[tz] FW: missing extension rules

Zefram zefram at fysh.org
Tue Oct 11 20:44:09 UTC 2011

I've found that zic normally copes correctly with zones that are
configured to observe DST rules and the ruleset has no future transitions.
The problem with Africa/Cairo is that when looking for the last rule
zic gets confused by there being two transitions in a single month.
It fails to distinguish between their dates, and incorrectly ends up
thinking that the transition to DST was latest.

The attached patch fixes this bug.  Africa/Cairo is the only tzfile
affected by the change, and the only change to it is to fill the
POSIX-TZ field.

I also pointed out America/Argentina/San_Luis.  It turns out that zic
is deliberately declining to fill the POSIX-TZ field, because of the
DSTness of the last observation.  This is the same reason why it left
that field empty in Africa/Cairo, once it had made the mistake about
which observation came last.  I have a plan for improving this situation,
which I'll address in a separate patch.

-------------- next part --------------
diff -ur tz2011j.build/zic.c tz2011j.mod1/zic.c
--- tz2011j.build/zic.c	2011-06-15 11:46:58.000000000 +0100
+++ tz2011j.mod1/zic.c	2011-10-11 21:34:44.000000000 +0100
@@ -1951,12 +1951,15 @@
 		** There are no rules running through "max".
 		** Let's find the latest rule.
+		zic_t when_latest = 0;
 		for (i = 0; i < zp->z_nrules; ++i) {
+			zic_t when;
 			rp = &zp->z_rules[i];
-			if (stdrp == NULL || rp->r_hiyear > stdrp->r_hiyear ||
-				(rp->r_hiyear == stdrp->r_hiyear &&
-				rp->r_month > stdrp->r_month))
-					stdrp = rp;
+			when = rpytime(rp, rp->r_hiyear);
+			if (stdrp == NULL || when > when_latest) {
+				stdrp = rp;
+				when_latest = when;
+			}
 		if (stdrp != NULL && stdrp->r_stdoff != 0)
 			return;	/* We end up in DST (a POSIX no-no). */

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