From f69bcf8d806dbfd1af673f2f8e3b803c7a76361c Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Wed, 8 Feb 2023 12:38:23 +0100
Subject: [PATCH] Deprecate QPropertyAlias

That use case for the class never materialized, and it was actually
meant for internal use. However, we put it into the public header, so
we cannot remove it (and while undocumented, someone actually used it at
some point, compare e4d62651c278c468f71ce097979bc1183ffd0713).

Mark it as deprecated instead so that it can be finally be removed in Qt
7.

Change-Id: I058c5831a44610121fbec6eaddebd8b33d4a16c9
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
---
 src/corelib/kernel/qproperty.cpp                    |  2 ++
 src/corelib/kernel/qproperty.h                      | 13 +++++++++++--
 src/corelib/kernel/qproperty_p.h                    |  6 ++++++
 .../auto/corelib/kernel/qproperty/tst_qproperty.cpp |  4 ++++
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/corelib/kernel/qproperty.cpp b/src/corelib/kernel/qproperty.cpp
index f54cd732789..4a8874caf4b 100644
--- a/src/corelib/kernel/qproperty.cpp
+++ b/src/corelib/kernel/qproperty.cpp
@@ -641,11 +641,13 @@ QPropertyObserver::QPropertyObserver(ChangeHandler changeHandler)
     d.setChangeHandler(changeHandler);
 }
 
+#if QT_DEPRECATED_SINCE(6, 6)
 QPropertyObserver::QPropertyObserver(QUntypedPropertyData *data)
 {
     aliasData = data;
     next.setTag(ObserverIsAlias);
 }
+#endif
 
 /*! \internal
 */
diff --git a/src/corelib/kernel/qproperty.h b/src/corelib/kernel/qproperty.h
index 297a3fe9740..5d8b908f31a 100644
--- a/src/corelib/kernel/qproperty.h
+++ b/src/corelib/kernel/qproperty.h
@@ -217,7 +217,9 @@ public:
         ObserverNotifiesBinding, // observer was installed to notify bindings that obsverved property changed
         ObserverNotifiesChangeHandler, // observer is a change handler, which runs on every change
         ObserverIsPlaceholder,  // the observer before this one is currently evaluated in QPropertyObserver::notifyObservers.
+#if QT_DEPRECATED_SINCE(6, 6)
         ObserverIsAlias
+#endif
     };
 protected:
     using ChangeHandler = void (*)(QPropertyObserver*, QUntypedPropertyData *);
@@ -257,7 +259,9 @@ public:
 
 protected:
     QPropertyObserver(ChangeHandler changeHandler);
-    QPropertyObserver(QUntypedPropertyData *aliasedPropertyPtr);
+#if QT_DEPRECATED_SINCE(6, 6)
+    QT_DEPRECATED QPropertyObserver(QUntypedPropertyData *aliasedPropertyPtr);
+#endif
 
     QUntypedPropertyData *aliasedProperty() const
     {
@@ -867,13 +871,16 @@ public:
     }
 };
 
+#if QT_DEPRECATED_SINCE(6, 6)
 template<typename T>
-class QPropertyAlias : public QPropertyObserver
+class QT_DEPRECATED_X("Class was only meant for internal use, use a QProperty and add a binding to the target")
+QPropertyAlias : public QPropertyObserver
 {
     Q_DISABLE_COPY_MOVE(QPropertyAlias)
     const QtPrivate::QBindableInterface *iface = nullptr;
 
 public:
+    QT_WARNING_PUSH QT_WARNING_DISABLE_DEPRECATED
     QPropertyAlias(QProperty<T> *property)
         : QPropertyObserver(property),
           iface(&QtPrivate::QBindableInterfaceForProperty<QProperty<T>>::iface)
@@ -989,7 +996,9 @@ public:
     {
         return aliasedProperty() != nullptr;
     }
+    QT_WARNING_POP
 };
+#endif
 
 template<typename Class, typename T, auto Offset, auto Signal = nullptr>
 class QObjectBindableProperty : public QPropertyData<T>
diff --git a/src/corelib/kernel/qproperty_p.h b/src/corelib/kernel/qproperty_p.h
index 42daca036a7..3ae1bfcc23b 100644
--- a/src/corelib/kernel/qproperty_p.h
+++ b/src/corelib/kernel/qproperty_p.h
@@ -124,13 +124,17 @@ struct QPropertyObserverPointer
     void unlink()
     {
         unlink_common();
+#if QT_DEPRECATED_SINCE(6, 6)
         if (ptr->next.tag() == QPropertyObserver::ObserverIsAlias)
             ptr->aliasData = nullptr;
+#endif
     }
 
     void unlink_fast()
     {
+#if QT_DEPRECATED_SINCE(6, 6)
         Q_ASSERT(ptr->next.tag() != QPropertyObserver::ObserverIsAlias);
+#endif
         unlink_common();
     }
 
@@ -881,8 +885,10 @@ inline void QPropertyObserverPointer::notify(QUntypedPropertyData *propertyDataP
         case QPropertyObserver::ObserverIsPlaceholder:
             // recursion is already properly handled somewhere else
             break;
+#if QT_DEPRECATED_SINCE(6, 6)
         case QPropertyObserver::ObserverIsAlias:
             break;
+#endif
         default: Q_UNREACHABLE();
         }
         observer = next;
diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index 335cc65b5ab..dbdcaa1a1b2 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -2240,6 +2240,8 @@ void tst_QProperty::selfBindingShouldNotCrash()
 
 void tst_QProperty::qpropertyAlias()
 {
+#if QT_DEPRECATED_SINCE(6, 6)
+    QT_WARNING_PUSH QT_WARNING_DISABLE_DEPRECATED
     std::unique_ptr<QProperty<int>> i {new QProperty<int>};
     QPropertyAlias<int> alias(i.get());
     QVERIFY(alias.isValid());
@@ -2251,6 +2253,8 @@ void tst_QProperty::qpropertyAlias()
     QCOMPARE(alias.value(), 42);
     i.reset();
     QVERIFY(!alias.isValid());
+    QT_WARNING_POP
+#endif
 }
 
 void tst_QProperty::scheduleNotify()