From 9d029939fb8aad4f61950da2d64cfa123d9b909a Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date: Tue, 19 Sep 2023 14:27:01 +0200
Subject: [PATCH] qobject_cast: add a couple of static_asserts

... for better error reporting.

Change-Id: I11afdef41f729b4357b743a3238c1f055a1d35d3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/corelib/kernel/qobject.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index a7b2648e45..824a29a5a4 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -384,6 +384,8 @@ bool QObject::setProperty(const char *name, QVariant &&value)
 template <class T>
 inline T qobject_cast(QObject *object)
 {
+    static_assert(std::is_pointer_v<T>,
+                  "qobject_cast requires to cast towards a pointer type");
     typedef typename std::remove_cv<typename std::remove_pointer<T>::type>::type ObjType;
     static_assert(QtPrivate::HasQ_OBJECT_Macro<ObjType>::Value,
                     "qobject_cast requires the type to have a Q_OBJECT macro");
@@ -393,6 +395,10 @@ inline T qobject_cast(QObject *object)
 template <class T>
 inline T qobject_cast(const QObject *object)
 {
+    static_assert(std::is_pointer_v<T>,
+                  "qobject_cast requires to cast towards a pointer type");
+    static_assert(std::is_const_v<std::remove_pointer_t<T>>,
+                  "qobject_cast cannot cast away constness (use const_cast)");
     typedef typename std::remove_cv<typename std::remove_pointer<T>::type>::type ObjType;
     static_assert(QtPrivate::HasQ_OBJECT_Macro<ObjType>::Value,
                       "qobject_cast requires the type to have a Q_OBJECT macro");