https://gcc.gnu.org/g:80d0f82e6961ff8991897454e2bac126488ea6b9
commit r12-10536-g80d0f82e6961ff8991897454e2bac126488ea6b9 Author: Jonathan Wakely <jwak...@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 122ff7e58630..5729554dc8da 100644 --- a/libstdc++-v3/include/std/optional +++ b/libstdc++-v3/include/std/optional @@ -1420,7 +1420,7 @@ _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 000000000000..2b8df2452199 --- /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;