Add code from p0645

CMakeLists.txt

@@ -147,7 +147,8 @@ if (HAVE_OPEN)
   set(FMT_SOURCES ${FMT_SOURCES} src/posix.cc)
 endif ()
 
-add_library(fmt ${FMT_SOURCES} ${FMT_HEADERS} README.rst ChangeLog.rst)
+add_library(fmt ${FMT_SOURCES} ${FMT_HEADERS} include/format README.rst
+            ChangeLog.rst)
 add_library(fmt::fmt ALIAS fmt)
 
 if (FMT_WERROR)

include/fmt/core.h

@@ -1042,7 +1042,7 @@ class context_base {
 
   // Checks if manual indexing is used and returns the argument with
   // specified index.
-  format_arg get_arg(unsigned arg_id) {
+  format_arg arg(unsigned arg_id) {
     return this->parse_context().check_arg_id(arg_id) ? this->do_get_arg(arg_id)
                                                       : format_arg();
   }
@@ -1125,11 +1125,11 @@ class basic_format_context
   void operator=(const basic_format_context&) = delete;
 
   typedef internal::context_base<OutputIt, basic_format_context, Char> base;
-  typedef typename base::format_arg format_arg;
-  using base::get_arg;
+  using base::arg;
 
  public:
   using typename base::iterator;
+  typedef typename base::format_arg format_arg;
 
   /**
    Constructs a ``basic_format_context`` object. References to the arguments are
@@ -1143,11 +1143,15 @@ class basic_format_context
   format_arg next_arg() {
     return this->do_get_arg(this->parse_context().next_arg_id());
   }
-  format_arg get_arg(unsigned arg_id) { return this->do_get_arg(arg_id); }
+  format_arg arg(unsigned arg_id) { return this->do_get_arg(arg_id); }
 
   // Checks if manual indexing is used and returns the argument with the
   // specified name.
-  format_arg get_arg(basic_string_view<char_type> name);
+  format_arg arg(basic_string_view<char_type> name);
+
+  // DEPRECATED!
+  format_arg get_arg(unsigned arg_id) { return arg(arg_id); }
+  format_arg get_arg(basic_string_view<char_type> name) { return arg(name); }
 };
 
 template <typename Char> struct buffer_context {

include/fmt/format.h

@@ -1662,10 +1662,9 @@ template <typename Handler> class specs_checker : public Handler {
   numeric_specs_checker<Handler> checker_;
 };
 
-template <template <typename> class Handler, typename T, typename Context,
+template <template <typename> class Handler, typename T, typename FormatArg,
           typename ErrorHandler>
-FMT_CONSTEXPR void set_dynamic_spec(T& value, basic_format_arg<Context> arg,
-                                    ErrorHandler eh) {
+FMT_CONSTEXPR void set_dynamic_spec(T& value, FormatArg arg, ErrorHandler eh) {
   unsigned long long big_value =
       visit_format_arg(Handler<ErrorHandler>(eh), arg);
   if (big_value > to_unsigned((std::numeric_limits<int>::max)()))
@@ -1698,14 +1697,15 @@ class specs_handler : public specs_setter<typename Context::char_type> {
   void on_error(const char* message) { context_.on_error(message); }
 
  private:
-  FMT_CONSTEXPR basic_format_arg<Context> get_arg(auto_id) {
-    return context_.next_arg();
-  }
+  // This is only needed for compatibility with gcc 4.4.
+  typedef typename Context::format_arg format_arg;
+
+  FMT_CONSTEXPR format_arg get_arg(auto_id) { return context_.next_arg(); }
 
   template <typename Id>
-  FMT_CONSTEXPR basic_format_arg<Context> get_arg(Id arg_id) {
+  FMT_CONSTEXPR format_arg get_arg(Id arg_id) {
     context_.parse_context().check_arg_id(arg_id);
-    return context_.get_arg(arg_id);
+    return context_.arg(arg_id);
   }
 
   Context& context_;
@@ -2174,12 +2174,12 @@ void handle_dynamic_spec(Spec& value, arg_ref<typename Context::char_type> ref,
   case arg_ref<char_type>::NONE:
     break;
   case arg_ref<char_type>::INDEX:
-    internal::set_dynamic_spec<Handler>(value, ctx.get_arg(ref.val.index),
+    internal::set_dynamic_spec<Handler>(value, ctx.arg(ref.val.index),
                                         ctx.error_handler());
     break;
   case arg_ref<char_type>::NAME: {
     const auto arg_id = ref.val.name.to_view(ctx.parse_context().begin());
-    internal::set_dynamic_spec<Handler>(value, ctx.get_arg(arg_id),
+    internal::set_dynamic_spec<Handler>(value, ctx.arg(arg_id),
                                         ctx.error_handler());
   } break;
   }
@@ -3050,7 +3050,7 @@ template <typename Char = char> class dynamic_formatter {
 
