4 files changed, 82 insertions, 39 deletions
diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index 16f14c45790..2210cae848a 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -928,6 +928,28 @@ QUrl QUrl::fromEncoded(const QByteArray &input, ParsingMode mode)
 #endif // QT_CORE_REMOVED_SINCE(6, 7)
 
 #if QT_CORE_REMOVED_SINCE(6, 8)
+#include "qabstractitemmodel.h"
+
+bool QPersistentModelIndex::operator<(const QPersistentModelIndex &other) const noexcept
+{
+    return is_lt(compareThreeWay(*this, other));
+}
+
+bool QPersistentModelIndex::operator==(const QPersistentModelIndex &other) const noexcept
+{
+    return comparesEqual(*this, other);
+}
+
+bool QPersistentModelIndex::operator==(const QModelIndex &other) const noexcept
+{
+    return comparesEqual(*this, other);
+}
+
+bool QPersistentModelIndex::operator!=(const QModelIndex &other) const noexcept
+{
+    return !comparesEqual(*this, other);
+}
+
 #include "qbitarray.h" // inlined API
 
 #include "qbytearray.h" // inlined API
diff --git a/src/corelib/itemmodels/qabstractitemmodel.cpp b/src/corelib/itemmodels/qabstractitemmodel.cpp
index 629ee9582af..216db3b42a5 100644
--- a/src/corelib/itemmodels/qabstractitemmodel.cpp
+++ b/src/corelib/itemmodels/qabstractitemmodel.cpp
@@ -288,6 +288,9 @@ void QPersistentModelIndexData::destroy(QPersistentModelIndexData *data)
   \brief The QPersistentModelIndex class is used to locate data in a data model.
 
   \ingroup model-view
+  \compares strong
+  \compareswith strong QModelIndex
+  \endcompareswith
 
   A QPersistentModelIndex is a model index that can be stored by an
   application, and later used to access information in a model.
@@ -375,45 +378,53 @@ QPersistentModelIndex::~QPersistentModelIndex()
 }
 
 /*!
-  Returns \c{true} if this persistent model index is equal to the \a other
-  persistent model index; otherwise returns \c{false}.
+    \fn bool QPersistentModelIndex::operator==(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs)
+    Returns \c{true} if \a lhs persistent model index is equal to the \a rhs
+    persistent model index; otherwise returns \c{false}.
 
-  The internal data pointer, row, column, and model values in the persistent
-  model index are used when comparing with another persistent model index.
+    The internal data pointer, row, column, and model values in the persistent
+    model index are used when comparing with another persistent model index.
 */
 
-bool QPersistentModelIndex::operator==(const QPersistentModelIndex &other) const noexcept
+/*!
+    \fn bool QPersistentModelIndex::operator!=(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs)
+    \since 4.2
+
+    Returns \c{true} if \a lhs persistent model index is not equal to the \a rhs
+    persistent model index; otherwise returns \c{false}.
+*/
+bool comparesEqual(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs) noexcept
 {
-    if (d && other.d)
-        return d->index == other.d->index;
-    return d == other.d;
+    if (lhs.d && rhs.d)
+        return lhs.d->index == rhs.d->index;
+    return lhs.d == rhs.d;
 }
 
 /*!
+    \fn bool QPersistentModelIndex::operator<(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs)
     \since 4.1
 
-    Returns \c{true} if this persistent model index is smaller than the \a other
+    Returns \c{true} if \a lhs persistent model index is smaller than the \a rhs
     persistent model index; otherwise returns \c{false}.
 
     The internal data pointer, row, column, and model values in the persistent
     model index are used when comparing with another persistent model index.
 */
-
-bool QPersistentModelIndex::operator<(const QPersistentModelIndex &other) const noexcept
+Qt::strong_ordering compareThreeWay(const QPersistentModelIndex &lhs,
+                                    const QPersistentModelIndex &rhs) noexcept
 {
-    if (d && other.d)
-        return d->index < other.d->index;
+    if (lhs.d && rhs.d)
+        return compareThreeWay(lhs.d->index, rhs.d->index);
 
-    return std::less<>{}(d, other.d);
+    using Qt::totally_ordered_wrapper;
+    return compareThreeWay(totally_ordered_wrapper{lhs.d}, totally_ordered_wrapper{rhs.d});
 }
 
-/*!
-    \fn bool QPersistentModelIndex::operator!=(const QPersistentModelIndex &other) const
-    \since 4.2
-
-    Returns \c{true} if this persistent model index is not equal to the \a
-    other persistent model index; otherwise returns \c{false}.
-*/
+Qt::strong_ordering compareThreeWay(const QPersistentModelIndex &lhs,
+                                    const QModelIndex &rhs) noexcept
+{
+    return compareThreeWay(lhs.d ? lhs.d->index : QModelIndex{}, rhs);
+}
 
 /*!
     Sets the persistent model index to refer to the same item in a model
@@ -470,32 +481,26 @@ QPersistentModelIndex::operator QModelIndex() const
 }
 
 /*!
-    Returns \c{true} if this persistent model index refers to the same location as
-    the \a other model index; otherwise returns \c{false}.
+    \fn bool QPersistentModelIndex::operator==(const QPersistentModelIndex &lhs, const QModelIndex &rhs)
+    Returns \c{true} if \a lhs persistent model index refers to the same location as
+    the \a rhs model index; otherwise returns \c{false}.
 
