bug#65927: the role and location of locale.alias

[Bruno Haible <bruno@clisp.org>]

Hi Ludo',

> > I explained the purpose of this file in
> > https://sourceware.org/pipermail/libc-alpha/2023-September/151524.html .
> > In summary, it's a configuration file whose initial contents is provided
> > for glibc, but which needs to be edited by the system administrator in
> > some situations.
> >
> > For this reason, in Debian 12, the file has been moved to
> > /etc/locale.alias, and /usr/share/locale/locale.alias is merely
> > a symbolic link to /etc/locale.alias. IMO, this is the correct
> > way to handle this configuration file.
> 
> Does glibc look for ‘locale.alias’ in $sysconfdir, or does it look for
> it in $localstatedir?

It looks for it in $(localedir), whose default value is $(datadir)/locale.
https://sourceware.org/git/?p=glibc.git;a=blob;f=intl/localealias.c;h=ea4f48b594fe13490f006d95b799213961146e23;hb=HEAD#l154
https://sourceware.org/git/?p=glibc.git;a=blob;f=intl/Makefile;h=d7223256eb699380ccdf6f6dd37b7490b342e8d3;hb=HEAD#l156
https://sourceware.org/git/?p=glibc.git;a=blob;f=Makeconfig;h=c48fcc59e8c1b150d40241c31fc63adf4d15ccb3;hb=HEAD#l202

The default value of $(datadir) is $(prefix)/share.
https://sourceware.org/git/?p=glibc.git;a=blob;f=Makeconfig;h=c48fcc59e8c1b150d40241c31fc63adf4d15ccb3;hb=HEAD#l182

> To follow the “correct way” as you described it, glibc should look for
> it in $sysconfdir by default.

I agree; cf. https://www.gnu.org/prep/standards/html_node/Directory-Variables.html
But it does not do so currently; therefore the distros fix up the
upstream behaviour.

> > 2) GNU gettext needs to access this file, in order to recognize the
> >    same aliases that glibc recognizes. But glibc does not export the
> >    _nl_expand_alias function. Therefore GNU gettext needs to know
> >    where the file is. But how could GNU gettext retrieve any of the
> >    file names
> >      /gnu/store/5h2w4qi9hk1qzzgi1w83220ydslinr4s-glibc-2.33/share/locale/locale.alias
> >      /gnu/store/ayc9r7162rphy4zjw8ch01pmyh214h82-glibc-2.33/share/locale/locale.alias
> >    ?
> >    If Guix had this configuration file moved to /etc, like Debian did, GNU gettext
> >    could be compiled with '-DLOCALE_ALIAS_PATH=\"/etc\"' and would then be able
> >    to access it.
> 
> Right now gettext in Guix ends up being compiled with:
> 
>   -DLOCALE_ALIAS_PATH=\"\"
> 
> (Example build log at
> <https://ci.guix.gnu.org/log/0yy8zmgvc6hy1pfc41gm1bi7nhj4aqf7-gettext-0.21>.)

In this case, localealias.c does not attempt to open a locale.alias file at all.

> What you propose is doable.  However, how many distros provide
> /etc/locale.alias?  What happens when it’s missing?
> 
> We have to keep in mind that Guix can be used on top of any distro.

When it's missing, localealias.c does not open a locale.alias file.
Negative effects can be seen after the ISO 639 language code of a language
changed or after the ISO 3166 country code of a territory changed. This is
currently not relevant, but may become relevant in the future again.

Which distros have it in /etc?
  - Guix 1.4.0: no
  - Debian 12, Ubuntu 23.10: yes, /usr/share/locale/locale.alias is a symlink.
  - CentOS Stream 9: no
  - Arch 19.11: no
  - openSUSE 15.5: no
  - Slackware 15: no

So, to solve the problem, Guix would need to customize glibc
  1. to install locale.alias in /etc (= $(sysconfdir)),
  2. compile with a LOCALE_ALIAS_PATH=$(sysconfdir):$(localedir)

Then GNU gettext could be compiled with LOCALE_ALIAS_PATH=$(sysconfdir):$(localedir)
as well. This would work in standalone Guix, as well as in
Guix-on-top-of-another-distro.

Bruno