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* [gcc r13-8674] libstdc++: Reverse arguments in constraint for std::optional's <=> [PR104606]
@ 2024-05-02 14:16 Jonathan Wakely
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From: Jonathan Wakely @ 2024-05-02 14:16 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:3d16f8f2aec9583422d00c531732ca9d33e6ef26
commit r13-8674-g3d16f8f2aec9583422d00c531732ca9d33e6ef26
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Mar 27 21:51:13 2024 +0000
libstdc++: Reverse arguments in constraint for std::optional's <=> [PR104606]
This is a workaround for a possible compiler bug that causes constraint
recursion in the operator<=>(const optional<T>&, const U&) overload.
libstdc++-v3/ChangeLog:
PR libstdc++/104606
* include/std/optional (operator<=>(const optional<T>&, const U&)):
Reverse order of three_way_comparable_with template arguments.
* testsuite/20_util/optional/relops/104606.cc: New test.
(cherry picked from commit 7f65d8267fbfd19cf21a3dc71d27e989e75044a3)
Diff:
---
libstdc++-v3/include/std/optional | 2 +-
.../testsuite/20_util/optional/relops/104606.cc | 18 ++++++++++++++++++
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index 29f534b9861..e4f3fc65340 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1434,7 +1434,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#ifdef __cpp_lib_three_way_comparison
template<typename _Tp, typename _Up>
requires (!__is_optional_v<_Up>)
- && three_way_comparable_with<_Tp, _Up>
+ && three_way_comparable_with<_Up, _Tp>
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/104606.cc b/libstdc++-v3/testsuite/20_util/optional/relops/104606.cc
new file mode 100644
index 00000000000..2b8df245219
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/optional/relops/104606.cc
@@ -0,0 +1,18 @@
+// { dg-do compile { target c++17 } }
+
+// Bug 104606 comparison operator resolution with std::optional and -std=c++20
+
+#include <optional>
+#include <variant>
+#include <vector>
+
+struct Value : std::variant<std::vector<Value>> { };
+
+struct Comparator {
+ template <typename T> bool operator<=(const T &) { return true; }
+};
+
+std::optional<Value> o;
+Comparator c;
+
+auto x = c <= o;
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