From ae515c3f2eb8ac83af99fb6fbcdb3080dd4a90a7 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Thu, 18 Jul 2024 21:25:03 +0200
Subject: [PATCH] Fix signature of QDebug::toString() (again)
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There are zero QDebug operators that take an rvalue RHS, so there's no
need to make toString() perfectly forwarding. It just causes four¹
different versions of the identical function to be instantiated. Not
all compilers can merge the binary representations and those that try,
violate the standard (same address for different functions).

¹ {rvalue, lvalue} × {const, non-const}

Fix by taking by cref.

Amends 40976532158fc49be45bb976455f48e98f9690cf.

[ChangeLog][Potentially Source-Incompatible Changes][QtCore][QDebug]
The toString() static function no longer allows the called
operator<<() to modify the argument. No Qt-provided operator<<() does
that, and operators that do are probably buggy.

Change-Id: Iac1ee9d29f93fd4840b75ffe363d354a2d19a96e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 13244eef6c913bb7f27cd8fbf459f5dfe9a0ed21)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/io/qdebug.cpp | 2 +-
 src/corelib/io/qdebug.h   | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/corelib/io/qdebug.cpp b/src/corelib/io/qdebug.cpp
index 64b693fea51..70832c3dbcb 100644
--- a/src/corelib/io/qdebug.cpp
+++ b/src/corelib/io/qdebug.cpp
@@ -996,7 +996,7 @@ QDebug &QDebug::resetFormat()
 */
 
 /*!
-    \fn template <class T> QString QDebug::toString(T &&object)
+    \fn template <class T> QString QDebug::toString(const T &object)
     \since 6.0
 
     \include qdebug-toString.qdocinc
diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index 44c3dea804b..6d48c7853d4 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -224,11 +224,11 @@ public:
 #endif // QT_SUPPORTS_INT128
 
     template <typename T>
-    static QString toString(T &&object)
+    static QString toString(const T &object)
     {
         QString buffer;
         QDebug stream(&buffer);
-        stream.nospace() << std::forward<T>(object);
+        stream.nospace() << object;
         return buffer;
     }
 };