bug#37633: Column part interpreted wrong in compilation mode

[Bernd Paysan]

Am Samstag, 5. Oktober 2019, 18:16:53 CEST schrieb Eli Zaretskii:
> > Date: Sat, 05 Oct 2019 19:08:21 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 37633@debbugs.gnu.org, anton@mips.complang.tuwien.ac.at
> > 
> > > Suggested solution: Use byte-to-position to calculate the position in
> > > compilation-move-to-column.
> > 
> > This only works in UTF-8 locales, and is not 100% even there, so it
> > isn't the right solution.
> 
> In general, byte-to-position is meant to be used only for converting
> between byte and character positions of text in Emacs buffers.
> 
> For byte offsets in external text we have bufferpos-to-filepos, but
> that requires us to know the encoding of the external text.  We need
> to find a reasonable way of getting that.  Suggestions and patches
> welcome.

We can likely assume that the auto-detected encoding is the correct one, i.e. 
buffer-file-coding-system can be used (the default for the optional encoding 
system parameter for bufferpos-to-filepos and filepos-to-bufferpos).

I.e. go to the line selected, do a bufferpos-to-filepos on that position, add 
the column-1 to that, and do a filepos-to-bufferpos.  Jump there.

Problem with precision: "exact" requires encoding the entire file, so it's 
slow for large files.  Particularly with automatically generated files, this 
is likely not acceptable, so "approximate" could be good enough.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
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https://net2o.de/

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