https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98822
--- Comment #3 from David Friberg <davveston at gmail dot com> --- I believe the current wording doesn't cover what should happen when instantiating a constrained non-template (hidden) friend, particularly instantiation of constrained (hidden) friends whose requires-clauses are not satisfied for the particular enclosing class template specialization being instantiated. I haven't found an open DR for this, though, so I've posted https://github.com/cplusplus/CWG/issues/47. Moreover, the Itanium C++ ABI currently not allowing unambiguously mangling these kind of friends. See https://github.com/itanium-cxx-abi/cxx-abi/issues/24#issuecomment-934713719.
