Reland: [libc++][format] P2637R3: Member visit (std::basic_format_arg) #76449

libcxx/docs/ReleaseNotes/19.rst

@@ -35,7 +35,7 @@ see the `releases page <https://llvm.org/releases/>`_.
 What's New in Libc++ 19.0.0?
 ==============================
 
-TODO
+- P2637R3 - Member ``visit``
 
 
 Implemented Papers

libcxx/docs/Status/Cxx2cPapers.csv

@@ -17,7 +17,7 @@
 "`P0792R14 <https://wg21.link/P0792R14>`__","LWG","``function_ref``: a type-erased callable reference","Varna June 2023","","",""
 "`P2874R2 <https://wg21.link/P2874R2>`__","LWG","Mandating Annex D Require No More","Varna June 2023","","",""
 "`P2757R3 <https://wg21.link/P2757R3>`__","LWG","Type-checking format args","Varna June 2023","","","|format|"
-"`P2637R3 <https://wg21.link/P2637R3>`__","LWG","Member ``visit``","Varna June 2023","|Partial|","18.0",""
+"`P2637R3 <https://wg21.link/P2637R3>`__","LWG","Member ``visit``","Varna June 2023","|Complete|","19.0",""
 "`P2641R4 <https://wg21.link/P2641R4>`__","CWG, LWG","Checking if a ``union`` alternative is active","Varna June 2023","","",""
 "`P1759R6 <https://wg21.link/P1759R6>`__","LWG","Native handles and file streams","Varna June 2023","|Complete|","18.0",""
 "`P2697R1 <https://wg21.link/P2697R1>`__","LWG","Interfacing ``bitset`` with ``string_view``","Varna June 2023","|Complete|","18.0",""

libcxx/docs/Status/FormatIssues.csv

@@ -16,7 +16,7 @@ Number,Name,Standard,Assignee,Status,First released version
 "`P2693R1 <https://wg21.link/P2693R1>`__","Formatting ``thread::id`` and ``stacktrace``","C++23","Mark de Wever","|In Progress|"
 "`P2510R3 <https://wg21.link/P2510R3>`__","Formatting pointers","C++26","Mark de Wever","|Complete|",17.0
 "`P2757R3 <https://wg21.link/P2757R3>`__","Type-checking format args","C++26","","",
-"`P2637R3 <https://wg21.link/P2637R3>`__","Member ``visit``","C++26","","",
+"`P2637R3 <https://wg21.link/P2637R3>`__","Member ``visit``","C++26","Hristo Hristov","|Complete|",19.0
 "`P2905R2 <https://wg21.link/P2905R2>`__","Runtime format strings","C++26 DR","Mark de Wever","|Complete|",18.0
 "`P2918R2 <https://wg21.link/P2918R2>`__","Runtime format strings II","C++26","Mark de Wever","|Complete|",18.0
 "`P2909R4 <https://wg21.link/P2909R4>`__","Fix formatting of code units as integers (Dude, where’s my ``char``?)","C++26 DR","Mark de Wever","|Complete|",18.0

libcxx/include/__config

@@ -1015,6 +1015,12 @@ typedef __char32_t char32_t;
 # define _LIBCPP_DEPRECATED_IN_CXX23
 # endif
 
+# if _LIBCPP_STD_VER >= 26
+# define _LIBCPP_DEPRECATED_IN_CXX26 _LIBCPP_DEPRECATED
+# else
+# define _LIBCPP_DEPRECATED_IN_CXX26
+# endif
+
 # if !defined(_LIBCPP_HAS_NO_CHAR8_T)
 # define _LIBCPP_DEPRECATED_WITH_CHAR8_T _LIBCPP_DEPRECATED
 # else

libcxx/include/__format/format_arg.h

@@ -96,7 +96,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr __arg_t __get_packed_type(uint64_t __types, size
 
 } // namespace __format
 
-// This function is not user obervable, so it can directly use the non-standard
+// This function is not user observable, so it can directly use the non-standard
 // types of the "variant". See __arg_t for more details.
 template <class _Visitor, class _Context>
 _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
@@ -147,6 +147,59 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
  __libcpp_unreachable();
 }
 
+# if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
+template <class _Rp, class _Visitor, class _Context>
+_LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+ switch (__arg.__type_) {
+ case __format::__arg_t::__none:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__monostate_);
+ case __format::__arg_t::__boolean:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__boolean_);
+ case __format::__arg_t::__char_type:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__char_type_);
+ case __format::__arg_t::__int:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__int_);
+ case __format::__arg_t::__long_long:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__long_long_);
+ case __format::__arg_t::__i128:
+# ifndef _LIBCPP_HAS_NO_INT128
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__i128_);
+# else
+ __libcpp_unreachable();
+# endif
+ case __format::__arg_t::__unsigned:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_);
+ case __format::__arg_t::__unsigned_long_long:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__unsigned_long_long_);
+ case __format::__arg_t::__u128:
+# ifndef _LIBCPP_HAS_NO_INT128
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__u128_);
+# else
+ __libcpp_unreachable();
+# endif
+ case __format::__arg_t::__float:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__float_);
+ case __format::__arg_t::__double:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__double_);
+ case __format::__arg_t::__long_double:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__long_double_);
+ case __format::__arg_t::__const_char_type_ptr:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__const_char_type_ptr_);
+ case __format::__arg_t::__string_view:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__string_view_);
+ case __format::__arg_t::__ptr:
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), __arg.__value_.__ptr_);
+ case __format::__arg_t::__handle:
+ return std::invoke_r<_Rp>(
+ std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__arg.__value_.__handle_});
+ }
+
+ __libcpp_unreachable();
+}
+
+# endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
 /// Contains the values used in basic_format_arg.
 ///
 /// This is a separate type so it's possible to store the values and types in
@@ -230,6 +283,52 @@ class _LIBCPP_TEMPLATE_VIS basic_format_arg {
 
  _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __type_ != __format::__arg_t::__none; }
 
+# if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
+ // This function is user facing, so it must wrap the non-standard types of
+ // the "variant" in a handle to stay conforming. See __arg_t for more details.
+ template <class _Visitor>
+ _LIBCPP_HIDE_FROM_ABI decltype(auto) visit(this basic_format_arg __arg, _Visitor&& __vis) {
+ switch (__arg.__type_) {
+# ifndef _LIBCPP_HAS_NO_INT128
+ case __format::__arg_t::__i128: {
+ typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+ return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+ }
+
+ case __format::__arg_t::__u128: {
+ typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+ return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+ }
+# endif
+ default:
+ return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
+ }
+ }
+
+ // This function is user facing, so it must wrap the non-standard types of
+ // the "variant" in a handle to stay conforming. See __arg_t for more details.
+ template <class _Rp, class _Visitor>
+ _LIBCPP_HIDE_FROM_ABI _Rp visit(this basic_format_arg __arg, _Visitor&& __vis) {
+ switch (__arg.__type_) {
+# ifndef _LIBCPP_HAS_NO_INT128
+ case __format::__arg_t::__i128: {
+ typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__i128_};
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+ }
+
+ case __format::__arg_t::__u128: {
+ typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
+ return std::invoke_r<_Rp>(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
+ }
+# endif
+ default:
+ return std::__visit_format_arg<_Rp>(std::forward<_Visitor>(__vis), __arg);
+ }
+ }
+
+# endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+
 private:
  using char_type = typename _Context::char_type;
 
@@ -270,7 +369,11 @@ class _LIBCPP_TEMPLATE_VIS basic_format_arg<_Context>::handle {
 // This function is user facing, so it must wrap the non-standard types of
 // the "variant" in a handle to stay conforming. See __arg_t for more details.
 template <class _Visitor, class _Context>
-_LIBCPP_HIDE_FROM_ABI decltype(auto) visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
+# if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+_LIBCPP_DEPRECATED_IN_CXX26
+# endif
+ _LIBCPP_HIDE_FROM_ABI decltype(auto)
+ visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
  switch (__arg.__type_) {
 # ifndef _LIBCPP_HAS_NO_INT128
  case __format::__arg_t::__i128: {
@@ -282,7 +385,7 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) visit_format_arg(_Visitor&& __vis, basic_fo
  typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
  return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
  }
-# endif
+# endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
  default:
  return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
  }

libcxx/include/__format/format_context.h

@@ -166,20 +166,25 @@ class _LIBCPP_TEMPLATE_VIS basic_format_context<typename __format::__retarget_bu
 # endif
  __ctx_(std::addressof(__ctx)),
  __arg_([](void* __c, size_t __id) {
- return std::visit_format_arg(
- [&](auto __arg) -> basic_format_arg<basic_format_context> {
- if constexpr (same_as<decltype(__arg), monostate>)
- return {};
- else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
- // At the moment it's not possible for formatting to use a re-targeted handle.
- // TODO FMT add this when support is needed.
- std::__throw_format_error("Re-targeting handle not supported");
- else
- return basic_format_arg<basic_format_context>{
- __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
- __basic_format_arg_value<basic_format_context>(__arg)};
- },
- static_cast<_Context*>(__c)->arg(__id));
+ auto __visitor = [&](auto __arg) -> basic_format_arg<basic_format_context> {
+ if constexpr (same_as<decltype(__arg), monostate>)
+ return {};
+ else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
+ // At the moment it's not possible for formatting to use a re-targeted handle.
+ // TODO FMT add this when support is needed.
+ std::__throw_format_error("Re-targeting handle not supported");
+ else
+ return basic_format_arg<basic_format_context>{
+ __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
+ __basic_format_arg_value<basic_format_context>(__arg)};
+ };
+# if _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+ return static_cast<_Context*>(__c)->arg(__id).visit(std::move(__visitor));
+# else
+ _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+ return std::visit_format_arg(std::move(__visitor), static_cast<_Context*>(__c)->arg(__id));
+ _LIBCPP_SUPPRESS_DEPRECATED_POP
+# endif // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
  }) {
  }
 

libcxx/include/format

@@ -170,7 +170,7 @@ namespace std {
  template<class Context> class basic_format_arg;
 
  template<class Visitor, class Context>
- see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+ see below visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg); // Deprecated in C++26
 
  // [format.arg.store], class template format-arg-store
  template<class Context, class... Args> struct format-arg-store; // exposition only