[gcc r15-2326] libstdc++: Add static_assert to std::expected for LWG 3843 and 3940

[Jonathan Wakely]

https://gcc.gnu.org/g:ea435261ad58ea3eb811cbd16d085976964bff2c

commit r15-2326-gea435261ad58ea3eb811cbd16d085976964bff2c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jul 25 14:17:34 2024 +0100

    libstdc++: Add static_assert to std::expected for LWG 3843 and 3940
    
    libstdc++-v3/ChangeLog:
    
            * include/std/expected (expected::value): Add assertions for LWG
            3843 requirements.
            (expected<cv void, E>::value): Add assertions for LWG 3940
            requirements.

Diff:
---
 libstdc++-v3/include/std/expected | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libstdc++-v3/include/std/expected b/libstdc++-v3/include/std/expected
index 3c52f7db01e2..515a1e6ab8f5 100644
--- a/libstdc++-v3/include/std/expected
+++ b/libstdc++-v3/include/std/expected
@@ -754,6 +754,7 @@ namespace __expected
       constexpr const _Tp&
       value() const &
       {
+	static_assert( is_copy_constructible_v<_Er> );
 	if (_M_has_value) [[likely]]
 	  return _M_val;
 	_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(_M_unex));
@@ -762,6 +763,7 @@ namespace __expected
       constexpr _Tp&
       value() &
       {
+	static_assert( is_copy_constructible_v<_Er> );
 	if (_M_has_value) [[likely]]
 	  return _M_val;
 	const auto& __unex = _M_unex;
@@ -771,6 +773,8 @@ namespace __expected
       constexpr const _Tp&&
       value() const &&
       {
+	static_assert( is_copy_constructible_v<_Er> );
+	static_assert( is_constructible_v<_Er, const _Er&&> );
 	if (_M_has_value) [[likely]]
 	  return std::move(_M_val);
 	_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
@@ -779,6 +783,8 @@ namespace __expected
       constexpr _Tp&&
       value() &&
       {
+	static_assert( is_copy_constructible_v<_Er> );
+	static_assert( is_constructible_v<_Er, _Er&&> );
 	if (_M_has_value) [[likely]]
 	  return std::move(_M_val);
 	_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
@@ -1510,6 +1516,7 @@ namespace __expected
       constexpr void
       value() const&
       {
+	static_assert( is_copy_constructible_v<_Er> );
 	if (_M_has_value) [[likely]]
 	  return;
 	_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(_M_unex));
@@ -1518,6 +1525,7 @@ namespace __expected
       constexpr void
       value() &&
       {
+	static_assert( is_copy_constructible_v<_Er> );
 	if (_M_has_value) [[likely]]
 	  return;
 	_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));