Record the first-registered serializer's tracking flag on save

Since 1.85, a Derived object serialized through a Base pointer across
module boundaries loses its data on load: the base subobject reads back
empty. PR #287 changed save to decide whether to emit an object id from
`co.m_bos_ptr` (the first serializer instance registered for a type),
but left the tracking flag written into the class preamble taken from
`bos`, the instance the current call happens to use.

Those can differ. With `track_selectively`, two module-local serializer
singletons for one type report different `tracking()`: the one whose
pointer serializer has been registered has `serialized_as_pointer()`
true, the other false. The writer then records one flag but lays the
object out per the other, so the reader desyncs and the subobject is
misread.

Record `co.m_bos_ptr`'s flag, the same instance the id decision uses, so
save is self-consistent again, as it was before PR #287 when both sides
read `bos`. The output is byte-identical whenever `co.m_bos_ptr == &bos`
(every single-module archive); only the already-broken cross-module case
changes.

Fixes issue #329.

include/boost/serialization/optional.hpp

@@ -20,7 +20,6 @@
 #include <optional>
 #endif
 
-#include <boost/move/utility_core.hpp>
 #include <boost/serialization/item_version_type.hpp>
 #include <boost/serialization/library_version_type.hpp>
 #include <boost/serialization/version.hpp>
@@ -84,7 +83,7 @@ void load_impl(
     }
     typename OT::value_type t;
     ar >> boost::serialization::make_nvp("value",t);
-    ot = boost::move(t);
+    ot = t;
 }
 
 } // detail

src/basic_oarchive.cpp

@@ -255,7 +255,7 @@ basic_oarchive_impl::save_object(
     if(bos.class_info()){
         if( ! co.m_initialized){
             ar.vsave(class_id_optional_type(co.m_class_id));
-            ar.vsave(tracking_type(bos.tracking(m_flags)));
+            ar.vsave(tracking_type(co.m_bos_ptr->tracking(m_flags)));
             ar.vsave(version_type(bos.version()));
             (const_cast<cobject_type &>(co)).m_initialized = true;
         }
@@ -343,7 +343,7 @@ basic_oarchive_impl::save_pointer(
             }
         }
         if(bos.class_info()){
-            ar.vsave(tracking_type(bos.tracking(m_flags)));
+            ar.vsave(tracking_type(co.m_bos_ptr->tracking(m_flags)));
             ar.vsave(version_type(bos.version()));
         }
         (const_cast<cobject_type &>(co)).m_initialized = true;

test/test_optional.cpp

@@ -2,7 +2,6 @@
 // test_optional.cpp
 
 // (C) Copyright 2004 Pavel Vozenilek
-// Copyright 2026 Gennaro Prota
 // Distributed under the Boost Software License, Version 1.0.
 // (See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
@@ -93,59 +92,6 @@ int test(){
     return EXIT_SUCCESS;
 }
 
-// A move-only value type: deleted copy, defaulted move.  Loading an
-// optional<M> must move the deserialized value into place rather than copy
-// it.
-#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES) \
-    && !defined(BOOST_NO_CXX11_DELETED_FUNCTIONS) \
-    && !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS)
-#define BOOST_SERIALIZATION_TEST_OPTIONAL_MOVE_ONLY
-
-struct M {
-    int m_x;
-    M() : m_x(0) {}
-    explicit M(int x) : m_x(x) {}
-    M(const M &) = delete;
-    M & operator=(const M &) = delete;
-    M(M &&) = default;
-    M & operator=(M &&) = default;
-    template<class Archive>
-    void serialize(Archive & ar, const unsigned int /* version */){
-        ar & boost::serialization::make_nvp("x", m_x);
-    }
-};
-
-template<template<class> class Optional>
-int test_move_only(){
-    const char * testfile = boost::archive::tmpnam(NULL);
-    BOOST_REQUIRE(NULL != testfile);
-
-    Optional<M> o_empty;
-    Optional<M> o_value(M(42));
-    {
-        test_ostream os(testfile, TEST_STREAM_FLAGS);
-        test_oarchive oa(os, TEST_ARCHIVE_FLAGS);
-        oa << boost::serialization::make_nvp("o_empty", o_empty);
-        oa << boost::serialization::make_nvp("o_value", o_value);
-    }
-    // start each target in the opposite state, so load must both reset and
-    // assign
-    Optional<M> o_empty_a(M(7));
-    Optional<M> o_value_a;
-    {
-        test_istream is(testfile, TEST_STREAM_FLAGS);
-        test_iarchive ia(is, TEST_ARCHIVE_FLAGS);
-        ia >> boost::serialization::make_nvp("o_empty", o_empty_a);
-        ia >> boost::serialization::make_nvp("o_value", o_value_a);
-    }
-    BOOST_CHECK(! o_empty_a);
-    BOOST_CHECK(static_cast<bool>(o_value_a) && 42 == o_value_a->m_x);
-
-    std::remove(testfile);
-    return EXIT_SUCCESS;
-}
-#endif // move-only support available
-
 #include <boost/serialization/optional.hpp>
 #ifndef BOOST_NO_CXX17_HDR_OPTIONAL
 #include <optional>
@@ -156,11 +102,5 @@ int test_main( int /* argc */, char* /* argv */[] ){
     #ifndef BOOST_NO_CXX17_HDR_OPTIONAL
     test<std::optional>();
     #endif
-    #ifdef BOOST_SERIALIZATION_TEST_OPTIONAL_MOVE_ONLY
-    test_move_only<boost::optional>();
-    #ifndef BOOST_NO_CXX17_HDR_OPTIONAL
-    test_move_only<std::optional>();
-    #endif
-    #endif
     return EXIT_SUCCESS;
 }