[libc++][chrono] Implements formatter year.

[Mordante]

Summary

Partially implements:

• P1361 Integration of chrono with text formatting

[Mordante]

Attempts to fix CI.

[Mordante]

Fixes CI.

[Mordante]

Attempts to fix the CI.

[Mordante]

Fixing CI.

[Mordante]

Attempts to fix CI.

[Mordante]

Removes accidentally duplicated line.

[Mordante]

Attempts to fix CI.

[Mordante]

CI.

[Mordante]

Attempts to fix CI, only testing the affected ones.

[Mordante]

Readd removed CI runners.

[Mordante]

Avoids templates in tests.

[Mordante]

Rebased

[Mordante]

Trigger CI.

[Mordante]

Rebased to trigger CI.

[Mordante]

Fixes CI.

[Mordante]

Attempts to fix the CI.

[Mordante]

Fixes CI.

[Mordante]

CI fixes.

[Mordante]

CI fixes

[Mordante]

Attempts to fix CI.

[Mordante]

Polishing.

[ldionne]

LGTM.

libcxx/include/__chrono/formatter.h

62–64

Since this is used in a single place, any reason not to inline it where it's used?

69

Let's perform the tm => int-from-year-0 conversion in the caller of this function instead. Applies above and below too.

72

I don't understand this comment.

81

126–129

libcxx/test/libcxx/transitive_includes/cxx20.csv

118

This should go away once you rebase onto main with the updated transitive includes tests.

libcxx/test/std/time/time.cal/time.cal.year/time.cal.year.nonmembers/ostream.pass.cpp

11

Here and in the other tests.

[Mordante]

Thanks for the review!

libcxx/include/__chrono/formatter.h

62–64

As discussed I prefer to keep code in switch statements short. However since this is a one-liner I moved it.

[Mordante]

Rebased and addresses review comments.

libcxx/docs/Status/FormatPaper.csv

 Section,Description,Dependencies,Assignee,Status,First released version
 `P1361 <https://wg21.link/P1361>`__ `P2372 <https://wg21.link/P2372>`__,"Formatting chrono"
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::duration<Rep, Period>``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::sys_time<Duration>``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::utc_time<Duration>``",A ``<chrono>`` implementation,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::tai_time<Duration>``",A ``<chrono>`` implementation,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::gps_time<Duration>``",A ``<chrono>`` implementation,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::file_time<Duration>``",,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::local_time<Duration>``",,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::local-time-format-t<Duration>``",A ``<chrono>`` implementation,Not assigned,,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::day``",,Mark de Wever,|Complete|, Clang 16
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::month``",,Mark de Wever,|In Progress|,
-`[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::year``",,Mark de Wever,|In Progress|,
+`[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::year``",,Mark de Wever,|Complete|, Clang 16
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::weekday``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::weekday_indexed``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::weekday_last``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::month_day``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::month_day_last``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::month_weekday``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::month_weekday_last``",,Mark de Wever,|In Progress|,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::year_month``",,Mark de Wever,|In Progress|,

libcxx/include/__chrono/convert_to_tm.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___CHRONO_CONVERT_TO_TM_H
 #define _LIBCPP___CHRONO_CONVERT_TO_TM_H
 
 #include <__chrono/day.h>
+#include <__chrono/year.h>
 #include <__concepts/same_as.h>
 #include <__config>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 17
 
 // Convert a chrono calendar time point to the given tm type,
 // which must have the same properties as std::tm.
 template <class _Tm, class _ChronoCalendarTimePoint>
 _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _ChronoCalendarTimePoint& __value) {
   _Tm __result = {};
 #  ifdef __GLIBC__
   __result.tm_zone = "UTC";
 #  endif
 
   if constexpr (same_as<_ChronoCalendarTimePoint, chrono::day>)
     __result.tm_mday = static_cast<unsigned>(__value);
+  else if constexpr (same_as<_ChronoCalendarTimePoint, chrono::year>)
+    __result.tm_year = static_cast<int>(__value) - 1900;
   else
     static_assert(sizeof(_ChronoCalendarTimePoint) == 0, "Add the missing type specialization");
 
   return __result;
 }
 
 #endif //if _LIBCPP_STD_VER > 17
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHRONO_CONVERT_TO_TM_H

libcxx/include/__chrono/formatter.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___CHRONO_FORMATTER_H
 #define _LIBCPP___CHRONO_FORMATTER_H
 
