libstdc++: Type-erase chrono-data for formatting [PR110739]

libstdc++: Type-erase chrono-data for formatting [PR110739]

This patch reworks the formatting for the chrono types, such that they are all
formatted in terms of _ChronoData class, that includes all required fields.
Populating each required field is performed in formatter for specific type,
based on the chrono-spec used.

To facilitate above, the _ChronoSpec now includes additional _M_needed field,
that represnts the chrono data that is referenced by format spec (this value
is also configured for __defSpec). This value differs from the value of
__parts passed to _M_parse, which does include all fields that can be computed
from input (e.g. weekday_indexed can be computed for year_month_day). Later
it is used to fill _ChronoData, in particular _M_fill_* family of functions,
to determine if given field needs to be set, and thus its value needs to be
computed.

In consequence _ChronoParts enum was extended with additional values, that
allows more fine grained identification:
 * _TimeOfDay is separated into _HoursMinutesSeconds and _Subseconds,
 * _TimeZone is separated into _ZoneAbbrev and _ZoneOffset,
 * _LocalDays, _WeekdayIndex are defined and in included in _Date,
 * _Duration is removed, and instead _EpochUnits and _UnitSuffix are
   introduced.
Furthermore, to avoid name conflicts _ChonoParts is now defined as enum class,
with additional operators that simplify uses.

In addition to fields that can be printed using chrono-spec, _ChronoData stores:
 * Total days in wall time (_M_ldays), day of year (_M_day_of_year) - used by
   struct tm construction, and for ISO calendar computation.
 * Total seconds in wall time (_M_lseconds) - this value may be different from
   sum of days, hours, minutes, seconds (e.g. see utc_time below). Included
   to allow future extension, like printing total minutes.
 * Total seconds since epoch - due offset different from above. Again to be
   used with future extension (e.g. %s as proposed in P2945R1).
 * Subseconds - count of attoseconds (10^(-18)), in addition to printing can
   be used to  compute fractional hours, minutes.
The both total seconds fields use single _TotalSeconds enumerator in
_ChronoParts, that when present in combination with _EpochUnits or _LocalDays
indicates that _M_eseconds (_EpochSeconds) or _M_lseconds (_LocalSeconds) are
provided/required.

To handle type formatting of time since epoch ('%Q'|_EpochUnits), we use the
format_args mechanism, where the result of +d.count() (see LWG4118) is erased
into make_format_args to local __arg_store, that is later referenced by
_M_ereps (_M_ereps.get(0)).

To handle precision values, and in prepartion to allow user to configure ones,
we store the precision as third element of _M_ereps (_M_ereps.get(2)), this
allows duration with precision to be printed using "{0:{2}}". For subseconds
the precision is handled differently depending on the representation:
 * for integral reps, _M_subseconds value is used to determine fractional value,
   precision is trimmed to 18 digits;
 * for floating-points, _M_ereps stores duration<Rep> initialized with only
   fractional seconds, that is later formatted with precision.
Always using _M_subseconds fields for integral duration, means that we do not
use formattter for user-defined durations that are considered to be integral
(see empty_spec.cc file change). To avoid potentially expensive computation
of _M_subseconds, we make sure that _ChronoParts::_Subseconds is set only if
_Subseconds are needed. In particular we remove this flag for localized ouput
in _M_parse.

Construction of the _M_ereps as described above is handled by __formatter_duration,
that is then used to format duration, hh_mm_ss and time_points specializations.
This class also handles _UnitSuffix, the _M_units_suffix field is populated
either with predefined suffix (chrono::__detail::__units_suffix) or one produced
locally.

Finally, formatters for types listed below contains type specific logic:
 * hh_mm_ss - we do not compute total duration and seconds, unless explicitly
   requested, as such computation may overflow;
 * utc_time - for time during leap second insertion, the _M_seconds field is
   increased to 60;
 * __local_time_fmt - exception is thrown if zone offset (_ZoneOffset) or
   abbrevation (_ZoneAbbrev) is requsted, but corresponding pointer is null,
   futhermore conversion from `char` to `wchar_t` for abbreviation is performed
   if needed.

	PR libstdc++/110739

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__format::__no_timezone_available):
	Removed, replaced with separate throws in formatter for
	__local_time_fmt
	(__format::_ChronoParts): Defined additional enumertors and
	declared as enum class.
	(__format::operator&(_ChronoParts, _ChronoParts))
	(__format::operator&=(_ChronoParts&, _ChronoParts))
	(__format::operator-(_ChronoParts, _ChronoParts))
	(__format::operator-=(_ChronoParts&, _ChronoParts))
	(__format::operator==(_ChronoParts, decltype(nullptr)))
	(_ChronoSpec::_M_time_only, _ChronoSpec::_M_floating_point_rep)
	(_ChronoSpec::_M_custom_rep, _ChronoSpec::_M_needed)
	(_ChronoSpec::_M_needs, __format::_ChronoData): Define.
	(__format::__formatter_chrono): Redefine to accept _ChronoData.
	(__formatter_chrono::_M_format_to_ostream): Moved to
	__formatter_duration.
	(__format::__formatter_duration): Define.
	(__formatter_chrono_info::format): Pass value-constructed
	_ChronoData.
	(std::formatter<chrono::day, _CharT>)
	(std::formatter<chrono::month, _CharT>)
	(std::formatter<chrono::year, _CharT>)
	(std::formatter<chrono::weekday, _CharT>)
	(std::formatter<chrono::weekday_indexed, _CharT>)
	(std::formatter<chrono::weekday_last, _CharT>)
	(std::formatter<chrono::month_day, _CharT>)
	(std::formatter<chrono::month_day_last, _CharT>)
	(std::formatter<chrono::month_weekday, _CharT>)
	(std::formatter<chrono::month_weekday_indexed, _CharT>)
	(std::formatter<chrono::month_weekday_last, _CharT>)
	(std::formatter<chrono::year_month, _CharT>)
	(std::formatter<chrono::year_month_day, _CharT>)
	(std::formatter<chrono::year_month_day_last, _CharT>)
	(std::formatter<chrono::year_month_weekday, _CharT>)
	(std::formatter<chrono::year_month_weekday_indexed, _CharT>)
	(std::formatter<chrono::year_month_weekday_last, _CharT>):
	Construct _ChronoData in format, and configure _M_needed in
	_ChronoSpec.
	(std::formatter<chrono::duration<_Rep, _Period>, _CharT>)
	(std::formatter<chrono::hh_mm_ss<_Duration>, _CharT>)
	(std::formatter<chrono::sys_time<_Duration>, _CharT>)
	(std::formatter<chrono::utc_time<_Duration>, _CharT>)
	(std::formatter<chrono::tai_time<_Duration>, _CharT>)
	(std::formatter<chrono::gps_time<_Duration>, _CharT>)
	(std::formatter<chrono::file_time<_Duration>, _CharT>)
	(std::formatter<chrono::local_time<_Duration>, _CharT>)
	(std::formatter<chrono::_detail::__local_time_fmt<_Duration>, _CharT>):
	Reworked in terms of __formatter_duration and _ChronoData.
	(std::formatter<chrono::_detail::__utc_leap_second<_Duration>, _CharT>):
	Removed.
	(_Parser<_Duration>::operator()): Adjusted for _ChronoParts
	being enum class.
	* include/std/chrono (__detail::__utc_leap_second): Removed,
	replaced with simply bumping _M_seconds in _ChronoData.
	* testsuite/std/time/format/empty_spec.cc: Updated %S integral
	ouput.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>