 template <typename Range, typename Char>
 typename basic_format_context<Range, Char>::format_arg
-basic_format_context<Range, Char>::get_arg(basic_string_view<char_type> name) {
+basic_format_context<Range, Char>::arg(basic_string_view<char_type> name) {
   map_.init(this->args());
   format_arg arg = map_.find(name);
   if (arg.type() == internal::none_type) this->on_error("argument not found");

include/fmt/printf.h

@@ -418,7 +418,7 @@ typename basic_printf_context<OutputIt, Char, AF>::format_arg
 basic_printf_context<OutputIt, Char, AF>::get_arg(unsigned arg_index) {
   if (arg_index == std::numeric_limits<unsigned>::max())
     return this->do_get_arg(this->parse_context().next_arg_id());
-  return base::get_arg(arg_index - 1);
+  return base::arg(arg_index - 1);
 }
 
 template <typename OutputIt, typename Char, typename AF>

include/format

@@ -0,0 +1,823 @@
+// Formatting library for C++ - the standard API implementation
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#ifndef FMT_FORMAT_
+#define FMT_FORMAT_
+
+#include <variant>
+#include "fmt/format.h"
+
+// This implementation verifies the correctness of the standard API proposed in
+// P0645 Text Formatting and is optimized for copy-pasting from the paper, not
+// for efficiency or readability. An efficient implementation should not use
+// std::variant and should store packed argument type tags separately from
+// values in basic_format_args for small number of arguments.
+
+#define FMT_REQUIRES(...)
+#define FMT_CONCEPT(C) typename
+
+namespace std {
+template<class T>
+constexpr bool Integral = is_integral_v<T>;
+
+template <class O>
+  using iter_difference_t = ptrdiff_t;
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.syn
+namespace std {
+  // [format.error], class format_error
+  class format_error;
+
+  // [format.formatter], formatter
+  template<class charT> class basic_format_parse_context;
+  using format_parse_context = basic_format_parse_context<char>;
+  using wformat_parse_context = basic_format_parse_context<wchar_t>;
+
+  template<class O, class charT> FMT_REQUIRES(OutputIterator<O, const charT&>)
+    class basic_format_context;
+  using format_context = basic_format_context<
+    /* unspecified */ std::back_insert_iterator<fmt::internal::basic_buffer<char>>,
+    char>;
+  using wformat_context = basic_format_context<
+    /* unspecified */ std::back_insert_iterator<fmt::internal::basic_buffer<wchar_t>>,
+    wchar_t>;
+
+  template<class T, class charT = char> struct formatter {
+    formatter() = delete;
+  };
+
+  // [format.arguments], arguments
+  template<class Context> class basic_format_arg;
+
+  template<class Visitor, class Context>
+    /* see below */ auto visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
+
+  template<class Context, class... Args> struct format_arg_store; // exposition only
+
+  template<class Context> class basic_format_args;
+  using format_args = basic_format_args<format_context>;
+  using wformat_args = basic_format_args<wformat_context>;
+
+  template<class O, class charT>
+    using format_args_t = basic_format_args<basic_format_context<O, charT>>;
+
+  template<class Context = format_context, class... Args>
+    format_arg_store<Context, Args...>
+      make_format_args(const Args&... args);
+  template<class... Args>
+    format_arg_store<wformat_context, Args...>
+      make_wformat_args(const Args&... args);
+
+  // [format.functions], formatting functions
+  template<class... Args>
+    string format(string_view fmt, const Args&... args);
+  template<class... Args>
+    wstring format(wstring_view fmt, const Args&... args);
+
+  string vformat(string_view fmt, format_args args);
+  wstring vformat(wstring_view fmt, wformat_args args);
+
+  template<FMT_CONCEPT(OutputIterator<const char&>) O, class... Args>
+    O format_to(O out, string_view fmt, const Args&... args);
+  template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O, class... Args>
+    O format_to(O out, wstring_view fmt, const Args&... args);
+
+  template<FMT_CONCEPT(OutputIterator<const char&>) O>
+    O vformat_to(O out, string_view fmt, format_args_t<O, char> args);
+  template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O>
+    O vformat_to(O out, wstring_view fmt, format_args_t<O, wchar_t> args);
+
+  template<class O>
+    struct format_to_n_result {
+      O out;
+      iter_difference_t<O> size;
+    };
+
+  template<FMT_CONCEPT(OutputIterator<const char&>) O, class... Args>
+    format_to_n_result<O> format_to_n(O out, iter_difference_t<O> n,
+                                      string_view fmt, const Args&... args);
+  template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O, class... Args>
+    format_to_n_result<O> format_to_n(O out, iter_difference_t<O> n,
+                                      wstring_view fmt, const Args&... args);
+
+  template<class... Args>
+    size_t formatted_size(string_view fmt, const Args&... args);
+  template<class... Args>
+    size_t formatted_size(wstring_view fmt, const Args&... args);
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.error
+namespace std {
+  class format_error : public runtime_error {
+  public:
+    explicit format_error(const string& what_arg) : runtime_error(what_arg) {}
+    explicit format_error(const char* what_arg) : runtime_error(what_arg) {}
+  };
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.parse_context
+namespace std {
+  template<class charT>
+  class basic_format_parse_context {
+  public:
+    using char_type = charT;
+    using const_iterator = typename basic_string_view<charT>::const_iterator;
+    using iterator = const_iterator;
+
+  private:
+    iterator begin_;                              // exposition only
+    iterator end_;                                // exposition only
+    enum indexing { unknown, manual, automatic }; // exposition only
+    indexing indexing_;                           // exposition only
+    size_t next_arg_id_;                          // exposition only
+
+  public:
+    explicit constexpr basic_format_parse_context(basic_string_view<charT> fmt) noexcept;
+    basic_format_parse_context(const basic_format_parse_context&) = delete;
+    basic_format_parse_context& operator=(const basic_format_parse_context&) = delete;
+
+    constexpr const_iterator begin() const noexcept;
+    constexpr const_iterator end() const noexcept;
+    constexpr void advance_to(iterator it);
+
+    constexpr size_t next_arg_id();
+    constexpr void check_arg_id(size_t id);
+
+    // Implementation detail:
+    constexpr void check_arg_id(fmt::string_view) {}
+    fmt::internal::error_handler error_handler() const { return {}; }
+    void on_error(const char* msg) { error_handler().on_error(msg); }
+  };
+}
+
+namespace std {
+template<class charT>
+/* explicit */ constexpr basic_format_parse_context<charT>::basic_format_parse_context(basic_string_view<charT> fmt) noexcept
+: begin_(fmt.begin()), end_(fmt.end()), indexing_(unknown), next_arg_id_(0) {}
+
+template<class charT>
+constexpr typename basic_format_parse_context<charT>::const_iterator basic_format_parse_context<charT>::begin() const noexcept { return begin_; }
+
+template<class charT>
+constexpr typename basic_format_parse_context<charT>::const_iterator basic_format_parse_context<charT>::end() const noexcept { return end_; }
+
+template<class charT>
+constexpr void basic_format_parse_context<charT>::advance_to(typename basic_format_parse_context<charT>::iterator it) { begin_ = it; }
+
+template<class charT>
+constexpr size_t basic_format_parse_context<charT>::next_arg_id() {
+  if (indexing_ == manual)
+    throw format_error("manual to automatic indexing");
+  if (indexing_ == unknown)
+    indexing_ = automatic;
+  return next_arg_id_++;
+}
+
+template<class charT>
+constexpr void basic_format_parse_context<charT>::check_arg_id(size_t) {
+  if (indexing_ == automatic)
+    throw format_error("automatic to manual indexing");
+  if (indexing_ == unknown)
+    indexing_ = manual;
+}
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.context
+namespace std {
+  template<class O, class charT> FMT_REQUIRES(OutputIterator<O, const charT&>)
+  class basic_format_context {
+    basic_format_parse_context<charT> parse_context_; // exposition only
+    basic_format_args<basic_format_context> args_;    // exposition only
+    O out_;                                           // exposition only
+
+  public:
+    using iterator = O;
+    using char_type = charT;
+
+    template<class T>
+      using formatter_type = formatter<T>;
+
+    basic_format_parse_context<charT>& parse_context() noexcept;
+    basic_format_arg<basic_format_context> arg(size_t id) const;
+
+    iterator out();
+    void advance_to(iterator it);
+
+    // Implementation details:
+    using format_arg = basic_format_arg<basic_format_context>;
+    basic_format_context(O out, fmt::string_view fmt, basic_format_args<basic_format_context> args, fmt::internal::locale_ref)
+    : out_(out), parse_context_({fmt.data(), fmt.size()}), args_(args) {}
+    basic_format_arg<basic_format_context> next_arg() {
+      return arg(parse_context_.next_arg_id());
+    }
+    fmt::internal::error_handler error_handler() const { return {}; }
+    basic_format_arg<basic_format_context> arg(fmt::basic_string_view<charT>) const {
+      return {}; // unused: named arguments are not supported yet
+    }
+    void on_error(const char* msg) { error_handler().on_error(msg); }
+  };
+}
+
+namespace std {
+template<class O, class charT>
+basic_format_parse_context<charT>& basic_format_context<O, charT>::parse_context() noexcept { return parse_context_; }
+
+template<class O, class charT>
+basic_format_arg<basic_format_context<O, charT>> basic_format_context<O, charT>::arg(size_t id) const { return args_.get(id); }
+
+template<class O, class charT>
+typename basic_format_context<O, charT>::iterator basic_format_context<O, charT>::out() { return out_; }
+
+template<class O, class charT>
+void basic_format_context<O, charT>::advance_to(typename basic_format_context<O, charT>::iterator it) { out_ = it; }
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.arg
+namespace std {
+  template<class Context>
+  class basic_format_arg {
+  public:
+    class handle;
+
+    using char_type = typename Context::char_type;                     // exposition only
+
+    variant<monostate, bool, char_type,
+            int, unsigned int, long long int, unsigned long long int,
+            double, long double,
+            const char_type*, basic_string_view<char_type>,
+            const void*, handle> value;                                // exposition only
+
+    basic_format_arg() noexcept;
+
+    template<FMT_CONCEPT(Integral) I, typename = std::enable_if_t<Integral<I>>> explicit basic_format_arg(I n) noexcept;      // exposition only
+    explicit basic_format_arg(float n) noexcept;                       // exposition only
+    explicit basic_format_arg(double n) noexcept;                      // exposition only
+    explicit basic_format_arg(long double n) noexcept;                 // exposition only
+    explicit basic_format_arg(const char_type* s) noexcept;            // exposition only
+    explicit basic_format_arg(nullptr_t) noexcept;                     // exposition only
+
+    template<class traits>
+      explicit basic_format_arg(
+        basic_string_view<char_type, traits> s) noexcept;              // exposition only
+
+    template<class traits, class Allocator>
+      explicit basic_format_arg(
+        const basic_string<char_type, traits, Allocator>& s) noexcept; // exposition only
+
+    template<class T, typename = std::enable_if_t<std::is_same_v<T, void>>>
+      explicit basic_format_arg(const T* p) noexcept;                  // exposition only
+
+    template<class T, typename = std::enable_if_t<
+               !Integral<T> && is_default_constructible_v<formatter<T, char_type>>>>
+      explicit basic_format_arg(const T& v) noexcept;                  // exposition only
+
+    explicit operator bool() const noexcept;
+  };
+}
+
+namespace std {
+template<class Context>
+basic_format_arg<Context>::basic_format_arg() noexcept {}
+
+template <typename T>
+constexpr bool is_standard_integer_v =
+    std::is_same_v<T, signed char> ||
+    std::is_same_v<T, short int> ||
+    std::is_same_v<T, int> ||
+    std::is_same_v<T, long int> ||
+    std::is_same_v<T, long long int>;
+
+template <typename T>
+constexpr bool is_standard_unsigned_integer_v =
+    std::is_same_v<T, unsigned char> ||
+    std::is_same_v<T, unsigned short int> ||
+    std::is_same_v<T, unsigned int> ||
+    std::is_same_v<T, unsigned long int> ||
+    std::is_same_v<T, unsigned long long int>;
+
+template<class Context>
+template<FMT_CONCEPT(Integral) I, typename>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(I n) noexcept {
+  if (std::is_same_v<I, bool> || std::is_same_v<I, char_type>)
+    value = n;
+  else if (std::is_same_v<I, char> || std::is_same_v<char_type, wchar_t>)
+    value = static_cast<wchar_t>(n);
+  else if (std::is_standard_integer_v<I> && sizeof(I) <= sizeof(int))
+    value = static_cast<int>(n);
+  else if (std::is_standard_integer_v<I> && sizeof(I) <= sizeof(unsigned))
+    value = static_cast<unsigned>(n);
+  else if (std::is_standard_integer_v<I>)
+    value = static_cast<long long int>(n);
+  else if (std::is_standard_integer_v<I>)
+    value = static_cast<unsigned long long int>(n);
+  else assert(false); // should be a compile-time error instead
+}
+
+template<class Context>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(float n) noexcept
+  : value(static_cast<double>(n)) {}
+
+template<class Context>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(double n) noexcept
+  : value(n) {}
+
+template<class Context>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(long double n) noexcept
+  : value(n) {}
+
+template<class Context>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(const typename basic_format_arg<Context>::char_type* s) noexcept
+  : value(s) {
+  assert(s != nullptr);
+}
+
+template<class Context>
+template<class traits>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(basic_string_view<char_type, traits> s) noexcept
+  : value(s) {}
+
+template<class Context>
+template<class traits, class Allocator>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(
+    const basic_string<char_type, traits, Allocator>& s) noexcept
+  : value(basic_string_view<char_type>(s.data(), s.size())) {}
+
+
+template<class Context>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(nullptr_t) noexcept
+  : value(static_cast<const void*>(nullptr)) {}
+
+template<class Context>
+template<class T, typename> /* explicit */ basic_format_arg<Context>::basic_format_arg(const T* p) noexcept
+  : value(p) {}
+
+template<class Context>
+template<class T, typename>
+/* explicit */ basic_format_arg<Context>::basic_format_arg(const T& v) noexcept
+  : value(handle(v)) {}
+}
+
+namespace std {
+  template<class Context>
+  class basic_format_arg<Context>::handle {
+    const void* ptr_;                                         // exposition only
+    void (*format_)(Context&, const void*);                   // exposition only
+
+  public:
+    template<class T> explicit handle(const T& val) noexcept; // exposition only
+
+    void format(Context& ctx) const;
+  };
+}
+
+namespace std {
+template<class Context>
+template<class T> /* explicit */ basic_format_arg<Context>::handle::handle(const T& val) noexcept
+  : ptr_(&val), format_([](Context& ctx, const void* ptr) {
+        typename Context::template formatter_type<T> f;
+        ctx.parse_context().advance_to(f.parse(ctx.parse_context()));
+        ctx.advance_to(f.format(*static_cast<const T*>(ptr), ctx));
+}) {}
+
+template<class Context>
+void basic_format_arg<Context>::handle::format(Context& ctx) const {
+  format_(ctx, ptr_);
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.visit
+template<class Visitor, class Context>
+  auto visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg) {
+    return visit(vis, arg.value);
+  }
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.store
+namespace std {
+  template<class Context, class... Args>
+  struct format_arg_store { // exposition only
+    array<basic_format_arg<Context>, sizeof...(Args)> args;
+  };
+}
+
+// http://fmtlib.net/Text%20Formatting.html#format.basic_args
+namespace std {
+  template<class Context>
+  class basic_format_args {
+    size_t size_;                           // exposition only
+    const basic_format_arg<Context>* data_; // exposition only
+
+  public:
+    basic_format_args() noexcept;
+
+    template<class... Args>
+      basic_format_args(const format_arg_store<Context, Args...>& store) noexcept;
+
+    basic_format_arg<Context> get(size_t i) const noexcept;
+  };
+}
+
+namespace std {
+
+template<class Context>
+basic_format_args<Context>::basic_format_args() noexcept : size_(0) {}
+
+template<class Context>
+template<class... Args>
+  basic_format_args<Context>::basic_format_args(const format_arg_store<Context, Args...>& store) noexcept
+  : size_(sizeof...(Args)), data_(store.args.data()) {}
+
+template<class Context>
+basic_format_arg<Context> basic_format_args<Context>::get(size_t i) const noexcept {
+  return i < size_ ? data_[i] : basic_format_arg<Context>();
+}
+}
+
+namespace std {
+// http://fmtlib.net/Text%20Formatting.html#format.make_args
+template<class Context /*= format_context*/, class... Args>
+  format_arg_store<Context, Args...> make_format_args(const Args&... args) {
+    return {basic_format_arg<Context>(args)...};
+  }
+
+// http://fmtlib.net/Text%20Formatting.html#format.make_wargs
+template<class... Args>
+  format_arg_store<wformat_context, Args...> make_wformat_args(const Args&... args) {
+    return {basic_format_arg<wformat_context>(args)...};
+  }
+}
+
+namespace std {
+namespace detail {
+
+template <typename Range>
+class arg_formatter
+    : public fmt::internal::function<
+          typename fmt::internal::arg_formatter_base<Range>::iterator>,
+      public fmt::internal::arg_formatter_base<Range> {
+ private:
+  typedef typename Range::value_type char_type;
+  typedef fmt::internal::arg_formatter_base<Range> base;
+  typedef std::basic_format_context<typename base::iterator, char_type> context_type;
+
+  context_type& ctx_;
+
+ public:
+  typedef Range range;
+  typedef typename base::iterator iterator;
+  typedef typename base::format_specs format_specs;
+
+  /**
+    \rst
+    Constructs an argument formatter object.
+    *ctx* is a reference to the formatting context,
+    *spec* contains format specifier information for standard argument types.
+    \endrst
+   */
+  explicit arg_formatter(context_type& ctx, fmt::format_specs* spec = FMT_NULL)
+      : base(Range(ctx.out()), spec, {}), ctx_(ctx) {}
+
+  using base::operator();
+
+  /** Formats an argument of a user-defined type. */
+  iterator operator()(typename std::basic_format_arg<context_type>::handle handle) {
+    handle.format(ctx_);
+    return this->out();
+  }
+
+  iterator operator()(monostate) {
+    throw format_error("");
+  }
+};
+
+template <typename Context>
+inline fmt::internal::type get_type(basic_format_arg<Context> arg) {
+  return visit_format_arg([&] (auto val) {
+    using char_type = typename Context::char_type;
+    using T = decltype(val);
+    if (std::is_same_v<T, monostate>)
+      return fmt::internal::none_type;
+    if (std::is_same_v<T, bool>)
+      return fmt::internal::bool_type;
+    if (std::is_same_v<T, char_type>)
+      return fmt::internal::char_type;
+    if (std::is_same_v<T, int>)
+      return fmt::internal::int_type;
+    if (std::is_same_v<T, unsigned int>)
+      return fmt::internal::uint_type;
+    if (std::is_same_v<T, long long int>)
+      return fmt::internal::long_long_type;
+    if (std::is_same_v<T, unsigned long long int>)
+      return fmt::internal::ulong_long_type;
+    if (std::is_same_v<T, double>)
+      return fmt::internal::double_type;
+    if (std::is_same_v<T, long double>)
+      return fmt::internal::long_double_type;
+    if (std::is_same_v<T, const char_type*>)
+      return fmt::internal::cstring_type;
+    if (std::is_same_v<T, basic_string_view<char_type>>)
+      return fmt::internal::string_type;
+    if (std::is_same_v<T, const void*>)
+      return fmt::internal::pointer_type;
+    assert(arg.value.index() == 12);
+    return fmt::internal::custom_type;
+  }, arg);
+}
+
+template <typename Char, typename Context>
+class custom_formatter {
+ private:
+  Context& ctx_;
+
+ public:
+  explicit custom_formatter(Context& ctx) : ctx_(ctx) {}
+
+  bool operator()(typename basic_format_arg<Context>::handle h) const {
+    h.format(ctx_);
+    return true;
+  }
+
+  template <typename T> bool operator()(T) const { return false; }
+};
+
+template <typename ArgFormatter, typename Char, typename Context>
+struct format_handler : fmt::internal::error_handler {
+  typedef typename ArgFormatter::range range;
+
+  format_handler(range r, basic_string_view<Char> str,
+                 basic_format_args<Context> format_args,
+                 fmt::internal::locale_ref loc)
+      : context(r.begin(), str, format_args, loc) {}
+
+  void on_text(const Char* begin, const Char* end) {
+    auto size = fmt::internal::to_unsigned(end - begin);
+    auto out = context.out();
+    auto&& it = fmt::internal::reserve(out, size);
+    it = std::copy_n(begin, size, it);
+    context.advance_to(out);
+  }
+
+  void on_arg_id() { arg = context.next_arg(); }
+  void on_arg_id(unsigned id) {
+    context.parse_context().check_arg_id(id);
+    arg = context.arg(id);
+  }
+  void on_arg_id(fmt::basic_string_view<Char> id) {}
+
+  void on_replacement_field(const Char* p) {
+    context.parse_context().advance_to(p);
+    custom_formatter<Char, Context> f(context);
+    if (!visit_format_arg(f, arg))
+      context.advance_to(visit_format_arg(ArgFormatter(context), arg));
+  }
+
+  const Char* on_format_specs(const Char* begin, const Char* end) {
+    auto& parse_ctx = context.parse_context();
+    parse_ctx.advance_to(begin);
+    custom_formatter<Char, Context> f(context);
+    if (visit_format_arg(f, arg)) return parse_ctx.begin();
+    fmt::basic_format_specs<Char> specs;
+    using fmt::internal::specs_handler;
+    fmt::internal::specs_checker<specs_handler<Context>> handler(
+        specs_handler<Context>(specs, context), get_type(arg));
+    begin = parse_format_specs(begin, end, handler);
+    if (begin == end || *begin != '}') on_error("missing '}' in format string");
+    parse_ctx.advance_to(begin);
+    context.advance_to(visit_format_arg(ArgFormatter(context, &specs), arg));
+    return begin;
+  }
+
+  Context context;
+  basic_format_arg<Context> arg;
+};
+
+template <typename T, typename Char>
+struct formatter {
+  // Parses format specifiers stopping either at the end of the range or at the
+  // terminating '}'.
+  template <typename ParseContext>
+  FMT_CONSTEXPR typename ParseContext::iterator parse(ParseContext& ctx) {
+    namespace internal = fmt::internal;
+    typedef internal::dynamic_specs_handler<ParseContext> handler_type;
+    auto type =
+        internal::get_type<typename fmt::buffer_context<Char>::type, T>::value;
+    internal::specs_checker<handler_type> handler(handler_type(specs_, ctx),
+                                                  type);
+    auto it = parse_format_specs(ctx.begin(), ctx.end(), handler);
+    auto type_spec = specs_.type;
+    auto eh = ctx.error_handler();
+    switch (type) {
+    case internal::none_type:
+    case internal::named_arg_type:
+      FMT_ASSERT(false, "invalid argument type");
+      break;
+    case internal::int_type:
+    case internal::uint_type:
+    case internal::long_long_type:
+    case internal::ulong_long_type:
+    case internal::bool_type:
+      handle_int_type_spec(type_spec,
+                           internal::int_type_checker<decltype(eh)>(eh));
+      break;
+    case internal::char_type:
+      handle_char_specs(
+          &specs_, internal::char_specs_checker<decltype(eh)>(type_spec, eh));
+      break;
+    case internal::double_type:
+    case internal::long_double_type:
+      handle_float_type_spec(type_spec,
+                             internal::float_type_checker<decltype(eh)>(eh));
+      break;
+    case internal::cstring_type:
+      internal::handle_cstring_type_spec(
+          type_spec, internal::cstring_type_checker<decltype(eh)>(eh));
+      break;
+    case internal::string_type:
+      internal::check_string_type_spec(type_spec, eh);
+      break;
+    case internal::pointer_type:
+      internal::check_pointer_type_spec(type_spec, eh);
+      break;
+    case internal::custom_type:
+      // Custom format specifiers should be checked in parse functions of
+      // formatter specializations.
+      break;
+    }
+    return it;
+  }
+
+  template <typename FormatContext>
+  auto format(const T& val, FormatContext& ctx) -> decltype(ctx.out()) {
+    fmt::internal::handle_dynamic_spec<fmt::internal::width_checker>(
+        specs_.width_, specs_.width_ref, ctx);
+    fmt::internal::handle_dynamic_spec<fmt::internal::precision_checker>(
+        specs_.precision, specs_.precision_ref, ctx);
+    typedef fmt::output_range<typename FormatContext::iterator,
+                         typename FormatContext::char_type>
+        range_type;
+    return visit_format_arg(arg_formatter<range_type>(ctx, &specs_),
+                            basic_format_arg<FormatContext>(val));
+  }
+
+ private:
+  fmt::internal::dynamic_format_specs<Char> specs_;
+};
+}  // namespace detail
+
+// http://fmtlib.net/Text%20Formatting.html#format.functions
+template<class... Args>
+  string format(string_view fmt, const Args&... args) {
+    return vformat(fmt, make_format_args(args...));
+  }
+
+template<class... Args>
+  wstring format(wstring_view fmt, const Args&... args) {
+    return vformat(fmt, make_wformat_args(args...));
+  }
+
+string vformat(string_view fmt, format_args args) {
+  fmt::memory_buffer mbuf;
+  fmt::internal::buffer& buf = mbuf;
+  typedef fmt::back_insert_range<fmt::internal::buffer> range;
+  detail::format_handler<detail::arg_formatter<range>, char, format_context>
+    h(range(std::back_inserter(buf)), fmt, args, {});
+  fmt::internal::parse_format_string<false>(fmt::to_string_view(fmt), h);
+  return to_string(mbuf);
+}
+
+wstring vformat(wstring_view fmt, wformat_args args);
+
+template<FMT_CONCEPT(OutputIterator<const char&>) O, class... Args>
+  O format_to(O out, string_view fmt, const Args&... args) {
+    return vformat_to(out, fmt, {make_format_args<basic_format_context<O, char>>(args...)});
+  }
+
+template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O, class... Args>
+  O format_to(O out, wstring_view fmt, const Args&... args) {
+    return vformat_to(out, fmt, {make_format_args<basic_format_context<O, wchar_t>>(args...)});
+  }
+
+template<FMT_CONCEPT(OutputIterator<const char&>) O>
+  O vformat_to(O out, string_view fmt, format_args_t<O, char> args) {
+    typedef fmt::output_range<O, char> range;
+    detail::format_handler<detail::arg_formatter<range>, char, format_context>
+      h(range(out), fmt, args, {});
+    fmt::internal::parse_format_string<false>(fmt::to_string_view(fmt), h);
+    return h.context.out();
+  }
+
+template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O>
+  O vformat_to(O out, wstring_view fmt, format_args_t<O, wchar_t> args);
+
+template<FMT_CONCEPT(OutputIterator<const char&>) O, class... Args>
+  format_to_n_result<O> format_to_n(O out, iter_difference_t<O> n,
+                                    string_view fmt, const Args&... args);
+template<FMT_CONCEPT(OutputIterator<const wchar_t&>) O, class... Args>
+  format_to_n_result<O> format_to_n(O out, iter_difference_t<O> n,
+                                    wstring_view fmt, const Args&... args);
+
+template<class... Args>
+  size_t formatted_size(string_view fmt, const Args&... args);
+template<class... Args>
+  size_t formatted_size(wstring_view fmt, const Args&... args);
+
+#define charT char
+
+template<> struct formatter<charT, charT> : detail::formatter<charT, charT> {};
+
+template<> struct formatter<char, wchar_t>;
+
+template<> struct formatter<charT*, charT> : detail::formatter<const charT*, charT> {};
+
+template<> struct formatter<const charT*, charT> : detail::formatter<const charT*, charT> {};
+
+template<size_t N> struct formatter<const charT[N], charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template<class traits, class Allocator>
+  struct formatter<std::basic_string<charT, traits, Allocator>, charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template<class traits>
+  struct formatter<std::basic_string_view<charT, traits>, charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template <> struct formatter<nullptr_t, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<void*, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<const void*, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<bool, charT> : detail::formatter<bool, charT> {};
+
+template <> struct formatter<signed char, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<short, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<int, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<long, charT>
+      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), int, long long>, charT> {};
+template <> struct formatter<long long, charT> : detail::formatter<long long, charT> {};
+template <> struct formatter<unsigned char, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned short, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned int, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned long, charT>
+      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), unsigned, unsigned long long>, charT> {};
+template <> struct formatter<unsigned long long, charT> : detail::formatter<unsigned long long, charT> {};
+
+template <> struct formatter<float, charT> : detail::formatter<double, charT> {};
+template <> struct formatter<double, charT> : detail::formatter<double, charT> {};
+template <> struct formatter<long double, charT> : detail::formatter<long double, charT> {};
+
+#undef charT
+
+#define charT wchar_t
+
+template<> struct formatter<charT, charT> : detail::formatter<charT, charT> {};
+
+template<> struct formatter<char, wchar_t> : detail::formatter<charT, charT> {};
+
+template<> struct formatter<charT*, charT> : detail::formatter<const charT*, charT> {};
+
+template<> struct formatter<const charT*, charT> : detail::formatter<const charT*, charT> {};
+
+template<size_t N> struct formatter<const charT[N], charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template<class traits, class Allocator>
+  struct formatter<std::basic_string<charT, traits, Allocator>, charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template<class traits>
+  struct formatter<std::basic_string_view<charT, traits>, charT>
+      : detail::formatter<std::basic_string_view<charT>, charT> {};
+
+template <> struct formatter<nullptr_t, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<void*, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<const void*, charT> : detail::formatter<const void*, charT> {};
+template <> struct formatter<bool, charT> : detail::formatter<bool, charT> {};
+
+template <> struct formatter<signed char, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<short, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<int, charT> : detail::formatter<int, charT> {};
+template <> struct formatter<long, charT>
+      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), int, long long>, charT> {};
+template <> struct formatter<long long, charT> : detail::formatter<long long, charT> {};
+template <> struct formatter<unsigned char, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned short, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned int, charT> : detail::formatter<unsigned int, charT> {};
+template <> struct formatter<unsigned long, charT>
+      : detail::formatter<std::conditional_t<sizeof(long) == sizeof(int), unsigned, unsigned long long>, charT> {};
+template <> struct formatter<unsigned long long, charT> : detail::formatter<unsigned long long, charT> {};
+
+template <> struct formatter<float, charT> : detail::formatter<double, charT> {};
+template <> struct formatter<double, charT> : detail::formatter<double, charT> {};
+template <> struct formatter<long double, charT> : detail::formatter<long double, charT> {};
+
+#undef charT
+
+  template<> struct formatter<const wchar_t, char> {
+    formatter() = delete;
+  };
+}
+
+#endif  // FMT_FORMAT_

test/format-test.cc

@@ -2142,13 +2142,14 @@ TEST(FormatTest, ConstexprParseFormatSpecs) {
 
 struct test_context {
   typedef char char_type;
+  typedef fmt::basic_format_arg<test_context> format_arg;
 
   FMT_CONSTEXPR fmt::basic_format_arg<test_context> next_arg() {
     return fmt::internal::make_arg<test_context>(11);
   }
 
   template <typename Id>
-  FMT_CONSTEXPR fmt::basic_format_arg<test_context> get_arg(Id) {
+  FMT_CONSTEXPR fmt::basic_format_arg<test_context> arg(Id) {
     return fmt::internal::make_arg<test_context>(22);
   }