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RE: Automatic recognition of some specific coding systems

From: Jürgen Hartmann
Subject: RE: Automatic recognition of some specific coding systems
Date: Tue, 24 Feb 2015 23:30:49 +0100

Thank you, Eli Zaretskii, for your speedy answer:

>> Is this conclusion correct?
> No, I don't think so.  There's no direct relation between categories
> and recognition of encoding.

I am very glad to hear that.

> If you have specific problems, i.e. if Emacs doesn't recognize the
> encoding of some file(s), please post the details.  (I'd suggest to
> try in "emacs -Q" first, because some problems might be caused by your
> customizations that need to be removed or adapted to the new version.)
> Then people here could review the problems and advise you about
> possible solutions, or ask you to file a bug report.
> But in general, there shouldn't be any regressions in recognizing
> encodings.

OK. I will try to give a specific example - it is rather artificial
but representative:

Consider an utf-8-unix encoded text file, meaningfully named
utf-8-unix, that just contains the seven German special characters

   äöüßÄÖÜ   ("a"o"u"s"A"O"U)

in one single line followed by a newline character. Now we make two
copies of this file and recode them to the other coding systems of

   cp utf-8-unix latin-9-unix
   recode ..l9 latin-9-unix

   cp utf-8-unix cp850-dos
   recode ..pc cp850-dos

Visiting all tree files in an Emacs session that was freshly started
by means of

   emacs -Q

- thank you for that important hint - yields a perfect recognition of
the respective coding in the case of

   latin-9-unix   (recognized as latin-1-unix, equivalent here)

but the recognition fails tor the cp850-dos encoded file, as it is
recognized as


encoded and its contents is displayed as


Looking on the contents of the variable coding-category-list, it has
the form

   (coding-category-utf-8 coding-category-charset ...
    coding-category-raw-text ...)

where the values of the variables coding-category-utf-8 and
coding-category-charset are utf-8 and iso-latin-1 respectively.

If I start again with a new Emacs session (emacs -Q), but this time
performing the commands

   prefer-coding-system cp850
   prefer-coding-system utf-8

prior to visiting the files, the codings of


are recognized correctly, while the file latin-9-unix is recognized as
cp850-unix encoded and its contents is displayed as some cryptic symbols.

The coding-category-list and the variable coding-category-utf-8 have
the same values as before, but the variable coding-category-charset
contains cp850 this time.

So my problem is to find a configuration of Emacs 24.4 that yields a
correct automatic recognition of all tree coding systems

   latin-9-unix or

when the files of the example above are visited. One has to keep in
mind that this was perfectly possible with Emacs 22.3, as I just
verified again.

Sorry for the rather long post, but I hope that I could state my
problem more precisely.



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