fix: XML archive closes a completed document even while unwinding

include/boost/archive/basic_xml_oarchive.hpp

@@ -10,6 +10,7 @@
 // basic_xml_oarchive.hpp
 
 // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com .
+// 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)
@@ -78,6 +79,15 @@ class BOOST_SYMBOL_VISIBLE basic_xml_oarchive :
     BOOST_ARCHIVE_OR_WARCHIVE_DECL void
     end_preamble();
 
+    // True once every element that was opened has been closed, i.e. the
+    // document is complete and its root element can be closed safely. Used
+    // by the derived destructor to tell an interrupted serialization (an
+    // element still open) apart from an unrelated exception unwinding past
+    // an already-complete archive.
+    bool document_complete() const {
+        return 0 == depth;
+    }
+
     // Anything not an attribute and not a name-value pair is an
     // error and should be trapped here.
     template<class T>

include/boost/archive/impl/xml_oarchive_impl.ipp

@@ -2,6 +2,7 @@
 // xml_oarchive_impl.ipp:
 
 // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com .
+// 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)
@@ -20,6 +21,7 @@ namespace std{
 #endif
 
 #include <boost/core/uncaught_exceptions.hpp>
+#include <boost/core/no_exceptions_support.hpp>
 #include <boost/archive/iterators/xml_escape.hpp>
 #include <boost/archive/iterators/ostream_iterator.hpp>
 
@@ -129,10 +131,20 @@ xml_oarchive_impl<Archive>::save_binary(const void *address, std::size_t count){
 template<class Archive>
 BOOST_ARCHIVE_DECL
 xml_oarchive_impl<Archive>::~xml_oarchive_impl(){
-    if(boost::core::uncaught_exceptions() > 0)
+    // The closing root tag is written here, at destruction. Skip it only
+    // when serialization was genuinely interrupted, i.e. when an exception
+    // is unwinding the stack and an element is still open, so the document
+    // is already truncated. When the document is complete, we must still
+    // attempt to close it, even while unwinding.
+    if(boost::core::uncaught_exceptions() > 0 && ! this->document_complete()){
         return;
-    if(0 == (this->get_flags() & no_header)){
-        this->put("</boost_serialization>\n");
+    }
+    if(0 == (this->get_flags() & no_header) && os.good()){
+        BOOST_TRY {
+            this->put("</boost_serialization>\n");
+        }
+        BOOST_CATCH(...) {}
+        BOOST_CATCH_END
     }
 }
 

include/boost/archive/impl/xml_woarchive_impl.ipp

@@ -2,6 +2,7 @@
 // xml_woarchive_impl.ipp:
 
 // (C) Copyright 2002 Robert Ramey - http://www.rrsd.com .
+// 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)
@@ -32,6 +33,7 @@ namespace std{
 #endif
 
 #include <boost/core/uncaught_exceptions.hpp>
+#include <boost/core/no_exceptions_support.hpp>
 
 #include <boost/archive/xml_woarchive.hpp>
 #include <boost/archive/detail/utf8_codecvt_facet.hpp>
@@ -138,10 +140,16 @@ xml_woarchive_impl<Archive>::xml_woarchive_impl(
 template<class Archive>
 BOOST_WARCHIVE_DECL
 xml_woarchive_impl<Archive>::~xml_woarchive_impl(){
-    if(boost::core::uncaught_exceptions() > 0)
+    // See the note in xml_oarchive_impl::~xml_oarchive_impl.
+    if(boost::core::uncaught_exceptions() > 0 && ! this->document_complete()){
         return;
-    if(0 == (this->get_flags() & no_header)){
-        os << L"</boost_serialization>";
+    }
+    if(0 == (this->get_flags() & no_header) && os.good()){
+        BOOST_TRY {
+            os << L"</boost_serialization>";
+        }
+        BOOST_CATCH(...) {}
+        BOOST_CATCH_END
     }
 }
 

test/Jamfile.v2

@@ -153,6 +153,7 @@ if ! $(BOOST_ARCHIVE_LIST) {
         [ test-bsl-run test_private_ctor ]
         [ test-bsl-run test_reset_object_address : A ]
         [ test-bsl-run test_void_cast ]
+        [ test-bsl-run test_xml_save_during_unwind ]
         [ test-bsl-run test_xml_trailing_whitespace ]
         [ test-bsl-run test_xml_missing_nvp ]
         [ test-bsl-run test_mult_archive_types : : : [ requires std_wstreambuf ] ]

test/test_xml_save_during_unwind.cpp

@@ -0,0 +1,58 @@
+/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
+// test_xml_save_during_unwind.cpp
+
+// Copyright 2026 Gennaro Prota
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// https://www.boost.org/LICENSE_1_0.txt)
+
+// Regression test for issue #188.  The XML output archive writes the closing
+// </boost_serialization> tag in its destructor.  It used to skip that write
+// whenever an exception was unwinding the stack (uncaught_exceptions() > 0),
+// which silently corrupted an otherwise complete archive when it happened to
+// be destroyed during unwinding for an unrelated reason.  A complete document
+// must be closed regardless; only a genuinely interrupted one (an element still
+// open) may be left unterminated.
+
+#include <sstream>
+#include <stdexcept>
+#include <string>
+
+#include <boost/archive/xml_iarchive.hpp>
+#include <boost/archive/xml_oarchive.hpp>
+#include <boost/serialization/nvp.hpp>
+
+#include "test_tools.hpp"
+
+int test_main(int /* argc */, char * /* argv */ []){
+    // Serialize a complete value, then throw an unrelated exception so the
+    // archive is destroyed while the stack unwinds.  `os` is declared outside
+    // the try block so it outlives the archive and we can inspect what the
+    // destructor wrote.
+    std::ostringstream os;
+    try {
+        boost::archive::xml_oarchive oa(os);
+        const int x = 42;
+        oa << boost::serialization::make_nvp("x", x);
+        throw std::runtime_error("unrelated");
+    }
+    catch(const std::runtime_error &){}
+
+    const std::string content = os.str();
+
+    // The complete document must have been closed despite the unwinding.
+    BOOST_CHECK(
+        content.find("</boost_serialization>") != std::string::npos
+    );
+
+    // And it must load back cleanly.
+    int y = 0;
+    {
+        std::istringstream is(content);
+        boost::archive::xml_iarchive ia(is);
+        ia >> boost::serialization::make_nvp("x", y);
+    }
+    BOOST_CHECK(42 == y);
+
+    return EXIT_SUCCESS;
+}