[Bug libstdc++/110719] Should chrono formatters always use std::time_put for locale's representation?

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110719

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:f4bce119f617dc4663fb43f55784908daf16b4b6

commit r14-2640-gf4bce119f617dc4663fb43f55784908daf16b4b6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jul 18 12:46:07 2023 +0100

    libstdc++: Implement correct locale-specific chrono formatting [PR110719]

    This fixes some TODOs in the C++20 <chrono> format support, where the
    locale-specific output was incorrect or unimplemented. The approach
    taken here is to either use the formatting locale's std::time_put facet
    to do the formatting, or to remove subsecond precision from time points
    so that locale-specific formats don't print fractional seconds. This
    ensures that we are consistent with what the std::time_put facet would
    print (which never includes fractional seconds) even if we actually
    reimplement the formatting by hand instead of using the facet.

    This also fixes a misplaced statement that allowed modifiers for %Z
    which should have been on %z instead. There was also some ill-formed
    code in an untested branch for formatting time zone names to wide
    characters. A new test for zoned_time I/O has been added to exercise
    that code properly.

    libstdc++-v3/ChangeLog:

            PR libstdc++/110719
            * include/bits/chrono_io.h (__formatter_chrono::_M_parse): Fix
            allowed modifiers for %z and %Z. Fix -Wparentheses and
            -Wnarrowing warnings.
            (__formatter_chrono::_M_format): Call new functions for %d, %e,
            %H, %I, %m and %M.
            (__formatter_chrono::_M_c): Use _S_floor_seconds to remove
            subsecond precision.
            (__formatter_chrono::_M_C_y_Y): Use _M_locale_fmt to handle
            modifiers.
            (__formatter_chrono::_M_e): Replace with _M_d_e and use
            _M_locale_fmt.
            (__formatter_chrono::_M_I): Replace with _M_H_I and use
            _M_locale_fmt.
            (__formatter_chrono::_M_m): New function.
            (__formatter_chrono::_M_M): New function.
            (__formatter_chrono::_M_r): Use _M_locale_fmt.
            (__formatter_chrono::_M_S): Likewise.
            (__formatter_chrono::_M_u_w): Likewise.
            (__formatter_chrono::_M_U_V_W): Likewise.
            (__formatter_chrono::_M_X): Use _S_floor_seconds.
            (__formatter_chrono::_M_Z): Fix untested branch for wchar_t.
            (__formatter_chrono::_S_altnum): Remove function.
            (__formatter_chrono::_S_dd_zero_fill): Remove function.
            (__formatter_chrono::_S_floor_seconds): New function.
            (__formatter_chrono::_M_locale_fmt): New function.
            * testsuite/std/time/clock/system/io.cc: Adjust expected output
            for locale-specific formats and check modified formats.
            * testsuite/std/time/clock/utc/io.cc: Likewise.
            * testsuite/std/time/zoned_time/io.cc: New test.