ListModel: Fix move handling in sync

When a ListModel is modified in a workerscript, we reconciliate the
state in ListModel::sync. However, the logic for moving elements was
wrong, causing crashes in endMoveRows due to invalid moves.
This patch ensures that elements are moved to the correct position.
Notably, whenever an element is moved, we must update the targetIndex of
all elements affected by that move.

Amends 3accc1dae76575120e71cadb547e961ecd50bcb0.

Task-number: QTBUG-85557
Change-Id: I1a1ffa43eab39ed2315f1916527d897b208c2c3b
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>
(cherry picked from commit 2996439993c587bc9c7169e4f152169f28247c21)
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

6 files changed, 385 insertions, 3 deletions

diff --git a/src/qmlmodels/qqmllistmodel.cpp b/src/qmlmodels/qqmllistmodel.cpp
index 8830e08097..e392c9e323 100644
--- a/src/qmlmodels/qqmllistmodel.cpp
+++ b/src/qmlmodels/qqmllistmodel.cpp
@@ -446,7 +446,8 @@ bool ListModel::sync(ListModel *src, ListModel *target)
     // to ensure things are kept in the correct order, emit inserts and moves first. This shouls ensure all persistent
     // model indices are updated correctly
     int rowsInserted = 0;
-    for (int i = 0 ; i < target->elements.count() ; ++i) {
+    const int targetElementCount = target->elements.count();
+    for (int i = 0 ; i < targetElementCount ; ++i) {
         ListElement *element = target->elements.at(i);
         ElementSync &s = elementHash.find(element->getUid()).value();
         Q_ASSERT(s.srcIndex >= 0);
@@ -456,13 +457,33 @@ bool ListModel::sync(ListModel *src, ListModel *target)
                 if (s.targetIndex == -1) {
                     targetModel->beginInsertRows(QModelIndex(), i, i);
                     targetModel->endInsertRows();
+                    ++rowsInserted;
                 } else {
-                    targetModel->beginMoveRows(QModelIndex(), i, i, QModelIndex(), s.srcIndex);
+                    bool validMove = targetModel->beginMoveRows(QModelIndex(), s.targetIndex, s.targetIndex, QModelIndex(), i);
+                    Q_ASSERT(validMove);
+                    Q_UNUSED(validMove); // fixes unused variable warning if asserts are disabled
                     targetModel->endMoveRows();
+                    // fixup target indices of elements that still need to move
+                    for (int j=i+1; j < targetElementCount; ++j) {
+                        ListElement *eToFix = target->elements.at(j);
+                        ElementSync &sToFix = elementHash.find(eToFix->getUid()).value();
+                        if (i < s.targetIndex) {
+                            // element was moved down
+                            if (sToFix.targetIndex > s.targetIndex || sToFix.targetIndex < i)
+                                continue; // unaffected by reordering
+                            else
+                                sToFix.targetIndex += 1;
+                        } else {
+                            // element was moved up
+                            if (sToFix.targetIndex < s.targetIndex || sToFix.targetIndex > i)
+                                continue; // unaffected by reordering
+                            else
+                                sToFix.targetIndex -= 1;
+                        }
+                    }
                 }
             }
             hasChanges = true;
-            ++rowsInserted;
         }
         if (s.targetIndex != -1 && !s.changedRoles.isEmpty()) {
             QModelIndex idx = targetModel->createIndex(i, 0);
diff --git a/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.mjs b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.mjs
new file mode 100644
index 0000000000..cfc1e1146f
--- /dev/null
+++ b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.mjs
@@ -0,0 +1,117 @@
+/* Copyright 2020 Esri
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+//------------------------------------------------------------------------------
+
+export const OrderAscending = 0
+export const OrderDescending = 1
+
+//------------------------------------------------------------------------------
+
+export function sort(model, sortKey, descending, useMove) {
+
+    _sort(model, sortKey, descending, useMove);
+}
+
+//------------------------------------------------------------------------------
+
+function _sort(model, sortKey, descending, useMove) {
+    var lessThan =  descending ? 1 : -1;
+    var greaterThan = -lessThan;
+
+    var indices = [...new Array(model.count).keys()];
+
+    function getKeyValue(index) {
+        return model.get(index)[sortKey];
+    }
+
+    function compareKey(index1, index2) {
+        var value1 = getKeyValue(index1);
+        var value2 = getKeyValue(index2);
+
+        return (value1 < value2)
+                ? lessThan
+                : (value1 > value2)
+                  ? greaterThan
+                  : 0;
+    }
+
+    indices.sort(compareKey);
+
+
+    function compareFrom(i1, i2) {
+        return (i1.from < i2.from)
+                ? -1
+                : (i1.from > i2.from)
+                  ? 1
+                  : 0;
+    }
+
+    var swapIndices = indices.map((e, i) => { return { from: e, to: i }}).sort(compareFrom).map(e => e.to);
+
+    function clone(o) {
+        return JSON.parse(JSON.stringify(o));
+    }
+
+    function cloneSwap(a, b) {
+        var o = clone(model.get(a));
+        model.set(a, model.get(b));
+        model.set(b, o);
+    }
+
+    function moveSwap(a, b) {
+        if (a < b) {
+            model.move(a, b, 1);
+            model.move(b - 1, a, 1);
+        }
+        else if (a > b) {
+            model.move(b, a, 1);
+            model.move(a - 1, b, 1);
+        }
+    }
+
+
+    var swap = useMove ? moveSwap : cloneSwap;
+    var swapCount = 0;
+
+
+    for (var iFrom = 0; iFrom < swapIndices.length; iFrom++) {
+        var iTo = swapIndices[iFrom];
+
+        if (iFrom === iTo) {
+            continue;
+        }
+
+        do {
+            swap(iFrom, iTo);
+
+            var t = swapIndices[iFrom];
+            swapIndices[iFrom] = swapIndices[iTo]
+            swapIndices[iTo] = t;
+
+            iTo = swapIndices[iFrom];
+
+            swapCount++;
+        }
+        while (iFrom !== iTo);
+    }
+
+}
+
+//------------------------------------------------------------------------------
+
+
+
diff --git a/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.qml b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.qml
new file mode 100644
index 0000000000..2679925c80
--- /dev/null
+++ b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSort.qml
@@ -0,0 +1,166 @@
+/* Copyright 2020 Esri
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+import QtQml 2.13
+import QtQml.Models 2.13
+
+import QtQuick 2.13
+import QtQuick.Layouts 1.12
+
+import "ListModelSort.mjs" as ListModelSort
+
+Item {
+    Component.onCompleted: {
+        fillModel(namesModel, "A, D, E, B, C, A");
+    }
+
+
+    function verify() {
+        let expected = ["A", "A", "B", "C", "D", "E"]
+        let sorted = listView.count === 6
+        for (let i = 0; i<listView.count;++i) {
+            sorted = sorted && (listView.itemAtIndex(i).name === expected[i])
+        }
+        return sorted
+    }
+
+    function doSort() {
+        sortAsync(namesModel, "name", false, false)
+    }
+
+
+    function random(n) {
+        return Math.round(Math.random(new Date().valueOf()) * n);
+    }
+
+    function fillModel(model, values) {
+        var names = values.split(",").map(name => name.trim()).filter(name => name > "");
+
+
+        model.clear();
+
+        for (const name of names) {
+            model.append({
+                             name: name,
+                             number: random(names.length)
+                         });
+        }
+    }
+
+    //--------------------------------------------------------------------------
+
+    ListModel {
+        id: namesModel
+
+        objectName: "namesModel"
+    }
+
+    //--------------------------------------------------------------------------
+    ColumnLayout {
+        anchors {
+            fill: parent
+            margins: 10
+        }
+
+        ListView {
+            id: listView
+
+            Layout.fillWidth: true
+            Layout.fillHeight: true
+
+            model: namesModel
+            clip: true
+            spacing: 5
+
+            delegate: Text {
+                required property string name
+                required property int number
+                width: ListView.view.width
+                text: "%1 (%2)".arg(name).arg(number)
+                horizontalAlignment: Text.AlignHCenter
+                wrapMode: Text.WrapAtWordBoundaryOrAnywhere
+            }
+
+            add: Transition {
+                NumberAnimation { property: "opacity"; from: 0; to: 1.0; duration: 400 }
+                NumberAnimation { property: "scale"; from: 0; to: 1.0; duration: 400 }
+            }
+
+            addDisplaced: Transition {
+                NumberAnimation { properties: "x,y"; duration: 100 }
+            }
+
+            move: Transition {
+                NumberAnimation { properties: "x,y"; duration: 100 }
