Add virtual methods "baseDeleted" and "debugName" to QQuickItemChangeListener that let us report whether the object that implements QQuickItemChangeListener is already being destroyed. Add a "safe" version of QQuickItemChangeListener that overrides that virtual method using CRTP: if the derived class that it is instantiated with has a member "inDestructor" (e.g. a QQuickItemPrivate) or "wasDeleted" (e.g. a QObjectPrivate), then return the value of that variable. If the derived type is a QObject or QQuickItem, access the member via QQmlData::wasDeleted. Ignore calls on listeners that are the same object as the caller. Use that new type in those classes where it isn't immediately obvious that they clean up after themselves: classes that don't implement a destructor are a red flag. In addition, add a list to safe listener version to add/remove each item it's listening on. Issue runtime warnings in developer-builds when listeners are called for which baseDestroyed() returns true, and when listeners are destroyed while they still have items on their list. Task-number: QTBUG-98790 Change-Id: I15ed66a36556caa0e6acf5b768dec2ae92b01d64 Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io> Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>