[Bug libstdc++/87538] [7/8 Regression] Incorrect noexcept specifier for not_fn

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87538

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |6.4.0
            Summary|Incorrect noexcept          |[7/8 Regression] Incorrect
                   |specifier for not_fn        |noexcept specifier for
                   |                            |not_fn
      Known to fail|                            |7.3.0, 8.2.0

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is a regression for std::experimental::not_fn because since gcc-7 it
shares the implementation with std::not_fn

#include <experimental/functional>

struct N { 
  int operator()(int i) { if (i == 0) throw -1; return i; }
};

N n;
auto not_n = std::experimental::not_fn(n);
static_assert( !noexcept(not_n(1)), "" );