clear the focus as early as possible, and then
disconnect in case activeFocusItemChanged() is emitted after
QQuickApplicationWindow is destroyed.

Task-number: QTBUG-57846
Change-Id: I4b1999e647b970394436a2d462b7f352f1c8a811
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

2 files changed, 116 insertions, 0 deletions

diff --git a/tests/auto/applicationwindow/data/clearfocusondestruction.qml b/tests/auto/applicationwindow/data/clearfocusondestruction.qml
new file mode 100644
index 00000000..3589439e
--- /dev/null
+++ b/tests/auto/applicationwindow/data/clearfocusondestruction.qml
@@ -0,0 +1,74 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick 2.7
+import QtQuick.Controls 2.1
+import QtQuick.Layouts 1.3
+import QtGraphicalEffects 1.0
+
+ApplicationWindow {
+    width: 200
+    height: 200
+    visible: true
+
+    property alias textfield: textfield
+
+    /*
+     * The code below is the simplest way we can trigger that the signal
+     * activeFocusItemChanged() is emitted during destruction of the
+     * ApplicationWindow. This caused a crash in QQuickApplicationWindow.
+     */
+    FastBlur {
+        id: fastBlur
+        anchors.fill: parent
+        radius: 30
+        source: ShaderEffectSource {
+            id: effectsource
+            sourceItem: textfield
+            sourceRect: Qt.rect( 0, 0, fastBlur.width, fastBlur.height )
+        }
+    }
+
+    TextField {
+        id: textfield
+        anchors.bottom: parent.bottom
+        focus: true
+    }
+}
diff --git a/tests/auto/applicationwindow/tst_applicationwindow.cpp b/tests/auto/applicationwindow/tst_applicationwindow.cpp
index 2a3f849c..b72bb8f2 100644
--- a/tests/auto/applicationwindow/tst_applicationwindow.cpp
+++ b/tests/auto/applicationwindow/tst_applicationwindow.cpp
@@ -72,6 +72,7 @@ private slots:
     void activeFocusControl_data();
     void activeFocusControl();
     void focusAfterPopupClosed();
+    void clearFocusOnDestruction();
     void layout();
 };
 
@@ -685,6 +686,47 @@ void tst_applicationwindow::focusAfterPopupClosed()
     QCOMPARE(spy.count(), 2);
 }
 
+void tst_applicationwindow::clearFocusOnDestruction()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine);
+    component.loadUrl(testFileUrl("clearfocusondestruction.qml"));
+    QScopedPointer<QQuickWindow> window(qobject_cast<QQuickWindow*>(component.create()));
+    QVERIFY(window);
+
+    window->show();
+    window->requestActivate();
+    QVERIFY(QTest::qWaitForWindowActive(window.data()));
+    QVERIFY(QGuiApplication::focusWindow() == window.data());
+
+    QQuickItem* contentItem = window->contentItem();
+    QVERIFY(contentItem);
+    QVERIFY(contentItem->hasActiveFocus());
+
+    QQuickItem* focusScope = window->property("textfield").value<QQuickItem*>();
+    QVERIFY(focusScope);
+    QVERIFY(focusScope->hasActiveFocus());
+
+    QSignalSpy spy(window.data(), SIGNAL(activeFocusControlChanged()));
+    // destroy the window, do not crash
+    window.reset();
+
+    /*
+       QQuickWindow::activeFocusItemChanged() is emitted inconsistently and
+       only for certain use cases. Ideally it should be emitted whenever a
+       QQuickWindow with a focus item is destroyed, but it doesn't... It might
+       also be favorable to not emit it for performance reason.
+
+       However, activeFocusControlChanged() is emitted more consistently, which
+       of course makes it inconsistent with the emission of
+       activeFocusItemChanged()....
+
+       Therefore, if you have good reasons to change the behavior (and not emit
+       it) take the test below with a grain of salt.
+     */
+    QCOMPARE(spy.count(), 1);
+}
+
 void tst_applicationwindow::layout()
 {
     QQmlEngine engine;