[patch] Implement std::experimental::source_location (sort of)

[Jonathan Wakely]

This is a non-conforming implementation of
https://rawgit.com/cplusplus/fundamentals-ts/v2/fundamentals-ts.html#reflection.src_loc

It doesn't provide any column numbers, and fails to meet the
requirement that using current() in a NSDMI will refer to the location
of the constructor ... but maybe it's good enough until we get the
necessary front-end support. It is experimental, after all.

Thoughts?


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// <experimental/source_location> -*- C++ -*-

// Copyright (C) 2015 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file experimental/source_location
 *  This is a TS C++ Library header.
 */

#ifndef _GLIBCXX_EXPERIMENTAL_SRCLOC
#define _GLIBCXX_EXPERIMENTAL_SRCLOC 1

#include <cstdint>

namespace std {
namespace experimental {
inline namespace fundamentals_v2 {
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  struct source_location
  {
    // 14.1.2, source_location creation
    static constexpr source_location
    current(const char* __file = __builtin_FILE(),
	    const char* __func = __builtin_FUNCTION(),
	    int __line = __builtin_LINE(),
	    int __col = 0) noexcept
    {
      source_location __loc;
      __loc._M_file = __file;
      __loc._M_func = __func;
      __loc._M_line = __line;
      __loc._M_col = __col;
      return __loc;
    }

    constexpr source_location() noexcept
    : _M_file("unknown"), _M_func(_M_file), _M_line(0), _M_col(0)
    { }

    // 14.1.3, source_location field access
    constexpr uint_least32_t line() const noexcept { return _M_line; }
    constexpr uint_least32_t column() const noexcept { return _M_col; }
    constexpr const char* file_name() const noexcept { return _M_file; }
    constexpr const char* function_name() const noexcept { return _M_func; }

  private:
    const char* _M_file;
    const char* _M_func;
    uint_least32_t _M_line;
    uint_least32_t _M_col;
  };

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace fundamentals_v2
} // namespace experimental
} // namespace std

#endif