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Make pg_interpret_timezone_abbrev() check sp->defaulttype too.

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This omission caused it to not recognize the furthest-back zone
abbreviation when working with timezone data compiled with relatively
recent zic (2018f or newer).  Older versions of zic produced a dummy
DST transition at the Big Bang, so that the oldest abbreviation could
always be found in the sp->types[] array; but newer versions don't do
that, so that we must examine defaulttype as well as the types[] array
to be sure of seeing all the abbreviations.

While this has been broken for six or so years, we'd managed not
to notice for two reasons: (1) many platforms are still using
ancient zic for compatibility reasons, so that the issue did not
manifest in builds using --with-system-tzdata; (2) the oldest
zone abbreviation is almost always "LMT", which we weren't
supporting anyway (but an upcoming patch will accept that).

While at it, update pg_next_dst_boundary() to use sp->defaulttype
as the time type for non-DST zones and times before the oldest
DST transition.  The existing code there predates upstream's
invention of the sp->defaulttype field, and its heuristic for
finding the oldest time type has now been subsumed into the
code that sets sp->defaulttype.

Possibly this should be back-patched, but I'm not currently aware
of any visible consequences of this bug in released branches.

Per report from Aleksander Alekseev and additional investigation.

Discussion: https://postgr.es/m/CAJ7c6TOATjJqvhnYsui0=CO5XFMF4dvTGH+skzB--jNhqSQu5g@mail.gmail.com
This commit is contained in:
Tom Lane
2025-01-16 12:43:03 -05:00
parent 901bd4a65a
commit bc10219b9c
1 changed files with 20 additions and 20 deletions
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40
src/timezone/localtime.c
View File

@ -1624,15 +1624,8 @@ pg_next_dst_boundary(const pg_time_t *timep,
sp = &tz->state;
if (sp->timecnt == 0)
{
/* non-DST zone, use lowest-numbered standard type */
i = 0;
while (sp->ttis[i].tt_isdst)
if (++i >= sp->typecnt)
{
i = 0;
break;
}
ttisp = &sp->ttis[i];
/* non-DST zone, use the defaulttype */
ttisp = &sp->ttis[sp->defaulttype];
*before_gmtoff = ttisp->tt_utoff;
*before_isdst = ttisp->tt_isdst;
return 0;
@ -1692,15 +1685,8 @@ pg_next_dst_boundary(const pg_time_t *timep,
}
if (t < sp->ats[0])
{
/* For "before", use lowest-numbered standard type */
i = 0;
while (sp->ttis[i].tt_isdst)
if (++i >= sp->typecnt)
{
i = 0;
break;
}
ttisp = &sp->ttis[i];
/* For "before", use the defaulttype */
ttisp = &sp->ttis[sp->defaulttype];
*before_gmtoff = ttisp->tt_utoff;
*before_isdst = ttisp->tt_isdst;
*boundary = sp->ats[0];
@ -1793,7 +1779,9 @@ pg_interpret_timezone_abbrev(const char *abbrev,
* abbreviation should get us what we want, since extrapolation would just
* be repeating the newest or oldest meanings.
*
* Use binary search to locate the first transition > cutoff time.
* Use binary search to locate the first transition > cutoff time. (Note
* that sp->timecnt could be zero, in which case this loop does nothing
* and only the defaulttype entry will be checked.)
*/
{
int lo = 0;
@ -1827,7 +1815,19 @@ pg_interpret_timezone_abbrev(const char *abbrev,
}
/*
* Not there, so scan forwards to find the first one after.
* Not found yet; check the defaulttype, which is notionally the era
* before any of the entries in sp->types[].
*/
ttisp = &sp->ttis[sp->defaulttype];
if (ttisp->tt_desigidx == abbrind)
{
*gmtoff = ttisp->tt_utoff;
*isdst = ttisp->tt_isdst;
return true;
}
/*
* Not there, so scan forwards to find the first one after the cutoff.
*/
for (i = cutoff; i < sp->timecnt; i++)
{