Deprecate arg_formatter

doc/api.rst

@@ -335,50 +335,6 @@ arguments, the container that stores pointers to them will be allocated using
 the default allocator. Also floating-point formatting falls back on ``sprintf``
 which may do allocations.
 
-Custom Formatting of Built-in Types
------------------------------------
-
-It is possible to change the way arguments are formatted by providing a
-custom argument formatter class::
-
-  using arg_formatter = fmt::arg_formatter<fmt::buffer_range<char>>;
-
-  // A custom argument formatter that formats negative integers as unsigned
-  // with the ``x`` format specifier.
-  class custom_arg_formatter : public arg_formatter {
-   public:
-    custom_arg_formatter(fmt::format_context& ctx,
-                         fmt::format_parse_context* parse_ctx = nullptr,
-                         fmt::format_specs* spec = nullptr)
-      : arg_formatter(ctx, parse_ctx, spec) {}
-
-    using arg_formatter::operator();
-
-    auto operator()(int value) {
-      if (specs() && specs()->type == 'x')
-        return (*this)(static_cast<unsigned>(value)); // convert to unsigned and format
-      return arg_formatter::operator()(value);
-    }
-  };
-
-  std::string custom_vformat(fmt::string_view format_str, fmt::format_args args) {
-    fmt::memory_buffer buffer;
-    // Pass custom argument formatter as a template arg to vformat_to.
-    fmt::vformat_to<custom_arg_formatter>(buffer, format_str, args);
-    return fmt::to_string(buffer);
-  }
-
-  template <typename ...Args>
-  inline std::string custom_format(
-      fmt::string_view format_str, const Args&... args) {
-    return custom_vformat(format_str, fmt::make_format_args(args...));
-  }
-
-  std::string s = custom_format("{:x}", -42); // s == "ffffffd6"
-
-.. doxygenclass:: fmt::arg_formatter
-   :members:
-
 .. _ranges-api:
 
 Ranges and Tuple Formatting