The r15-2326-gea435261ad58ea change missed a static_assert for
is_move_constructible_v in expected<cv void, E>::value()&&. When
exceptions are enabled, the program is ill-formed if the error type is
not move constructible, because we can't construct the
std::bad_expected_access. But when using -fno-exceptions, we never
construct an exception, so don't need to copy/move the error value. So
that the same code compiles with/without exceptions enabled, we should
enforce the requirement explicitly.
Add the static_assert, and a test that verifies the Mandates:
conditions added by LWG 3843 and 3490 are enforced even with
-fno-exceptions.
libstdc++-v3/ChangeLog:
* include/std/expected (expected<cv void,E>::value()&&):
Add missing static_assert for LWG 3940.
* testsuite/20_util/expected/lwg3843.cc: New test.
---
Tested x86_64-linux.
libstdc++-v3/include/std/expected | 1 +
.../testsuite/20_util/expected/lwg3843.cc | 69 +++++++++++++++++++
2 files changed, 70 insertions(+)
create mode 100644 libstdc++-v3/testsuite/20_util/expected/lwg3843.cc
diff --git a/libstdc++-v3/include/std/expected
b/libstdc++-v3/include/std/expected
index 7de2aeffc70..5dc1dfbe5b8 100644
--- a/libstdc++-v3/include/std/expected
+++ b/libstdc++-v3/include/std/expected
@@ -1541,6 +1541,7 @@ namespace __expected
value() &&
{
static_assert( is_copy_constructible_v<_Er> );
+ static_assert( is_move_constructible_v<_Er> );
if (_M_has_value) [[likely]]
return;
_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));
diff --git a/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc
b/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc
new file mode 100644
index 00000000000..2afb9cc680b
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc
@@ -0,0 +1,69 @@
+// { dg-do compile { target c++23 } }
+// { dg-options "-fno-exceptions" }
+
+#include <expected>
+
+// 3843. std::expected<T,E>::value() & assumes E is copy constructible
+void
+test_lwg3843()
+{
+ struct E1 {
+ E1(int) { }
+ E1(E1&) { }
+ E1(const E1&) = delete;
+ };
+ std::expected<int, E1> v1;
+ v1.value(); // { dg-error "here" }
+ const auto& v1c = v1;
+ v1c.value(); // { dg-error "here" }
+
+ struct E2 {
+ E2(int) { }
+ E2(const E2&) { }
+ E2(E2&&) = delete;
+ };
+ std::expected<int, E2> v2;
+ v2.value();
+ std::move(v2).value(); // { dg-error "here" }
+ const auto& v2c = v2;
+ v2c.value();
+ std::move(v2c).value();
+
+ struct E3 {
+ E3(int) { }
+ E3(const E3&) { }
+ E3(E3&&) { }
+ E3(const E3&&) = delete;
+ };
+ std::expected<int, E3> v3;
+ v3.value();
+ std::move(v3).value();
+ const auto& v3c = v3;
+ v3c.value();
+ std::move(v3c).value(); // { dg-error "here" }
+}
+
+// 3940. std::expected<void, E>::value() also needs E to be copy constructible
+void
+test_lwg3940()
+{
+ struct E1 {
+ E1(int) { }
+ E1(E1&) { }
+ E1(const E1&) = delete;
+ };
+ std::expected<void, E1> v1;
+ v1.value(); // { dg-error "here" }
+
+ struct E2 {
+ E2(int) { }
+ E2(const E2&) { }
+ E2(E2&&) = delete;
+ };
+ std::expected<void, E2> v2;
+ std::move(v2).value(); // { dg-error "here" }
+}
+
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }
+// { dg-prune-output "use of deleted function" }
+// { dg-prune-output "control reaches end of non-void function" }
--
2.48.1
