From 200a3c92972473476d8323dd8ff8e4b8fbc182f7 Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date: Fri, 20 May 2022 18:36:48 +0200
Subject: [PATCH] QMetaType: disable conversion from smart pointer<const
 QObject>
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QMetaType can register a converter from a smart pointer class to
QObject *. The code tries to do so even if the smart pointer is
actually holding a pointer to a _const_ QObject
(e.g. shared_ptr<const QObject>), causing a compile error:

  ../src/qt5/qtbase/build/include/QtCore/../../../src/corelib/kernel/qmetatype.h:1208:32: error: invalid conversion from ‘const QObject*’ to ‘QObject*’ [-fpermissive]
   1208 |             return p.operator->();
        |                    ~~~~~~~~~~~~^~
        |                                |
        |                                const QObject*

Disable the conversion if indeed the source is const qualified.

Change-Id: I9e9bc5992f74131e5cfd6ece9b83d4f26d370e92
Fixes: QTBUG-103741
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit c613dd4765637a00837dd66abc2b940632022a60)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/kernel/qmetatype.h                  |  2 +-
 .../auto/corelib/kernel/qobject/tst_qobject.cpp | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/corelib/kernel/qmetatype.h b/src/corelib/kernel/qmetatype.h
index a7796966131..2a341b870a3 100644
--- a/src/corelib/kernel/qmetatype.h
+++ b/src/corelib/kernel/qmetatype.h
@@ -1520,7 +1520,7 @@ struct SharedPointerMetaTypeIdHelper<SMART_POINTER<T>, true> \
 }; \
 template<typename T> \
 struct MetaTypeSmartPointerHelper<SMART_POINTER<T> , \
-        typename std::enable_if<IsPointerToTypeDerivedFromQObject<T*>::Value>::type> \
+        typename std::enable_if<IsPointerToTypeDerivedFromQObject<T*>::Value && !std::is_const_v<T>>::type> \
 { \
     static bool registerConverter() \
     { \
diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 6f3d8ba091e..d639cdec26c 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -8143,5 +8143,22 @@ void tst_QObject::objectNameBinding()
 static_assert(QtPrivate::HasQ_OBJECT_Macro<tst_QObject>::Value);
 static_assert(!QtPrivate::HasQ_OBJECT_Macro<SiblingDeleter>::Value);
 
+Q_DECLARE_SMART_POINTER_METATYPE(std::shared_ptr)
+Q_DECLARE_SMART_POINTER_METATYPE(std::unique_ptr)
+
+
+// QTBUG-103741: OK to use smart pointers to const QObject in signals/slots
+class SenderWithSharedPointerConstQObject : public QObject
+{
+    Q_OBJECT
+
+signals:
+    void aSignal1(const QSharedPointer<const QObject> &);
+    void aSignal2(const QWeakPointer<const QObject> &);
+    void aSignal3(const QPointer<const QObject> &);
+    void aSignal4(const std::shared_ptr<const QObject> &);
+    void aSignal5(const std::unique_ptr<const QObject> &);
+};
+
 QTEST_MAIN(tst_QObject)
 #include "tst_qobject.moc"