[Development] RFC: Defaulting to or enforcing UTF-8 locales on Unix systems

[Kevin Kofler]

Thiago Macieira wrote:
> 2) QtCore size
> As I said above, removing the legacy codecs we have code for is not a
> problem. They are already disabled in Qt builds where ICU is present, so
> we'd additionally remove them from all other builds. Where ICU is present,
> there's no loss of functionality for user applications, since ICU provides
> far more codecs than we do. For those without ICU, it stands to reason
> that the user chose size so they are aware of the limitations. Plus, one
> can always instantiate their own QTextCodec and add to the list (at least,
> with today's implementation).

Isn't ICU already a hard requirement on *nix? Since we are talking about 
locales on *nix systems only, we should be able to assume a Qt build with 
ICU, shouldn't we?

> Turns out, there's one locale that we can be sure that its non-UTF-8
> default is decodable under UTF-8 and that'st he "C" locale. So we don't
> *have* to qputenv "C.UTF-8" if the locale is explicitly "C" (as opposed to
> being unset).
> 
> But I think we should.

Please be warned that C.UTF-8 is a recent introduction. (Has upstream glibc 
even accepted it yet?) So setting the locale to C.UTF-8 will produce warning 
spam or even fatal errors (depending on the application) on many older 
distributions and possibly even on some current ones. (E.g., Fedora has 
introduced this in Fedora 24 and in updates to Fedora 22 and 23. I don't 
know whether this was backported to RHEL releases up to RHEL 7. RHEL 8 has 
probably inherited it from recent Fedora, at least.)

        Kevin Kofler