Re: Coding system to encode arguments to groff?

[Eli Zaretskii <eliz@gnu.org>]

> From: Tim Landscheidt <tim@tim-landscheidt.de>
> Date: Wed, 29 Sep 2021 08:01:12 +0000
> 
> I pass text arguments from Emacs Lisp to a groff command
> with the "-d" option.  For ASCII strings, this is trivial;
> for strings with umlauts, I need to use:
> 
> | (encode-coding-string variable-to-pass 'iso-latin-1)

What is your default locale's codeset on that system?  In general, if
the default locale matches the encoding you need to use, the above
should happen automagically.

> For strings with other Unicode characters like "–" (#x2013),
> I need to call groff's preconv like:
> 
> | (shell-command-to-string (concat "preconv -r <(echo " (shell-quote-argument variable-to-pass) ")"))
> 
> which for "ä–ö" returns something like:
> 
> | \[u00E4]\[u2013]\[u00F6]

This is just the original "ä–ö" string, so I'm not quite sure what did
the above accomplish.

> Now in Emacs, this looks very much like what a coding system
> would do.  The info documentation for elisp just laconically
> says:
> 
> |    How to define a coding system is an arcane matter, and is not
> | documented here.
> 
> Has someone implemented such a coding system for groff so
> that something like:
> 
> | (encode-coding-string variable-to-pass 'x-groff)

I don't think you should need a new coding-system.  But you didn't
explain why you need to explicitly encode the command-line arguments,
so it's hard to give an accurate advice.  What kind of Groff command
needs this jumping through hoops from you?  E.g., why isn't it enough
to bind coding-system-for-write to whatever you need, around the call
to call-process or whatever?

IOW, please describe in more detail the Groff-related context in which
this problem happens, so that we could have an intelligent discussion
of the issues you might have.