 #include <__chrono/convert_to_tm.h>
 #include <__chrono/day.h>
 #include <__chrono/parser_std_format_spec.h>
+#include <__chrono/statically_widen.h>
+#include <__chrono/year.h>
 #include <__config>
 #include <__format/concepts.h>
+#include <__format/format_functions.h>
 #include <__format/format_parse_context.h>
 #include <__format/formatter.h>
 #include <__format/formatter_output.h>
 #include <__format/parser_std_format_spec.h>
+#include <__memory/addressof.h>
+#include <cmath>
 #include <ctime>
 #include <sstream>
 #include <string>
 #include <string_view>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

 ///
 /// \pre When the (abbreviated) weekday or month name are used, the caller
 ///      validates whether the value is valid. So the caller handles that
 ///      requirement of Table 97: Meaning of conversion specifiers
 ///      [tab:time.format.spec].
 ///
 /// When no chrono-specs are provided it uses the stream formatter.
 
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void __format_year(int __year, basic_stringstream<_CharT>& __sstr) {
+  if (__year < 0) {
+    __sstr << _CharT('-');
+    __year = -__year;
+  }
+
+  // TODO FMT Write an issue
+  //   If the result has less than four digits it is zero-padded with 0 to two digits.
+  // is less -> has less
+  // left-padded -> zero-padded, otherwise the proper value would be 000-0.
+
+  // Note according to the wording it should be left padded, which is odd.
+  __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:04}"), __year);
+}
+
+template <class _CharT>
+_LIBCPP_HIDE_FROM_ABI void __format_century(int __year, basic_stringstream<_CharT>& __sstr) {
+  // TODO FMT Write an issue
+  // [tab:time.format.spec]
+  //   %C The year divided by 100 using floored division. If the result is a
+  //   single decimal digit, it is prefixed with 0.
+
+  bool __negative = __year < 0;
+  int __century   = (__year - (99 * __negative)) / 100; // floored division
+  __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __century);
+}
+
 template <class _CharT, class _Tp>
 _LIBCPP_HIDE_FROM_ABI void __format_chrono_using_chrono_specs(
     const _Tp& __value, basic_stringstream<_CharT>& __sstr, basic_string_view<_CharT> __chrono_specs) {
   tm __t              = std::__convert_to_tm<tm>(__value);
   const auto& __facet = std::use_facet<time_put<_CharT>>(__sstr.getloc());
   for (auto __it = __chrono_specs.begin(); __it != __chrono_specs.end(); ++__it) {
     if (*__it == _CharT('%')) {
       auto __s = __it;
       ++__it;
       // We only handle the types that can't be directly handled by time_put.
       // (as an optimization n, t, and % are also handled directly.)
       switch (*__it) {
       case _CharT('n'):
         __sstr << _CharT('\n');
         break;
       case _CharT('t'):
         __sstr << _CharT('\t');
         break;
       case _CharT('%'):
         __sstr << *__it;
         break;
 
