[tz] [tz-announce] 2018i release of tz code and data available

Paul Eggert eggert at cs.ucla.edu
Sat Jan 5 01:10:40 UTC 2019

On 1/4/19 2:54 PM, Michael H Deckers via tz wrote:
>      Nothing disallows the "rearguard" format for Africa/Casablanca
>      to describe exactly the same data as the "vanguard" format,
>      including the same setting of the dst bit -- it is just a matter
>      of additional ZONE lines in the "rearguard" format.

True, and possibly the same thing could be said for Europe/Prague and 
Africa/Windhoek, although not for Europe/Dublin (at least, not until the 
EU DST stuff gets resolved). This is because all but Ireland currently 
have a small number of transitions using non-rearguard rules, and each 
such transition can be represented by a Zone line.

That being said, it'd be a bit of a pain to convert the Rule lines to 
corresponding Zone lines and the benefit is almost nil. So I'm somewhat 
more inclined to document the current situation than to change it.

>      the description in the NEWS file is incorrect....
>      Also in either case, we must state that it is the "vanguard"
>      format that exactly describes the data we want to describe, 

I attempted to do that by installing the attached patch into the 
development version. Thanks for mentioning the problem.

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From 9625c481960006c4a2e29b321a1659577032f3be Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert at cs.ucla.edu>
Date: Fri, 4 Jan 2019 16:59:19 -0800
Subject: [PROPOSED] Improve description of vanguard/main/rearguard
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Problem reported by Michael Deckers in:
* Makefile (DATEFORM): Add clarifying comments.
* NEWS (2018d): Don’t say the files “represent the same data as
closely as the formats allow”, as this wasn’t strictly true.
 Makefile | 5 ++++-
 NEWS     | 5 +++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index d8d8e21..b88eca4 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,10 @@ VERSION=	unknown
 # Email address for bug reports.
 BUGEMAIL=	tz at iana.org
-# Choose source data features.  To get new features right away, use:
+# DATAFORM selects the data format.
+# Available formats represent essentially the same data, albeit
+# possibly with minor discrepancies that users are not likely to notice.
+# To get new features and the best data right away, use:
 #	DATAFORM=	vanguard
 # To wait a while before using new features, to give downstream users
 # time to upgrade zic (the default), use:
diff --git a/NEWS b/NEWS
index 37f2281..ee28735 100644
--- a/NEWS
+++ b/NEWS
@@ -400,8 +400,9 @@ Release 2018d - 2018-03-22 07:05:46 -0700
       downstream parsers do not support it.
     * The build procedure constructs three files vanguard.zi, main.zi,
-      and rearguard.zi, one for each format.  The files represent the
-      same data as closely as the formats allow.  These three files
+      and rearguard.zi, one for each format.  Although the files
+      represent essentially the same data, they may have minor
+      discrepancies that users are not likely to notice.  The files
       are intended for downstream data consumers and are not
       installed.  Zoneinfo parsers that do not support negative SAVE values
       should start using rearguard.zi, so that they will be unaffected

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