exception.hpp

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// SPDX-FileCopyrightText: 2026 Jarosław Pelczar <jarek@jpelczar.com>
//
// SPDX-License-Identifier: BSD-2-Clause
 
#pragma once
 
// std-interop-file: opt-in formatter for std::exception-derived types and std::system_error.
 
#include "../microfmt.hpp"
#include <exception>
#include <system_error>
#include <type_traits>
 
namespace microfmt {
 
template <typename T> struct formatter<T, std::enable_if_t<std::is_base_of_v<std::exception, T>>> {
  constexpr void parse(format_parse_context &) noexcept {}
 
  // low-level formatting: raw character pointers and integer width conversions bounded by the buffer sizes checked
  // here.
  RELOCO_BEGIN_UNSAFE_CODE
  void format(const T &value, const sink &out) const noexcept {
    const char *msg = value.what();
    if (msg != nullptr) {
      out.write(msg);
    } else {
      out.write("<unknown exception>");
    }
  }
  RELOCO_END_UNSAFE_CODE
};
 
template <> struct formatter<std::system_error> {
  constexpr void parse(format_parse_context &) noexcept {}
 
  // low-level formatting: raw character pointers and integer width conversions bounded by the buffer sizes checked
  // here.
  RELOCO_BEGIN_UNSAFE_CODE
  void format(const std::system_error &value, const sink &out) const noexcept {
    const char *msg = value.what();
    if (msg != nullptr) {
      out.write(msg);
    }
 
    const auto ec = value.code();
    out.write(" [");
    out.write(ec.category().name());
    out.write(":");
 
    // Directly format the error value as an integer
    const formatter<int> int_fmt;
    int_fmt.format(ec.value(), out);
 
    out.write("]");
  }
  RELOCO_END_UNSAFE_CODE
};
 
} // namespace microfmt