Improve locale support

include/fmt/format-inl.h

@@ -17,6 +17,7 @@
 #include <cstring>  // std::memmove
 #include <cwchar>
 #include <exception>
+#include <sstream>
 
 #ifndef FMT_STATIC_THOUSANDS_SEPARATOR
 #  include <locale>
@@ -27,8 +28,11 @@
 #endif
 
 #include "format.h"
+#include "locale.h"
 
 FMT_BEGIN_NAMESPACE
+template <typename Char> std::locale::id num_format_facet<Char>::id;
+
 namespace detail {
 
 FMT_FUNC void assert_fail(const char* file, int line, const char* message) {
@@ -115,6 +119,28 @@ template <typename Char> FMT_FUNC Char decimal_point_impl(locale_ref) {
   return '.';
 }
 #endif
+
+template <typename Char>
+FMT_FUNC auto write_int(unsigned long long value, locale_ref loc)
+    -> std::basic_string<Char> {
+#ifndef FMT_STATIC_THOUSANDS_SEPARATOR
+  auto&& ios = std::basic_ios<Char>(nullptr);
+  auto locale = loc.get<std::locale>();
+  ios.imbue(locale);
+  auto&& buf = std::basic_stringbuf<Char>();
+  auto out = std::ostreambuf_iterator<Char>(&buf);
+  // We cannot use the num_put<char> facet because it may produce output in
+  // a wrong encoding.
+  using facet_t = conditional_t<std::is_same<Char, char>::value,
+                                num_format_facet<>, std::num_put<Char>>;
+  if (std::has_facet<facet_t>(locale)) {
+    std::use_facet<facet_t>(locale).put(out, ios, ' ', value);
+    return buf.str();
+  }
+#endif
+  return {};
+}
+
 }  // namespace detail
 
 #if !FMT_MSC_VERSION

include/fmt/format.h

@@ -1992,10 +1992,11 @@ template <typename Char> class digit_grouping {
   }
 };
 
+// Writes a decimal integer with digit grouping.
 template <typename OutputIt, typename UInt, typename Char>
-auto write_int_localized(OutputIt out, UInt value, unsigned prefix,
+auto write_int(OutputIt out, UInt value, unsigned prefix,
-                         const basic_format_specs<Char>& specs,
+               const basic_format_specs<Char>& specs,
-                         const digit_grouping<Char>& grouping) -> OutputIt {
+               const digit_grouping<Char>& grouping) -> OutputIt {
   static_assert(std::is_same<uint64_or_128_t<UInt>, UInt>::value, "");
   int num_digits = count_digits(value);
   char digits[40];
@@ -2012,12 +2013,32 @@ auto write_int_localized(OutputIt out, UInt value, unsigned prefix,
       });
 }
 
+template <typename Char>
+FMT_API auto write_int(unsigned long long value, locale_ref loc)
+    -> std::basic_string<Char>;
+
 template <typename OutputIt, typename UInt, typename Char>
-auto write_int_localized(OutputIt& out, UInt value, unsigned prefix,
+auto write_int(OutputIt& out, UInt value, unsigned prefix,
-                         const basic_format_specs<Char>& specs, locale_ref loc)
+               const basic_format_specs<Char>& specs, locale_ref loc) -> bool {
-    -> bool {
+  using char_t =
-  auto grouping = digit_grouping<Char>(loc);
+      conditional_t<std::is_same<Char, wchar_t>::value, wchar_t, char>;
-  out = write_int_localized(out, value, prefix, specs, grouping);
+  auto str = std::basic_string<char_t>();
+  if (sizeof(value) <= sizeof(unsigned long long))
+    str = write_int<char_t>(static_cast<unsigned long long>(value), loc);
+  if (str.empty()) {
+    auto grouping = digit_grouping<Char>(loc);
+    out = write_int(out, value, prefix, specs, grouping);
+    return true;
+  }
+  size_t size = to_unsigned((prefix != 0 ? 1 : 0) + str.size());
+  out = write_padded<align::right>(
+      out, specs, size, size, [&](reserve_iterator<OutputIt> it) {
+        if (prefix != 0) {
+          char sign = static_cast<char>(prefix);
+          *it++ = static_cast<Char>(sign);
+        }
+        return copy_str<Char>(str.data(), str.data() + str.size(), it);
+      });
   return true;
 }
 
