Re: C.UTF-8 review

[Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>]

On 7/14/21 7:57 AM, Florian Weimer wrote:
> Carlos,
> 
> I reviewed your changes on the codonell/c-utf8 branch and have some
> comments.
> 
> I believe the replacement character should U+FFFD REPLACEMENT CHARACTER,
> not U+003F QUESTION MARK:

Unfortunately we can't use U+FFFD.

During the final transliteration (__gconv_transliterate()) we use
_NL_CTYPE_TRANSLIT_DEFAULT_MISSING to replace characters that have no
transliteration.

When you convert from UTF-8 to ASCII, even with TRANSLIT,IGNORE the framework
attempts to use U+FFFD for the ASCII output and that immediately fails with
a conversion error.

So "default_missing" must be valid in all possible output encodings, which
means U+FFFD is not usable (today), and likely why U+003F is being used.

To fix this we would have to attempt a final transliteration of default_missing
within __gconv_transliterate, but I feel like that's a follow-on change we
could do in the future.
 
> +% Include the neutral transliterations.  The builtin C and
> +% POSIX locales have +1600 transliterations that are built into
> +% the locales, and these are a superset of those.
> +translit_start
> +include "translit_neutral";""
> +default_missing <U003F>
> +translit_end
> 
> I guess this menas that C and C.UTF-8 LC_CTYPE diverge.

Yes, in locale/C-ctype.c we have very minimal data.

For C.UTF-8 the LC_CTYPE is much broader and I think this meets
user expectations for developers and harmonizes across what downstreams
have learned from using C.UTF-8.

> The strcmp_collation keyword is reasonably explicit.  I would appreciate
> if we could produce an error if it is used along with other collation
> directives.  Right now, those are silently ignored.
> 
> There is a trailing newline in localedata/locales/C.

Fixed.
 
> But overall it's very nice.  We should have shipped this many years ago.

Agreed. All my fault here.

I'll update my branch tomorrow with a new test for C.UTF-8, I found a
defect in the current branch.

-- 
Cheers,
Carlos.