[libc++][TZDB] Adds sys_info formatter. (#85896)

Implements parts of:
- P0355 Extending <chrono> to Calendars and Time Zones
- P1361 Integration of chrono with text formatting

Author: mordante

libcxx/docs/Status/FormatPaper.csv

@@ -24,7 +24,7 @@ Section,Description,Dependencies,Assignee,Status,First released version
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::year_month_weekday``",,Mark de Wever,|Complete|,16.0
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::year_month_weekday_last``",,Mark de Wever,|Complete|,16.0
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::hh_mm_ss<duration<Rep, Period>>``",,Mark de Wever,|Complete|,17.0
-`[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::sys_info``",A ``<chrono>`` implementation,Mark de Wever,,
+`[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::sys_info``",,Mark de Wever,|Complete|,19.0
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::local_info``",A ``<chrono>`` implementation,Mark de Wever,,
 `[time.syn] <https://wg21.link/time.syn>`_,"Formatter ``chrono::zoned_time<Duration, TimeZonePtr>``",A ``<chrono>`` implementation,Mark de Wever,,
 

libcxx/include/__chrono/convert_to_tm.h

@@ -20,6 +20,7 @@
 #include <__chrono/month_weekday.h>
 #include <__chrono/monthday.h>
 #include <__chrono/statically_widen.h>
+#include <__chrono/sys_info.h>
 #include <__chrono/system_clock.h>
 #include <__chrono/time_point.h>
 #include <__chrono/weekday.h>
@@ -171,6 +172,10 @@ _LIBCPP_HIDE_FROM_ABI _Tm __convert_to_tm(const _ChronoT& __value) {
       if (__value.hours().count() > std::numeric_limits<decltype(__result.tm_hour)>::max())
         std::__throw_format_error("Formatting hh_mm_ss, encountered an hour overflow");
     __result.tm_hour = __value.hours().count();
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  } else if constexpr (same_as<_ChronoT, chrono::sys_info>) {
+    // Has no time information.
+#  endif
   } else
     static_assert(sizeof(_ChronoT) == 0, "Add the missing type specialization");
 

libcxx/include/__chrono/formatter.h

@@ -24,6 +24,7 @@
 #include <__chrono/ostream.h>
 #include <__chrono/parser_std_format_spec.h>
 #include <__chrono/statically_widen.h>
+#include <__chrono/sys_info.h>
 #include <__chrono/system_clock.h>
 #include <__chrono/time_point.h>
 #include <__chrono/weekday.h>
@@ -186,10 +187,11 @@ __format_zone_offset(basic_stringstream<_CharT>& __sstr, chrono::seconds __offse
 
   chrono::hh_mm_ss __hms{__offset};
   std::ostreambuf_iterator<_CharT> __out_it{__sstr};
+  // Note HMS does not allow formatting hours > 23, but the offset is not limited to 24H.
+  std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __hms.hours().count());
   if (__modifier)
-    std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:%H:%M}"), __hms);
-  else
-    std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:%H%M}"), __hms);
+    __sstr << _CharT(':');
+  std::format_to(__out_it, _LIBCPP_STATICALLY_WIDEN(_CharT, "{:02}"), __hms.minutes().count());
 }
 
 // Helper to store the time zone information needed for formatting.
@@ -202,7 +204,12 @@ struct _LIBCPP_HIDE_FROM_ABI __time_zone {
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI __time_zone __convert_to_time_zone([[maybe_unused]] const _Tp& __value) {
-  return {"UTC", chrono::seconds{0}};
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  if constexpr (same_as<_Tp, chrono::sys_info>)
+    return {__value.abbrev, __value.offset};
+  else
+#  endif
+    return {"UTC", chrono::seconds{0}};
 }
 
 template <class _CharT, class _Tp>
@@ -409,6 +416,10 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool __weekday_ok(const _Tp& __value) {
     return __value.weekday().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  else if constexpr (same_as<_Tp, chrono::sys_info>)
+    return true;
+#  endif
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
@@ -449,6 +460,10 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool __weekday_name_ok(const _Tp& __value) {
     return __value.weekday().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  else if constexpr (same_as<_Tp, chrono::sys_info>)
+    return true;
+#  endif
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
@@ -489,6 +504,10 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool __date_ok(const _Tp& __value) {
     return __value.ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  else if constexpr (same_as<_Tp, chrono::sys_info>)
+    return true;
+#  endif
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
@@ -529,6 +548,10 @@ _LIBCPP_HIDE_FROM_ABI constexpr bool __month_name_ok(const _Tp& __value) {
     return __value.month().ok();
   else if constexpr (__is_hh_mm_ss<_Tp>)
     return true;
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+  else if constexpr (same_as<_Tp, chrono::sys_info>)
+    return true;
+#  endif
   else
     static_assert(sizeof(_Tp) == 0, "Add the missing type specialization");
 }
@@ -858,6 +881,20 @@ struct formatter<chrono::hh_mm_ss<_Duration>, _CharT> : public __formatter_chron
     return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time);
   }
 };
+
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+template <__fmt_char_type _CharT>
+struct formatter<chrono::sys_info, _CharT> : public __formatter_chrono<_CharT> {
+public:
+  using _Base = __formatter_chrono<_CharT>;
+
+  template <class _ParseContext>
+  _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
+    return _Base::__parse(__ctx, __format_spec::__fields_chrono, __format_spec::__flags::__time_zone);
+  }
+};
+#  endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
 #endif // if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__chrono/ostream.h

