From 43742adf7bc6a092b59f187fde977a39ebdc70b8 Mon Sep 17 00:00:00 2001
From: Dennis Oberst <dennis.oberst@qt.io>
Date: Tue, 23 May 2023 13:25:54 +0200
Subject: [PATCH] CompareAgainstLiteralZero: fix SFINAE considerations

This issue arose during the comparison of two different ordering types.
When comparing QPartialOrdering::Less to QStrongOrdering::Less, an
unintended overload was considered due to the SFINAE ctor-overload of
CompareAgainstLiteralZero. For example:

static_assert(QPartialOrdering::Less == QStrongOrdering::Less);

would consider:

friend constexpr bool operator==(QtPrivate::CompareAgainstLiteralZero,
                                 QStrongOrdering rhs) noexcept

as an overload. To address this, a stricter approach is now used
by triggering the SFINAE-check on std::nullptr_t instead.
This resolves the ambiguity while still rejecting std::nullptr_t
as intended. As the compiler is unable to resolve this automatically,
this refactoring is required.

Change-Id: I9ab7e55d2822980198f38f5a66143387999a4d94
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 1d487e559367e5a71d111fe2c3e13dca0188306c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/global/qcompare_impl.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/corelib/global/qcompare_impl.h b/src/corelib/global/qcompare_impl.h
index a2670a2b495..2556f4af6b0 100644
--- a/src/corelib/global/qcompare_impl.h
+++ b/src/corelib/global/qcompare_impl.h
@@ -22,7 +22,7 @@ public:
     using SafeZero = void (CompareAgainstLiteralZero::*)();
     Q_IMPLICIT constexpr CompareAgainstLiteralZero(SafeZero) noexcept {}
 
-    template <typename T, std::enable_if_t<!std::is_same_v<T, int>, bool> = false>
+    template <typename T, std::enable_if_t<std::is_null_pointer_v<T>, bool> = true>
     CompareAgainstLiteralZero(T) = delete;
 };