On Thu, 12 Jun 2025, 16:24 Tomasz Kamiński, <tkami...@redhat.com> wrote:
> In contrast to other calendar types if empty chrono-spec is used for
> duration
> we are required to format it (and its representation type) via ostream.
> Handling this case was now moved to be part of the format function
> for duration. To facilitate that __formatter_chrono::_M_format_to_ostream
> function was made public.
>
> However, for standard integral types, we know that the result of inserting
> them into ostream is same as for calling format. In consequence we can
> format
> them directly. This is handled by configuring default format spec to "%Q%q"
> for such types.
>
> As we no longer use __formatter_chrono::_M_format with empty chrono-spec,
> this function now requires that _M_chrono_specs are not empty,
> and conditional call to _M_format_to_ostream is removed. This allows
> _M_format_to_ostream to be reduced to accept only duration.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/chrono_io.h (__formatter_chrono::_M_format):
> Remove handling of empty _M_chrono_specs.
> (__formatter_chrono::_M_format_to_ostream): Changed to accept
> only chrono::duration and made public.
> (std::formatter<chrono::duration<_Rep, _Period>, _CharT>):
> Configure __defSpec and handle empty chrono-spec locally.
> ---
> The v2 patch uses "Qq" only for integral types, as there is difference
> between osteam ouput for floating point and integral types. Adjusted
> the description.
>
> Testing on x86_64-linux. OK for trunk?
OK thanks
>
> libstdc++-v3/include/bits/chrono_io.h | 88 ++++++++++++++-------------
> 1 file changed, 45 insertions(+), 43 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/chrono_io.h
> b/libstdc++-v3/include/bits/chrono_io.h
> index 5fa07364f64..40e80589059 100644
> --- a/libstdc++-v3/include/bits/chrono_io.h
> +++ b/libstdc++-v3/include/bits/chrono_io.h
> @@ -606,14 +606,12 @@ namespace __format
> // that we instantiate fewer different specializations. Similar to
> // _Sink_iter for std::format. Replace each _S_year, _S_day etc.
> with
> // member functions of that type.
> + // pre: !_M_spec._M_chrono_specs.empty()
> template<typename _Tp, typename _FormatContext>
> typename _FormatContext::iterator
> _M_format(const _Tp& __t, _FormatContext& __fc,
> bool __is_neg = false) const
> {
> - if (_M_spec._M_chrono_specs.empty())
> - return _M_format_to_ostream(__t, __fc, __is_neg);
> -
> #if defined _GLIBCXX_USE_NL_LANGINFO_L && __CHAR_BIT__ == 8
> // _GLIBCXX_RESOLVE_LIB_DEFECTS
> // 3565. Handling of encodings in localized formatting
> @@ -812,6 +810,24 @@ namespace __format
> return std::move(__out);
> }
>
> + // Format duration for empty chrono-specs, e.g. "{}" (C++20
> [time.format] p6).
> + template<typename _Rep, typename _Period, typename _FormatContext>
> + typename _FormatContext::iterator
> + _M_format_to_ostream(const chrono::duration<_Rep, _Period>& __d,
> + bool __is_neg, _FormatContext& __fc) const
> + {
> + basic_ostringstream<_CharT> __os;
> + __os.imbue(_M_locale(__fc));
> +
> + if (__is_neg) [[unlikely]]
> + __os << _S_plus_minus[1];
> + __os << __d;
> +
> + auto __str = std::move(__os).str();
> + return __format::__write_padded_as_spec(__str, __str.size(),
> + __fc, _M_spec);
> + }
> +
> _ChronoSpec<_CharT> _M_spec;
>
> private:
> @@ -826,41 +842,6 @@ namespace __format
> return __fc.locale();
> }
>
> - // Format for empty chrono-specs, e.g. "{}" (C++20 [time.format]
> p6).
> - // TODO: consider moving body of every operator<< into this function
> - // and use std::format("{}", t) to implement those operators. That
> - // would avoid std::format("{}", t) calling operator<< which calls
> - // std::format again.
> - template<typename _Tp, typename _FormatContext>
> - typename _FormatContext::iterator
> - _M_format_to_ostream(const _Tp& __t, _FormatContext& __fc,
> - bool __is_neg) const
> - {
> - using ::std::chrono::__detail::__utc_leap_second;
> - using ::std::chrono::__detail::__local_time_fmt;
> -
> - basic_ostringstream<_CharT> __os;
> - __os.imbue(_M_locale(__fc));
> -
> - if constexpr (__is_specialization_of<_Tp, __local_time_fmt>)
> - __builtin_trap();
> - else if constexpr (__is_specialization_of<_Tp,
> __utc_leap_second>)
> - __builtin_trap();
> - else if constexpr (chrono::__is_time_point_v<_Tp>)
> - __builtin_trap();
> - else
> - {
> - if constexpr (chrono::__is_duration_v<_Tp>)
> - if (__is_neg) [[unlikely]]
> - __os << _S_plus_minus[1];
> - __os << __t;
> - }
> -
> - auto __str = std::move(__os).str();
> - return __format::__write_padded_as_spec(__str, __str.size(),
> - __fc, _M_spec);
> - }
> -
> static constexpr const _CharT* _S_chars
> = _GLIBCXX_WIDEN("0123456789:/ +-{}");
> static constexpr _CharT _S_colon = _S_chars[10];
> @@ -2027,7 +2008,7 @@ namespace __format
> parse(basic_format_parse_context<_CharT>& __pc)
> {
> using namespace __format;
> - auto __it = _M_f._M_parse(__pc, _Duration|_TimeOfDay);
> + auto __it = _M_f._M_parse(__pc, _Duration|_TimeOfDay, __defSpec);
> if constexpr (!is_floating_point_v<_Rep>)
> if (_M_f._M_spec._M_prec_kind != __format::_WP_none)
> __throw_format_error("format error: invalid precision for
> duration");
> @@ -2049,16 +2030,37 @@ namespace __format
> using _URep = make_unsigned_t<_Rep>;
> auto __ucnt = -static_cast<_URep>(__d.count());
> auto __ud = chrono::duration<_URep, _Period>(__ucnt);
> - return _M_f._M_format(__ud, __fc, true);
> + return _M_format(__ud, true, __fc);
> }
> else
> - return _M_f._M_format(-__d, __fc, true);
> + return _M_format(-__d, true, __fc);
> }
> - return _M_f._M_format(__d, __fc, false);
> + return _M_format(__d, false, __fc);
> }
>
> private:
> - __format::__formatter_chrono<_CharT> _M_f;
> + static constexpr __format::_ChronoSpec<_CharT> __defSpec = []
> + {
> + __format::_ChronoSpec<_CharT> __res{};
> + __res._M_localized = !is_integral_v<_Rep>;
> + if constexpr (is_integral_v<_Rep>)
> + __res._M_chrono_specs = _GLIBCXX_WIDEN("%Q%q");
> + return __res;
> + }();
> +
> + template<typename _Rep2, typename _Out>
> + typename basic_format_context<_Out, _CharT>::iterator
> + _M_format(const chrono::duration<_Rep2, _Period>& __d,
> + bool __is_neg,
> + basic_format_context<_Out, _CharT>& __fc) const
> + {
> + if constexpr (!is_integral_v<_Rep>)
> + if (_M_f._M_spec._M_chrono_specs.empty())
> + return _M_f._M_format_to_ostream(__d, __is_neg, __fc);
> + return _M_f._M_format(__d, __fc, __is_neg);
> + }
> +
> + __format::__formatter_chrono<_CharT> _M_f{__defSpec};
> };
>
> template<__format::__char _CharT>
> --
> 2.49.0
>
>
