// { dg-do compile { target c++17 } }

// Copyright (C) 2017-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3.  If not see
// <http://www.gnu.org/licenses/>.

#include <string>

template<typename CT>
  constexpr bool
  test_assign()
  {
    using char_type = typename CT::char_type;
    char_type s1[2] = {};
    const char_type s2[2] = {1, 0};
    CT::assign(s1[0], s2[0]);
    return s1[0] == char_type{1};
  }

template<typename CT>
  constexpr bool
  test_compare()
  {
    using char_type = typename CT::char_type;
    const char_type s1[3] = {1, 2, 3};
    const char_type s2[3] = {1, 2, 3};
    if (CT::compare(s1, s2, 3) != 0)
      return false;
    if (CT::compare(s2, s1, 3) != 0)
      return false;
    if (CT::compare(s1+1, s2, 2) <= 0)
      return false;
    return true;
  }

template<typename CT>
  constexpr bool
  test_length()
  {
    using char_type = typename CT::char_type;
    const char_type s1[4] = {1, 2, 3, 0};
    if (CT::length(s1) != 3)
      return false;
    if (CT::length(s1+1) != 2)
      return false;
    return true;
  }

template<typename CT>
  constexpr bool
  test_find()
  {
    using char_type = typename CT::char_type;
    const char_type s1[3] = {1, 2, 3};
    if (CT::find(s1, 3, char_type{2}) != s1+1)
      return false;
    if (CT::find(s1, 3, char_type{4}) != nullptr)
      return false;
    return true;
  }

#ifndef __cpp_lib_constexpr_string
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_string < (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value
#endif

// We also provide this non-standard macro for P0426R1 (and P1032R1 in C++20).
#ifndef __cpp_lib_constexpr_char_traits
# error Feature-test macro for constexpr char_traits is missing
#elif __cpp_lib_constexpr_char_traits != (__cplusplus == 201703 ? 201611 : 201811)
# error Feature-test macro for constexpr char_traits has the wrong value
#endif

static_assert( test_assign<std::char_traits<char>>() );
static_assert( test_compare<std::char_traits<char>>() );
static_assert( test_length<std::char_traits<char>>() );
static_assert( test_find<std::char_traits<char>>() );
#ifdef _GLIBCXX_USE_WCHAR_T
static_assert( test_assign<std::char_traits<wchar_t>>() );
static_assert( test_compare<std::char_traits<wchar_t>>() );
static_assert( test_length<std::char_traits<wchar_t>>() );
static_assert( test_find<std::char_traits<wchar_t>>() );
#endif
#ifdef _GLIBCXX_USE_CHAR8_T
static_assert( test_assign<std::char_traits<char8_t>>() );
static_assert( test_compare<std::char_traits<char8_t>>() );
static_assert( test_length<std::char_traits<char8_t>>() );
static_assert( test_find<std::char_traits<char8_t>>() );
#endif
static_assert( test_assign<std::char_traits<char16_t>>() );
static_assert( test_compare<std::char_traits<char16_t>>() );
static_assert( test_length<std::char_traits<char16_t>>() );
static_assert( test_find<std::char_traits<char16_t>>() );
static_assert( test_assign<std::char_traits<char32_t>>() );
static_assert( test_compare<std::char_traits<char32_t>>() );
static_assert( test_length<std::char_traits<char32_t>>() );
static_assert( test_find<std::char_traits<char32_t>>() );

struct C { unsigned char c; };
constexpr bool operator==(const C& c1, const C& c2) { return c1.c == c2.c; }
constexpr bool operator<(const C& c1, const C& c2) { return c1.c < c2.c; }
static_assert( test_assign<std::char_traits<C>>() );
static_assert( test_compare<std::char_traits<C>>() );
static_assert( test_length<std::char_traits<C>>() );
static_assert( test_find<std::char_traits<C>>() );