This adds the missing C++20 features to <chrono>.
I've implemented my proposed resolutions to LWG issues 3960, 3961, and
3962. There are some unimplemented flags such as %OI which I think are
not implementable in general. It might be possible to use na_llanginfo
with ALT_DIGITS, but that isn't available on all targets. I intend to
file another LWG issue about that.
libstdc++-v3/ChangeLog:
PR libstdc++/104167
* include/bits/chrono_io.h (operator|=, operator|): Add noexcept
to _ChronoParts operators.
(from_stream, parse): Define new functions.
(__detail::_Parse, __detail::_Parser): New class templates.
* include/std/chrono (__cpp_lib_chrono): Define to 201907L for
C++20.
* include/std/version (__cpp_lib_chrono): Likewise.
* testsuite/20_util/duration/arithmetic/constexpr_c++17.cc:
Adjust expected value of feature test macro.
* testsuite/20_util/duration/io.cc: Test parsing.
* testsuite/std/time/clock/file/io.cc: Likewise.
* testsuite/std/time/clock/gps/io.cc: Likewise.
* testsuite/std/time/clock/system/io.cc: Likewise.
* testsuite/std/time/clock/tai/io.cc: Likewise.
* testsuite/std/time/clock/utc/io.cc: Likewise.
* testsuite/std/time/day/io.cc: Likewise.
* testsuite/std/time/month/io.cc: Likewise.
* testsuite/std/time/month_day/io.cc: Likewise.
* testsuite/std/time/weekday/io.cc: Likewise.
* testsuite/std/time/year/io.cc: Likewise.
* testsuite/std/time/year_month/io.cc: Likewise.
* testsuite/std/time/year_month_day/io.cc: Likewise.
* testsuite/std/time/syn_c++20.cc: Check value of macro and for
the existence of parse and from_stream in namespace chrono.
* testsuite/std/time/clock/local/io.cc: New test.
* testsuite/std/time/parse.cc: New test.
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