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 //
 // Copyright (c) 2019-2025 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
 #ifndef BOOST_MYSQL_WITH_DIAGNOSTICS_HPP
 #define BOOST_MYSQL_WITH_DIAGNOSTICS_HPP
 
 #include <boost/mysql/detail/access.hpp>
 
 #include <type_traits>
 #include <utility>
 
 namespace boost {
 namespace mysql {
 
 /**
  * \brief A completion token adapter used to include server diagnostics in exceptions.
  * \details
  * When passed to an async initiating function, transforms its handler signature from `void(error_code, T...)`
  * to `void(std::exception_ptr, T...)`.
  * Uses knowledge of Boost.MySQL internals to grab any \ref diagnostics
  * that the operation may produce to create a `std::exception_ptr` pointing to an \ref error_with_diagnostics
  * object. On success, the generated `std::exception_ptr` will be `nullptr`.
  *
  * Using `with_diagnostics` to wrap tokens that throw exceptions (like `deferred` + `co_await` or
  * `yield_context`) enhances the thrown exceptions with diagnostics information, matching the ones thrown by
  * sync functions. If you don't use this token, Asio will use `system_error` exceptions, containing less info.
  *
  * This token can only be used with operations involving Boost.MySQL, as it relies on its internals.
  *
  * Like `asio::as_tuple`, this class wraps another completion token. For instance,
  * `with_diagnostics(asio::deferred)` will generate a deferred operation with an adapted
  * signature, which will throw `error_with_diagnostics` when `co_await`'ed.
  *
  * If this token is applied to a function with a handler signature that
  * does not match `void(error_code, T...)`, the token acts as a pass-through:
  * it does not modify the signature, and calls the underlying token's initiation directly.
  * This has the following implications:
  *
  *   - `asio::as_tuple(with_diagnostics(X))` is equivalent to `asio::as_tuple(X)`.
  *   - `asio::redirect_error(with_diagnostics(X))` is equivalent to `asio::redirect_error(X)`.
  *   - Tokens like `asio::as_tuple` and `asio::redirect_error` can be used as partial tokens
  *     when `with_diagnostics` is the default completion token, as is the case for \ref any_connection.
  */
 template <class CompletionToken>
 class with_diagnostics_t
 {
     CompletionToken impl_;
 
 #ifndef BOOST_MYSQL_DOXYGEN
     friend struct detail::access;
 #endif
 
 public:
     /**
      * \brief Default constructor.
      * \details
      * Only valid if `CompletionToken` is default-constructible.
      *
      * \par Exception safety
      * Strong guarantee. Any exceptions thrown by default-constructing
      * `CompletionToken` are propagated.
      */
     constexpr with_diagnostics_t() : impl_{} {}
 
     /**
      * \brief Constructor.
      * \details
      * The passed `token` should be convertible to `CompletionToken`.
      *
      * \par Exception safety
      * Strong guarantee. Any exceptions thrown by constructing `CompletionToken` are propagated.
      */
     template <class T>
     constexpr explicit with_diagnostics_t(T&& token) : impl_(std::forward<T>(token))
     {
     }
 };
 
 /**
  * \brief Creates a \ref with_diagnostics_t from a completion token.
  * \details
  * The passed token is decay-copied into the \ref with_diagnostics_t object.
  *
  * \par Exception safety
  * Strong guarantee. Any exceptions thrown by constructing `CompletionToken` are propagated.
  */
 template <class CompletionToken>
 constexpr with_diagnostics_t<typename std::decay<CompletionToken>::type> with_diagnostics(
     CompletionToken&& token
 )
 {
     return with_diagnostics_t<typename std::decay<CompletionToken>::type>(std::forward<CompletionToken>(token)
     );
 }
 
 }  // namespace mysql
 }  // namespace boost
 
 #include <boost/mysql/impl/with_diagnostics.hpp>
 
 #endif

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