[Bug c++/81507] map header kills variant of vectors

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81507

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
/home/bebuch/media/programme/gcc-7/include/c++/7.1.1/tuple:1670:44:   required
from 'constexpr decltype(auto) std::apply(_Fn&&, _Tuple&&) [with _Fn = const
std::vector<int>&; _Tuple = long unsigned int]'

^^^ there's your hint. It tells you that std::apply was called.