@@ -19,6 +19,7 @@
 #include <__chrono/month_weekday.h>
 #include <__chrono/monthday.h>
 #include <__chrono/statically_widen.h>
+#include <__chrono/sys_info.h>
 #include <__chrono/system_clock.h>
 #include <__chrono/weekday.h>
 #include <__chrono/year.h>
@@ -262,6 +263,25 @@ operator<<(basic_ostream<_CharT, _Traits>& __os, const hh_mm_ss<_Duration> __hms
   return __os << std::format(__os.getloc(), _LIBCPP_STATICALLY_WIDEN(_CharT, "{:L%T}"), __hms);
 }
 
+#  if !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
+template <class _CharT, class _Traits>
+_LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
+operator<<(basic_ostream<_CharT, _Traits>& __os, const sys_info& __info) {
+  // __info.abbrev is always std::basic_string<char>.
+  // Since these strings typically are short the conversion should be cheap.
+  std::basic_string<_CharT> __abbrev{__info.abbrev.begin(), __info.abbrev.end()};
+  return __os << std::format(
+             _LIBCPP_STATICALLY_WIDEN(_CharT, "[{:%F %T}, {:%F %T}) {:%T} {:%Q%q} \"{}\""),
+             __info.begin,
+             __info.end,
+             hh_mm_ss{__info.offset},
+             __info.save,
+             __abbrev);
+}
+
+#  endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_TZDB)
+
 } // namespace chrono
 
 #endif // if _LIBCPP_STD_VER >= 20

libcxx/include/__chrono/sys_info.h

@@ -42,7 +42,7 @@ struct sys_info {
 
 } // namespace chrono
 
-#  endif //_LIBCPP_STD_VER >= 20
+#  endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

libcxx/include/chrono

@@ -733,6 +733,10 @@ struct sys_info {
   string        abbrev;
 };
 
+template<class charT, class traits>                                              // C++20
+  basic_ostream<charT, traits>&
+    operator<<(basic_ostream<charT, traits>& os, const sys_info& si);
+
 // 25.10.5, class time_zone                                                      // C++20
 enum class choose {earliest, latest};
 class time_zone {
@@ -829,6 +833,7 @@ namespace std {
   template<class charT> struct formatter<chrono::year_month_weekday_last, charT>; // C++20
   template<class Rep, class Period, class charT>
     struct formatter<chrono::hh_mm_ss<duration<Rep, Period>>, charT>;             // C++20
+  template<class charT> struct formatter<chrono::sys_info, charT>;                // C++20
 } // namespace std
 
 namespace chrono {

libcxx/test/libcxx/time/time.zone/time.zone.info/time.zone.info.sys/ostream.pass.cpp

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// TODO FMT This test should not require std::to_chars(floating-point)
+// XFAIL: availability-fp_to_chars-missing
+
+// XFAIL: libcpp-has-no-incomplete-tzdb
+
+// <chrono>
+
+// template<class charT, class traits>
+//   basic_ostream<charT, traits>&
+//     operator<<(basic_ostream<charT, traits>& os, const sys_info& r);
+
+// [time.zone.info.sys]
+//   7 Effects: Streams out the sys_info object r in an unspecified format.
+//   8 Returns: os.
+//
+// Tests the output produced by this function.
+
+#include <cassert>
+#include <chrono>
+#include <memory>
+#include <sstream>
+
+#include "assert_macros.h"
+#include "test_macros.h"
+#include "make_string.h"
+#include "concat_macros.h"
+
+#define SV(S) MAKE_STRING_VIEW(CharT, S)
+
+template <class CharT>
+static void test(std::basic_string_view<CharT> expected, std::chrono::sys_info&& info) {
+  std::basic_stringstream<CharT> sstr;
+  sstr << info;
+  std::basic_string<CharT> output = sstr.str();
+
+  TEST_REQUIRE(expected == output,
+               TEST_WRITE_CONCATENATED("\nExpected output ", expected, "\nActual output   ", output, '\n'));
+}
+
+template <class CharT>
+static void test() {
+  using namespace std::literals::chrono_literals;
+  namespace tz = std::chrono;
+
+  test(SV("[-10484-10-16 15:30:08, 14423-03-17 15:30:07) 00:00:00 0min \"TZ\""),
+       tz::sys_info{tz::sys_seconds::min(), tz::sys_seconds::max(), 0s, 0min, "TZ"});
+
+  test(SV("[1970-01-01 00:00:00, 2038-12-31 00:00:00) 12:23:45 -67min \"DMY\""),
+       tz::sys_info{static_cast<tz::sys_days>(tz::year_month_day{1970y, tz::January, 1d}),
+                    static_cast<tz::sys_days>(tz::year_month_day{2038y, tz::December, 31d}),
+                    12h + 23min + 45s,
+                    -67min,
+                    "DMY"});
+}
+
+int main(int, const char**) {
+  test<char>();
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+  test<wchar_t>();
+#endif
+
+  return 0;
+}