localeToCharset()

Thanks to Ivan for the patch to support C.UTF-8 in localeToCharset, I've 
added it to R-devel.
Dear Tomas,

thanks a lot. I do understand the explanation of Simon - I was not aware of the standardization issue. My conclusion is that I should rely on another approach to detect the session charset, and your suggestions are my first option.

My final thought: For users who do not know the POSIX standards and recent aberrations , a warning might be helpful, something such as:
If (startsWith(locale, "C.")) warning (sprintf("%s is a non-standard locale", locale))
Dear Andreas, "C" and "POSIX" (and "") are the only two locales with 
standard names (defined by POSIX), so people necessarily have to rely on 
the non-standard ones and when new ones are introduced, such as in this 
case, we need to update localeToCharset() to support them. Thanks for 
your report.

Best
Tomas
As far as I am concerned, I take away a lot from this discussion! Thank you!

Kind regards
Andreas

?Am 31.01.22, 13:32 schrieb "Tomas Kalibera" <tomas.kalibera at gmail.com>:

     Hi Andreas,

     is there still any higher-level problem left you need to solve? Ideally
     one wouldn't need to query what is the native encoding, but directly use
     iconv() or indirectly other R functions to convert the data from/to the
     native encoding. iconv() will find out internally what is the native
     encoding (via data that is available also by l10n_info(), but with care
     for differences between OSes).

     Best
     Tomas

     On 1/31/22 12:38, Bl?tte, Andreas wrote:
     > Dear Ivan,
     >
     > this is a very helpful explanation!  I think it is important to make output of localeToCharset() more predictable. My problem is essentially not to set the locale such that things will work after all. I think the problem is that you see unexpected results.  I guess I owe a suggestion how to improve the code, but your suggestion looks like a very good starting point.
     >
     > Andreas
     >
     > Am 31.01.22, 12:32 schrieb "Ivan Krylov" <krylov.r00t at gmail.com>:
     >
     >      On Mon, 31 Jan 2022 09:56:27 +0000
     >      "Bl?tte, Andreas" <andreas.blaette at uni-due.de> wrote:
     >
     >      > After starting R with a re-defined locale (`env LC_CTYPE=en_US.UTF-8
     >      > R`,  the output of `localeToCharset()` is:
     >      > [1] "UTF-8"     "ISO8859-1"
     >
     >      > why ISO8859-1 might be a fallback option here?
     >
     >      ISO8859-1 seems to be offered because it covers the alphabet of
     >      American English. Obviously, this doesn't guarantee that the guess is
     >      correct. For example, I could symlink the ru_RU.KOI8-R locale on my
     >      system to name it "ru_RU", and localeToCharset() would return
     >      "ISO8859-5", not knowing the correct answer. ??????, anyone?
     >
     >      > Part of my analysis of the code of `localeToCharset()` is that it
     >      > targets special scenarios on Windows and macOS, but not on Linux.
     >
     >      Well, it almost does the right thing. GNU/Linux locales are typically
     >      named like <language>_<country>.<encoding>, and localeToCharset()
     >      respects the <encoding> part, but only if the language and the country
     >      are specified. A quick fix for that would be to add one final case:
     >
     >      Index: src/library/utils/R/iconv.R
     >      ===================================================================
     >      --- src/library/utils/R/iconv.R (revision 81596)
     >      +++ src/library/utils/R/iconv.R (working copy)
     >      @@ -135,6 +135,7 @@
     >                   if(enc == "utf8") return(c("UTF-8", guess(ll)))
     >                   else return(guess(ll))
     >               }
     >      +        if (enc == "utf8") return("UTF-8") # fallback for ???.UTF-8
     >               return(NA_character_)
     >           }
     >       }
     >
     >      (Non-UTF-8 encodings on POSIX are handled above, in the if(nzchar(enc)
     >      && enc != "utf8") branch.)
     >
     >      Maybe a better fix would be to restructure the code a bit, to always
     >      take the encoding hint and then also try to guess if the locale looks
     >      like it provides a language code.
     >
     >      --
     >      Best regards,
     >      Ivan
     >
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