Re: [PATCH] libstdc++: Constrain formatters for chrono types [PR119517]

Fri, 04 Apr 2025 13:58:14 -0700 

On 28/03/25 16:31 +0100, Tomasz Kamiński wrote:

The formatters for chrono types defined the parse/format methods
as accepting unconstrained types, this in combination with lack
of constrain on _CharT lead to them falsy statisfying formattable
requirements for any type used as character.

This patch adjust the fromatter<T, CharT>::parse signature to:
constexpr typename basic_format_parse_context<_CharT>::iterator
parse(basic_format_parse_context<_CharT>& __pc);
And formatter<T, CharT>::format to:
template<typename _Out>
  typename basic_format_context<_Out, _CharT>::iterator
  format(const T& __t,
         basic_format_context<_Out, _CharT>& __fc) const;

Furthermore we _CharT with __format::__char (char or wchar_t),

        PR libstdc++/119517

libstdc++-v3/ChangeLog:

        * include/bits/chrono_io.h (formatter):
        Add __format::__char for _CharT and adjust parse and format
        method signatures.
        * testsuite/std/time/format/pr119517.cc: New test.
---
Testing on x86_64-linux, std/time/format tests passed.
OK for trunk?

libstdc++-v3/include/bits/chrono_io.h         | 448 +++++++++---------
.../testsuite/std/time/format/pr119517.cc     |  44 ++
2 files changed, 262 insertions(+), 230 deletions(-)
create mode 100644 libstdc++-v3/testsuite/std/time/format/pr119517.cc

diff --git a/libstdc++-v3/include/bits/chrono_io.h 
b/libstdc++-v3/include/bits/chrono_io.h
index c55b651d049..3a5bc5695fb 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -1785,277 +1785,272 @@ namespace __format
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::day, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Day); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Day); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::day& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::day& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::month, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Month); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Month); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::month& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::month& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Year); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Year); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::year& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::year& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::weekday, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Weekday); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Weekday); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::weekday& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::weekday& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::weekday_indexed, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Weekday); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Weekday); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::weekday_indexed& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::weekday_indexed& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::weekday_last, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Weekday); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Weekday); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::weekday_last& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::weekday_last& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::month_day, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Month|__format::_Day); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Month|__format::_Day); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::month_day& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::month_day& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::month_day_last, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Month|__format::_Day); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Month|__format::_Day); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::month_day_last& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::month_day_last& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::month_weekday, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Month|__format::_Weekday); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Month|__format::_Weekday); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::month_weekday& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::month_weekday& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::month_weekday_last, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Month|__format::_Weekday); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Month|__format::_Weekday); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
        format(const chrono::month_weekday_last& __t,
-              _FormatContext& __fc) const
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year_month, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Year|__format::_Month); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Year|__format::_Month); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::year_month& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::year_month& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year_month_day, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Date); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Date); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::year_month_day& __t, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::year_month_day& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year_month_day_last, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Date); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Date); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
        format(const chrono::year_month_day_last& __t,
-              _FormatContext& __fc) const
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year_month_weekday, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Date); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Date); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
        format(const chrono::year_month_weekday& __t,
-              _FormatContext& __fc) const
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::year_month_weekday_last, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_Date); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_Date); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
        format(const chrono::year_month_weekday_last& __t,
-              _FormatContext& __fc) const
-       { return _M_f._M_format(__t, __fc); }
+              basic_format_context<_Out, _CharT>& __fc) const
+       { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Rep, typename _Period, typename _CharT>
+  template<typename _Rep, typename _Period, __format::__char _CharT>
    struct formatter<chrono::hh_mm_ss<chrono::duration<_Rep, _Period>>, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_TimeOfDay); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_TimeOfDay); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
        format(const chrono::hh_mm_ss<chrono::duration<_Rep, _Period>>& __t,
-              _FormatContext& __fc) const
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__t, __fc); }

    private:
@@ -2063,34 +2058,34 @@ namespace __format
    };

