Add xchar support to chrono formatter

include/fmt/chrono.h

@@ -289,16 +289,32 @@ inline null<> localtime_s(...) { return null<>(); }
 inline null<> gmtime_r(...) { return null<>(); }
 inline null<> gmtime_s(...) { return null<>(); }
 
+template <typename Char>
 inline auto do_write(const std::tm& time, const std::locale& loc, char format,
-                     char modifier) -> std::string {
+                     char modifier) -> std::basic_string<Char> {
-  auto&& os = std::ostringstream();
+  auto&& os = std::basic_ostringstream<Char>();
   os.imbue(loc);
-  using iterator = std::ostreambuf_iterator<char>;
+  using iterator = std::ostreambuf_iterator<Char>;
-  const auto& facet = std::use_facet<std::time_put<char, iterator>>(loc);
+  const auto& facet = std::use_facet<std::time_put<Char, iterator>>(loc);
-  auto end = facet.put(os, os, ' ', &time, format, modifier);
+  auto end = facet.put(os, os, Char(' '), &time, format, modifier);
   if (end.failed()) FMT_THROW(format_error("failed to format time"));
-  auto str = os.str();
+  return std::move(os).str();
-  if (!detail::is_utf8() || loc == std::locale::classic()) return str;
+}
+
+template <typename Char, typename OutputIt,
+          FMT_ENABLE_IF(!std::is_same<Char, char>::value)>
+auto write(OutputIt out, const std::tm& time, const std::locale& loc,
+           char format, char modifier = 0) -> OutputIt {
+  auto str = do_write<Char>(time, loc, format, modifier);
+  return std::copy(str.begin(), str.end(), out);
+}
+
+template <typename Char, typename OutputIt,
+          FMT_ENABLE_IF(std::is_same<Char, char>::value)>
+auto write(OutputIt out, const std::tm& time, const std::locale& loc,
+           char format, char modifier = 0) -> OutputIt {
+  auto str = do_write<char>(time, loc, format, modifier);
+  if (detail::is_utf8() && loc != std::locale::classic()) {
     // char16_t and char32_t codecvts are broken in MSVC (linkage errors) and
     // gcc-4.
 #if FMT_MSC_VER != 0 || \
@@ -358,15 +374,10 @@ inline auto do_write(const std::tm& time, const std::locale& loc, char format,
         FMT_THROW(format_error("failed to format time"));
       }
     }
-  return str;
   }
-
-template <typename OutputIt>
-auto write(OutputIt out, const std::tm& time, const std::locale& loc,
-           char format, char modifier = 0) -> OutputIt {
-  auto str = do_write(time, loc, format, modifier);
   return std::copy(str.begin(), str.end(), out);
 }
+
 }  // namespace detail
 
 FMT_MODULE_EXPORT_BEGIN
@@ -1067,7 +1078,7 @@ struct chrono_formatter {
     if (isnan(val)) return write_nan();
     const auto& loc = localized ? context.locale().template get<std::locale>()
                                 : std::locale::classic();
-    out = detail::write(out, time, loc, format, modifier);
+    out = detail::write<char_type>(out, time, loc, format, modifier);
   }
 
   void on_text(const char_type* begin, const char_type* end) {
@@ -1215,12 +1226,13 @@ class year_month_day {};
 #endif
 
 // A rudimentary weekday formatter.
-template <> struct formatter<weekday> {
+template <typename Char> struct formatter<weekday, Char> {
  private:
   bool localized = false;
 
  public:
-  FMT_CONSTEXPR auto parse(format_parse_context& ctx) -> decltype(ctx.begin()) {
+  FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
+      -> decltype(ctx.begin()) {
     auto begin = ctx.begin(), end = ctx.end();
     if (begin != end && *begin == 'L') {
       ++begin;
@@ -1229,12 +1241,13 @@ template <> struct formatter<weekday> {
     return begin;
   }
 
-  auto format(weekday wd, format_context& ctx) -> decltype(ctx.out()) {
+  template <typename FormatContext>
+  auto format(weekday wd, FormatContext& ctx) const -> decltype(ctx.out()) {
     auto time = std::tm();
     time.tm_wday = static_cast<int>(wd.c_encoding());
     const auto& loc = localized ? ctx.locale().template get<std::locale>()
                                 : std::locale::classic();
-    return detail::write(ctx.out(), time, loc, 'a');
+    return detail::write<Char>(ctx.out(), time, loc, 'a');
   }
 };
 

test/xchar-test.cc

@@ -15,9 +15,11 @@
 #include "fmt/color.h"
 #include "fmt/ostream.h"
 #include "fmt/ranges.h"
-#include "gtest/gtest.h"
+#include "gtest-extra.h"  // Contains
+#include "util.h"         // get_locale
 
 using fmt::detail::max_value;
+using testing::Contains;
 
 namespace test_ns {
 template <typename Char> class test_string {
@@ -466,4 +468,20 @@ TEST(locale_test, complex) {
   EXPECT_EQ(fmt::format("{:8}", std::complex<double>(1, 2)), "  (1+2i)");
 }
 
+TEST(locale_test, chrono_weekday) {
+  auto loc = get_locale("ru_RU.UTF-8", "Russian_Russia.1251");
+  auto loc_old = std::locale::global(loc);
+  auto mon = fmt::weekday(1);
+  EXPECT_EQ(fmt::format(L"{}", mon), L"Mon");
+  if (loc != std::locale::classic()) {
+    // {L"\x43F\x43D", L"\x41F\x43D", L"\x43F\x43D\x434", L"\x41F\x43D\x434"}
+    // {L"пн", L"Пн", L"пнд", L"Пнд"}
+    EXPECT_THAT(
+        (std::vector<std::wstring>{L"\x43F\x43D", L"\x41F\x43D",
+                                   L"\x43F\x43D\x434", L"\x41F\x43D\x434"}),
+        Contains(fmt::format(loc, L"{:L}", mon)));
+  }
+  std::locale::global(loc_old);
+}
+
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR