Bug#924657: Buggy gettext() after switching locale (#924657)

[intrigeri <intrigeri@debian.org>]

Hi,

@kibi, tl;dr: my test results about this problem in similar code
confirm the problem and validate Iain's fix ⇒ +1 to apply :)

Cyril Brulebois:
> Looping in the Perl team for additional eyes and also awareness. Other
> packages might be affected, and it might make sense to conduct some
> sources.d.o/codesearch-based check…

>From Iain's report I understand that since Perl 5.28, gettext() calls
are cached, so after switching the locale, in order to get correct
results, one needs to invalidate the cache somehow, e.g. by calling
bindtextdomain() and then textdomain().

I've looked for problematic patterns on codesearch:

  https://codesearch.debian.net/search?q=filetype%3Aperl+ENV{LANGUAGE}
  https://codesearch.debian.net/search?q=filetype%3Aperl+ENV%7B%27LANGUAGE%27%7D
  https://codesearch.debian.net/search?q=filetype%3Aperl+ENV%7B%22LANGUAGE%22%7D
  https://codesearch.debian.net/search?q=filetype%3Aperl+setlocale%5C%28

… and checked a subset of the results. I've only spotted two
potentially problematic cases.

1. sympa: dgettext sub in src/lib/Sympa/Language.pm

   Only works because the BEGIN block explicitly selects one of the
   'gettext_dumb' and 'gettext_pp' implementations. Without this, or
   if using the default implementation ('gettext_xs'),
   Sympa::Language::dgettext() would return cached results, unless
   using the trick proposed by Iain to invalidate the cache.

2. texinfo: tp/Texinfo/Report.pm

   Similarly to Sympa, it should work fine because the code explicitly
   selects the 'gettext_pp' implementation… with a comment that reads
   "we want a reliable way to switch locale, so we don't use the
   system gettext".

I've searched for 'gettext_xs' and only found relevant occurrences in
its own implementation (libintl-perl). No package seems to explicitly
pick that implementation. But that implementation is the default so
any package that uses Locale::Messages or a higher-level Perl API to
gettext is potentially affected. I hope that my search for
$ENV{LANGUAGE} and friends covered all those that dynamically switch
locales at runtime.

Potentially relevant upstream issues:

  https://github.com/gflohr/libintl-perl/issues/3
  https://rt.cpan.org/Public/Bug/Display.html?id=120446

(Some of the issues there are attributed to the local environment but
I suspect some of them might actually be caused by the problem
Iain found.)

Cheers,
-- 
intrigeri