Fix QML property cache leaks of delegate items

The delegate items are destroyed through an event loop by a call to a
deleteLater(). This, however, doesn't work when the application is
in the process of exiting and the event loop is already closed (i.e.
we're in a stack unwinding part that starts after app.exec())

Combat this situation by setting a parent of the to-be-deleted object
to some QObject that will be destroyed e.g. QCoreApplication::instance()
before the program finishes. As QObjects clean their children on
destruction, this will make sure that we cleanup the previously leaking
thing regardless of the event loop

Added a test to check that delegates are destroyed (as a separate binary
due to differences in main() function)

Fixes: QTBUG-87228
Change-Id: I59066603b77497fe4fd8d051798c3e4b47c119f0
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 3a5617dc45e281552b9c1f7a04f0561b8fa14d94)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

5 files changed, 156 insertions, 0 deletions

diff --git a/tests/auto/quick/CMakeLists.txt b/tests/auto/quick/CMakeLists.txt
index 838d0917fb..70574110ed 100644
--- a/tests/auto/quick/CMakeLists.txt
+++ b/tests/auto/quick/CMakeLists.txt
@@ -60,6 +60,7 @@ if(QT_FEATURE_private_tests)
     add_subdirectory(qquicktextinput)
     add_subdirectory(qquickvisualdatamodel)
     add_subdirectory(qquickview)
+    add_subdirectory(qquickview_extra)
     add_subdirectory(qquickcanvasitem)
     add_subdirectory(qquickdesignersupport)
     add_subdirectory(qquickscreen)
diff --git a/tests/auto/quick/qquickview_extra/CMakeLists.txt b/tests/auto/quick/qquickview_extra/CMakeLists.txt
new file mode 100644
index 0000000000..16cc36a127
--- /dev/null
+++ b/tests/auto/quick/qquickview_extra/CMakeLists.txt
@@ -0,0 +1,39 @@
+# Generated from qquickview.pro.
+
+#####################################################################
+## tst_qquickview_extra Test:
+#####################################################################
+
+# Collect test data
+file(GLOB_RECURSE test_data_glob
+    RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}
+    data/*)
+list(APPEND test_data ${test_data_glob})
+
+qt_internal_add_test(tst_qquickview_extra
+    SOURCES
+        ../../shared/util.cpp ../../shared/util.h
+        tst_qquickview_extra.cpp
+    DEFINES
+        QT_QMLTEST_DATADIR=\\\"${CMAKE_CURRENT_SOURCE_DIR}/data\\\"
+    PUBLIC_LIBRARIES
+        Qt::CorePrivate
+        Qt::Gui
+        Qt::GuiPrivate
+        Qt::QmlPrivate
+        Qt::QuickPrivate
+    TESTDATA ${test_data}
+)
+
+## Scopes:
+#####################################################################
+
+qt_internal_extend_target(tst_qquickview_extra CONDITION ANDROID OR IOS
+    DEFINES
+        QT_QMLTEST_DATADIR=\\\":/data\\\"
+)
+
+qt_internal_extend_target(tst_qquickview_extra CONDITION NOT ANDROID AND NOT IOS
+    DEFINES
+        QT_QMLTEST_DATADIR=\\\"${CMAKE_CURRENT_SOURCE_DIR}/data\\\"
+)
diff --git a/tests/auto/quick/qquickview_extra/data/qtbug_87228.qml b/tests/auto/quick/qquickview_extra/data/qtbug_87228.qml
new file mode 100644
index 0000000000..ff10eba23d
--- /dev/null
+++ b/tests/auto/quick/qquickview_extra/data/qtbug_87228.qml
@@ -0,0 +1,30 @@
+import QtQml 2.12
+import QtQml.Models 2.12
+import QtQuick 2.12
+
+Item {
+    height: 480
+    width: 320
+    Rectangle {
+        id: rootRect
+
+        function addItem(desc) {
+            myModel.append({"desc": desc});
+        }
+
+        Rectangle {
+            ListView {
+                objectName: "listView"
+                delegate: Text {
+                    required property string desc
+                    text: desc
+                }
+                model: ListModel { id: myModel }
+            }
+        }
+
+        Component.onCompleted: {
+            addItem("Test creation of a delegate with a property");
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickview_extra/qquickview_extra.pro b/tests/auto/quick/qquickview_extra/qquickview_extra.pro
new file mode 100644
index 0000000000..6cee00f387
--- /dev/null
+++ b/tests/auto/quick/qquickview_extra/qquickview_extra.pro
@@ -0,0 +1,9 @@
+CONFIG += testcase
+TARGET = tst_qquickview_extra
+macx:CONFIG -= app_bundle
+
+SOURCES += tst_qquickview_extra.cpp
+
+TESTDATA = data/*
+
+QT += core-private gui-private qml-private quick-private testlib
diff --git a/tests/auto/quick/qquickview_extra/tst_qquickview_extra.cpp b/tests/auto/quick/qquickview_extra/tst_qquickview_extra.cpp
new file mode 100644
index 0000000000..f697a438bd
--- /dev/null
+++ b/tests/auto/quick/qquickview_extra/tst_qquickview_extra.cpp
@@ -0,0 +1,77 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#include <qtest.h>
+#include <QtTest/QSignalSpy>
+#include <QtQuick/qquickview.h>
+#include <QtQuick/qquickitem.h>
+#include <QtQml/qqmlengine.h>
+#include "../../shared/util.h"
+#include <QtCore/QDebug>
+#include <QtCore/QTimer>
+
+// Extra app-less tests
+class tst_QQuickViewExtra : public QQmlDataTest
+{
+    Q_OBJECT
+public:
+    tst_QQuickViewExtra();
+
+private slots:
+    void qtbug_87228();
+};
+
+tst_QQuickViewExtra::tst_QQuickViewExtra() { }
+
+void tst_QQuickViewExtra::qtbug_87228()
+{
+    QScopedPointer<QSignalSpy> deletionSpy;
+    {
+        int argc = 0;
+        QGuiApplication app(argc, nullptr);
+        QQuickView view;
+
+        view.setSource(testFileUrl("qtbug_87228.qml"));
+        view.show();
+        QTimer::singleShot(500, &app, QCoreApplication::quit);
+        app.exec();
+
+        QObject *listView = view.findChild<QObject *>("listView");
+        QVERIFY(listView);
+        QQuickItem *contentItem = listView->property("contentItem").value<QQuickItem *>();
+        QVERIFY(contentItem);
+        auto children = contentItem->childItems();
+        QVERIFY(children.size() > 0);
+        // for the sake of this test, any child would be suitable, so pick first
+        deletionSpy.reset(new QSignalSpy(children[0], SIGNAL(destroyed(QObject *))));
+    }
+    QCOMPARE(deletionSpy->count(), 1);
+}
+
+QTEST_APPLESS_MAIN(tst_QQuickViewExtra)
+
+#include "tst_qquickview_extra.moc"