On 2024-04-07 08:45:38+0700, Đoàn Trần Công Danh <congdanhqx@xxxxxxxxx> wrote:
> On 2024-04-06 21:33:12-0400, Jeff King <peff@xxxxxxxx> wrote:
> > On Sat, Apr 06, 2024 at 10:29:10AM +0700, Đoàn Trần Công Danh wrote:
> >
> > > CST6CDT and the like are POSIX timezone, with no rule for transition.
> > > And POSIX doesn't enforce how to interpret the rule if it's omited.
> > > Some libc resorted back to IANA (formerly Olson) db rules for those
> > > timezones. Other libc (e.g. musl) interpret that as no transition at
> > > all [1].
> > >
> > > In addition, distributions (notoriously Debian-derived, which uses IANA
> > > db for CST6CDT and the like) started to split "legacy" timezones
> > > like CST6CDT, EST5EDT into `tzdata-legacy', which will not be installed
> > > by default [2].
> > >
> > > In those cases, t9604 will run into failure.
> > >
> > > Let's switch to POSIX timezone with rules to change timezone.
> >
> > This made me wonder if we are losing EST5, etc. We use that in t0006,
> > for example. But I guess not, since I do not have tzdata-legacy
> > installed (I am on Debian unstable) and haven't run into issues (I
> > didn't notice the cvsimport one because I lack other prereqs to run
> > those tests).
>
> Nah, EST5 is a conformance POSIX timezone. It read:
>
> The timezone name is EST, offset is 5hours behinds Universal timezone.
Correction: it reads
The timezone name is EST, offset is 5hours behinds Universal timezone,
all year round.
Since POSIX says that:
if dst is missing, then the alternative time does not apply in
this locale.
>
> You can check by trying today (or on anyday with DST on):
>
> TZ=EST5 date
> TZ=EST5EDT date
> TZ=America/New_York date
>
> - The first one will always interpret 5 hours behinds UTC.
> - The second one is implementation defined behavior, on glibc system,
> it will depends on the existence of /usr/share/zoneinfo/EST5EDT
> - The third one will interpret today time as 4 hours behinds UTC.
>
> glibc normally check if a timezone exist in /usr/share/zoneinfo first,
> if not, it will interpret by POSIX rule.
>
> --
> Danh
--
Danh
