Re: missing possibility to use alternative translated month names in to_char function

Hi

st 12. 8. 2026 v 23:51 odesílatel Bernd Reiß <bd_reiss(at)gmx(dot)at> napsal:

> Hi Pavel,
>
> I've looked into your patch and provide the review below.
>
> Threads I found touching TMMONTH + glibc:
>
> https://www.postgresql.org/message-id/CALSKcLS3Zi4o0Ak5pNOheqmAiKWcez%2B%2BqwKvyPccvOz2v62QZQ%40mail.gmail.com
> (Russian)
> https://www.postgresql.org/message-id/14717914.JAiOoc7IO7%40utklippan
>
> I did not come across a prior thread proposing an implementation of what
> this patch does. Worth noting that in the utklippan thread above, Tom Lane
> suggested that a new format code or modifier would be the palatable way to
> address a similar problem.
>
> Contents & Purpose
> ==================
> This patch gives users control over the case (genitive vs. nominative)
> to use when pulling localized month names from glibc via the function
> to_char(). The author proposes to add a TAMMONTH option for formatting
> dates.
>
> Intended behaviour: TMMONTH uses the genitive form (if applicable to the
> language; equivalent to %B) while TAMMONTH uses the nominative
> (equivalent to %OB).
>
> The patch contains regression test cases. It also adds a corresponding
> entry in the documentation.
>
> Initial Run
> ===========
> The patch applies cleanly to HEAD. The regression tests all pass
> successfully against the new patch, but fail against pre-patched HEAD,
> so the test cases are sane and do cover the new behavior.
>
> Manual Testing
> ==============
> The provided examples all work fine. However, I realized that the
> shortened form TAMMON falls back to English instead of honouring
> lc_time:
>
> postgres=# set lc_time to 'de_DE.UTF-8';
> SET
> postgres=# SELECT to_char(date '2026-03-01'::date, 'DD TMMON');
> SELECT to_char(date '2026-03-01'::date, 'DD TAMMON');
> to_char
> ---------
> 01 MÄR
> (1 row)
>
> to_char
> ---------
> 01 MAR
> (1 row)
>
> It looks like only the full-month cases (DCH_MONTH/Month/month) were
> wired up for
> TAM; the abbreviated cases (DCH_MON/Mon/mon) still test IS_SUFFIX_TM
> only, so TAM
> silently drops to the default English abbreviation. I'd expect TAMMON to
> stay
> localized.
>

TAMMON is not implemented, because glibc doesn't provide an alternative
form for abbreviated month names.
It is a question if it is better to raise an error, return a non
alternative name or just ignore this flag. I have not strong
opinion about this. Inside DCH_to_char the prefix TM is ignored when it is
not used. So I did the same.

But I can imagine using localized abbreviation. It is possible for the
Czech language - but I have not idea if it is true for other languages.

>
> Code Review
> ===========
> I am not sure if this condition can be ever true:
>
> + if (IS_SUFFIX_TM(n->suffix) && IS_SUFFIX_TAM(n->suffix))
>
> In case this is not possible the subsequent error message will never be
> thrown and the whole block is dead code.
>
> However, if there is a reason for this check, it would be nice to
> have a comment mention it.
>

Yes, I badly expected that prefixes could be mixed. I checked the code, and
this is not possible, so I removed this check

>
> One thing I am not entirely sure about is this line:
>
> + if (strftime_l(bufptr, MAX_L10N_DATA, "%OB", timeinfo, locale) <= 0)
> + strftimefail = true;
>
> As far as I checked %OB is not supported on Windows:
>
>
> https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/strftime-wcsftime-strftime-l-wcsftime-l?view=msvc-170
>
> I was, however, not able to confirm this on a Windows machine right now.
> I might be able to do so on the weekend.
>
> However, the same problem exists with older glibc versions not supporting
> %OB. As far as I understand strftime_l this will lead to it returning 0 and
> therefore setting strftimefail to true always. Since this if statement
> is evaluated
> unconditionally I expect this to also influence the behaviour of TM.
>

I am afraid about this case too, and I expect maybe some fallback mode
there. But because
I have not a Window machine or some machine with older glibc I decided to
don't touch it
for this moment.

glibc older than 2.28 doesn't support %OB. On the second hand the result of
%B is probably
equal to expected result %B.

> Nitpicking & Conclusion
> =======================
> I feel like the documentation could explicitly mention the difference
> between TMMONTH and TAMMONTH (i.e., mentioning genitive and nominative
> like the Locale docs you mentioned do). I also think it would be
> beneficial to
> mention that this linguistic detail is specific to certain languages.
>

please, if you can write this part of the doc. My English is not good
enough to write well about these linguistic details.
It is a problem primarily for slavic languages - like Czech or Russian -
but maybe it can be a wide problem.

> Furthermore, in general I feel like the code could have more comments.
> The single comment /* TAM suffix - localized alternative month name */
> I would rather put outside the if-else block and set TAM directly in
> relation
> to TM there.
>
> All in all, this topic seems to have been a pain point for many people
> as the discussion threads mentioned in the beginning attest. The patch
> offers a solution to make glibc behaviour more predictable for users.
> I see a very real use case here.
>

Thank you very much for this immediate review

Regards

Pavel

> Best
> Bernd
>
> On 12/08/2026 09:13, Pavel Stehule wrote:
> > Hi
> >
> > út 11. 8. 2026 v 17:14 odesílatel Pavel Stehule
> > <pavel(dot)stehule(at)gmail(dot)com> napsal:
> >
> >
> >
> > út 11. 8. 2026 v 17:06 odesílatel Pavel Stehule
> > <pavel(dot)stehule(at)gmail(dot)com> napsal:
> >
> > Hi
> >
> > My customer reported an interesting issue. He needs translated
> > month name, and then he use
> > to_char(current_date, 'tmmonth');
> >
> > Unfortunately, glibc returns nouns in the genitive case
> > instead of the nominative case.
> >
> > This is a glibc feature from the 2.28 release. Genitive case
> > makes sense, when the result holds a day, but without it, it
> > is messy.
> >
> > glibc has alternative month names, that can be taken by usage
> > placeholder '%OB' of function strftime.
> >
> https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap07.html
> > - see alt_mon.
> >
> > Can we enhance prefixes (maybe tmo) to be possible to use
> > alternative names?
> >
> >
> > example:
> >
> > pavel(at)nemesis:~/src/orafce$ date +'%B'
> > srpna
> > pavel(at)nemesis:~/src/orafce$ date +'%OB'
> > srpen
> > pavel(at)nemesis:~/src/orafce$ LANG=C date +'%OB'
> > August
> >
> >
> > attached patch that implements 'TAM' modifier for data/timestamp
> > formatting
> >
> > Regards
> >
> > Pavel
> >
> >
> > Regards
> >
> > Pavel
> >
> >
> >
> >
> >
>
>