#if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::sys_info, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ChronoParts{}); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ChronoParts{}); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::sys_info& __i, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::sys_info& __i,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__i, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _CharT>
+  template<__format::__char _CharT>
    struct formatter<chrono::local_info, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ChronoParts{}); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ChronoParts{}); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::local_info& __i, _FormatContext& __fc) const
+      template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::local_info& __i,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return _M_f._M_format(__i, __fc); }

    private:
@@ -2098,25 +2093,24 @@ namespace __format
    };
#endif

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::sys_time<_Duration>, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       {
-         auto __next = _M_f._M_parse(__pc, __format::_ZonedDateTime);
-         if constexpr (!__stream_insertable)
-           if (_M_f._M_spec._M_chrono_specs.empty())
-             __format::__invalid_chrono_spec(); // chrono-specs can't be empty
-         return __next;
-       }
-
-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::sys_time<_Duration>& __t,
-              _FormatContext& __fc) const
-       { return _M_f._M_format(__t, __fc); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      {
+       auto __next = _M_f._M_parse(__pc, __format::_ZonedDateTime);
+       if constexpr (!__stream_insertable)
+         if (_M_f._M_spec._M_chrono_specs.empty())
+           __format::__invalid_chrono_spec(); // chrono-specs can't be empty
+       return __next;
+     }
+
+     template<typename _Out>
+       typename basic_format_context<_Out, _CharT>::iterator
+       format(const chrono::sys_time<_Duration>& __t,
+             basic_format_context<_Out, _CharT>& __fc) const
+       { return _M_f._M_format(__t, __fc); }

    private:
      static constexpr bool __stream_insertable
@@ -2126,19 +2120,18 @@ namespace __format
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::utc_time<_Duration>, _CharT>
    : __format::__formatter_chrono<_CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::utc_time<_Duration>& __t,
-              _FormatContext& __fc) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::utc_time<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        {
          // Adjust by removing leap seconds to get equivalent sys_time.
          // We can't just use clock_cast because we want to know if the time
@@ -2161,19 +2154,18 @@ namespace __format
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::tai_time<_Duration>, _CharT>
    : __format::__formatter_chrono<_CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::tai_time<_Duration>& __t,
-              _FormatContext& __fc) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::tai_time<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        {
          // Convert to __local_time_fmt with abbrev "TAI" and offset 0s.
          // We use __local_time_fmt and not sys_time (as the standard implies)
@@ -2193,19 +2185,18 @@ namespace __format
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::gps_time<_Duration>, _CharT>
    : __format::__formatter_chrono<_CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::gps_time<_Duration>& __t,
-              _FormatContext& __fc) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::gps_time<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        {
          // Convert to __local_time_fmt with abbrev "GPS" and offset 0s.
          // We use __local_time_fmt and not sys_time (as the standard implies)
@@ -2225,72 +2216,69 @@ namespace __format
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::file_time<_Duration>, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::file_time<_Duration>& __t,
-              _FormatContext& __ctx) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::file_time<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        {
          using namespace chrono;
-         return _M_f._M_format(chrono::clock_cast<system_clock>(__t), __ctx);
+         return _M_f._M_format(chrono::clock_cast<system_clock>(__t), __fc);
        }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::local_time<_Duration>, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_DateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      {  return _M_f._M_parse(__pc, __format::_DateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::local_time<_Duration>& __t,
-              _FormatContext& __ctx) const
-       { return _M_f._M_format(__t, __ctx); }
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::local_time<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
+       { return _M_f._M_format(__t, __fc); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::__detail::__local_time_fmt<_Duration>, _CharT>
    {
-      template<typename _ParseContext>
-       constexpr typename _ParseContext::iterator
-       parse(_ParseContext& __pc)
-       { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }
+      constexpr typename basic_format_parse_context<_CharT>::iterator
+      parse(basic_format_parse_context<_CharT>& __pc)
+      { return _M_f._M_parse(__pc, __format::_ZonedDateTime); }

-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::__detail::__local_time_fmt<_Duration>& __t,
-              _FormatContext& __ctx) const
-       { return _M_f._M_format(__t, __ctx, /* use %Z for {} */ true); }
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::__detail::__local_time_fmt<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
+       { return _M_f._M_format(__t, __fc, /* use %Z for {} */ true); }

    private:
      __format::__formatter_chrono<_CharT> _M_f;
    };

#if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
-  template<typename _Duration, typename _TimeZonePtr, typename _CharT>
+  template<typename _Duration, typename _TimeZonePtr, __format::__char _CharT>
    struct formatter<chrono::zoned_time<_Duration, _TimeZonePtr>, _CharT>
    : formatter<chrono::__detail::__local_time_fmt_for<_Duration>, _CharT>
    {
-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::zoned_time<_Duration, _TimeZonePtr>& __tp,
-              _FormatContext& __ctx) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::zoned_time<_Duration, _TimeZonePtr>& __tp,
+              basic_format_context<_Out, _CharT>& __fc) const


For zoned_time the standard does specify the signature of this
function, and it is supposed to look how I implemented it (see
[time.format] p19).  I don't remember, but that's probably what
inspired me to do the same for all the other chrono formatters.