+      case _CharT('C'): {
+        // strftime's output is only defined in the range [00, 99].
+        int __year = __t.tm_year + 1900;
+        if (__year < 1000 || __year > 9999)
+          __formatter::__format_century(__year, __sstr);
+        else
+          __facet.put({__sstr}, __sstr, _CharT(' '), std::addressof(__t), __s, __it + 1);
+      } break;
+
+      // Unlike time_put and strftime the formatting library requires %Y
+      //
+      // [tab:time.format.spec]
+      //   The year as a decimal number. If the result is less than four digits
+      //   it is left-padded with 0 to four digits.
+      //
+      // This means years in the range (-1000, 1000) need manual formatting.
+      // It's unclear whether %EY needs the same treatment. For example the
+      // Japanese EY contains the era name and year. This is zero-padded to 2
+      // digits in time_put (note that older glibc versions didn't do
+      // padding.) However most eras won't reach 100 years, let alone 1000.
+      // So padding to 4 digits seems unwanted for Japanese.
+      //
+      // The same applies to %Ex since that too depends on the era.
+      //
+      // %x the locale's date representation is currently doesn't handle the
+      // zero-padding too.
+      //
+      // The 4 digits can be implemented better at a later time. On POSIX
+      // systems the required information can be extracted by nl_langinfo
+      // https://man7.org/linux/man-pages/man3/nl_langinfo.3.html
+      //
+      // Note since year < -1000 is expected to be rare it uses the more
+      // expensive year routine.
+      //
+      // TODO FMT evaluate the comment above.
+
+#  if defined(__GLIBC__) || defined(_AIX)
+      case _CharT('y'):
+        // Glibc fails for negative values, AIX for positive values too.
+        __sstr << std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), (std::abs(__t.tm_year + 1900)) % 100);
+        break;
+#  endif // defined(__GLIBC__) || defined(_AIX)
+
+      case _CharT('Y'): {
+        int __year = __t.tm_year + 1900;
+        if (__year < 1000)
+          __formatter::__format_year(__year, __sstr);
+        else
+          __facet.put({__sstr}, __sstr, _CharT(' '), std::addressof(__t), __s, __it + 1);
+      } break;
+
       case _CharT('O'):
+      case _CharT('E'):
         ++__it;
         [[fallthrough]];
       default:
         __facet.put({__sstr}, __sstr, _CharT(' '), std::addressof(__t), __s, __it + 1);
         break;
       }
     } else {
       __sstr << *__it;
public:
   using _Base = __formatter_chrono<_CharT>;
 
   _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
       -> decltype(__parse_ctx.begin()) {
     return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__day);
   }
 };
 
-#endif //if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
+template <__fmt_char_type _CharT>
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT formatter<chrono::year, _CharT>
+    : public __formatter_chrono<_CharT> {
+public:
+  using _Base = __formatter_chrono<_CharT>;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto parse(basic_format_parse_context<_CharT>& __parse_ctx)
+      -> decltype(__parse_ctx.begin()) {
+    return _Base::__parse(__parse_ctx, __format_spec::__fields_chrono, __format_spec::__flags::__year);
+  }
+};
+
+#endif // if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif //  _LIBCPP___CHRONO_FORMATTER_H

libcxx/include/__chrono/ostream.h

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___CHRONO_OSTREAM_H
 #define _LIBCPP___CHRONO_OSTREAM_H
 
 #include <__chrono/day.h>
 #include <__chrono/statically_widen.h>
+#include <__chrono/year.h>
 #include <__config>
 #include <__format/format_functions.h>
 #include <ostream>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
return __os
               // Note this error differs from the wording of the Standard. The
               // Standard wording doesn't work well on AIX or Windows. There
               // the formatted day seems to be either modulo 100 or completely
               // omitted. Judging by the wording this is valid.
               // TODO FMT Write a paper of file an LWG issue.
               : std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:02} is not a valid day"), static_cast<unsigned>(__d)));
 }
 
+template <class _CharT, class _Traits>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT basic_ostream<_CharT, _Traits>&
+operator<<(basic_ostream<_CharT, _Traits>& __os, const year& __y) {
+  return __os << (__y.ok() ? std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:%Y}"), __y)
+                           : std::format(_LIBCPP_STATICALLY_WIDEN(_CharT, "{:%Y} is not a valid year"), __y));
+}
+
 } // namespace chrono
 
 #endif //if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_FORMAT)
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___CHRONO_OSTREAM_H

libcxx/include/chrono

 class year;
 constexpr bool operator==(const year& x, const year& y) noexcept;
 constexpr strong_ordering operator<=>(const year& x, const year& y) noexcept;
 
 constexpr year  operator+(const year&  x, const years& y) noexcept;
 constexpr year  operator+(const years& x, const year&  y) noexcept;
 constexpr year  operator-(const year&  x, const years& y) noexcept;
 constexpr years operator-(const year&  x, const year&  y) noexcept;
+template<class charT, class traits>
+  basic_ostream<charT, traits>&
+    operator<<(basic_ostream<charT, traits>& os, const year& y);
 
