From e24d28fd2f3da4779d8ac40cd1faf3d09d30d8ba Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Fri, 10 Jan 2025 15:13:30 -0500 Subject: [PATCH v2 4/4] Make pg_interpret_timezone_abbrev() check sp->defaulttype too. This omission caused it to miss the furthest-back zone abbreviation when working with timezone data compiled with relatively recent zic (2018e or newer, I think). Older versions of zic produced a phony 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 until the current patch series. While here, 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 here 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 fills in sp->defaulttype. Possibly this should be back-patched, but I'm unsure whether there are any visible consequences in released branches. Per report from Aleksander Alekseev and additional investigation. Discussion: https://postgr.es/m/CAJ7c6TOATjJqvhnYsui0=CO5XFMF4dvTGH+skzB--jNhqSQu5g@mail.gmail.com --- src/timezone/localtime.c | 40 ++++++++++++++++++++-------------------- 1 file changed, 20 insertions(+), 20 deletions(-) diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c index 9f76212b7b..8eb02ef146 100644 --- a/src/timezone/localtime.c +++ b/src/timezone/localtime.c @@ -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++) { -- 2.43.5