From b9c1d1f7a15c7fdbb1f3ee69dc7529526e6079a5 Mon Sep 17 00:00:00 2001
From: Ivan Solovev <ivan.solovev@qt.io>
Date: Tue, 21 Jan 2025 12:26:09 +0100
Subject: [PATCH] Fix SFINAE constraint in flags debug streaming operator

So that it allows overloading.
Also move the type T declaration into the function scope, as it
could never be used as a constraint anyway, and we do not want
users to pass custom type there.

Amends 0c707c6ebece18677deaccccdfec5d48c587106f.

Found in 6.9 API review.

Change-Id: I086d65bdef7be2f9e0e67e96cc8a9ac76eaa5b0f
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit f1d2d47f609cfb3c4cf9b2a86072613b3c9e0642)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/io/qdebug.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index b5053e827a1..582ee942952 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -628,10 +628,10 @@ void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, Int value)
 }
 
 template <class Flags,
-          typename = std::enable_if_t<QtPrivate::IsQFlags<Flags>::value, void>,
-          typename T = typename Flags::enum_type>
+          std::enable_if_t<QtPrivate::IsQFlags<Flags>::value, bool> = true>
 inline QDebug operator<<(QDebug debug, Flags flags)
 {
+    using T = typename Flags::enum_type;
     using UInt = typename QIntegerForSizeof<T>::Unsigned;
 #if !defined(QT_NO_QOBJECT)
     if constexpr (QtPrivate::IsQEnumHelper<T>::Value || QtPrivate::IsQEnumHelper<Flags>::Value) {