From 638fefedd09256b928f05e2aaf11f0a941df4b22 Mon Sep 17 00:00:00 2001
From: Antony Polukhin <antoshkka@gmail.com>
Date: Wed, 24 Mar 2021 09:58:20 +0300
Subject: [PATCH] Allow reflection of aggregates with non movable fields if
 guaranteed copy elision is on

---
 include/boost/pfr/detail/fields_count.hpp |  6 ++-
 test/run/non_movable.cpp                  | 45 +++++++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)
 create mode 100644 test/run/non_movable.cpp

diff --git a/include/boost/pfr/detail/fields_count.hpp b/include/boost/pfr/detail/fields_count.hpp
index 5c2bea3..7b2b79b 100644
--- a/include/boost/pfr/detail/fields_count.hpp
+++ b/include/boost/pfr/detail/fields_count.hpp
@@ -41,8 +41,8 @@ struct ubiq_lref_constructor {
 ///////////////////// Structure that can be converted to rvalue reference to anything
 struct ubiq_rref_constructor {
     std::size_t ignore;
-    template <class Type> /*constexpr*/ operator Type&&() const && noexcept {  // Allows initialization of rvalue reference fields and move-only types
-        return detail::unsafe_declval<Type&&>();
+    template <class Type> /*constexpr*/ operator Type() const && noexcept {  // Allows initialization of rvalue reference fields and move-only types
+        return detail::unsafe_declval<Type>();
     };
 };
 
@@ -210,6 +210,7 @@ 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
     static_assert(
         std::is_copy_constructible<std::remove_all_extents_t<type>>::value || (
             std::is_move_constructible<std::remove_all_extents_t<type>>::value
@@ -217,6 +218,7 @@ constexpr std::size_t fields_count() noexcept {
         ),
         "====================> 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
 
     static_assert(
         !std::is_polymorphic<type>::value,
diff --git a/test/run/non_movable.cpp b/test/run/non_movable.cpp
new file mode 100644
index 0000000..90b7f4a
--- /dev/null
+++ b/test/run/non_movable.cpp
@@ -0,0 +1,45 @@
+// Copyright (c) 2018-2021 Antony Polukhin
+//
+// 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)
+
+#include <boost/pfr/tuple_size.hpp>
+
+#include <boost/core/lightweight_test.hpp>
+
+struct X {
+    X() = default;
+    X(X&&) = delete;
+    X(const X&) = delete;
+
+    X& operator=(X&&) = delete;
+    X& operator=(const X&) = delete;
+};
+struct S { X x0; X x1; int x2; X x3; };
+
+int main() {
+#ifdef __cpp_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; };
+    static_assert(boost::pfr::tuple_size_v<S5_0> == 5, "");
+
+    struct S5_1 { X x0; int x1; int x2; int x3; int x4; };
+    static_assert(boost::pfr::tuple_size_v<S5_1> == 5, "");
+
+    struct S5_2 { int x0; int x1; X x2; int x3; int x4; };
+    static_assert(boost::pfr::tuple_size_v<S5_2> == 5, "");
+
+    struct S5_3 { int x0; int x1; X x2; int x3; X x4; };
+    static_assert(boost::pfr::tuple_size_v<S5_3> == 5, "");
+
+    struct S5_4 { X x0; X x1; X x2; X x3; X x4; };
+    static_assert(boost::pfr::tuple_size_v<S5_4> == 5, "");
+
+    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
+
+    return boost::report_errors();
+}
+