 // 25.8.6, class weekday    // C++20
 class weekday;
 
 constexpr bool operator==(const weekday& x, const weekday& y) noexcept;
 constexpr bool operator!=(const weekday& x, const weekday& y) noexcept;
 constexpr weekday operator+(const weekday& x, const days&    y) noexcept;
 constexpr weekday operator+(const days&    x, const weekday& y) noexcept;

 bool operator<(const time_zone& x, const time_zone& y) noexcept;
 bool operator>(const time_zone& x, const time_zone& y) noexcept;
 bool operator<=(const time_zone& x, const time_zone& y) noexcept;
 bool operator>=(const time_zone& x, const time_zone& y) noexcept;
 }  // chrono
 
 namespace std {
   template<class charT> struct formatter<chrono::day, charT>;                     // C++20
+  template<class charT> struct formatter<chrono::year, charT>;                    // C++20
 } // namespace std
 
 namespace chrono {
 // calendrical constants
 inline constexpr last_spec                              last{};       // C++20
 inline constexpr chrono::weekday                        Sunday{0};    // C++20
 inline constexpr chrono::weekday                        Monday{1};    // C++20
 inline constexpr chrono::weekday                        Tuesday{2};   // C++20

libcxx/test/libcxx/transitive_includes/cxx20.csv

 charconv cstring
 charconv initializer_list
 charconv iosfwd
 charconv limits
 charconv type_traits
 chrono array
 chrono bit
 chrono charconv
+chrono cmath
 chrono compare
 chrono concepts
 chrono cstddef
 chrono cstdint
 chrono cstdlib
 chrono cstring
 chrono ctime
 chrono limits
 chrono locale
 chrono optional
 chrono ostream
 chrono ratio
 chrono sstream
 chrono stdexcept
 chrono string
 chrono string_view
 chrono type_traits

libcxx/test/libcxx/transitive_includes/cxx2b.csv

 charconv cstdlib
 charconv cstring
 charconv initializer_list
 charconv limits
 charconv type_traits
 chrono array
 chrono bit
 chrono charconv
+chrono cmath
 chrono compare
 chrono concepts
 chrono cstddef
 chrono cstdint
 chrono cstdlib
 chrono cstring
 chrono ctime
 chrono initializer_list

libcxx/test/libcxx/utilities/format/format.formatter/format.formatter.spec/formattable.compile.pass.cpp

#ifndef TEST_HAS_NO_LOCALIZATION
   //assert_is_formattable<std::chrono::utc_time<std::chrono::microseconds>, CharT>();
   //assert_is_formattable<std::chrono::tai_time<std::chrono::microseconds>, CharT>();
   //assert_is_formattable<std::chrono::gps_time<std::chrono::microseconds>, CharT>();
   assert_is_not_formattable<std::chrono::file_time<std::chrono::microseconds>, CharT>();
   assert_is_not_formattable<std::chrono::local_time<std::chrono::microseconds>, CharT>();
 
   assert_is_formattable<std::chrono::day, CharT>();
   assert_is_not_formattable<std::chrono::month, CharT>();
-  assert_is_not_formattable<std::chrono::year, CharT>();
+  assert_is_formattable<std::chrono::year, CharT>();
 
   assert_is_not_formattable<std::chrono::weekday, CharT>();
   assert_is_not_formattable<std::chrono::weekday_indexed, CharT>();
   assert_is_not_formattable<std::chrono::weekday_last, CharT>();
 
   assert_is_not_formattable<std::chrono::month_day, CharT>();
   assert_is_not_formattable<std::chrono::month_day_last, CharT>();
   assert_is_not_formattable<std::chrono::month_weekday, CharT>();

