Workaround MSVC issue for the guaranteed copy elision

alexey-romanov · Mar 26, 2021 · f33c357 · f33c357
1 parent 3b6d3a4
commit f33c357
Show file tree

Hide file tree

Showing 5 changed files with 14 additions and 4 deletions.
diff --git a/doc/pfr.qbk b/doc/pfr.qbk
@@ -466,6 +466,7 @@ By default Boost.PFR [*auto-detects your compiler abilities] and automatically d
     [[*BOOST_PFR_USE_CPP17*] [Define to `1` if you wish to override Boost.PFR choice and use C++17 structured bindings for reflection. Define to `0` to override Boost.PFR choice and disable C++17 structured bindings usage.]]
     [[*BOOST_PFR_USE_LOOPHOLE*] [Define to `1` if you wish to override Boost.PFR choice and exploit [@http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#2118 CWG 2118] for reflection. Define to `0` to override Boost.PFR choice and disable CWG 2118 usage.]]
     [[*BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE*] [Define to `0` if you are hit by the template instantiation depth issues with `std::make_integer_sequence` and wish to use Boost.PFR version of that metafunction. Define to `1` to override Boost.PFR detection logic. ]]
+    [[*BOOST_PFR_HAS_GUARANTEED_COPY_ELISION*] [Define to `0` if your compiler does not implement C++17 guaranteed copy elision properly and fails to reflect aggregates with non-movable fields. Define to `1` to override Boost.PFR detection logic. ]]
 ]
 
 

diff --git a/include/boost/pfr/detail/config.hpp b/include/boost/pfr/detail/config.hpp
@@ -66,6 +66,14 @@
 #   endif
 #endif
 
+#ifndef BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
+#   if  defined(__cpp_guaranteed_copy_elision) && (!defined(_MSC_VER) || _MSC_VER > 1928)
+#       define BOOST_PFR_HAS_GUARANTEED_COPY_ELISION 1
+#   else
+#       define BOOST_PFR_HAS_GUARANTEED_COPY_ELISION 0
+#   endif
+#endif
+
 #if defined(__has_cpp_attribute)
 #   if __has_cpp_attribute(maybe_unused)
 #       define BOOST_PFR_MAYBE_UNUSED [[maybe_unused]]

diff --git a/include/boost/pfr/detail/fields_count.hpp b/include/boost/pfr/detail/fields_count.hpp
@@ -210,15 +210,15 @@ constexpr std::size_t fields_count() noexcept {
         "====================> Boost.PFR: Attempt to get fields count on a reference. This is not allowed because that could hide an issue and different library users expect different behavior in that case."
     );
 
-#ifndef __cpp_guaranteed_copy_elision
+#if !BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
     static_assert(
         std::is_copy_constructible<std::remove_all_extents_t<type>>::value || (
             std::is_move_constructible<std::remove_all_extents_t<type>>::value
             && std::is_move_assignable<std::remove_all_extents_t<type>>::value
         ),
         "====================> Boost.PFR: Type and each field in the type must be copy constructible (or move constructible and move assignable)."
     );
-#endif  // #ifndef __cpp_guaranteed_copy_elision
+#endif  // #if !BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
 
     static_assert(
         !std::is_polymorphic<type>::value,

diff --git a/test/print_config.cpp b/test/print_config.cpp
@@ -12,6 +12,7 @@ int main() {
         << "BOOST_PFR_USE_CPP17 == " << BOOST_PFR_USE_CPP17 << '\n'
         << "BOOST_PFR_USE_LOOPHOLE == " << BOOST_PFR_USE_LOOPHOLE << '\n'
         << "BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == " << BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE << '\n'
+        << "BOOST_PFR_HAS_GUARANTEED_COPY_ELISION == " << BOOST_PFR_HAS_GUARANTEED_COPY_ELISION << '\n'
         << "__cplusplus == " << __cplusplus << '\n'
 #ifdef __cpp_structured_bindings
         << "__cpp_structured_bindings == " << __cpp_structured_bindings << '\n'

diff --git a/test/run/non_movable.cpp b/test/run/non_movable.cpp
@@ -18,7 +18,7 @@ struct X {
 struct S { X x0; X x1; int x2; X x3; };
 
 int main() {
-#ifdef __cpp_guaranteed_copy_elision
+#if BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
     static_assert(boost::pfr::tuple_size_v<S> == 4, "");
 
     struct S5_0 { int x0; int x1; int x2; int x3; X x4; };
@@ -38,7 +38,7 @@ int main() {
 
     struct S6 { X x0; X x1; X x2; X x3; X x4;  X x5;};
     static_assert(boost::pfr::tuple_size_v<S6> == 6, "");
-#endif  // #ifdef __cpp_guaranteed_copy_elision
+#endif  // #if BOOST_PFR_HAS_GUARANTEED_COPY_ELISION
 
     return boost::report_errors();
 }