[Bug libstdc++/77760] get_time needs to set tm_wday amd tm_yday

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77760

Alexandre Oliva <aoliva at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |aoliva at gcc dot gnu.org

--- Comment #3 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
I'm looking at a case in which __clang__ is defined, despite compiling with
GCC, and "%I...%p" parsing fails because the hack to pass state around doesn't
work when __clang__ is defined.

This got me thinking that there are more than enough bits in struct tm to
encode all of __time_get_state in it, even with redundancy, so that overwritten
fields could get recovered.  I'm thinking that, before calling do_get, get
would transfer its state onto struct tm in such a recoverable way, and, after
calling it, it would restore state from struct tm and remove the extra
out-of-range encodings.  Our do_get, in turn, would extract state from struct
tm, do its current job, and then pack the state back into struct tm.

AFAICT this could be put in in an ABI-compatible way, dropping the hack and
enabling libstdc++-specific do_get specializations to deal with such extended
states, should we document them.

Has anything along these lines already been considered and ruled out?