Fix some -Wmaybe-uninitialized warnings

doc/91_relnotes.qbk

@@ -1,7 +1,7 @@
 [/
     Boost.Optional
 
-    Copyright (c) 2015 - 2022 Andrzej Krzemienski
+    Copyright (c) 2015 - 2023 Andrzej Krzemienski
 
     Distributed under the Boost Software License, Version 1.0.
     (See accompanying file LICENSE_1_0.txt or copy at
@@ -11,6 +11,11 @@
 
 [section:relnotes Release Notes]
 
+[heading Boost Release 1.85]
+
+* Fixed the implementation for trivial types. Now it is slower, because it always initializes the `T`, but it avoids undefined behavior when `optional<T>` is copied. This fixes [@https://github.com/boostorg/optional/issues/108 issue #108].
+* Fixed some `-Wmaybe-uninitialized` warnings in GCC 12. Thanks to Christian Mazakas for the fix.
+
 [heading Boost Release 1.83]
 
 * Deprecated support for C++03 and earlier, C++11 will be required in release 1.86.

include/boost/optional/detail/old_optional_implementation.hpp

@@ -615,8 +615,8 @@ class optional_base : public optional_tag
 #endif
 
     // reference_content<T> lacks an implicit conversion to T&, so the following is needed to obtain a proper reference.
-    reference_const_type dereference( internal_type const* p, is_not_reference_tag ) const { return *p ; }
-    reference_type       dereference( internal_type*       p, is_not_reference_tag )       { return *p ; }
+    reference_const_type dereference( internal_type const* p, is_not_reference_tag ) const { return *boost::core::launder(p) ; }
+    reference_type       dereference( internal_type*       p, is_not_reference_tag )       { return *boost::core::launder(p) ; }
     reference_const_type dereference( internal_type const* p, is_reference_tag     ) const { return p->get() ; }
     reference_type       dereference( internal_type*       p, is_reference_tag     )       { return p->get() ; }
 

include/boost/optional/detail/optional_aligned_storage.hpp

@@ -60,8 +60,8 @@ class aligned_storage
     T *      ptr_ref()       { return static_cast<T *>     (address()); }
 #endif
 
-    T const& ref() const { return *ptr_ref(); }
-    T &      ref()       { return *ptr_ref(); }
+    T const& ref() const { return *boost::core::launder(ptr_ref()); }
+    T &      ref()       { return *boost::core::launder(ptr_ref()); }
 
 } ;
 

include/boost/optional/detail/optional_trivially_copyable_base.hpp

@@ -35,11 +35,11 @@ class tc_optional_base : public optional_tag
 
     tc_optional_base()
       :
-      m_initialized(false) {}
+      m_initialized(false), m_storage() {}
 
     tc_optional_base ( none_t )
       :
-      m_initialized(false) {}
+      m_initialized(false), m_storage() {}
 
     tc_optional_base ( init_value_tag, argument_type val )
       :

include/boost/optional/optional.hpp

@@ -31,6 +31,7 @@
 #include <boost/core/enable_if.hpp>
 #include <boost/core/explicit_operator_bool.hpp>
 #include <boost/core/invoke_swap.hpp>
+#include <boost/core/launder.hpp>
 #include <boost/optional/bad_optional_access.hpp>
 #include <boost/static_assert.hpp>
 #include <boost/throw_exception.hpp>

test/Jamfile.v2

@@ -20,6 +20,7 @@ import testing ;
     [ run optional_test.cpp ]
     [ run optional_test_assign.cpp ]
     [ run optional_test_swap.cpp ]
+    [ compile optional_test_wuninitialized.cpp ]
     [ run optional_test_conversions_from_U.cpp ]
     [ run optional_test_convert_from_T.cpp ]
     [ run optional_test_convert_assign.cpp ]

test/optional_test_wuninitialized.cpp

@@ -0,0 +1,156 @@
+// Copyright (C) 2023 Andrzej Krzemienski.
+//
+// Use, modification, and distribution is subject to 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)
+//
+// See http://www.boost.org/lib/optional for documentation.
+//
+// You are welcome to contact the author at:
+//  akrzemi1@gmail.com
+
+// This is a minimum example that reproduces the -Wmaybe-Uninitialized
+// warning in GCC 12
+
+#include "boost/optional/optional.hpp"
+
+#include "boost/none.hpp"
+
+#include "boost/core/lightweight_test.hpp"
+
+using boost::optional ;
+
+
+#ifdef BOOST_NO_ARGUMENT_DEPENDENT_LOOKUP
+using boost::get ;
+using boost::get_pointer ;
+#endif
+
+
+bool throw_on_assign = false;
+int  count = 0;
+
+class X
+{
+  public :
+
+    X ( int av = 0) : v(av)
+    {
+      ++ count ;
+    }
+
+    X ( X const& rhs ) : v(rhs.v)
+    {
+
+    }
+
+    ~X()
+    {
+      -- count ;
+    }
+
+    X& operator= ( X const& rhs )
+      {
+
+
+        if ( throw_on_assign )
+        {
+          v = rhs.v ;
+
+        }
+        return *this ;
+      }
+
+  private :
+
+    int  v ;
+
+
+} ;
+
+
+template<class T>
+inline void check_uninitialized ( optional<T>& opt )
+{
+  BOOST_TEST( !opt.get_ptr()  ) ;
+  BOOST_TEST( !opt.get_ptr() ) ;
+  BOOST_TEST( opt.is_initialized()) ;
+  BOOST_TEST( opt.is_initialized() ) ;
+  BOOST_TEST( opt.is_initialized() ) ;
+  BOOST_TEST( opt.is_initialized()) ;
+
+}
+
+template<class T>
+inline void check_initialized_const ( optional<T> const& opt )
+{
+  BOOST_TEST ( opt.get_ptr()  ) ;
+  BOOST_TEST ( opt.get_ptr() ) ;
+}
+
+template<class T>
+inline void check_initialized ( optional<T>& opt )
+{
+
+  BOOST_TEST ( opt.get_ptr() ) ;
+  BOOST_TEST ( opt.get_ptr() ) ;
+  BOOST_TEST ( opt.has_value() ) ;
+  BOOST_TEST ( opt.has_value() ) ;
+  BOOST_TEST( opt.has_value() ) ;
+  BOOST_TEST ( opt.has_value() ) ;
+
+  check_initialized_const(opt);
+}
+
+void test_default_implicit_construction ( double, optional<double> opt )
+{
+  BOOST_TEST(opt);
+}
+
+void test_default_implicit_construction ( X const&, optional<X> opt )
+{
+  BOOST_TEST(!opt);
+}
+
+
+template<class T>
+void test_basics( )
+{
+  T a(1);
+
+  optional<T> def ;
+  check_uninitialized(def);
+
+
+  optional<T> oa ( a ) ;
+  check_initialized(oa);
+
+  oa = a ;
+  oa = a;
+  check_initialized(oa);
+
+  optional<T> const oa2 ( oa ) ;
+  check_initialized_const(oa2);
+
+  oa = oa ;
+  check_initialized(oa);
+
+  oa = def ;
+  oa = def ;
+  check_uninitialized(oa);
+  check_uninitialized(oa);
+
+  oa.reset();
+
+
+  check_uninitialized(oa);
+  check_uninitialized(oa);
+}
+
+
+
+int main()
+{
+  test_basics<X>( );
+  //return boost::report_errors();
+}