[tz] [PATCH 2/3] Replace some zones with links when that doesn't lose non-LMT info.

[Brian Inglis]

On 2013-09-03 01:34, Paul Eggert wrote:
...
> Link to America/Port_of_Spain instead of having a separate zone
> that differs only in LMT.  Each LMT entry is just a placeholder for
> unavailable info, and by itself does not justify a separate zone.
> Using just one zone simplifies maintenance, makes the runtime
> a bit smaller, and can help simplify user selection of zones.
> * southamerica (America/Aruba): Likewise, for America/Curacao.
> * backward (America/Virgin):
> * northamerica (America/St_Barthelemy, America/Marigot):

Folks seem to have forgotten that initial LMT entries contain the Standard Time 
start date, as well as the prior GMTOFF based on longitude of that location.

While I agree that merging zones with different GMTOFF makes no significant 
difference, merging zones with different Standard Time start date loses useful 
historical data, unless the tzdb is seen mainly as a source of DST changes since 
1970.

In the changes highlighted below, Standard Time start dates vary from 1890-1921, 
with some different dates in 1911-1912.

Zones should be merged only if all linked locations have the same Standard Time 
start date, if we wish to maintain the history of when Standard Time was 
established in each time zone.

...
>   # Anguilla
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/Anguilla	-4:12:16 -	LMT	1912 Mar 2
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/Anguilla
>
>   # Antigua and Barbuda
>   # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> @@ -2871,9 +2869,7 @@ Zone	America/Havana	-5:29:28 -	LMT	1890
>   			-5:00	Cuba	C%sT
>
>   # Dominica
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/Dominica	-4:05:36 -	LMT	1911 Jul 1 0:01		# Roseau
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/Dominica
>
>   # Dominican Republic
>
> @@ -2922,18 +2918,13 @@ Zone America/El_Salvador -5:56:48 -	LMT	1921		# San Salvador
>   			-6:00	Salv	C%sT
>
>   # Grenada
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone	America/Grenada	-4:07:00 -	LMT	1911 Jul	# St George's
> -			-4:00	-	AST
> -
> +Link America/Port_of_Spain America/Grenada
>   # Guadeloupe
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/Guadeloupe	-4:06:08 -	LMT	1911 Jun 8	# Pointe a Pitre
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/Guadeloupe
...
>   # Montserrat
> -# From Paul Eggert (2006-03-22):
> -# In 1995 volcanic eruptions forced evacuation of Plymouth, the capital.
> -# world.gazetteer.com says Cork Hill is the most populous location now.
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/Montserrat	-4:08:52 -	LMT	1911 Jul 1 0:01   # Cork Hill
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/Montserrat
...
>   # St Kitts-Nevis
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/St_Kitts	-4:10:52 -	LMT	1912 Mar 2	# Basseterre
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/St_Kitts
>
>   # St Lucia
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/St_Lucia	-4:04:00 -	LMT	1890		# Castries
> -			-4:04:00 -	CMT	1912	    # Castries Mean Time
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/St_Lucia
...
>   # St Vincent and the Grenadines
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/St_Vincent	-4:04:56 -	LMT	1890		# Kingstown
> -			-4:04:56 -	KMT	1912	   # Kingstown Mean Time
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/St_Vincent
...
>   # British Virgin Is
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/Tortola	-4:18:28 -	LMT	1911 Jul    # Road Town
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/Tortola
>
>   # Virgin Is
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone America/St_Thomas	-4:19:44 -	LMT	1911 Jul    # Charlotte Amalie
> -			-4:00	-	AST
> +Link America/Port_of_Spain America/St_Thomas
...
>   # Aruba
> -# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
> -Zone	America/Aruba	-4:40:24 -	LMT	1912 Feb 12	# Oranjestad
> -			-4:30	-	ANT	1965 # Netherlands Antilles Time
> -			-4:00	-	AST
> +Link America/Curacao America/Aruba