P3560R2 Error Handling in Reflection

Author: Eisenwave

source/meta.tex

@@ -2582,6 +2582,9 @@
 namespace std::meta {
   using info = decltype(^^::);
 
+  // \ref{meta.reflection.exception}, class \tcode{exception}
+  class exception;
+
   // \ref{meta.reflection.operators}, operator representations
   enum class operators {
     @\seebelow@;
@@ -2968,6 +2971,135 @@
 \end{codeblock}
 \end{example}
 
+\rSec2[meta.reflection.exception]{Class \tcode{exception}}
+
+\indexlibraryglobal{exception}%
+\begin{itemdecl}
+class exception : public std::exception
+{
+private:
+  optional<string> @\exposid{what_}@;       // \expos
+  u8string @\exposid{u8what_}@;             // \expos
+  info @\exposid{from_}@;                   // \expos
+  source_location @\exposid{where_}@;       // \expos
+
+public:
+  consteval exception(u8string_view what, info from,
+                      source_location where = source_location::current()) noexcept;
+
+  consteval exception(string_view what, info from,
+                      source_location where = source_location::current()) noexcept;
+
+  exception(const exception&) = default;
+  exception(exception&&) = default;
+
+  exception& operator=(const exception&) = default;
+  exception& operator=(exception&&) = default;
+
+  constexpr const char* what() const noexcept override;
+  consteval u8string_view u8what() const noexcept;
+  consteval info from() const noexcept;
+  consteval source_location where() const noexcept;
+};
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+Reflection functions throw exceptions of type \tcode{meta::exception}
+to signal an error.
+\tcode{meta::exception} is a consteval-only type.
+\end{itemdescr}
+
+\indexlibraryctor{exception}%
+\begin{itemdecl}
+consteval exception(u8string_view what, info from,
+                    source_location where = source_location::current()) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes
+\exposid{u8what_} with \tcode{what},
+\exposid{from_} with \tcode{from}, and
+\exposid{where_} with \tcode{where}.
+If \tcode{what} can be represented in the ordinary literal encoding,
+initializes \exposid{what_} with \tcode{what},
+transcoded from UTF-8 to the ordinary literal encoding.
+Otherwhise, \exposid{what_} is value-initialized.
+\end{itemdescr}
+
+\indexlibraryctor{exception}%
+\begin{itemdecl}
+consteval exception(string_view what, info from,
+                    source_location where = source_location::current()) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constantwhen
+\tcode{what} designates a sequence of characters
+that can be encoded in UTF-8.
+
+\pnum
+\effects
+Initializes
+\exposid{what_} with \tcode{what},
+\exposid{u8what_} with \tcode{what}
+transcoded from the ordinary literal encoding to UTF-8,
+%FIXME: Oxford comma before "and"
+\exposid{from_} with \tcode{from} and
+\exposid{where_} with \tcode{where}.
+\end{itemdescr}
+
+\indexlibrarymember{what}{exception}%
+\begin{itemdecl}
+constexpr const char* what() const noexcept override;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\constantwhen
+\tcode{\exposid{what_}.has_value()} is \tcode{true}.
+
+\pnum
+\returns
+\tcode{\exposid{what_}->c_str()}.
+\end{itemdescr}
+
+\indexlibrarymember{u8what}{exception}%
+\begin{itemdecl}
+consteval u8string_view what() const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\exposid{u8what_}.
+\end{itemdescr}
+
+\indexlibrarymember{from}{exception}%
+\begin{itemdecl}
+consteval info from() const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\exposid{from_}.
+\end{itemdescr}
+
+\indexlibrarymember{where}{exception}%
+\begin{itemdecl}
+consteval source_location where() const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\exposid{where_}.
+\end{itemdescr}
+
 \rSec2[meta.reflection.operators]{Operator representations}
 
 \begin{itemdecl}

source/support.tex

@@ -791,6 +791,7 @@
 #define @\defnlibxname{cpp_lib_rcu}@                               202306L // also in \libheader{rcu}
 #define @\defnlibxname{cpp_lib_reference_from_temporary}@          202202L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_reference_wrapper}@                 202403L // freestanding, also in \libheader{functional}
+#define @\defnlibxname{cpp_lib_reflection}@                        202506L // also in \libheader{meta}
 #define @\defnlibxname{cpp_lib_remove_cvref}@                      201711L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_result_of_sfinae}@                  201210L
   // freestanding, also in \libheader{functional}, \libheader{type_traits}