libcxx/test/std/time/time.cal/time.cal.year/time.cal.year.nonmembers/ostream.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: no-localization
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Investigate Windows issues.
+// UNSUPPORTED: msvc, target={{.+}}-windows-gnu
+
+// REQUIRES: locale.fr_FR.UTF-8
+// REQUIRES: locale.ja_JP.UTF-8
+
+// <chrono>
+// class year;
+
+// template<class charT, class traits>
+//   basic_ostream<charT, traits>&
+//     operator<<(basic_ostream<charT, traits>& os, const year& year);
+
+#include <chrono>
+#include <cassert>
+#include <sstream>
+
+#include "make_string.h"
+#include "platform_support.h" // locale name macros
+#include "test_macros.h"
+
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+static std::basic_string<CharT> stream_c_locale(std::chrono::year year) {
+  std::basic_stringstream<CharT> sstr;
+  sstr << year;
+  return sstr.str();
+}
+
+template <class CharT>
+static std::basic_string<CharT> stream_fr_FR_locale(std::chrono::year year) {
+  std::basic_stringstream<CharT> sstr;
+  const std::locale locale(LOCALE_fr_FR_UTF_8);
+  sstr.imbue(locale);
+  sstr << year;
+  return sstr.str();
+}
+
+template <class CharT>
+static std::basic_string<CharT> stream_ja_JP_locale(std::chrono::year year) {
+  std::basic_stringstream<CharT> sstr;
+  const std::locale locale(LOCALE_ja_JP_UTF_8);
+  sstr.imbue(locale);
+  sstr << year;
+  return sstr.str();
+}
+
+template <class CharT>
+static void test() {
+  assert(stream_c_locale<CharT>(std::chrono::year{-32'768}) == SV("-32768 is not a valid year"));
+  assert(stream_c_locale<CharT>(std::chrono::year{-32'767}) == SV("-32767"));
+  assert(stream_c_locale<CharT>(std::chrono::year{0}) == SV("0000"));
+  assert(stream_c_locale<CharT>(std::chrono::year{1970}) == SV("1970"));
+  assert(stream_c_locale<CharT>(std::chrono::year{32'767}) == SV("32767"));
+
+  assert(stream_fr_FR_locale<CharT>(std::chrono::year{-32'768}) == SV("-32768 is not a valid year"));
+  assert(stream_fr_FR_locale<CharT>(std::chrono::year{-32'767}) == SV("-32767"));
+  assert(stream_fr_FR_locale<CharT>(std::chrono::year{0}) == SV("0000"));
+  assert(stream_fr_FR_locale<CharT>(std::chrono::year{1970}) == SV("1970"));
+  assert(stream_fr_FR_locale<CharT>(std::chrono::year{32'767}) == SV("32767"));
+
+  assert(stream_ja_JP_locale<CharT>(std::chrono::year{-32'768}) == SV("-32768 is not a valid year"));
+  assert(stream_ja_JP_locale<CharT>(std::chrono::year{-32'767}) == SV("-32767"));
+  assert(stream_ja_JP_locale<CharT>(std::chrono::year{0}) == SV("0000"));
+  assert(stream_ja_JP_locale<CharT>(std::chrono::year{1970}) == SV("1970"));
+  assert(stream_ja_JP_locale<CharT>(std::chrono::year{32'767}) == SV("32767"));
+}
+
+int main(int, char**) {
+  test<char>();
+
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
+  return 0;
+}

