From 788e9d7faa1ad5cc47cc87981af1620f783ec293 Mon Sep 17 00:00:00 2001
From: Ville Voutilainen <ville.voutilainen@qt.io>
Date: Sun, 16 Jun 2024 16:31:46 +0300
Subject: [PATCH] Fix building qcompare code in MSVC in C++20 mode

MSVC quite incorrectly errors out saying that weak_ordering's
conversion to partial_ordering cannot access the private constructor
that takes the internal order.

The problem goes away when the types are forward-declared before they
are declared as friends.

Fixes: QTBUG-126386
Change-Id: I50ad6d08ee648eb15109dde4a9ec9c753ee18e68
Pick-to: 6.7
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit d2b4aec865bd834747cd824658e567b83bf081e6)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/global/qcompare.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/corelib/global/qcompare.h b/src/corelib/global/qcompare.h
index 9dd244c8f92..fb5a40f0529 100644
--- a/src/corelib/global/qcompare.h
+++ b/src/corelib/global/qcompare.h
@@ -62,6 +62,9 @@ constexpr O reversed(O o) noexcept
 
 namespace Qt {
 
+class weak_ordering;
+class strong_ordering;
+
 class partial_ordering
 {
 public: