bug#46859: 28.0.50; [PATCH]: Add option to truncate long lines in xref.el

[Eli Zaretskii]

> Date: Thu, 04 Mar 2021 09:19:50 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: 46859@debbugs.gnu.org
> 
> > While you discuss all those possibilities, please be aware that byte 
> > offsets have one more problem: converting them to character offsets or 
> > columns might not be trivial, especially if the encoding of the file is 
> > not UTF-8.  (Apologies if you already discussed this.)
> >
> 
> We did not discuss this, thanks for pointing that out.
> 
> Is this not easy to do with byte-to-position?

No.  byte-to-position works for text in an Emacs buffer, whereas we
are talking about the text in its original file on disk.  Unless that
file is encoded in UTF-8, byte-to-position will give you wrong
results.  You need to use filepos-to-bufferpos, and you will need to
specify the file's encoding.  And it's relatively slow for non-UTF-8
encoded files.

> What I would suggest is to use "grep -nbo '.\{0,50\}PATTERN.\{0,50\}'", to 
> hide the byte position in the xref buffer, and when the user jumps to an 
> occurrence to use something like (goto-char (byte-to-position 
> (get-byte-position))).  Does that make sense?

Yes, but see above about encodings other than UTF-8.  For example, if
the original file is in Latin-1, each character is 1 byte, but in an
Emacs buffer non-ASCII Latin-1 characters will take 2 bytes.