libcxx/test/std/time/time.syn/formatter.year.pass.cpp

+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: no-localization
+// UNSUPPORTED: libcpp-has-no-incomplete-format
+
+// TODO FMT Investigate Windows issues.
+// UNSUPPORTED: msvc, target={{.+}}-windows-gnu
+
+// REQUIRES: locale.fr_FR.UTF-8
+// REQUIRES: locale.ja_JP.UTF-8
+
+// <chrono>
+
+// template<class charT> struct formatter<chrono::year, charT>;
+
+#include <chrono>
+#include <format>
+
+#include <cassert>
+#include <concepts>
+#include <locale>
+#include <iostream>
+#include <type_traits>
+
+#include "formatter_tests.h"
+#include "make_string.h"
+#include "platform_support.h" // locale name macros
+#include "string_literal.h"
+#include "test_macros.h"
+
+template <class CharT>
+static void test_no_chrono_specs() {
+  check(SV("-32767"), SV("{}"), std::chrono::year{-32'767});
+  check(SV("-1000"), SV("{}"), std::chrono::year{-1000});
+  check(SV("-0100"), SV("{}"), std::chrono::year{-100});
+  check(SV("-0010"), SV("{}"), std::chrono::year{-10});
+  check(SV("-0001"), SV("{}"), std::chrono::year{-1});
+  check(SV("0000"), SV("{}"), std::chrono::year{0});
+  check(SV("0001"), SV("{}"), std::chrono::year{1});
+  check(SV("0010"), SV("{}"), std::chrono::year{10});
+  check(SV("0100"), SV("{}"), std::chrono::year{100});
+  check(SV("1000"), SV("{}"), std::chrono::year{1000});
+  check(SV("32727"), SV("{}"), std::chrono::year{32'727});
+
+  // Invalid year
+  check(SV("-32768 is not a valid year"), SV("{}"), std::chrono::year{-32'768});
+  check(SV("-32768 is not a valid year"), SV("{}"), std::chrono::year{32'768});
+}
+
+template <class CharT>
+static void test_valid_values() {
+  constexpr std::basic_string_view<CharT> fmt = SV(
+      "{:"
+      "%%C='%C'%t"
+      "%%EC='%EC'%t"
+      "%%y='%y'%t"
+      "%%Ey='%Ey'%t"
+      "%%Oy='%Oy'%t"
+      "%%Y='%Y'%t"
+      "%%EY='%EY'%t"
+      "%n}");
+  constexpr std::basic_string_view<CharT> lfmt = SV(
+      "{:L"
+      "%%C='%C'%t"
+      "%%EC='%EC'%t"
+      "%%y='%y'%t"
+      "%%Ey='%Ey'%t"
+      "%%Oy='%Oy'%t"
+      "%%Y='%Y'%t"
+      "%%EY='%EY'%t"
+      "%n}");
+
+  const std::locale loc(LOCALE_ja_JP_UTF_8);
+  std::locale::global(std::locale(LOCALE_fr_FR_UTF_8));
+
+  // Non localized output using C-locale
+  check(SV("%C='00'\t"
+#if defined(__APPLE__)
+           "%EC='00'\t"
+#else
+           "%EC='0'\t"
+#endif
+           "%y='00'\t"
+           "%Ey='00'\t"
+           "%Oy='00'\t"
+           "%Y='0000'\t"
+#if defined(__APPLE__)
+           "%EY='0000'\t"
+#elif defined(_AIX)
+           "%EY=''\t"
+#else
+           "%EY='0'\t"
+#endif
+           "\n"),
+        fmt,
+        std::chrono::year{0});
+
+  check(SV("%C='19'\t"
+           "%EC='19'\t"
+           "%y='70'\t"
+           "%Ey='70'\t"
+           "%Oy='70'\t"
+           "%Y='1970'\t"
+           "%EY='1970'\t"
+           "\n"),
+        fmt,
+        std::chrono::year{1970});
+
+  check(SV("%C='20'\t"
+           "%EC='20'\t"
+           "%y='38'\t"
+           "%Ey='38'\t"
+           "%Oy='38'\t"
+           "%Y='2038'\t"
+           "%EY='2038'\t"
+           "\n"),
+        fmt,
+        std::chrono::year{2038});
+
+  // Use the global locale (fr_FR)
+  check(SV("%C='00'\t"
+#if defined(__APPLE__)
+           "%EC='00'\t"
+#else
+           "%EC='0'\t"
+#endif
+           "%y='00'\t"
+           "%Ey='00'\t"
+           "%Oy='00'\t"
+           "%Y='0000'\t"
+#if defined(__APPLE__)
+           "%EY='0000'\t"
+#elif defined(_AIX)
+           "%EY=''\t"
+#else
+           "%EY='0'\t"
+#endif
+           "\n"),
+        lfmt,
+        std::chrono::year{0});
+
+  check(SV("%C='19'\t"
+           "%EC='19'\t"
+           "%y='70'\t"
+           "%Ey='70'\t"
+           "%Oy='70'\t"
+           "%Y='1970'\t"
+           "%EY='1970'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{1970});
+
+  check(SV("%C='20'\t"
+           "%EC='20'\t"
+           "%y='38'\t"
+           "%Ey='38'\t"
+           "%Oy='38'\t"
+           "%Y='2038'\t"
+           "%EY='2038'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{2038});
+
+  // Use supplied locale (ja_JP). This locale has a different alternate.
+#if defined(__APPLE__) || defined(_AIX)
