https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98842
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:3a415b6a93765f29bffd0582a001bf03c4b93f3c commit r10-9996-g3a415b6a93765f29bffd0582a001bf03c4b93f3c Author: Jonathan Wakely <jwak...@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 <jwak...@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)
