From 7a65abb50eb638de445e24c2746d7f90c1b89f06 Mon Sep 17 00:00:00 2001
From: Milian Wolff <milian.wolff@kdab.com>
Date: Thu, 8 Aug 2024 11:40:03 +0200
Subject: [PATCH] Don't increase the refcount if qobject_cast failed

Follow the dynamicCast/dynamic_pointer_cast implementation for
objectCast/object_pointer_cast since a qobject_cast can fail
just like a dynamic dast.
Also see: https://eel.is/c++draft/util.smartptr.shared.cast#6.2

See commit this commit from 2013 for more historical context:
a094bf5a893c3cccffff10c1420bfbe3a3c02a7c

Pick-to: 6.8 6.7 6.5
Change-Id: I9a54af55a7a1cf106cace52e9cf3bc103ae0bd42
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/tools/qsharedpointer_impl.h          |  6 +++++-
 .../tools/qsharedpointer/tst_qsharedpointer.cpp  | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index 5982afd7a9b..9816c6198fc 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/src/corelib/tools/qsharedpointer_impl.h
@@ -901,6 +901,8 @@ template <class X, class T>
 Q_INLINE_TEMPLATE QSharedPointer<X> qSharedPointerObjectCast(const QSharedPointer<T> &src)
 {
     X *ptr = qobject_cast<X *>(src.data());
+    if (!ptr)
+        return QSharedPointer<X>();
     return QtSharedPointer::copyAndSetPointer(ptr, src);
 }
 template <class X, class T>
@@ -943,7 +945,9 @@ template <typename X, class T>
 std::shared_ptr<X> qobject_pointer_cast(const std::shared_ptr<T> &src)
 {
     using element_type = typename std::shared_ptr<X>::element_type;
-    return std::shared_ptr<X>(src, qobject_cast<element_type *>(src.get()));
+    if (auto ptr = qobject_cast<element_type *>(src.get()))
+        return std::shared_ptr<X>(src, ptr);
+    return std::shared_ptr<X>();
 }
 
 template <typename X, class T>
diff --git a/tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp b/tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp
index 056ce4281cf..1579d04bdf0 100644
--- a/tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp
+++ b/tests/auto/corelib/tools/qsharedpointer/tst_qsharedpointer.cpp
@@ -60,6 +60,7 @@ private slots:
     void weakQObjectFromSharedPointer();
     void objectCast();
     void objectCastStdSharedPtr();
+    void objectCastFailureNoLeak();
     void differentPointers();
     void virtualBaseDifferentPointers();
     void virtualBaseWeakPointerConversions();
@@ -1109,6 +1110,21 @@ void tst_QSharedPointer::objectCast()
     safetyCheck();
 }
 
+void tst_QSharedPointer::objectCastFailureNoLeak()
+{
+    // verify that a failing object cast doesn't keep the original object alive
+    auto ptr = QSharedPointer<QObject>::create();
+    auto qptr = QPointer(ptr.data());
+    auto ptr2 = ptr.objectCast<tst_QSharedPointer>();
+
+    QVERIFY(ptr);
+    QVERIFY(qptr);
+    QVERIFY(!ptr2);
+
+    ptr.reset();
+    QVERIFY(!ptr);
+    QVERIFY(!qptr);
+}
 
 void tst_QSharedPointer::objectCastStdSharedPtr()
 {