+
+  check(SV("%C='00'\t"
+#  if defined(__APPLE__)
+           "%EC='00'\t"
+#  else
+           "%EC='0'\t"
+#  endif
+           "%y='00'\t"
+           "%Ey='00'\t"
+           "%Oy='00'\t"
+           "%Y='0000'\t"
+#  if defined(_AIX)
+           "%EY=''\t"
+#  else
+           "%EY='0000'\t"
+#  endif
+           "\n"),
+        lfmt,
+        std::chrono::year{0});
+
+  check(SV("%C='19'\t"
+           "%EC='19'\t"
+           "%y='70'\t"
+           "%Ey='70'\t"
+           "%Oy='70'\t"
+           "%Y='1970'\t"
+           "%EY='1970'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{1970});
+
+  check(SV("%C='20'\t"
+           "%EC='20'\t"
+           "%y='38'\t"
+           "%Ey='38'\t"
+           "%Oy='38'\t"
+           "%Y='2038'\t"
+           "%EY='2038'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{2038});
+
+#else // defined(__APPLE__) || defined(_AIX)
+  check(loc,
+        SV("%C='00'\t"
+           "%EC='紀元前'\t"
+           "%y='00'\t"
+// https://sourceware.org/bugzilla/show_bug.cgi?id=23758
+#  if defined(__GLIBC__) && __GLIBC__ <= 2 && __GLIBC_MINOR__ < 29
+           "%Ey='1'\t"
+#  else
+           "%Ey='01'\t"
+#  endif
+           "%Oy='〇'\t"
+           "%Y='0000'\t"
+// https://sourceware.org/bugzilla/show_bug.cgi?id=23758
+#  if defined(__GLIBC__) && __GLIBC__ <= 2 && __GLIBC_MINOR__ < 29
+           "%EY='紀元前1年'\t"
+#  else
+           "%EY='紀元前01年'\t"
+#  endif
+           "\n"),
+        lfmt,
+        std::chrono::year{0});
+
+  check(loc,
+        SV("%C='19'\t"
+           "%EC='昭和'\t"
+           "%y='70'\t"
+           "%Ey='45'\t"
+           "%Oy='七十'\t"
+           "%Y='1970'\t"
+           "%EY='昭和45年'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{1970});
+
+  // Note this test will fail if the Reiwa era ends before 2038.
+  check(loc,
+        SV("%C='20'\t"
+           "%EC='令和'\t"
+           "%y='38'\t"
+           "%Ey='20'\t"
+           "%Oy='三十八'\t"
+           "%Y='2038'\t"
+           "%EY='令和20年'\t"
+           "\n"),
+        lfmt,
+        std::chrono::year{2038});
+#endif // defined(__APPLE__) || defined(_AIX)
+
+  std::locale::global(std::locale::classic());
+}
+
+template <class CharT>
+static void test_padding() {
+  constexpr std::basic_string_view<CharT> fmt = SV("{:%%C='%C'%t%%y='%y'%t%%Y='%Y'%t%n}");
+
+  check(SV("%C='-100'\t%y='99'\t%Y='-9999'\t\n"), fmt, std::chrono::year{-9'999});
+  check(SV("%C='-10'\t%y='99'\t%Y='-0999'\t\n"), fmt, std::chrono::year{-999});
+  check(SV("%C='-1'\t%y='99'\t%Y='-0099'\t\n"), fmt, std::chrono::year{-99});
+  check(SV("%C='-1'\t%y='09'\t%Y='-0009'\t\n"), fmt, std::chrono::year{-9});
+  check(SV("%C='00'\t%y='00'\t%Y='0000'\t\n"), fmt, std::chrono::year{0});
+  check(SV("%C='00'\t%y='09'\t%Y='0009'\t\n"), fmt, std::chrono::year{9});
+  check(SV("%C='00'\t%y='99'\t%Y='0099'\t\n"), fmt, std::chrono::year{99});
+  check(SV("%C='09'\t%y='99'\t%Y='0999'\t\n"), fmt, std::chrono::year{999});
+  check(SV("%C='99'\t%y='99'\t%Y='9999'\t\n"), fmt, std::chrono::year{9'999});
+  check(SV("%C='100'\t%y='00'\t%Y='10000'\t\n"), fmt, std::chrono::year{10'000});
+}
+
+template <class CharT>
+static void test() {
+  test_no_chrono_specs<CharT>();
+  test_valid_values<CharT>();
+  test_padding<CharT>();
+  check_invalid_types<CharT>(
+      {SV("C"), SV("y"), SV("Y"), SV("EC"), SV("Ey"), SV("EY"), SV("Oy")}, std::chrono::year{1970});
+
+  check_exception("Expected '%' or '}' in the chrono format-string", SV("{:A"), std::chrono::year{1970});
+  check_exception("The chrono-specs contains a '{'", SV("{:%%{"), std::chrono::year{1970});
+  check_exception("End of input while parsing the modifier chrono conversion-spec", SV("{:%"), std::chrono::year{1970});
+  check_exception("End of input while parsing the modifier E", SV("{:%E"), std::chrono::year{1970});
+  check_exception("End of input while parsing the modifier O", SV("{:%O"), std::chrono::year{1970});
+
+  // Precision not allowed
+  check_exception("Expected '%' or '}' in the chrono format-string", SV("{:.3}"), std::chrono::year{1970});
+}
+
+int main(int, char**) {
+  test<char>();
+
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
+  return 0;
+}

