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
Pick-to: 5.15 6.0
Change-Id: I1a1ffa43eab39ed2315f1916527d897b208c2c3b
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>

1 files changed, 23 insertions, 0 deletions

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
+    }
+}