[Bug c++/80691] Narrowing conversion in {} allowed in a SFINAE context

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80691

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-05-09
     Ever confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This only happens in C++17 mode. With -std=gnu++14 it compiles OK, and also
with -std=c++14 if you make it C++14-compatible:

#include <utility>
#include <type_traits>

template<typename...> using void_t = void;

template<typename T, typename U, typename = void>
struct is_nonnarrowing_conversion : std::false_type {};

template<typename T, typename U>
struct is_nonnarrowing_conversion<T, U,
    void_t<decltype(T{ std::declval<U>() })>> : std::true_type {};

template<typename T>
class wrapper
{
public:
    wrapper(T) {}
};

static_assert(!is_nonnarrowing_conversion<int, float>(), "");
static_assert(!is_nonnarrowing_conversion<wrapper<int>, float>(), "");