https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80654
--- Comment #7 from Ville Voutilainen <ville.voutilainen at gmail dot com> --- That's not a bug. You need to make the copy constructor of s conditionally deleted depending on whether T is copyconstructible. Otherwise the trait will result in true but the code will not compile due to an ill-formed definition of the copy constructor of s, and you'll get the same answer on every C++ compiler.
