Howdy,

As part of the implementation of the new zoneinfo module for the Python standard library, I have been attempting to generate some version 1 files for test purposes (in the sadly likely event that some people only have version 1 TZif files deployed). I have done this by taking existing TZif files, truncating them at the second TZif header, and changing the version number in the truncated file.

I notice, however, that with the 2019c version of zdump, the files generated this way are considered invalid:

$ zdump --version
zdump (tzcode) 2019c
$ zdump -i -c2038,2039 $(realpath .)/America/Los_Angeles
/tmp/zoneinfon3c1bcna/v1/America/Los_Angeles: Invalid argument
$ zdump -i -c2010,2011 $(realpath .)/America/Los_Angeles
/tmp/zoneinfon3c1bcna/v1/America/Los_Angeles: Invalid argument

Interestingly, if I do not truncate the file and just change the version to "1" (in both the first *and* second header), it will read the file and it will clearly use the version 2/3 data:

$ file Australia/Sydney
Australia/Sydney: timezone data, version 1, no gmt time flags, 5 std time flags, no leap seconds, 142 transition times, 5 abbreviation chars
$ zdump -i -c2200,2201 $(realpath .)/Australia/Sydney

TZ="/tmp/zoneinfot3h5_eyf/v1/Australia/Sydney"
-       -       +11     AEDT    1
2200-04-06      02      +10     AEST
2200-10-05      03      +11     AEDT    1

So I guess my question is: does zdump support well-formed version 1 files, and I am failing to create well-formed version 1 files, or does 2019c's zdump have no support for version 1 files?

I'll note that this whole thing came up because I was wondering what zdump does for times after the last transition in a version 1 file. RFC 8536 indicates that this behavior is undefined - I was planning to hold the value of the offset after the last transition, but I figured I might as well check what zdump does.

Thanks,
Paul