+            }
+
+            moveDisplaced: Transition {
+                NumberAnimation { properties: "x,y"; duration: 100 }
+            }
+
+            displaced: Transition {
+                NumberAnimation { properties: "x,y"; duration: 40; easing.type: Easing.OutBounce }
+            }
+
+            populate: Transition {
+                NumberAnimation { properties: "x,y"; duration: 100 }
+            }
+
+            remove: Transition {
+                ParallelAnimation {
+                    NumberAnimation { property: "opacity"; to: 0; duration: 100 }
+                    NumberAnimation { properties: "x,y"; to: 100; duration: 100 }
+                }
+            }
+
+            removeDisplaced: Transition {
+                NumberAnimation { properties: "x,y"; duration: 100 }
+            }
+        }
+        }
+
+
+    function sortSync(model, sortKey, descending, useMove) {
+
+        ListModelSort.sort(model, sortKey, descending, useMove);
+    }
+
+    //--------------------------------------------------------------------------
+
+    function sortAsync(model, sortKey, descending, useMove) {
+
+        var params = {
+            debug: true,
+            model: model,
+            sortKey: sortKey,
+            descending: descending,
+            useMove: useMove
+        };
+
+
+        sortWorker.sendMessage(params);
+    }
+
+    WorkerScript {
+        id: sortWorker
+
+        source: "ListModelSortWorker.mjs"
+    }
+
+    //--------------------------------------------------------------------------
+
+}
+
diff --git a/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSortWorker.mjs b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSortWorker.mjs
new file mode 100644
index 0000000000..fa3b5c27ec
--- /dev/null
+++ b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/ListModelSortWorker.mjs
@@ -0,0 +1,38 @@
+/* Copyright 2020 Esri
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+import * as ListModelSort from "ListModelSort.mjs";
+
+//------------------------------------------------------------------------------
+
+WorkerScript.onMessage = function(params) {
+
+    params.model.sync();
+
+    const debug = params.debug;
+
+    ListModelSort.sort(params.model, params.sortKey, !!params.descending, !!params.useMove);
+
+    params.model.sync();
+
+
+    WorkerScript.sendMessage({
+                                 text: "Sorted"
+                             });
+}
+
+//------------------------------------------------------------------------------
+
diff --git a/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/main.qml b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/main.qml
new file mode 100644
index 0000000000..88a23511fa
--- /dev/null
+++ b/tests/auto/qml/qqmllistmodelworkerscript/data/listmodel_async_sort/main.qml
@@ -0,0 +1,23 @@
+import QtQuick 2.13
+import QtQuick.Window 2.13
+
+Window {
+    visible: true
+    width: 640
+    height: 640
+    title: qsTr("Hello World")
+
+    ListModelSort {
+        id: lms
+        anchors.fill: parent
+    }
+
+    function doSort() {
+        lms.doSort()
+    }
+
+    function verify(): bool {
+        let ok = lms.verify()
+        return ok
+    }
+}
diff --git a/tests/auto/qml/qqmllistmodelworkerscript/tst_qqmllistmodelworkerscript.cpp b/tests/auto/qml/qqmllistmodelworkerscript/tst_qqmllistmodelworkerscript.cpp
index b5e8800d0e..edcfc4994d 100644
--- a/tests/auto/qml/qqmllistmodelworkerscript/tst_qqmllistmodelworkerscript.cpp
+++ b/tests/auto/qml/qqmllistmodelworkerscript/tst_qqmllistmodelworkerscript.cpp
@@ -104,6 +104,7 @@ private slots:
     void worker_remove_list();
     void dynamic_role_data();
     void dynamic_role();
+    void correctMoves();
 };
 
 bool tst_qqmllistmodelworkerscript::compareVariantList(const QVariantList &testList, QVariant object)
@@ -842,6 +843,22 @@ void tst_qqmllistmodelworkerscript::dynamic_role()
     qApp->processEvents();
 }
 
+void tst_qqmllistmodelworkerscript::correctMoves()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("listmodel_async_sort/main.qml"));
+    QScopedPointer<QObject> root {component.create()};
+    QVERIFY2(root, qPrintable(component.errorString()));
+    bool ok =QMetaObject::invokeMethod(root.get(), "doSort");
+    QVERIFY(ok);
+    auto check = [&](){
+        bool success = false;
+        QMetaObject::invokeMethod(root.get(), "verify", Q_RETURN_ARG(bool, success));
+        return success;
+    };
+    QTRY_VERIFY(check());
+}
+
 QTEST_MAIN(tst_qqmllistmodelworkerscript)
 
 #include "tst_qqmllistmodelworkerscript.moc"