From 07ed8acdf98cd6c058fb9f5d62953e863c1f7886 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Wed, 29 Nov 2023 20:11:46 +0100
Subject: [PATCH] QPartialOrdering: add missing conversions to/from
 Qt::_ordering types

Since QPartialOrdering is supposed to be a drop-in-replacement for
Qt::partial_ordering, it need to have the same conversions from
Qt::_ordering types that Qt::partial_ordering has.

Fix by adding the necessary conversion and relational operators and
conversion constructors.

Change-Id: Ib8e78c850b43c8bcb3bb15c5f7d25be9d0da7339
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
---
 src/corelib/global/qcompare.h                 | 48 +++++++++++++++++++
 .../corelib/global/qcompare/tst_qcompare.cpp  |  1 +
 2 files changed, 49 insertions(+)

diff --git a/src/corelib/global/qcompare.h b/src/corelib/global/qcompare.h
index 529f79c797a..f7fa7c65a7b 100644
--- a/src/corelib/global/qcompare.h
+++ b/src/corelib/global/qcompare.h
@@ -700,6 +700,54 @@ public:
     friend constexpr bool operator!=(QPartialOrdering lhs, QPartialOrdering rhs) noexcept
     { return lhs.m_order != rhs.m_order; }
 
+    constexpr Q_IMPLICIT QPartialOrdering(Qt::partial_ordering order) noexcept
+        : m_order{} // == equivalent
+    {
+        if (order == Qt::partial_ordering::less)
+            m_order = static_cast<QtPrivate::CompareUnderlyingType>(QtPrivate::Ordering::Less);
+        else if (order == Qt::partial_ordering::greater)
+            m_order = static_cast<QtPrivate::CompareUnderlyingType>(QtPrivate::Ordering::Greater);
+        else if (order == Qt::partial_ordering::unordered)
+            m_order = static_cast<QtPrivate::CompareUnderlyingType>(QtPrivate::LegacyUncomparable::Unordered);
+    }
+
+    constexpr Q_IMPLICIT QPartialOrdering(Qt::weak_ordering stdorder) noexcept
+        : QPartialOrdering(Qt::partial_ordering{stdorder}) {}
+
+    constexpr Q_IMPLICIT QPartialOrdering(Qt::strong_ordering stdorder) noexcept
+        : QPartialOrdering(Qt::partial_ordering{stdorder}) {}
+
+    constexpr Q_IMPLICIT operator Qt::partial_ordering() const noexcept
+    {
+        using O = QtPrivate::Ordering;
+        using U = QtPrivate::LegacyUncomparable;
+        using R = Qt::partial_ordering;
+        switch (m_order) {
+        case qToUnderlying(O::Less):       return R::less;
+        case qToUnderlying(O::Greater):    return R::greater;
+        case qToUnderlying(O::Equivalent): return R::equivalent;
+        case qToUnderlying(U::Unordered):  return R::unordered;
+        }
+        // GCC 8.x does not treat __builtin_unreachable() as constexpr
+#if !defined(Q_CC_GNU_ONLY) || (Q_CC_GNU >= 900)
+        // NOLINTNEXTLINE(qt-use-unreachable-return): Triggers on Clang, breaking GCC 8
+        Q_UNREACHABLE();
+#endif
+        return R::unordered;
+    }
+
+    friend constexpr bool operator==(QPartialOrdering lhs, Qt::partial_ordering rhs) noexcept
+    { Qt::partial_ordering qt = lhs; return qt == rhs; }
+
+    friend constexpr bool operator!=(QPartialOrdering lhs, Qt::partial_ordering rhs) noexcept
+    { Qt::partial_ordering qt = lhs; return qt != rhs; }
+
+    friend constexpr bool operator==(Qt::partial_ordering lhs, QPartialOrdering rhs) noexcept
+    { Qt::partial_ordering qt = rhs; return lhs == qt; }
+
+    friend constexpr bool operator!=(Qt::partial_ordering lhs, QPartialOrdering rhs) noexcept
+    { Qt::partial_ordering qt = rhs; return lhs != qt; }
+
 #ifdef __cpp_lib_three_way_comparison
     constexpr Q_IMPLICIT QPartialOrdering(std::partial_ordering stdorder) noexcept
     {
diff --git a/tests/auto/corelib/global/qcompare/tst_qcompare.cpp b/tests/auto/corelib/global/qcompare/tst_qcompare.cpp
index f473c1706d9..e02eb61fded 100644
--- a/tests/auto/corelib/global/qcompare/tst_qcompare.cpp
+++ b/tests/auto/corelib/global/qcompare/tst_qcompare.cpp
@@ -148,6 +148,7 @@ void tst_QCompare::legacyConversions()
         CHECK_CONVERTS(NS ::strong_ordering,  QPartialOrdering); \
     } while (false)
 
+    CHECK_ALL(Qt);
 #ifdef __cpp_lib_three_way_comparison
     CHECK_ALL(std);
 #endif // __cpp_lib_three_way_comparison