@@ -2058,10 +2079,9 @@ FMT_CONSTEXPR FMT_INLINE auto write_int(OutputIt out, write_int_arg<T> arg,
   case presentation_type::none:
   case presentation_type::dec: {
     if (specs.localized &&
-        write_int_localized(out, static_cast<uint64_or_128_t<T>>(abs_value),
+        write_int(out, static_cast<uint64_or_128_t<T>>(abs_value), prefix,
-                            prefix, specs, loc)) {
+                  specs, loc))
       return out;
-    }
     auto num_digits = count_digits(abs_value);
     return write_int(
         out, num_digits, prefix, specs, [=](reserve_iterator<OutputIt> it) {
@@ -3914,7 +3934,7 @@ template <typename T> struct formatter<group_digits_view<T>> : formatter<T> {
                                                        specs_.width_ref, ctx);
     detail::handle_dynamic_spec<detail::precision_checker>(
         specs_.precision, specs_.precision_ref, ctx);
-    return detail::write_int_localized(
+    return detail::write_int(
         ctx.out(), static_cast<detail::uint64_or_128_t<T>>(t.value), 0, specs_,
         detail::digit_grouping<char>({"\3", ','}));
   }

include/fmt/locale.h

@@ -0,0 +1,26 @@
+// Formatting library for C++ - optional locale support
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#ifndef FMT_LOCALE_H_
+#define FMT_LOCALE_H_
+
+#include <locale>  // std::num_put
+
+#include "core.h"
+
+FMT_BEGIN_NAMESPACE
+
+// A locale facet that formats numeric values in UTF-8.
+template <typename Char = char>
+class num_format_facet : public std::num_put<Char> {
+ public:
+  static FMT_API std::locale::id id;
+};
+
+FMT_END_NAMESPACE
+
+#endif  // FMT_LOCALE_H_

src/format.cc

@@ -22,6 +22,9 @@ template FMT_API auto locale_ref::get<std::locale>() const -> std::locale;
 
 // Explicit instantiations for char.
 
+template FMT_API auto write_int(unsigned long long, locale_ref)
+    -> std::basic_string<char>;
+
 template FMT_API auto thousands_sep_impl(locale_ref)
     -> thousands_sep_result<char>;
 template FMT_API auto decimal_point_impl(locale_ref) -> char;
@@ -37,6 +40,9 @@ template FMT_API void vformat_to(buffer<char>&, string_view,
 
 // Explicit instantiations for wchar_t.
 
+template FMT_API auto write_int(unsigned long long, locale_ref)
+    -> std::basic_string<wchar_t>;
+
 template FMT_API auto thousands_sep_impl(locale_ref)
     -> thousands_sep_result<wchar_t>;
 template FMT_API auto decimal_point_impl(locale_ref) -> wchar_t;

test/xchar-test.cc

@@ -7,12 +7,14 @@
 
 #include "fmt/xchar.h"
 
+#include <algorithm>
 #include <complex>
 #include <cwchar>
 #include <vector>
 
 #include "fmt/chrono.h"
 #include "fmt/color.h"
+#include "fmt/locale.h"
 #include "fmt/ostream.h"
 #include "fmt/ranges.h"
 #include "gtest-extra.h"  // Contains
@@ -344,6 +346,7 @@ TEST(xchar_test, escape_string) {
 TEST(xchar_test, to_wstring) { EXPECT_EQ(L"42", fmt::to_wstring(42)); }
 
 #ifndef FMT_STATIC_THOUSANDS_SEPARATOR
+
 template <typename Char> struct numpunct : std::numpunct<Char> {
  protected:
   Char do_decimal_point() const override { return '?'; }
@@ -441,7 +444,7 @@ TEST(locale_test, wformat) {
             fmt::format(small_grouping_loc, L"{:L}", max_value<uint32_t>()));
 }
 
-TEST(locale_test, double_formatter) {
+TEST(locale_test, int_formatter) {
   auto loc = std::locale(std::locale(), new special_grouping<char>());
   auto f = fmt::formatter<int>();
   auto parse_ctx = fmt::format_parse_context("L");
@@ -518,4 +521,22 @@ TEST(locale_test, sign) {
   EXPECT_EQ(fmt::format(std::locale(), L"{:L}", -50), L"-50");
 }
 
+class num_format : public fmt::num_format_facet<> {
+ protected:
+  using fmt::num_format_facet<>::do_put;
+  iter_type do_put(iter_type out, std::ios_base&, char,
+                   unsigned long long) const override;
+};
+
+num_format::iter_type num_format::do_put(iter_type out, std::ios_base&, char,
+                                         unsigned long long) const {
+  const char s[] = "foo";
+  return std::copy_n(s, sizeof(s) - 1, out);
+}
+
+TEST(locale_test, num_format) {
+  auto loc = std::locale(std::locale(), new num_format());
+  EXPECT_EQ(fmt::format(loc, "{:L}", 42), "foo");
+}
+
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR