Revert "[libc++][format] P2637R3: Member `visit` (`std::basic_format_arg`) (#76449)"

This reverts commit 7d9b5aa65b09126031e1c2903605a7d34aea4bc1 since
std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
is failing on Windows when building with Clang-cl.

2 files changed, 17 insertions, 125 deletions

diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
index 02ee3ce..10fca15d 100644
--- a/libcxx/include/__format/format_arg.h
+++ b/libcxx/include/__format/format_arg.h
@@ -93,7 +93,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr __arg_t __get_packed_type(uint64_t __types, size
 
 } // namespace __format
 
-// This function is not user observable, so it can directly use the non-standard
+// This function is not user obervable, 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) {
@@ -144,59 +144,6 @@ _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
@@ -280,52 +227,6 @@ public:
 
   _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;
 
@@ -366,11 +267,7 @@ private:
 // 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>
-#  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) {
+_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: {
@@ -382,7 +279,7 @@ _LIBCPP_DEPRECATED_IN_CXX26
     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 // _LIBCPP_STD_VER >= 26 && defined(_LIBCPP_HAS_EXPLICIT_THIS_PARAMETER)
+#  endif
   default:
     return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
   }
diff --git a/libcxx/include/__format/format_context.h b/libcxx/include/__format/format_context.h
index 0beaa84..5b252b8 100644
--- a/libcxx/include/__format/format_context.h
+++ b/libcxx/include/__format/format_context.h
@@ -163,25 +163,20 @@ public:
 #  endif
         __ctx_(std::addressof(__ctx)),
         __arg_([](void* __c, size_t __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)
+          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));
         }) {
   }