From 228efa08af2590081c163dc9617f785d88850cf3 Mon Sep 17 00:00:00 2001
From: Axel Spoerl <axel.spoerl@qt.io>
Date: Tue, 20 Jun 2023 14:21:18 +0200
Subject: [PATCH] QQmlDelegateModelPrivate::itemsRemoved - keep persisted items
 in cache

QQmlDelegateModelPrivate::itemsRemoved removes unreferenced items from
the cache. If an item is persisted and unreferenced, it's disappearance
from the cache will prevent display models (e.g. qqmllistmodel) from
looping over all delegates. This can lead incomplete clear operations
and dangling screen artifacts.

This patch adds a condition to prevent persited items from being
removed from the cache.

It adds a test function in tst_QQmlDelegateModel.

Fixes: QTBUG-98365
Change-Id: I52e6344be85ca64eadbf44378de32cde126ff07a
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit da38eaf433ac1c241a29766ea8a82237caa497b5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/qmlmodels/qqmldelegatemodel.cpp           |  2 +-
 .../data/persistedItemsCache.qml              | 62 +++++++++++++++++++
 .../tst_qqmldelegatemodel.cpp                 | 17 +++++
 3 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 tests/auto/qml/qqmldelegatemodel/data/persistedItemsCache.qml

diff --git a/src/qmlmodels/qqmldelegatemodel.cpp b/src/qmlmodels/qqmldelegatemodel.cpp
index 444379818a..c6e06ac6f4 100644
--- a/src/qmlmodels/qqmldelegatemodel.cpp
+++ b/src/qmlmodels/qqmldelegatemodel.cpp
@@ -1617,7 +1617,7 @@ void QQmlDelegateModelPrivate::itemsRemoved(
                         emitDestroyingItem(object);
                     cacheItem->scriptRef -= 1;
                 }
-                if (!cacheItem->isReferenced()) {
+                if (!cacheItem->isReferenced() && !remove.inGroup(Compositor::Persisted)) {
                     m_compositor.clearFlags(Compositor::Cache, cacheIndex, 1, Compositor::CacheFlag);
                     m_cache.removeAt(cacheIndex);
                     delete cacheItem;
diff --git a/tests/auto/qml/qqmldelegatemodel/data/persistedItemsCache.qml b/tests/auto/qml/qqmldelegatemodel/data/persistedItemsCache.qml
new file mode 100644
index 0000000000..5ae2038e1f
--- /dev/null
+++ b/tests/auto/qml/qqmldelegatemodel/data/persistedItemsCache.qml
@@ -0,0 +1,62 @@
+import QtQuick
+import QtQuick.Window
+import QtQml.Models
+
+Window {
+    id: win
+    visible: true
+    width: 640
+    height: 480
+    property int destroyCount : 0;
+    property int createCount : 0;
+    property alias testListModel: mdl
+
+    DelegateModel {
+        id: visualModel
+        model: ListModel {
+            id: mdl
+            ListElement {
+                name: "a"
+                hidden: false
+            }
+            ListElement {
+                name: "b"
+                hidden: true
+            }
+            ListElement {
+                name: "c"
+                hidden: false
+            }
+        }
+
+        filterOnGroup: "selected"
+
+        groups: [
+            DelegateModelGroup {
+                name: "selected"
+                includeByDefault: true
+            }
+        ]
+
+        delegate: Text {
+            visible: DelegateModel.inSelected
+            property var idx
+            Component.onCompleted: {
+                ++createCount
+                idx = index
+                DelegateModel.inPersistedItems = true
+                DelegateModel.inSelected = !model.hidden
+            }
+            Component.onDestruction: ++destroyCount
+            text: model.name
+        }
+    }
+
+    ListView {
+    id: listView
+        model: visualModel
+        anchors.fill: parent
+        focus: true
+    }
+
+}
diff --git a/tests/auto/qml/qqmldelegatemodel/tst_qqmldelegatemodel.cpp b/tests/auto/qml/qqmldelegatemodel/tst_qqmldelegatemodel.cpp
index 8b433d346c..4169690ed0 100644
--- a/tests/auto/qml/qqmldelegatemodel/tst_qqmldelegatemodel.cpp
+++ b/tests/auto/qml/qqmldelegatemodel/tst_qqmldelegatemodel.cpp
@@ -6,6 +6,7 @@
 #include <QtGui/QStandardItemModel>
 #include <QtQml/qqmlcomponent.h>
 #include <QtQmlModels/private/qqmldelegatemodel_p.h>
+#include <QtQmlModels/private/qqmllistmodel_p.h>
 #include <QtQuick/qquickview.h>
 #include <QtQuick/qquickitem.h>
 #include <QtQuickTestUtils/private/qmlutils_p.h>
@@ -28,6 +29,7 @@ private slots:
     void nestedDelegates();
     void typedModelData();
     void deleteRace();
+    void persistedItemsStayInCache();
 };
 
 class AbstractItemModel : public QAbstractItemModel
@@ -289,6 +291,21 @@ void tst_QQmlDelegateModel::deleteRace()
     QTRY_COMPARE(o->property("count").toInt(), 0);
 }
 
+void tst_QQmlDelegateModel::persistedItemsStayInCache()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("persistedItemsCache.qml"));
+    QVERIFY2(component.isReady(), qPrintable(component.errorString()));
+    std::unique_ptr<QObject> object(component.create());
+    QVERIFY(object);
+    const QVariant properyListModel = object->property("testListModel");
+    QQmlListModel *listModel = qvariant_cast<QQmlListModel *>(properyListModel);
+    QVERIFY(listModel);
+    QTRY_COMPARE(object->property("createCount").toInt(), 3);
+    listModel->clear();
+    QTRY_COMPARE(object->property("destroyCount").toInt(), 3);
+}
+
 QTEST_MAIN(tst_QQmlDelegateModel)
 
 #include "tst_qqmldelegatemodel.moc"