Proposed resolution:

This wording is relative to N5008.

1. Modify [bitset.cons] as indicated:

   
   template<class charT>
     constexpr explicit bitset(
       const charT* str,
       typename basic_string_view<charT>::size_type n = basic_string_view<charT>::npos,
       charT zero = charT(’0’),
       charT one = charT(’1’));
   

   -?- Constraints:

   • is_array_v<charT> is `false`,
   • is_trivially_copyable_v<charT> is `true`,
   • is_standard_layout_v<charT> is `true`, and
   • is_trivially_default_constructible_v<charT> is `true`.

   -8- Effects: As if by:

   bitset(n == basic_string_view<charT>::npos
             ? basic_string_view<charT>(str)
             : basic_string_view<charT>(str, n),
          0, n, zero, one)
   

This code might be ill-formed, with an error outside the immediate context that users cannot prevent:

#include <bitset>
struct NonTrivial { ~NonTrivial() { } };
static_assert( ! std::is_constructible_v<std::bitset<1>, NonTrivial*> );

The problem is that the `bitset(const CharT*)` constructor tries to instantiate basic_string_view<NonTrivial> to find its `size_type`, and that instantiation might ill-formed, e.g. if `std::basic_string_view` or `std::char_traits` has a static assert enforcing the requirement for their character type to be sufficiently char-like. [strings.general] defines a char-like type as "any non-array trivially copyable standard-layout ([basic.types.general]) type `T` where is_trivially_default_constructible_v<T> is `true`."