But despite that, I agree that it should be fixed.


        {
          using _Ltf = chrono::__detail::__local_time_fmt_for<_Duration>;
          using _Base = formatter<_Ltf, _CharT>;
@@ -2298,20 +2286,20 @@ namespace __format
          const auto __lf = chrono::local_time_format(__tp.get_local_time(),
                                                      &__info.abbrev,
                                                      &__info.offset);
-         return _Base::format(__lf, __ctx);
+         return _Base::format(__lf, __fc);
        }
    };
#endif

  // Partial specialization needed for %c formatting of __utc_leap_second.
-  template<typename _Duration, typename _CharT>
+  template<typename _Duration, __format::__char _CharT>
    struct formatter<chrono::__detail::__utc_leap_second<_Duration>, _CharT>
    : formatter<chrono::utc_time<_Duration>, _CharT>
    {
-      template<typename _FormatContext>
-       typename _FormatContext::iterator
-       format(const chrono::__detail::__utc_leap_second<_Duration>& __t,
-              _FormatContext& __fc) const
+      template<typename _Out>
+        typename basic_format_context<_Out, _CharT>::iterator
+        format(const chrono::__detail::__utc_leap_second<_Duration>& __t,
+              basic_format_context<_Out, _CharT>& __fc) const
        { return this->_M_f._M_format(__t, __fc); }
    };

diff --git a/libstdc++-v3/testsuite/std/time/format/pr119517.cc 
b/libstdc++-v3/testsuite/std/time/format/pr119517.cc
new file mode 100644
index 00000000000..d1fc466eaab
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/time/format/pr119517.cc
@@ -0,0 +1,44 @@
+// { dg-do compile { target c++23 } }
+
+#include <chrono>
+#include <format>
+#include <testsuite_hooks.h>


You don't need testsuite_hooks.h because this is a compile-only test
that doesn't use the runtime assertion VERIFY.

With that change, the patch is OK for trunk, thanks.

We should probably backport it to gcc-14 after a delay.


+static_assert( std::formattable<std::chrono::weekday, char> );
+static_assert( std::formattable<std::chrono::weekday, wchar_t> );
+static_assert( !std::formattable<std::chrono::weekday, char16_t> );
+
+static_assert( std::formattable<std::chrono::sys_days, char> );
+static_assert( std::formattable<std::chrono::sys_days, wchar_t> );
+static_assert( !std::formattable<std::chrono::sys_days, char16_t> );
+
+static_assert( !std::formattable<std::chrono::seconds, int> );
+
+static_assert( !std::formattable<std::chrono::day, int> );
+static_assert( !std::formattable<std::chrono::month, int> );
+static_assert( !std::formattable<std::chrono::year, int> );
+static_assert( !std::formattable<std::chrono::weekday, int> );
+static_assert( !std::formattable<std::chrono::weekday_indexed, int> );
+static_assert( !std::formattable<std::chrono::weekday_last, int> );
+static_assert( !std::formattable<std::chrono::month_day, int> );
+static_assert( !std::formattable<std::chrono::month_day_last, int> );
+static_assert( !std::formattable<std::chrono::month_weekday, int> );
+static_assert( !std::formattable<std::chrono::month_weekday_last, int> );
+static_assert( !std::formattable<std::chrono::year_month_day, int> );
+static_assert( !std::formattable<std::chrono::year_month_day_last, int> );
+static_assert( !std::formattable<std::chrono::year_month_weekday, int> );
+static_assert( !std::formattable<std::chrono::year_month_weekday_last, int> );
+static_assert( !std::formattable<std::chrono::hh_mm_ss<std::chrono::seconds>, 
int> );
+
+static_assert( !std::formattable<std::chrono::sys_seconds, int> );
+static_assert( !std::formattable<std::chrono::utc_seconds, int> );
+static_assert( !std::formattable<std::chrono::tai_seconds, int> );
+static_assert( !std::formattable<std::chrono::gps_seconds, int> );
+static_assert( !std::formattable<std::chrono::local_seconds, int> );
+static_assert( !std::formattable<std::chrono::file_time<std::chrono::seconds>, 
int> );
+#if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
+static_assert( !std::formattable<std::chrono::zoned_seconds, int> );
+
+static_assert( !std::formattable<std::chrono::sys_info, int> );
+static_assert( !std::formattable<std::chrono::local_info, int> );
+#endif
--
2.48.1

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