[tz] Metazones in the tzdb (was Re: Why did you rename Russian zone name abbreviations)

[Guy Harris]

On Nov 2, 2016, at 9:55 PM, Random832 <random832 at fastmail.com> wrote:

> You have to take the tzid and an effective date to find out the
> "metazone", then the "metazone" knows what its abbreviations are. I've
> advocated in the past for tz files to identify the metazone of each
> transition because the CLDR should really not be responsible for keeping
> this up to date.

One way to do that might be to

	1) have items either in the source files or in a separate file defining metazones and their tzdb-supplied abbreviations;

	2) replace the FORMAT column with a METAZONE column and give the metazone name.

However, that might break code (other than zic, which we'd change) that reads the *source* files rather than the *compiled* files; if that's an issue, we might have to do something such as:

	give the new files names ending with ".tz" or some extension;

	have part of the process for building a release be running a program or script that takes the .tz files and, if the metazones are in a separate file, the metazone file, and generates old-style files with a FORMAT column.

We'd also have version 4 of the compiled files; one possibility would be to append a count of metazones, a list of metazone names, and a table of metazone name table indices, indexed by the same value that's used as an index in the struct ttinfo table.  We could add an API that, for a given time_t value, returns the metazone name.  That could be used to look up data in the CLDR.