[Bug c++/94517] incorrect use of enable_if compiles but should not

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94517

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is we don't instantiate the constructor until we need it as shown by:
#include <functional>

struct NoDefault
{
    NoDefault() = delete;
};

// compiles while should not
struct X : public NoDefault
{
    template<std::enable_if_t
        <   
            std::is_default_constructible_v
            <
                NoDefault
            >
        >* = nullptr>
    X() : NoDefault{}
    {
    //    static_assert(std::is_default_constructible_v<NoDefault>);
    }
};
void f(void)
{
    X x;
}