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* [gcc r10-9996] libstdc++: Constrain three-way comparison for std::optional [PR 98842]
@ 2021-07-22 15:34 Jonathan Wakely
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From: Jonathan Wakely @ 2021-07-22 15:34 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:3a415b6a93765f29bffd0582a001bf03c4b93f3c
commit r10-9996-g3a415b6a93765f29bffd0582a001bf03c4b93f3c
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jun 7 13:02:15 2021 +0100
libstdc++: Constrain three-way comparison for std::optional [PR 98842]
The operator<=>(const optional<T>&, const U&) operator is supposed to be
constrained with three_way_comparable_with<U, T> so that it can only be
used when T and U are weakly-equality-comparable and also three-way
comparable.
Adding that constrain completely breaks std::optional comparisons,
because it causes constraint recursion. To avoid that, an additional
check that U is not a specialization of std::optional is needed. That
appears to be a defect in the standard and should be reported to LWG.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/98842
* include/std/optional (operator<=>(const optional<T>& const U&)):
Add missing constraint and add workaround for template
recursion.
* testsuite/20_util/optional/relops/three_way.cc: Check that
type without equality comparison cannot be compared when wrapped
in std::optional.
(cherry picked from commit adec14811714e22a6c1f7f0199adc05370f0d8b0)
Diff:
---
libstdc++-v3/include/std/optional | 7 +++++++
.../testsuite/20_util/optional/relops/three_way.cc | 22 ++++++++++++++++++++--
2 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index e3fbe625f25..4975bc6f922 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1210,7 +1210,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ return !__rhs || __lhs >= *__rhs; }
#ifdef __cpp_lib_three_way_comparison
+ template<typename _Tp>
+ inline constexpr bool __is_optional_v = false;
+ template<typename _Tp>
+ inline constexpr bool __is_optional_v<optional<_Tp>> = true;
+
template<typename _Tp, typename _Up>
+ requires (!__is_optional_v<_Up>)
+ && three_way_comparable_with<_Tp, _Up>
constexpr compare_three_way_result_t<_Tp, _Up>
operator<=>(const optional<_Tp>& __x, const _Up& __v)
{ return bool(__x) ? *__x <=> __v : strong_ordering::less; }
diff --git a/libstdc++-v3/testsuite/20_util/optional/relops/three_way.cc b/libstdc++-v3/testsuite/20_util/optional/relops/three_way.cc
index d7bd16bf32a..416e6a9b891 100644
--- a/libstdc++-v3/testsuite/20_util/optional/relops/three_way.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/relops/three_way.cc
@@ -15,8 +15,8 @@
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
-// { dg-options "-std=gnu++2a" }
-// { dg-do compile { target c++2a } }
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
#include <optional>
@@ -74,3 +74,21 @@ test02()
static_assert( nullopt <= O{} );
static_assert( nullopt <= O{1} );
}
+
+template<typename T>
+ concept has_spaceship = requires (const T& t) { t <=> t; };
+
+void
+test03()
+{
+ struct E
+ {
+ auto operator<=>(const E&) const { return std::strong_ordering::equal; }
+ };
+ static_assert( !std::three_way_comparable<E> ); // not equality comparable
+ using O = std::optional<E>;
+ static_assert( !std::three_way_comparable<O> );
+ static_assert( ! has_spaceship<O> ); // PR libstdc++/98842
+ struct U : O { };
+ static_assert( ! has_spaceship<U> );
+}
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