https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70543
--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #1)
>
> If the marked line is changed to
>
> static constexpr unsigned int value = calc<0> ();
>
> it compiles fine.
However, if doing that "trick" in the bigger production code, there is some new
error:
c++/6.0.0/type_traits:868:48: error: constructor required before non-static
data member for '...' has been parsed
template<typename _Tp, typename = decltype(_Tp())>
^~~~