     The internal data pointer, row, column, and model values in the persistent
     model index are used when comparing with another model index.
-*/
-
-bool QPersistentModelIndex::operator==(const QModelIndex &other) const noexcept
-{
-    if (d)
-        return d->index == other;
-    return !other.isValid();
-}
+ */
 
 /*!
-    \fn bool QPersistentModelIndex::operator!=(const QModelIndex &other) const
+    \fn bool QPersistentModelIndex::operator!=(const QPersistentModelIndex &lhs, const QModelIndex &rhs)
 
-    Returns \c{true} if this persistent model index does not refer to the same
-    location as the \a other model index; otherwise returns \c{false}.
+    Returns \c{true} if \a lhs persistent model index does not refer to the same
+    location as the \a rhs model index; otherwise returns \c{false}.
 */
 
-bool QPersistentModelIndex::operator!=(const QModelIndex &other) const noexcept
+bool comparesEqual(const QPersistentModelIndex &lhs, const QModelIndex &rhs) noexcept
 {
-    if (d)
-        return d->index != other;
-    return other.isValid();
+    if (lhs.d)
+        return lhs.d->index == rhs;
+    return !rhs.isValid();
 }
 
 /*!
diff --git a/src/corelib/itemmodels/qabstractitemmodel.h b/src/corelib/itemmodels/qabstractitemmodel.h
index 1e9c58334de..418fc6b864f 100644
--- a/src/corelib/itemmodels/qabstractitemmodel.h
+++ b/src/corelib/itemmodels/qabstractitemmodel.h
@@ -178,17 +178,21 @@ public:
     QPersistentModelIndex(const QModelIndex &index);
     QPersistentModelIndex(const QPersistentModelIndex &other);
     ~QPersistentModelIndex();
+#if QT_CORE_REMOVED_SINCE(6, 8)
     bool operator<(const QPersistentModelIndex &other) const noexcept;
     bool operator==(const QPersistentModelIndex &other) const noexcept;
     inline bool operator!=(const QPersistentModelIndex &other) const noexcept
     { return !operator==(other); }
+#endif
     QPersistentModelIndex &operator=(const QPersistentModelIndex &other);
     inline QPersistentModelIndex(QPersistentModelIndex &&other) noexcept
         : d(std::exchange(other.d, nullptr)) {}
     QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPersistentModelIndex)
     void swap(QPersistentModelIndex &other) noexcept { qt_ptr_swap(d, other.d); }
+#if QT_CORE_REMOVED_SINCE(6, 8)
     bool operator==(const QModelIndex &other) const noexcept;
     bool operator!=(const QModelIndex &other) const noexcept;
+#endif
     QPersistentModelIndex &operator=(const QModelIndex &other);
     operator QModelIndex() const;
     int row() const;
@@ -208,6 +212,18 @@ private:
     friend size_t qHash(const QPersistentModelIndex &, size_t seed) noexcept;
     friend bool qHashEquals(const QPersistentModelIndex &a, const QPersistentModelIndex &b) noexcept
     { return a.d == b.d; }
+    friend Q_CORE_EXPORT bool
+    comparesEqual(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs) noexcept;
+    friend Q_CORE_EXPORT bool
+    comparesEqual(const QPersistentModelIndex &lhs, const QModelIndex &rhs) noexcept;
+    friend Q_CORE_EXPORT Qt::strong_ordering // ### Qt 7: partial_ordering?
+    compareThreeWay(const QPersistentModelIndex &lhs, const QPersistentModelIndex &rhs) noexcept;
+    friend Q_CORE_EXPORT Qt::strong_ordering // ### Qt 7: partial_ordering?
+    compareThreeWay(const QPersistentModelIndex &lhs, const QModelIndex &rhs) noexcept;
+#if !QT_CORE_REMOVED_SINCE(6, 8)
+    Q_DECLARE_STRONGLY_ORDERED(QPersistentModelIndex)
+    Q_DECLARE_STRONGLY_ORDERED(QPersistentModelIndex, QModelIndex)
+#endif
 #ifndef QT_NO_DEBUG_STREAM
     friend Q_CORE_EXPORT QDebug operator<<(QDebug, const QPersistentModelIndex &);
 #endif
diff --git a/src/corelib/itemmodels/qitemselectionmodel.h b/src/corelib/itemmodels/qitemselectionmodel.h
index c4b8dadc97b..aaf32e68ef7 100644
--- a/src/corelib/itemmodels/qitemselectionmodel.h
+++ b/src/corelib/itemmodels/qitemselectionmodel.h
@@ -77,7 +77,7 @@ private:
     friend bool comparesEqual(const QItemSelectionRange &lhs,
                               const QItemSelectionRange &rhs) noexcept
     {
-        return (lhs.tl == rhs.tl && lhs.br == rhs.br);
+        return comparesEqual(lhs.tl, rhs.tl) && comparesEqual(lhs.br, rhs.br);
     }
     Q_DECLARE_EQUALITY_COMPARABLE(QItemSelectionRange)
     QPersistentModelIndex tl, br;