[fpc-devel] Timezones

[Zachary Vance]

Oops. Re-sending this as I apparently replied privately to Michael. Sorry for the duplicate email, Michael.

On 11/15/2015 03:00 AM, Michael Van Canneyt wrote:
>
>
> On Sat, 14 Nov 2015, Zachary Vance wrote:
>
>> I'm reporting a bug the Debian reproducibility team came across (in 2.6.4-1), trying to make Pascal builds reproducible. The end goal is to see UTC timestamped output of ppudump.
>>
>> My understanding of the current behavior is that the timezone file is chosen something like this:
>>
>> TIMEZONE_FILE = [CONTENT of /etc/timezone if it exists]:/etc/localtime:/usr/lib/zoneinfo/localtime[:/usr/share/zoneinfo if BSD]:/var/db/timezone/localtime:localtime
>> If TIMEZONE_FILE doesn't start with / (is a relative path), prepend (${TZDIR} or /usr/share/zoneinfo)
>>
>> This means that if /etc/timezone or /etc/localtime exist, there is no way to specify that UTC should be used.
>>
>> ---
>>
>> The desired behavior probably be to respect the TZ environment variable, which is currently ignored, so the new list would be:
>>
>> TIMEZONE_FILE = ${TZ}:[CONTENT of /etc/timezone if it exists]:/etc/localtime:/usr/lib/zoneinfo/localtime[:/usr/share/zoneinfo if BSD]:/var/db/timezone/localtime:localtime
>> If TIMEZONE_FILE doesn't start with / (is a relative path), prepend (${TZDIR} or /usr/share/zoneinfo)
>>
>> Additionally, POSIX says that if TZ is set but invalid or empty, it should default to UTC, not to localtime.
>
> Observing the contents of the TZ variable is of course an option, that should not be a problem.
> But the default to localtime will most likely not be changed for 2 reasons
> a) compatibility with Delphi.
> b) backwards compatibility.
> FPC does not pretend to be POSIX.

I'm not suggesting changing behavior for all methods to evaluate the timezone, only specifically if the TZ environment variable is set and empty/invalid. That said, either fix would solve Debian Reproducible Builds' issue.

>
> Looking at
>   http://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html
>
> I have the following code to determine the name of the timezone file based on the contents of TZ:
>
> fn:=fpgetenv('TZ');
> if (fn<>'') then
>   if (fn[1]=':') then  // :filename
>     begin
>     delete(fn,1,1); // Strip :
>     if (fn<>'') then
>       begin
>       if (fn[1]<>'/') then // not absolute
>         Exit('/usr/share/zoneinfo/'+fn)
>       Exit(fn);  // absolute
>       end;
>     end;
>
> Would you say this is correct ?
>
> Michael.

Thanks for investigating this, Michael.

I only learnt about the TZ variable investigating this bug and don't know Pascal. That said, this seems to match the page you linked. I'm unclear if the content of literal timezones and timezone files are the same--my local ones on my computer look different, so I'd definitely test to make sure the example strings on the linked page work. If you need someone to test timezone parsing methods because you're not on Linux, try the debian-reproducible IRC. (I'd offer but I don't know fpc at all). You might want to replace '/usr/share/zoneinfo/' by the value of TZDIR if it's defined, for consistency with the rest of fpc?

If you want to try our original failing test case, which is from Arch Linux but should run on any Linux system:
1. Delete /etc/timezone
2. Symlink /etc/localtime to your timezone file (not UTC, please)
3. Run TZ='' ppadump ... [If you're not modifying things, I guess it would be TZ='UTC']
Output currently uses the content of /etc/localtime, but should be in UTC.