libcxx/test/std/utilities/format/format.formatter/format.formatter.spec/types.compile.pass.cpp

#ifndef TEST_HAS_NO_LOCALIZATION
   //assert_formatter_is_enabled<std::chrono::utc_time<std::chrono::microseconds>, CharT>();
   //assert_formatter_is_enabled<std::chrono::tai_time<std::chrono::microseconds>, CharT>();
   //assert_formatter_is_enabled<std::chrono::gps_time<std::chrono::microseconds>, CharT>();
   assert_formatter_is_disabled<std::chrono::file_time<std::chrono::microseconds>, CharT>();
   assert_formatter_is_disabled<std::chrono::local_time<std::chrono::microseconds>, CharT>();
 
   assert_formatter_is_enabled<std::chrono::day, CharT>();
   assert_formatter_is_disabled<std::chrono::month, CharT>();
-  assert_formatter_is_disabled<std::chrono::year, CharT>();
+  assert_formatter_is_enabled<std::chrono::year, CharT>();
 
   assert_formatter_is_disabled<std::chrono::weekday, CharT>();
   assert_formatter_is_disabled<std::chrono::weekday_indexed, CharT>();
   assert_formatter_is_disabled<std::chrono::weekday_last, CharT>();
 
   assert_formatter_is_disabled<std::chrono::month_day, CharT>();
   assert_formatter_is_disabled<std::chrono::month_day_last, CharT>();
   assert_formatter_is_disabled<std::chrono::month_weekday, CharT>();

libcxx/utils/ci/run-buildbot

if [ -s ${BUILD_DIR}/generated_output.status ]; then
         false
     fi
 
     # Reject patches that introduce non-ASCII characters or hard tabs.
     # Depends on LC_COLLATE set at the top of this script.
     ! grep -rn '[^ -~]' libcxx/include libcxx/src libcxx/test libcxx/benchmarks \
            --exclude '*.dat' \
            --exclude 'format_tests.h' \
-           --exclude 'formatter.day.pass.cpp' \
+           --exclude 'formatter.*.pass.cpp' \
            --exclude 'grep.pass.cpp' \
            --exclude 'locale-specific_form.pass.cpp' \
            --exclude 'std_format_spec_string_unicode.bench.cpp' \
            || false
 
     # Reject code with trailing whitespace
     ! grep -rn '[[:blank:]]$' libcxx/include libcxx/src libcxx/test libcxx/benchmarks || false
 ;;